Lens of the eye dose calculation for neuro-interventional procedures and CBCT scans of the head

NASA Astrophysics Data System (ADS)

Xiong, Zhenyu; Vijayan, Sarath; Rana, Vijay; Jain, Amit; Rudin, Stephen; Bednarek, Daniel R.

2016-03-01

The aim of this work is to develop a method to calculate lens dose for fluoroscopically-guided neuro-interventional procedures and for CBCT scans of the head. EGSnrc Monte Carlo software is used to determine the dose to the lens of the eye for the projection geometry and exposure parameters used in these procedures. This information is provided by a digital CAN bus on the Toshiba Infinix C-Arm system which is saved in a log file by the real-time skin-dose tracking system (DTS) we previously developed. The x-ray beam spectra on this machine were simulated using BEAMnrc. These spectra were compared to those determined by SpekCalc and validated through measured percent-depth-dose (PDD) curves and half-value-layer (HVL) measurements. We simulated CBCT procedures in DOSXYZnrc for a CTDI head phantom and compared the surface dose distribution with that measured with Gafchromic film, and also for an SK150 head phantom and compared the lens dose with that measured with an ionization chamber. Both methods demonstrated good agreement. Organ dose calculated for a simulated neuro-interventional-procedure using DOSXYZnrc with the Zubal CT voxel phantom agreed within 10% with that calculated by PCXMC code for most organs. To calculate the lens dose in a neuro-interventional procedure, we developed a library of normalized lens dose values for different projection angles and kVp's. The total lens dose is then calculated by summing the values over all beam projections and can be included on the DTS report at the end of the procedure.

Radiation exposure in interventional radiology

NASA Astrophysics Data System (ADS)

Pinto, N. G. V.; Braz, D.; Vallim, M. A.; Filho, L. G. P.; Azevedo, F. S.; Barroso, R. C.; Lopes, R. T.

2007-09-01

The aim of this study is to evaluate dose values in patients and staff involved in some interventional radiology procedures. Doses have been measured using thermoluminescent dosemeters for single procedures (such as renal and cerebral arteriography, transjungular intrahepatic portasystemic shunt (TIPS) and chemoembolization). The magnitude of doses through the hands of interventional radiologists has been studied. Dose levels were evaluated in three points for patients (eye, thyroid and gonads). The dose-area product (DAP) was also investigated using a Diamentor (PTW-M2). The dose in extremities was estimated for a professional who generally performed one TIPS, two chemoembolizations, two cerebral arteriographies and two renal arteriographies in a week. The estimated annual radiation dose was converted to effective dose as suggested by the 453-MS/Brazil norm The annual dose values were 137.25 mSv for doctors, 40.27 mSv for nurses and 51.95 mSv for auxiliary doctors, and all these annual dose values are below the limit established. The maximum values of the dose obtained for patients were 6.91, 10.92 and 15.34 mGy close to eye, thyroid and gonads, respectively. The DAP values were evaluated for patients in the same interventional radiology procedures. The dose and DAP values obtained are in agreement with values encountered in the literature.

Variation of indoor radon concentration and ambient dose equivalent rate in different outdoor and indoor environments.

PubMed

Stojanovska, Zdenka; Boev, Blazo; Zunic, Zora S; Ivanova, Kremena; Ristova, Mimoza; Tsenova, Martina; Ajka, Sorsa; Janevik, Emilija; Taleski, Vaso; Bossew, Peter

2016-05-01

Subject of this study is an investigation of the variations of indoor radon concentration and ambient dose equivalent rate in outdoor and indoor environments of 40 dwellings, 31 elementary schools and five kindergartens. The buildings are located in three municipalities of two, geologically different, areas of the Republic of Macedonia. Indoor radon concentrations were measured by nuclear track detectors, deployed in the most occupied room of the building, between June 2013 and May 2014. During the deploying campaign, indoor and outdoor ambient dose equivalent rates were measured simultaneously at the same location. It appeared that the measured values varied from 22 to 990 Bq/m(3) for indoor radon concentrations, from 50 to 195 nSv/h for outdoor ambient dose equivalent rates, and from 38 to 184 nSv/h for indoor ambient dose equivalent rates. The geometric mean value of indoor to outdoor ambient dose equivalent rates was found to be 0.88, i.e. the outdoor ambient dose equivalent rates were on average higher than the indoor ambient dose equivalent rates. All measured can reasonably well be described by log-normal distributions. A detailed statistical analysis of factors which influence the measured quantities is reported.

Dose verification to cochlea during gamma knife radiosurgery of acoustic schwannoma using MOSFET dosimeter.

PubMed

Sharma, Sunil D; Kumar, Rajesh; Akhilesh, Philomina; Pendse, Anil M; Deshpande, Sudesh; Misra, Basant K

2012-01-01

Dose verification to cochlea using metal oxide semiconductor field effect transistor (MOSFET) dosimeter using a specially designed multi slice head and neck phantom during the treatment of acoustic schwannoma by Gamma Knife radiosurgery unit. A multi slice polystyrene head phantom was designed and fabricated for measurement of dose to cochlea during the treatment of the acoustic schwannoma. The phantom has provision to position the MOSFET dosimeters at the desired location precisely. MOSFET dosimeters of 0.2 mm x 0.2 mm x 0.5 μm were used to measure the dose to the cochlea. CT scans of the phantom with MOSFETs in situ were taken along with Leksell frame. The treatment plans of five patients treated earlier for acoustic schwannoma were transferred to the phantom. Dose and coordinates of maximum dose point inside the cochlea were derived. The phantom along with the MOSFET dosimeters was irradiated to deliver the planned treatment and dose received by cochlea were measured. The treatment planning system (TPS) estimated and measured dose to the cochlea were in the range of 7.4 - 8.4 Gy and 7.1 - 8 Gy, respectively. The maximum variation between TPS calculated and measured dose to cochlea was 5%. The measured dose values were found in good agreement with the dose values calculated using the TPS. The MOSFET dosimeter can be a suitable choice for routine dose verification in the Gamma Knife radiosurgery.

Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms

PubMed Central

Zhang, Di; Savandi, Ali S.; Demarco, John J.; Cagnon, Chris H.; Angel, Erin; Turner, Adam C.; Cody, Dianna D.; Stevens, Donna M.; Primak, Andrew N.; McCollough, Cynthia H.; McNitt-Gray, Michael F.

2009-01-01

The larger coverage afforded by wider z-axis beams in multidetector CT (MDCT) creates larger cone angles and greater beam divergence, which results in substantial surface dose variation for helical and contiguous axial scans. This study evaluates the variation of absorbed radiation dose in both cylindrical and anthropomorphic phantoms when performing helical or contiguous axial scans. The approach used here was to perform Monte Carlo simulations of a 64 slice MDCT. Simulations were performed with different radiation profiles (simulated beam widths) for a given collimation setting (nominal beam width) and for different pitch values and tube start angles. The magnitude of variation at the surface was evaluated under four different conditions: (a) a homogeneous CTDI phantom with different combinations of pitch and simulated beam widths, (b) a heterogeneous anthropomorphic phantom with one measured beam collimation and various pitch values, (c) a homogeneous CTDI phantom with fixed beam collimation and pitch, but with different tube start angles, and (d) pitch values that should minimize variations of surface dose—evaluated for both homogeneous and heterogeneous phantoms. For the CTDI phantom simulations, peripheral dose patterns showed variation with percent ripple as high as 65% when pitch is 1.5 and simulated beam width is equal to the nominal collimation. For the anterior surface dose on an anthropomorphic phantom, the percent ripple was as high as 40% when the pitch is 1.5 and simulated beam width is equal to the measured beam width. Low pitch values were shown to cause beam overlaps which created new peaks. Different x-ray tube start angles create shifts of the peripheral dose profiles. The start angle simulations showed that for a given table position, the surface dose could vary dramatically with minimum values that were 40% of the peak when all conditions are held constant except for the start angle. The last group of simulations showed that an “ideal” pitch value can be determined which reduces surface dose variations, but this pitch value must take into account the measured beam width. These results reveal the complexity of estimating surface dose and demonstrate a range of dose variability at surface positions for both homogeneous cylindrical and heterogeneous anthropomorphic phantoms. These findings have potential implications for small-sized dosimeter measurements in phantoms, such as with TLDs or small Farmer chambers. PMID:19378763

Neutron field measurement at the Experimental Advanced Superconducting Tokamak using a Bonner sphere spectrometer

NASA Astrophysics Data System (ADS)

Hu, Zhimeng; Zhong, Guoqiang; Ge, Lijian; Du, Tengfei; Peng, Xingyu; Chen, Zhongjing; Xie, Xufei; Yuan, Xi; Zhang, Yimo; Sun, Jiaqi; Fan, Tieshuan; Zhou, Ruijie; Xiao, Min; Li, Kai; Hu, Liqun; Chen, Jun; Zhang, Hui; Gorini, Giuseppe; Nocente, Massimo; Tardocchi, Marco; Li, Xiangqing; Chen, Jinxiang; Zhang, Guohui

2018-07-01

The neutron field measurement was performed in the Experimental Advanced Superconducting Tokamak (EAST) experimental hall using a Bonner sphere spectrometer (BSS) based on a 3He thermal neutron counter. The measured spectra and the corresponding integrated neutron fluence and dose values deduced from the spectra at two exposed positions were compared to the calculated results obtained by a general Monte Carlo code MCNP5, and good agreements were found. The applicability of a homemade dose survey meter installed at EAST was also verified with the comparison of the ambient dose equivalent H*(10) values measured by the meter and BSS.

Comparison of dosimetric properties among four commercial multi-detector computed tomography scanners.

PubMed

Ohno, Takeshi; Araki, Fujio; Onizuka, Ryota; Hatemura, Masahiro; Shimonobou, Toshiaki; Sakamoto, Takashi; Okumura, Shuichiro; Ideguchi, Daichi; Honda, Keiichi; Kawata, Kenji

2017-03-01

This study compared dosimetric properties among four commercial multi-detector CT (MDCT) scanners. The X-ray beam characteristics were obtained from photon intensity attenuation curves of aluminum and off-center ratio (OCR) profiles in air, which were measured with four commercial MDCT scanners. The absorbed dose for MDCT scanners was evaluated with Farmer ionization chamber measurements at the center and four peripheral points in the body- and head-type cylindrical water phantoms. Measured collected charge was converted to absorbed dose using a 60 Co absorbed dose-to-water calibration factor and Monte Carlo (MC)-calculated correction factors. Four MDCT scanners were modeled to correspond with measured X-ray beam characteristics using GMctdospp (IMPS, Germany) software. Al half-value layers (Al-HVLs) with a body-bowtie filter determined from measured Al-attenuation curves ranged 7.2‒9.1mm at 120kVp and 6.1‒8.0mm at 100kVp. MC-calculated Al-HVLs and OCRs in air were in acceptable agreement within 0.5mm and 5% of measured values, respectively. The percentage difference between nominal and actual beam width was greater with decreasing collimation width. The absorbed doses for MDCT scanners at 120kVp ranged 5.1‒7.1mGy and 10.8‒17.5mGy per 100mAs at the center in the body- and head-type water phantoms, respectively. Measured doses at four peripheral points were within 5% agreement of MC-calculated values. The absorbed dose at the center in both water phantoms increased with decreasing Al-HVL for the same charge on the focus. In this study the X-ray beam characteristics and the absorbed dose were measured and compared with calculated values for four MDCT scanners. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Effects of caffeine on fractional flow reserve values measured using intravenous adenosine triphosphate.

PubMed

Nakayama, Masafumi; Chikamori, Taishiro; Uchiyama, Takashi; Kimura, Yo; Hijikata, Nobuhiro; Ito, Ryosuke; Yuhara, Mikio; Sato, Hideaki; Kobori, Yuichi; Yamashina, Akira

2018-04-01

We investigated the effects of caffeine intake on fractional flow reserve (FFR) values measured using intravenous adenosine triphosphate (ATP) before cardiac catheterization. Caffeine is a competitive antagonist for adenosine receptors; however, it is unclear whether this antagonism affects FFR values. Patients were evenly randomized into 2 groups preceding the FFR study. In the caffeine group (n = 15), participants were given coffee containing 222 mg of caffeine 2 h before the catheterization. In the non-caffeine group (n = 15), participants were instructed not to take any caffeine-containing drinks or foods for at least 12 h before the catheterization. FFR was performed in patients with more than intermediate coronary stenosis using the intravenous infusion of ATP at 140 μg/kg/min (normal dose) and 170 μg/kg/min (high dose), and the intracoronary infusion of papaverine. FFR was followed for 30 s after maximal hyperemia. In the non-caffeine group, the FFR values measured with ATP infusion were not significantly different from those measured with papaverine infusion. However, in the caffeine group, the FFR values were significantly higher after ATP infusion than after papaverine infusion (P = 0.002 and P = 0.007, at normal and high dose ATP vs. papaverine, respectively). FFR values with ATP infusion were significantly increased 30 s after maximal hyperemia (P = 0.001 and P < 0.001 for normal and high dose ATP, respectively). The stability of the FFR values using papaverine showed no significant difference between the 2 groups. Caffeine intake before the FFR study affected FFR values and their stability. These effects could not be reversed by an increased ATP dose.

Evaluation of material heterogeneity dosimetric effects using radiochromic film for COMS eye plaques loaded with {sup 125}I seeds (model I25.S16)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Acar, Hilal; Chiu-Tsao, Sou-Tung; Oezbay, Ismail

Purpose: (1) To measure absolute dose distributions in eye phantom for COMS eye plaques with {sup 125}I seeds (model I25.S16) using radiochromic EBT film dosimetry. (2) To determine the dose correction function for calculations involving the TG-43 formalism to account for the presence of the COMS eye plaque using Monte Carlo (MC) method specific to this seed model. (3) To test the heterogeneous dose calculation accuracy of the new version of Plaque Simulator (v5.3.9) against the EBT film data for this seed model. Methods: Using EBT film, absolute doses were measured for {sup 125}I seeds (model I25.S16) in COMS eyemore » plaques (1) along the plaque's central axis for (a) uniformly loaded plaques (14-20 mm in diameter) and (b) a 20 mm plaque with single seed, and (2) in off-axis direction at depths of 5 and 12 mm for all four plaque sizes. The EBT film calibration was performed at {sup 125}I photon energy. MC calculations using MCNP5 code for a single seed at the center of a 20 mm plaque in homogeneous water and polystyrene medium were performed. The heterogeneity dose correction function was determined from the MC calculations. These function values at various depths were entered into PS software (v5.3.9) to calculate the heterogeneous dose distributions for the uniformly loaded plaques (of all four sizes). The dose distributions with homogeneous water assumptions were also calculated using PS for comparison. The EBT film measured absolute dose rate values (film) were compared with those calculated using PS with homogeneous assumption (PS Homo) and heterogeneity correction (PS Hetero). The values of dose ratio (film/PS Homo) and (film/PS Hetero) were obtained. Results: The central axis depth dose rate values for a single seed in 20 mm plaque measured using EBT film and calculated with MCNP5 code (both in ploystyrene phantom) were compared, and agreement within 9% was found. The dose ratio (film/PS Homo) values were substantially lower than unity (mostly between 0.8 and 0.9) for all four plaque sizes, indicating dose reduction by COMS plaque compared with homogeneous assumption. The dose ratio (film/PS Hetero) values were close to unity, indicating the PS Hetero calculations agree with those from the film study. Conclusions: Substantial heterogeneity effect on the {sup 125}I dose distributions in an eye phantom for COMS plaques was verified using radiochromic EBT film dosimetry. The calculated doses for uniformly loaded plaques using PS with heterogeneity correction option enabled were corroborated by the EBT film measurement data. Radiochromic EBT film dosimetry is feasible in measuring absolute dose distributions in eye phantom for COMS eye plaques loaded with single or multiple {sup 125}I seeds. Plaque Simulator is a viable tool for the calculation of dose distributions if one understands its limitations and uses the proper heterogeneity correction feature.« less

Poster — Thur Eve — 20: CTDI Measurements using a Radiochromic Film-based clinical protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quintero, C.; Bekerat, H.; DeBlois, F.

2014-08-15

The purpose of the study was evaluating accuracy and reproducibility of a radiochromic film-based protocol to measure computer tomography dose index (CTDI) as a part of annual QA on CT scanners and kV-CBCT systems attached to linear accelerators. Energy dependence of Gafchromic XR-QA2 ® film model was tested over imaging beam qualities (50 – 140 kVp). Film pieces were irradiated in air to known values of air-kerma (up to 10 cGy). Calibration curves for each beam quality were created (Film reflectance change Vs. Air-kerma in air). Film responses for same air-kerma values were compared. Film strips were placed into holesmore » of a CTDI phantom and irradiated for several clinical scanning protocols. Film reflectance change was converted into dose to water and used to calculate CTDIvol values. Measured and tabulated CTDIvol values were compared. Average variations of ±5.2% in the mean film reflectance change were observed in the energy range of 80 to 140 keV, and 11.1% between 50 and 140 keV. Measured CTDI values were in average 10% lower than tabulated CTDI values for CT-simulators, and 44% higher for CBCT systems. Results presented a mean variation for the same machine and protocol of 2.6%. Variation of film response is within ±5% resulting in ±15% systematic error in dose estimation if a single calibration curve is used. Relatively large discrepancy between measured and tabulated CTDI values strongly support the trend towards replacing CTDI value with equilibrium dose measurement in the center of cylindrical phantom, as suggested by TG- 111.« less

SU-E-T-50: Automatic Validation of Megavoltage Beams Modeled for Clinical Use in Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melchior, M; Salinas Aranda, F; 21st Century Oncology, Ft. Myers, FL

2014-06-01

Purpose: To automatically validate megavoltage beams modeled in XiO™ 4.50 (Elekta, Stockholm, Sweden) and Varian Eclipse™ Treatment Planning Systems (TPS) (Varian Associates, Palo Alto, CA, USA), reducing validation time before beam-on for clinical use. Methods: A software application that can automatically read and analyze DICOM RT Dose and W2CAD files was developed using MatLab integrated development environment.TPS calculated dose distributions, in DICOM RT Dose format, and dose values measured in different Varian Clinac beams, in W2CAD format, were compared. Experimental beam data used were those acquired for beam commissioning, collected on a water phantom with a 2D automatic beam scanningmore » system.Two methods were chosen to evaluate dose distributions fitting: gamma analysis and point tests described in Appendix E of IAEA TECDOC-1583. Depth dose curves and beam profiles were evaluated for both open and wedged beams. Tolerance parameters chosen for gamma analysis are 3% and 3 mm dose and distance, respectively.Absolute dose was measured independently at points proposed in Appendix E of TECDOC-1583 to validate software results. Results: TPS calculated depth dose distributions agree with measured beam data under fixed precision values at all depths analyzed. Measured beam dose profiles match TPS calculated doses with high accuracy in both open and wedged beams. Depth and profile dose distributions fitting analysis show gamma values < 1. Relative errors at points proposed in Appendix E of TECDOC-1583 meet therein recommended tolerances.Independent absolute dose measurements at points proposed in Appendix E of TECDOC-1583 confirm software results. Conclusion: Automatic validation of megavoltage beams modeled for their use in the clinic was accomplished. The software tool developed proved efficient, giving users a convenient and reliable environment to decide whether to accept or not a beam model for clinical use. Validation time before beam-on for clinical use was reduced to a few hours.« less

The radiation dose from a proposed measurement of arsenic and selenium in human skin

NASA Astrophysics Data System (ADS)

Gherase, Mihai R.; Mader, Joanna E.; Fleming, David E. B.

2010-09-01

Dose measurements following 10 min irradiations with a portable x-ray fluorescence spectrometer composed of a miniature x-ray tube and a silicon PiN diode detector were performed using thermoluminescent dosimeters consisting of LiF:Mg,Ti chips of 3 mm diameter and 0.4 mm thickness. The table-top setup of the spectrometer was used for all measurements. The setup included a stainless steel lid which served as a radiation shield. Two rectangular polyethylene skin/soft tissue phantoms with two cylindrical plaster of Paris bone phantoms were used to study the effect of x-ray beam attenuation and backscatter on the measured dose. Eight different irradiation experiments were performed. The average dose rate values measured with TLD chips within a 1 × 1 cm2 area were between 4.8 and 12.8 mGy min-1. The equivalent dose for a 1 × 1 cm2 skin area was estimated to be 13.2 mSv. The maximum measured dose rate values with a single TLD chip were between 7.5 and 25.1 mGy min-1. The effective dose corresponding to a proposed arsenic/selenium skin measurement was estimated to be 0.13 µSv for a 2 min irradiation.

Estimating systemic exposure to ethinyl estradiol from an oral contraceptive.

PubMed

Westhoff, Carolyn L; Pike, Malcolm C; Tang, Rosalind; DiNapoli, Marianne N; Sull, Monica; Cremers, Serge

2015-05-01

This study was conducted to compare single-dose pharmacokinetics of ethinyl estradiol in an oral contraceptive with steady-state values and to assess whether any simpler measures could provide an adequate proxy of the "gold standard" 24-hour steady-state area under the curve (AUC) value. Identification of a simple, less expensive measure of systemic ethinyl estradiol exposure would be useful for larger studies that are designed to assess the relationship between an individual's ethinyl estradiol exposure and side-effects. We collected 13 samples over 24 hours for pharmacokinetic analysis on days 1 and 21 of the first cycle of a monophasic oral contraceptive that contained 30 μg ethinyl estradiol and 150 μg levonorgestrel in 17 nonobese healthy white women. We also conducted an abbreviated single-dose 9-sample pharmacokinetic analysis after a month washout. Ethinyl estradiol was measured by liquid chromatography-tandem mass spectrometry. We compared results of a full 13-sample steady-state pharmacokinetic analysis with results that had been calculated with the use of fewer samples (9 or 5) and after the single doses. We calculated Pearson correlation coefficients to evaluate the relationships between these estimates of systemic ethinyl estradiol exposure. The AUC, maximum, and 24-hour values were similar after the 2 single oral contraceptive doses (AUC; r=0.92). The steady-state 13-sample 24-hour AUC value was correlated highly with the average 9-sample AUC value after the 2 single doses (r=0.81; P=.0002). This correlation remained the same if the number of single-dose samples was reduced to 4, taken at time 1, 2.5, 4, and 24 hours. The 24-hour value at steady-state was correlated highly with the 24-hour steady-state AUC value (r=0.92; P<.0001). The average of the 24-hour values after the 2 single doses was also correlated quite highly with the steady-state AUC value (r=0.72; P=.0026). Limited blood sampling, including results from 2 single doses, gave highly correlated estimates of an oral contraceptive user's steady-state ethinyl estradiol exposure. Copyright © 2015 Elsevier Inc. All rights reserved.

In vivo quality assurance of volumetric modulated arc therapy for ano-rectal cancer with thermoluminescent dosimetry and image-guidance.

PubMed

Dipasquale, Giovanna; Nouet, Philippe; Rouzaud, Michel; Dubouloz, Angèle; Miralbell, Raymond; Zilli, Thomas

2014-06-01

To assess in vivo dose distribution using cone-beam computed tomography scans (CBCTs) and thermoluminescent dosimeters (TLDs) in patients with anal or rectal cancer treated with volumetric modulated arc therapy (VMAT). Intracavitary (IC) in vivo dosimetry (IVD) was performed in 11 patients using adapted endorectal probes containing TLDs, with extra measurements at the perianal skin (PS) for anal margin tumors. Measured doses were compared to calculated ones obtained from image fusion of CBCT with CT treatments plans. A total of 55 IC and 6 PS measurements were analyzed. IC TLD median planned and measured doses were 1.81 Gy (range, 0.25-2.02 Gy) and 1.82 Gy (range, 0.19-2.12 Gy), respectively. In comparison to the planned doses all IC TLD dose measurements differed by a median dose of 0.02 Gy (range, -0.11/+0.19 Gy, p=0.102) (median difference of 1.1%, range -6.1%/+10.6%). Overall, 95% of IC measurements were within ±7.7% of the expected percentage doses and only 1 value was above +10%. For PS measurements, only one was not within ±7.7% of expected values (i.e., -8.9%). Image guidance using CBCT for IVD with TLDs is helpful to validate the delivered doses in patients treated with VMAT for ano-rectal tumors. Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Quantifying the effect of air gap, depth, and range shifter thickness on TPS dosimetric accuracy in superficial PBS proton therapy.

PubMed

Shirey, Robert J; Wu, Hsinshun Terry

2018-01-01

This study quantifies the dosimetric accuracy of a commercial treatment planning system as functions of treatment depth, air gap, and range shifter thickness for superficial pencil beam scanning proton therapy treatments. The RayStation 6 pencil beam and Monte Carlo dose engines were each used to calculate the dose distributions for a single treatment plan with varying range shifter air gaps. Central axis dose values extracted from each of the calculated plans were compared to dose values measured with a calibrated PTW Markus chamber at various depths in RW3 solid water. Dose was measured at 12 depths, ranging from the surface to 5 cm, for each of the 18 different air gaps, which ranged from 0.5 to 28 cm. TPS dosimetric accuracy, defined as the ratio of calculated dose relative to the measured dose, was plotted as functions of depth and air gap for the pencil beam and Monte Carlo dose algorithms. The accuracy of the TPS pencil beam dose algorithm was found to be clinically unacceptable at depths shallower than 3 cm with air gaps wider than 10 cm, and increased range shifter thickness only added to the dosimetric inaccuracy of the pencil beam algorithm. Each configuration calculated with Monte Carlo was determined to be clinically acceptable. Further comparisons of the Monte Carlo dose algorithm to the measured spread-out Bragg Peaks of multiple fields used during machine commissioning verified the dosimetric accuracy of Monte Carlo in a variety of beam energies and field sizes. Discrepancies between measured and TPS calculated dose values can mainly be attributed to the ability (or lack thereof) of the TPS pencil beam dose algorithm to properly model secondary proton scatter generated in the range shifter. © 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

Ambient dose equivalent and effective dose from scattered x-ray spectra in mammography for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations.

PubMed

Künzel, R; Herdade, S B; Costa, P R; Terini, R A; Levenhagen, R S

2006-04-21

In this study, scattered x-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammographic conditions by using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 and 30 kV tube voltages. Energy spectra of the scattered x-rays have been measured with a Cd(0.9)Zn(0.1)Te (CZT) detector for scattering angles between 30 degrees and 165 degrees . Measurement and correction processes have been evaluated through the comparison between the values of the half-value layer (HVL) and air kerma calculated from the corrected spectra and measured with an ionization chamber in a nonclinical x-ray system with a W/Mo anode/filter combination. The shape of the corrected x-ray spectra measured in the nonclinical system was also compared with those calculated using semi-empirical models published in the literature. Scattered x-ray spectra measured in the clinical x-ray system have been characterized through the calculation of HVL and mean photon energy. Values of the air kerma, ambient dose equivalent and effective dose have been evaluated through the corrected x-ray spectra. Mean conversion coefficients relating the air kerma to the ambient dose equivalent and to the effective dose from the scattered beams for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations were also evaluated. Results show that for the scattered radiation beams the ambient dose equivalent provides an overestimate of the effective dose by a factor of about 5 in the mammography energy range. These results can be used in the control of the dose limits around a clinical unit and in the calculation of more realistic protective shielding barriers in mammography.

Solar UV radiation exposure of seamen - Measurements, calibration and model calculations of erythemal irradiance along ship routes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feister, Uwe; Meyer, Gabriele; Kirst, Ulrich

2013-05-10

Seamen working on vessels that go along tropical and subtropical routes are at risk to receive high doses of solar erythemal radiation. Due to small solar zenith angles and low ozone values, UV index and erythemal dose are much higher than at mid-and high latitudes. UV index values at tropical and subtropical Oceans can exceed UVI = 20, which is more than double of typical mid-latitude UV index values. Daily erythemal dose can exceed the 30-fold of typical midlatitude winter values. Measurements of erythemal exposure of different body parts on seamen have been performed along 4 routes of merchant vessels.more » The data base has been extended by two years of continuous solar irradiance measurements taken on the mast top of RV METEOR. Radiative transfer model calculations for clear sky along the ship routes have been performed that use satellite-based input for ozone and aerosols to provide maximum erythemal irradiance and dose. The whole data base is intended to be used to derive individual erythemal exposure of seamen during work-time.« less

Estimation of skin entrance doses (SEDs) for common medical X-ray diagnostic examinations in India and proposed diagnostic reference levels (DRLs).

PubMed

Sonawane, A U; Shirva, V K; Pradhan, A S

2010-02-01

Skin entrance doses (SEDs) were estimated by carrying out measurements of air kerma from 101 X-ray machines installed in 45 major and selected hospitals in the country by using a silicon detector-based dose Test-O-Meter. 1209 number of air kerma measurements of diagnostic projections for adults have been analysed for seven types of common diagnostic examinations, viz. chest (AP, PA, LAT), lumbar spine (AP, LAT), thoracic spine (AP, LAT), abdomen (AP), pelvis (AP), hip joints (AP) and skull (PA, LAT) for different film-screen combinations. The values of estimated diagnostic reference levels (DRLs) (third quartile values of SEDs) were compared with guidance levels/DRLs of doses published by the IAEA-BSS-Safety Series No. 115, 1996; HPA (NRPB) (2000 and 2005), UK; CRCPD/CDRH (USA), European Commission and other national values. The values of DRLs obtained in this study are comparable with the values published by the IAEA-BSS-115 (1996); HPA (NRPB) (2000 and 2005) UK; EC and CRCPD/CDRH, USA including values obtained in previous studies in India.

Role of the standard deviation in the estimation of benchmark doses with continuous data.

PubMed

Gaylor, David W; Slikker, William

2004-12-01

For continuous data, risk is defined here as the proportion of animals with values above a large percentile, e.g., the 99th percentile or below the 1st percentile, for the distribution of values among control animals. It is known that reducing the standard deviation of measurements through improved experimental techniques will result in less stringent (higher) doses for the lower confidence limit on the benchmark dose that is estimated to produce a specified risk of animals with abnormal levels for a biological effect. Thus, a somewhat larger (less stringent) lower confidence limit is obtained that may be used as a point of departure for low-dose risk assessment. It is shown in this article that it is important for the benchmark dose to be based primarily on the standard deviation among animals, s(a), apart from the standard deviation of measurement errors, s(m), within animals. If the benchmark dose is incorrectly based on the overall standard deviation among average values for animals, which includes measurement error variation, the benchmark dose will be overestimated and the risk will be underestimated. The bias increases as s(m) increases relative to s(a). The bias is relatively small if s(m) is less than one-third of s(a), a condition achieved in most experimental designs.

Assessment of radiation exposure in dental cone-beam computerized tomography with the use of metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters and Monte Carlo simulations.

PubMed

Koivisto, J; Kiljunen, T; Tapiovaara, M; Wolff, J; Kortesniemi, M

2012-09-01

The aims of this study were to assess the organ and effective dose (International Commission on Radiological Protection (ICRP) 103) resulting from dental cone-beam computerized tomography (CBCT) imaging using a novel metal-oxide semiconductor field-effect transistor (MOSFET) dosimeter device, and to assess the reliability of the MOSFET measurements by comparing the results with Monte Carlo PCXMC simulations. Organ dose measurements were performed using 20 MOSFET dosimeters that were embedded in the 8 most radiosensitive organs in the maxillofacial and neck area. The dose-area product (DAP) values attained from CBCT scans were used for PCXMC simulations. The acquired MOSFET doses were then compared with the Monte Carlo simulations. The effective dose measurements using MOSFET dosimeters yielded, using 0.5-cm steps, a value of 153 μSv and the PCXMC simulations resulted in a value of 136 μSv. The MOSFET dosimeters placed in a head phantom gave results similar to Monte Carlo simulations. Minor vertical changes in the positioning of the phantom had a substantial affect on the overall effective dose. Therefore, the MOSFET dosimeters constitute a feasible method for dose assessment of CBCT units in the maxillofacial region. Copyright © 2012 Elsevier Inc. All rights reserved.

A method to correct for temperature dependence and measure simultaneously dose and temperature using a plastic scintillation detector

PubMed Central

Therriault-Proulx, Francois; Wootton, Landon; Beddar, Sam

2015-01-01

Plastic scintillation detectors (PSDs) work well for radiation dosimetry. However, they show some temperature dependence, and a priori knowledge of the temperature surrounding the PSD is required to correct for this dependence. We present a novel approach to correct PSD response values for temperature changes instantaneously and without the need for prior knowledge of the temperature value. In addition to rendering the detector temperature-independent, this approach allows for actual temperature measurement using solely the PSD apparatus. With a temperature-controlled water tank, the temperature was varied from room temperature to more than 40°C and the PSD was used to measure the dose delivered from a cobalt-60 photon beam unit to within an average of 0.72% from the expected value. The temperature was measured during each acquisition with the PSD and a thermocouple and values were within 1°C of each other. The depth-dose curve of a 6-MV photon beam was also measured under warm non-stable conditions and this curve agreed to within an average of −0.98% from the curve obtained at room temperature. The feasibility of rendering PSDs temperature-independent was demonstrated with our approach, which also enabled simultaneous measurement of both dose and temperature. This novel approach improves both the robustness and versatility of PSDs. PMID:26407188

Dose measurements and radiation protection measures in gynecological radium therapy for medical-technical assistants and nursing staff (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, B.

Thesis. Appropriate measures to decrease radiation exposure of medical- technical assistants and nursing staff of hospitals with radiotherapy departments require personnel dose measurements during the different working operations. The measured values were in all cases below the maximum permissible doses; they are presented in tabular form for the various operations. Proposals are made for a further reduction of radiation exposure in particular fields of application. (GE)

Comparison of skin dose measurement using nanoDot® dosimeter and machine readings of radiation dose during cardiac catheterization in children

PubMed Central

Balaguru, Duraisamy; Rodriguez, Matthew; Leon, Stephanie; Wagner, Louis K; Beasley, Charles W; Sultzer, Andrew; Numan, Mohammed T

2018-01-01

Objectives: Direct measurement of skin dose of radiation for children using optically stimulated luminescence (OSL) technology using nanoDot® (Landauer, Glenwood, IL, USA). Background: Radiation dose is estimated as cumulative air kerma (AK) and dosearea product based on standards established for adult size patients. Body size of pediatric patients who undergo cardiac catheterization for congenital heart disease vary widely from newborn to adolescence. Direct, skindose measurement applying OSL technology may eliminate errors in the estimate. Materials and Methods: The nanoDot® (1 cm × 1 cm × flat plastic cassette) is applied to patient's skin using adhesive tape during cardiac catheterization and radiation skin doses were read within 24 hrs. nanoDot® values were compared to the currently available cumulative AK values estimated and displayed on fluoroscopy monitor. Results: A total of 12 children were studied, aged 4 months to 18 years (median 1.1 years) and weight range 5.3–86 kg (median 8.4 kg). nanoDot® readings ranged from 2.58 mGy to 424.8 mGy (median 84.1 mGy). Cumulative AK ranged from 16.2 mGy to 571.2 mGy (median 171.1 mGy). Linear correlation was noted between nanoDot® values and AK values (R2 = 0.88, R = 0.94). nanoDot® readings were approximately 65% of the estimated cumulative AK estimated using the International Electrotechnical Commission standards. Conclusions: Application of OSL technology using nanoDot® provides an alternative to directly measure fluoroscopic skin dose in children during cardiac catheterization. Our data show that the actual skin dose for children is approximately one-third lower than the AK estimated using international standards for adult size patients. PMID:29440825

Comparison of skin dose measurement using nanoDot® dosimeter and machine readings of radiation dose during cardiac catheterization in children.

PubMed

Balaguru, Duraisamy; Rodriguez, Matthew; Leon, Stephanie; Wagner, Louis K; Beasley, Charles W; Sultzer, Andrew; Numan, Mohammed T

2018-01-01

Direct measurement of skin dose of radiation for children using optically stimulated luminescence (OSL) technology using nanoDot ® (Landauer, Glenwood, IL, USA). Radiation dose is estimated as cumulative air kerma (AK) and dosearea product based on standards established for adult size patients. Body size of pediatric patients who undergo cardiac catheterization for congenital heart disease vary widely from newborn to adolescence. Direct, skindose measurement applying OSL technology may eliminate errors in the estimate. The nanoDot ® (1 cm × 1 cm × flat plastic cassette) is applied to patient's skin using adhesive tape during cardiac catheterization and radiation skin doses were read within 24 hrs. nanoDot ® values were compared to the currently available cumulative AK values estimated and displayed on fluoroscopy monitor. A total of 12 children were studied, aged 4 months to 18 years (median 1.1 years) and weight range 5.3-86 kg (median 8.4 kg). nanoDot® readings ranged from 2.58 mGy to 424.8 mGy (median 84.1 mGy). Cumulative AK ranged from 16.2 mGy to 571.2 mGy (median 171.1 mGy). Linear correlation was noted between nanoDot® values and AK values ( R 2 = 0.88, R = 0.94). nanoDot® readings were approximately 65% of the estimated cumulative AK estimated using the International Electrotechnical Commission standards. Application of OSL technology using nanoDot® provides an alternative to directly measure fluoroscopic skin dose in children during cardiac catheterization. Our data show that the actual skin dose for children is approximately one-third lower than the AK estimated using international standards for adult size patients.

Individual dose reconstruction among residents living in the vicinity of the Semipalatinsk nuclear test site using EPR spectroscopy of tooth enamel.

PubMed

Ivannikov, A I; Zhumadilov, Zh; Gusev, B I; Miyazawa, Ch; Jiao, L; Skvortsov, V G; Stepanenko, V F; Takada, J; Hoshi, M

2002-08-01

Individual accumulated doses were determined by EPR spectroscopy of tooth enamel for 26 adult persons residing in territories adjacent to the Semipalatinsk Nuclear Test Site (SNTS). The absorbed dose values due to radiation from nuclear tests were obtained after subtracting the contribution of natural background radiation from the total accumulated dose. The determined dose values ranged up to 250 mGy, except for one person from Semipalatinsk city with a measured dose of 2.8 +/- 0.4 Gy. Increased dose values were determined for the individuals whose teeth were formed before 1962, the end of the atmospheric nuclear tests. These values were found to be significantly larger than those obtained for a group of younger residents of heavily exposed territories and the residents of territories not exposed to radioactive fallout. These increased dose values are consistent with those based on officially registered data for the Northeastern part of Kazakstan adjacent to SNTS, which was exposed to high levels of radioactive fallout from nuclear tests in period 1949-1962.

SU-F-T-08: Brachytherapy Film Dosimetry in a Water Phantom for a Ring and Tandem HDR Applicator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, B; Grelewicz, Z; Kang, Z

2016-06-15

Purpose: The feasibility of dose measurement using new generation EBT3 film was explored in a water phantom for a ring and tandem HDR applicator for measurements tracking mucosal dose during cervical brachytherapy. Methods: An experimental fixture was assembled to position the applicator in a water phantom. Prior to measurement, calibration curves for EBT3 film in water and in solidwater were verified. EBT3 film was placed at different known locations around the applicator in the water tank. A CT scan of the phantom with applicator was performed using clinical protocol. A typical cervical cancer treatment plan was then generated by Oncentramore » brachytherapy planning system. A dose of 500 cGy was prescribed to point A (2 cm, 2 cm). Locations measured by film included the outer surface of the ring, measurement point A-m (2.2 cm, 2.2 cm), and profiles extending from point A-m parallel to the tandem. Three independent measurements were conducted. The doses recorded by film were carefully analyzed and compared with values calculated by the treatment planning system. Results: Assessment of the EBT3 films indicate that the dose at point A matches the values predicted by the planning system. Dose to the point A-m was 411.5 cGy, and the outer circumferential surface dose of the ring was between 500 and 1150 cGy. It was found that from the point A-m, the dose drops 60% within 4.5 cm on the line parallel to the tandem. The measurement doses agree with the treatment planning system. Conclusion: Use of EBT3 film is feasible for in-water measurements for brachytherapy. A carefully machined apparatus will likely improve measurement accuracy. In a typical plan, our study found that the ring surface dose can be 2.5 times larger than the point A prescription dose. EBT3 film can be used to monitor mucosal dose in brachytherapy treatments.« less

WE-DE-201-07: Measurement of Real-Time Dose for Tandem and Ovoid Brachytherapy Procedures Using a High Precision Optical Fiber Radiation Detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belley, MD; Current Address Rhode Island Hospital, Providence, RI; Faught, A

Purpose: Development of a novel on-line dosimetry tool is needed to move toward patient-specific quality assurance measurements for Ir-192 HDR brachytherapy to verify accurate dose delivery to the intended location. This work describes the development and use of a nano-crystalline yttrium oxide inorganic scintillator based optical-fiber detector capable of acquiring real-time high-precision dose measurements during tandem and ovoid (T&O) gynecological (GYN) applicator Ir-192 HDR brachytherapy procedures. Methods: An optical-fiber detector was calibrated by acquiring light output measurements in liquid water at 3, 5, 7, and 9cm radial source-detector-distances from an Ir-192 HDR source. A regression model was fit to themore » data to describe the relative light output per unit dose (TG-43 derived) as a function of source-detector-distance. Next, the optical-fiber detector was attached to a vaginal balloon fixed to a Varian Fletcher-Suit-Delclos-style applicator (to mimic clinical setup), and localized by acquiring high-resolution computed tomography (CT) images. To compare the physical point dose to the TPS calculated values (TG-43 and Acuros-BV), a phantom measurement was performed, by submerging the T&O applicator in a liquid water bath and delivering a treatment template representative of a clinical T&O procedure. The fiber detector collected scintillation signal as a function of time, and the calibration data was applied to calculate both real-time dose rate, and cumulative dose. Results: Fiber cumulative dose values were 100.0cGy, 94.3cGy, and 348.9cGy from the tandem, left ovoid, and right ovoid dwells, respectively (total of 443.2cGy). A plot of real time dose rate during the treatment was also acquired. The TPS values at the fiber location were 458.4cGy using TG-43, and 437.6cGy using Acuros-BV calculated as Dm,m (per TG-186). Conclusion: The fiber measured dose value agreement was 3% vs TG-43 and −1% vs Acuros-BV. This fiber detector opens up new possibilities for performing patient-specific quality assurance for Ir-192 HDR GYN procedures. Funding from Coulter Foundation, Duke Bio-medical Engineering. Company is being created around the detector technology. Duke holds patents on the technology.« less

Real Time Radiation Monitoring Using Nanotechnology

NASA Technical Reports Server (NTRS)

Li, Jing (Inventor); Hanratty, James J. (Inventor); Wilkins, Richard T. (Inventor); Lu, Yijiang (Inventor)

2016-01-01

System and method for monitoring receipt and estimating flux value, in real time, of incident radiation, using two or more nanostructures (NSs) and associated terminals to provide closed electrical paths and to measure one or more electrical property change values .DELTA.EPV, associated with irradiated NSs, during a sequence of irradiation time intervals. Effects of irradiation, without healing and with healing, of the NSs, are separately modeled for first order and second order healing. Change values.DELTA.EPV are related to flux, to cumulative dose received by NSs, and to radiation and healing effectivity parameters and/or.mu., associated with the NS material and to the flux. Flux and/or dose are estimated in real time, based on EPV change values, using measured .DELTA.EPV values. Threshold dose for specified changes of biological origin (usually undesired) can be estimated. Effects of time-dependent radiation flux are analyzed in pre-healing and healing regimes.

A pragmatic approach to determine the optimal kVp in cone beam CT: balancing contrast-to-noise ratio and radiation dose

PubMed Central

Silkosessak, O; Jacobs, R; Bogaerts, R; Bosmans, H; Panmekiate, S

2014-01-01

Objectives: To determine the optimal kVp setting for a particular cone beam CT (CBCT) device by maximizing technical image quality at a fixed radiation dose. Methods: The 3D Accuitomo 170 (J. Morita Mfg. Corp., Kyoto, Japan) CBCT was used. The radiation dose as a function of kVp was measured in a cylindrical polymethyl methacrylate (PMMA) phantom using a small-volume ion chamber. Contrast-to-noise ratio (CNR) was measured using a PMMA phantom containing four materials (air, aluminium, polytetrafluoroethylene and low-density polyethylene), which was scanned using 180 combinations of kVp/mA, ranging from 60/1 to 90/8. The CNR was measured for each material using PMMA as background material. The pure effect of kVp and mAs on the CNR values was analysed. Using a polynomial fit for CNR as a function of mA for each kVp value, the optimal kVp was determined at five dose levels. Results: Absorbed doses ranged between 0.034 mGy mAs−1 (14 × 10 cm, 60 kVp) and 0.108 mGy mAs−1 (14 × 10 cm, 90 kVp). The relation between kVp and dose was quasilinear (R2 > 0.99). The effect of mA and kVp on CNR could be modelled using a second-degree polynomial. At a fixed dose, there was a tendency for higher CNR values at increasing kVp values, especially at low dose levels. A dose reduction through mA was more efficient than an equivalent reduction through kVp in terms of image quality deterioration. Conclusions: For the investigated CBCT model, the most optimal contrast at a fixed dose was found at the highest available kVp setting. There is great potential for dose reduction through mA with a minimal loss in image quality. PMID:24708447

128 slice computed tomography dose profile measurement using thermoluminescent dosimeter

NASA Astrophysics Data System (ADS)

Salehhon, N.; Hashim, S.; Karim, M. K. A.; Ang, W. C.; Musa, Y.; Bahruddin, N. A.

2017-05-01

The increasing use of computed tomography (CT) in clinical practice marks the needs to understand the dose descriptor and dose profile. The purposes of the current study were to determine the CT dose index free-in-air (CTDIair) in 128 slice CT scanner and to evaluate the single scan dose profile (SSDP). Thermoluminescent dosimeters (TLD-100) were used to measure the dose profile of the scanner. There were three sets of CT protocols where the tube potential (kV) setting was manipulated for each protocol while the rest of parameters were kept constant. These protocols were based from routine CT abdominal examinations for male adult abdomen. It was found that the increase of kV settings made the values of CTDIair increased as well. When the kV setting was changed from 80 kV to 120 kV and from 120 kV to 140 kV, the CTDIair values were increased as much as 147.9% and 53.9% respectively. The highest kV setting (140 kV) led to the highest CTDIair value (13.585 mGy). The p-value of less than 0.05 indicated that the results were statistically different. The SSDP showed that when the kV settings were varied, the peak sharpness and height of Gaussian function profiles were affected. The full width at half maximum (FWHM) of dose profiles for all protocols were coincided with the nominal beam width set for the measurements. The findings of the study revealed much information on the characterization and performance of 128 slice CT scanner.

Reduction in radiation dose with reconstruction technique in the brain perfusion CT

NASA Astrophysics Data System (ADS)

Kim, H. J.; Lee, H. K.; Song, H.; Ju, M. S.; Dong, K. R.; Chung, W. K.; Cho, M. S.; Cho, J. H.

2011-12-01

The principal objective of this study was to verify the utility of the reconstruction imaging technique in the brain perfusion computed tomography (PCT) scan by assessing reductions in the radiation dose and analyzing the generated images. The setting used for image acquisition had a detector coverage of 40 mm, a helical thickness of 0.625 mm, a helical shuttle mode scan type and a rotation time of 0.5 s as the image parameters used for the brain PCT scan. Additionally, a phantom experiment and an animal experiment were carried out. In the phantom and animal experiments, noise was measured in the scanning with the tube voltage fixed at 80 kVp (kilovolt peak) and the level of the adaptive statistical iterative reconstruction (ASIR) was changed from 0% to 100% at 10% intervals. The standard deviation of the CT coefficient was measured three times to calculate the mean value. In the phantom and animal experiments, the absorbed dose was measured 10 times under the same conditions as the ones for noise measurement before the mean value was calculated. In the animal experiment, pencil-type and CT-dedicated ionization chambers were inserted into the central portion of pig heads for measurement. In the phantom study, as the level of the ASIR changed from 0% to 100% under identical scanning conditions, the noise value and dose were proportionally reduced. In our animal experiment, the noise value was lowest when the ASIR level was 50%, unlike in the phantom study. The dose was reduced as in the phantom study.

Radiation exposure of contrast-enhanced spectral mammography compared with full-field digital mammography.

PubMed

Jeukens, Cécile R L P N; Lalji, Ulrich C; Meijer, Eduard; Bakija, Betina; Theunissen, Robin; Wildberger, Joachim E; Lobbes, Marc B I

2014-10-01

Contrast-enhanced spectral mammography (CESM) shows promising initial results but comes at the cost of increased dose as compared with full-field digital mammography (FFDM). We aimed to quantitatively assess the dose increase of CESM in comparison with FFDM. Radiation exposure-related data (such as kilovoltage, compressed breast thickness, glandularity, entrance skin air kerma (ESAK), and average glandular dose (AGD) were retrieved for 47 CESM and 715 FFDM patients. All examinations were performed on 1 mammography unit. Radiation dose values reported by the unit were validated by phantom measurements. Descriptive statistics of the patient data were generated using a statistical software package. Dose values reported by the mammography unit were in good qualitative agreement with those of phantom measurements. Mean ESAK was 10.5 mGy for a CESM exposure and 7.46 mGy for an FFDM exposure. Mean AGD for a CESM exposure was 2.80 mGy and 1.55 mGy for an FFDM exposure. Compared with our institutional FFDM, the AGD of a single CESM exposure is increased by 1.25 mGy (+81%), whereas ESAK is increased by 3.07 mGy (+41%). Dose values of both techniques meet the recommendations for maximum dose in mammography.

Eye lens dosimetry in interventional cardiology: results of staff dose measurements and link to patient dose levels.

PubMed

Antic, V; Ciraj-Bjelac, O; Rehani, M; Aleksandric, S; Arandjic, D; Ostojic, M

2013-01-01

Workers involved in interventional cardiology procedures receive high eye lens dose if protection is not used. Currently, there is no suitable method for routine use for the measurement of eye dose. Since most angiography machines are equipped with suitable patient dosemeters, deriving factors linking staff eye doses to the patient doses can be helpful. In this study the patient kerma-area product, cumulative dose at an interventional reference point and eye dose in terms of Hp(3) of the cardiologists, nurses and radiographers for interventional cardiology procedures have been measured. Correlations between the patient dose and the staff eye dose were obtained. The mean eye dose was 121 µSv for the first operator, 33 µSv for the second operator/nurse and 12 µSv for radiographer. Normalised eye lens doses per unit kerma-area product were 0.94 µSv Gy⁻¹ cm⁻² for the first operator, 0.33 µSv Gy⁻¹ cm⁻² for the second operator/nurse and 0.16 µSv Gy⁻¹ cm⁻² for radiographers. Statistical analysis indicated that there is a weak but significant (p < 0.01) correlation between the eye dose and the kerma-area product for all three staff categories. These values are based on a local practice and may provide useful reference for other studies for validation and for wider utilisation in assessing the eye dose using patient dose values.

High Atomic Number Contrast Media Offer Potential for Radiation Dose Reduction in Contrast-Enhanced Computed Tomography.

PubMed

Roessler, Ann-Christin; Hupfer, Martin; Kolditz, Daniel; Jost, Gregor; Pietsch, Hubertus; Kalender, Willi A

2016-04-01

Spectral optimization of x-ray computed tomography (CT) has led to substantial radiation dose reduction in contrast-enhanced CT studies using standard iodinated contrast media. The purpose of this study was to analyze the potential for further dose reduction using high-atomic-number elements such as hafnium and tungsten. As in previous studies, spectra were determined for which the patient dose necessary to provide a given contrast-to-noise ratio (CNR) is minimized. We used 2 different quasi-anthropomorphic phantoms representing the liver cross-section of a normal adult and an obese adult patient with the lateral widths of 360 and 460 mm and anterior-posterior heights of 200 and 300 mm, respectively. We simulated and measured on 2 different scanners with x-ray spectra from 80 to 140 kV and from 70 to 150 kV, respectively. We determined the contrast for iodine-, hafnium-, and tungsten-based contrast media, the noise, and 3-dimensional dose distributions at all available tube voltages by measurements and by simulations. The dose-weighted CNR was determined as optimization parameter. Simulations and measurements were in good agreement regarding their dependence on energy for all parameters investigated. Hafnium provided the best performance for normal and for obese patient phantoms, indicating a dose reduction potential of 30% for normal and 50% for obese patients at 120 kV compared with iodine; this advantage increased further with higher kV values. Dose-weighted CNR values for tungsten were always slightly below the hafnium results. Iodine proved to be the superior choice at voltage values of 80 kV and below. Hafnium and tungsten both seem to be candidates for contrast-medium-enhanced CT of normal and obese adult patients with strongly reduced radiation dose at unimpaired image quality. Computed tomography examinations of obese patients will decrease in dose for higher kV values.

Dosimetry and image quality assessment in a direct radiography system

PubMed Central

Oliveira, Bruno Beraldo; de Oliveira, Marcio Alves; Paixão, Lucas; Teixeira, Maria Helena Araújo; Nogueira, Maria do Socorro

2014-01-01

Objective To evaluate the mean glandular dose with a solid state detector and the image quality in a direct radiography system, utilizing phantoms. Materials and Methods Irradiations were performed with automatic exposure control and polymethyl methacrylate slabs with different thicknesses to calculate glandular dose values. The image quality was evaluated by means of the structures visualized on the images of the phantoms. Results Considering the uncertainty of the measurements, the mean glandular dose results are in agreement with the values provided by the equipment and with internationally adopted reference levels. Results obtained from images of the phantoms were in agreement with the reference values. Conclusion The present study contributes to verify the equipment conformity as regards dose values and image quality. PMID:25741119

[Impact of exposure dose reduction of radiation treatment planning CT using low tube voltage technique].

PubMed

Kouno, Takuya; Kuga, Noriyuki; Enzaki, Masahiro; Yamashita, Yuuki; Kitazato, Yumiko; Shimotabira, Haruhiko; Jinnouchi, Takashi; Kusuhara, Kazuo; Kawamura, Shinji

2015-04-01

The aim of this study was to reduce the exposed dose of radiotherapy treatment planning computed tomography (CT) by using low tube voltage technique. We used tube voltages of 80 kV, 100 kV, and 120 kV, respectively. First, we evaluated exposure dose with CT dose index (CTDI) for each voltage. Second, we compared image quality indexes such as modulation transfer function (MTF), noise power spectrum (NPS), and contrast to noise ratio (CNR) of phantom images with each voltage. Third, CT to electron density tables were measured in three voltages and monitor unit value was calculated along with clinical cases. Finally, CT surface exposed dose of chest skin was measured by thermoluminescent dosimeter (TLD). In image evaluation MTF and NPS were approximately equal; CNR slightly decreased, 2.0% for 100 kV. We performed check radiation dose accuracy for each tube voltage with each model phantom. As a result, the difference of MU value was not accepted. Finally, compared with 120 kV, CTDIvol and TLD value showed markedly decreased radiation dose, 60% for 80 kV and 30% for 100 kV. Using a technique with low tube voltages, especially 100 kV, is useful in radiotherapy treatment planning to obtain 20% dose reduction without compromising 120 kV image quality.

In-vivo rectal dose measurements with diodes to avoid misadministrations during intracavitary high dose rate brachytherapy for carcinoma of the cervix.

PubMed

Alecu, R; Alecu, M

1999-05-01

Our purpose in this paper is to present an in vivo dosimetry program designed both for measuring the rectal dose and for avoiding misadministrations in gynecological intracavitary implants. A device containing an energy compensated diode was specially designed for these measurements. Our calibration procedure as well as the clinical protocol is described. Measurements have been performed for 50 treatments delivered with a Fletcher Suit Delclos applicator. The calculated and in vivo measured values for the "20% reading," i.e., the dose delivered to the diode by the initial 20% of the total dwell time, agreed to within 15%.

[Determination of radioactivity by smartphones].

PubMed

Hartmann, H; Freudenberg, R; Andreeff, M; Kotzerke, J

2013-01-01

The interest in the detection of radioactive materials has strongly increased after the accident in the nuclear power plant Fukushima and has led to a bottleneck of suitable measuring instruments. Smartphones equipped with a commercially available software tool could be used for dose rate measurements following a calibration according to the specific camera module. We examined whether such measurements provide reliable data for typical activities and radionuclides in nuclear medicine. For the nuclides 99mTc (10 - 1000 MBq), 131I (3.7 - 1800 MBq, therapy capsule) and 68Ga (50 - 600 MBq) radioactivity with defined geometry in different distances was measured. The smartphones Milestone Droid 1 (Motorola) and HTC Desire (HTC Corporation) were compared with the standard instruments AD6 (automess) and DoseGUARD (AEA Technology). Measurements with the smartphones and the other devices show a good agreement: linear signal increase with rising activity and dose rate. The long time measurement (131I, 729 MBq, 0.5 m, 60 min) demonstrates a considerably higher variation (by 20%) of the measured smartphone data values compared with the AD6. For low dose rates (< 1 µGy/h), the sensitivity decreases so that measurements of e. g. the natural radiation exposure do not lead to valid results. The calibration of the camera responsivity for the smartphone has a big influence on the results caused by the small detector surface of the camera semiconductor. With commercial software the camera module of a smartphone can be used for the measurement of radioactivity. Dose rates resulting from typical nuclear medicine procedures can be measured reliably (e. g., dismissal dose after radioiodine therapy). The signal shows a high correlation to measured values of conventional dose measurement devices.

Estimation of Eye Lens Dose During Brain Scans Using Gafchromic Xr-QA2 Film in Various Multidetector CT Scanners.

PubMed

Akhilesh, Philomina; Kulkarni, Arti R; Jamhale, Shramika H; Sharma, S D; Kumar, Rajesh; Datta, D

2017-04-25

The purpose of this study was to estimate eye lens dose during brain scans in 16-, 64-, 128- and 256-slice multidetector computed tomography (CT) scanners in helical acquisition mode and to test the feasibility of using radiochromic film as eye lens dosemeter during CT scanning. Eye lens dose measurements were performed using Gafchromic XR-QA2 film on a polystyrene head phantom designed with outer dimensions equivalent to the head size of a reference Indian man. The response accuracy of XR-QA2 film was validated by using thermoluminescence dosemeters. The eye lens dose measured using XR-QA2 film on head phantom for plain brain scanning in helical mode ranged from 43.8 to 45.8 mGy. The XR-QA2 film measured dose values were in agreement with TLD measured dose values within a maximum variation of 8.9%. The good correlation between the two data sets confirms the viability of using XR-QA2 film for eye lens dosimetry. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The evaluation of the neutron dose equivalent in the two-bend maze.

PubMed

Tóth, Á Á; Petrović, B; Jovančević, N; Krmar, M; Rutonjski, L; Čudić, O

2017-04-01

The purpose of this study was to explore the effect of the second bend of the maze, on the neutron dose equivalent, in the 15MV linear accelerator vault, with two bend maze. These two bends of the maze were covered by 32 points where the neutron dose equivalent was measured. There is one available method for estimation of the neutron dose equivalent at the entrance door of the two bend maze which was tested using the results of the measurements. The results of this study show that the neutron equivalent dose at the door of the two bend maze was reduced almost three orders of magnitude. The measured TVD in the first bend (closer to the inner maze entrance) is about 5m. The measured TVD result is close to the TVD values usually used in the proposed models for estimation of neutron dose equivalent at the entrance door of the single bend maze. The results also determined that the TVD in the second bend (next to the maze entrance door) is significantly lower than the TVD values found in the first maze bend. Copyright © 2017 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Assessment of target dose delivery in anal cancer using in vivo thermoluminescent dosimetry.

PubMed

Weber, D C; Nouet, P; Kurtz, J M; Allal, A S

2001-04-01

To measure anal dose during external beam radiotherapy (EBRT) using in vivo dosimetry, to study the difference of measured from prescribed dose values, and to evaluate possible associations of such differences with acute and late skin/mucosal toxicity and anorectal function. Thirty-one patients with localized anal carcinoma underwent in vivo measurements during the first EBRT session. Themoluminescent dosimeters (TLD) were placed at the center of the anal verge according to a localization protocol. No bolus was used. Patients received a median dose of 39.6 Gy (range: 36-45 Gy) by anteroposterior opposed AP/PA pelvic fields with 6 or 18 MV photons, followed by a median boost dose of 20 Gy (range: 13-24 Gy). Concomitant chemotherapy (CCT), consisting of 1-2 cycles of continuous infusion 5-fluorouracil (5-FU) and bolus mitomycin-C (MMC), was usually administered during the first weeks of the pelvic and boost EBRT courses. Acute and late skin/mucosal reactions were recorded according to the Radiation Therapy Oncology Group (RTOG) toxicity scale. Anal sphincter function was assessed using the Memorial Sloan Kettering Cancer Center (MSKCC) scale. TLD anal doses differed by a mean of 5.8% (SD: 5.8) in comparison to the central axis prescribed dose. Differences of at least 10% and at least 15% were observed in eight (26%) and three (9.7%) patients, respectively. TLD doses did not significantly correlate with acute or late grade 2-3 skin or mucosal toxicity. However, patients having good-fair MSKCC anal function had a significantly greater mean difference in anal TLD dose (10.5%, SD: 5.9) than patients having excellent function (3.8%, SD: 4.6) (P = 0.004). Prescribed dose values, length of follow-up, and age at diagnosis did not correlate with late sphincter function. These data show that AP/PA fields using megavoltage photons deliver adequate dose to the anal verge. However, in about one quarter of patients treated with this technique the anal dose varied from the prescribed dose by at least 10%. The observed correlation of TLD values and late sphincter function suggests that direct measurement of the dose delivered to the anal verge might be clinically relevant.

A Dosimetry Study of Deuterium-Deuterium Neutron Generator-based In Vivo Neutron Activation Analysis.

PubMed

Sowers, Daniel; Liu, Yingzi; Mostafaei, Farshad; Blake, Scott; Nie, Linda H

2015-12-01

A neutron irradiation cavity for in vivo neutron activation analysis (IVNAA) to detect manganese, aluminum, and other potentially toxic elements in human hand bone has been designed and its dosimetric specifications measured. The neutron source is a customized deuterium-deuterium neutron generator that produces neutrons at 2.45 MeV by the fusion reaction 2H(d, n)3He at a calculated flux of 7 × 10(8) ± 30% s(-1). A moderator/reflector/shielding [5 cm high density polyethylene (HDPE), 5.3 cm graphite and 5.7 cm borated (HDPE)] assembly has been designed and built to maximize the thermal neutron flux inside the hand irradiation cavity and to reduce the extremity dose and effective dose to the human subject. Lead sheets are used to attenuate bremsstrahlung x rays and activation gammas. A Monte Carlo simulation (MCNP6) was used to model the system and calculate extremity dose. The extremity dose was measured with neutron and photon sensitive film badges and Fuji electronic pocket dosimeters (EPD). The neutron ambient dose outside the shielding was measured by Fuji NSN3, and the photon dose was measured by a Bicron MicroREM scintillator. Neutron extremity dose was calculated to be 32.3 mSv using MCNP6 simulations given a 10-min IVNAA measurement of manganese. Measurements by EPD and film badge indicate hand dose to be 31.7 ± 0.8 mSv for neutrons and 4.2 ± 0.2 mSv for photons for 10 min; whole body effective dose was calculated conservatively to be 0.052 mSv. Experimental values closely match values obtained from MCNP6 simulations. These are acceptable doses to apply the technology for a manganese toxicity study in a human population.

An environmental dose experiment

NASA Astrophysics Data System (ADS)

Peralta, Luis

2017-11-01

Several radiation sources worldwide contribute to the delivered dose to the human population. This radiation also acts as a natural background when detecting radiation, for instance from radioactive sources. In this work a medium-sized plastic scintillation detector is used to evaluate the dose delivered by natural radiation sources. Calibration of the detector involved the use of radioactive sources and Monte Carlo simulation of the energy deposition per disintegration. A measurement of the annual dose due to background radiation to the body was then estimated. A dose value compatible with the value reported by the United Nations Scientific Committee on the Effects of Atomic Radiation was obtained.

INTERCOMPARISON ON THE MEASUREMENT OF THE QUANTITY PERSONAL DOSE EQUIVALENT HP(10) IN PHOTON FIELDS. LINEARITY DEPENDENCE, LOWER LIMIT OF DETECTION AND UNCERTAINTY IN MEASUREMENT OF DOSIMETRY SYSTEMS OF INDIVIDUAL MONITORING SERVICES IN GABON AND GHANA.

PubMed

Ondo Meye, P; Schandorf, C; Amoako, J K; Manteaw, P O; Amoatey, E A; Adjei, D N

2017-12-01

An inter-comparison study was conducted to assess the capability of dosimetry systems of individual monitoring services (IMSs) in Gabon and Ghana to measure personal dose equivalent Hp(10) in photon fields. The performance indicators assessed were the lower limit of detection, linearity and uncertainty in measurement. Monthly and quarterly recording levels were proposed with corresponding values of 0.08 and 0.025 mSv, and 0.05 and 0.15 mSv for the TLD and OSL systems, respectively. The linearity dependence of the dosimetry systems was performed following the requirement given in the Standard IEC 62387 of the International Electrotechnical Commission (IEC). The results obtained for the two systems were satisfactory. The procedure followed for the uncertainty assessment is the one given in the IEC technical report TR62461. The maximum relative overall uncertainties, in absolute value, expressed in terms of Hp(10), for the TL dosimetry system Harshaw 6600, are 44. 35% for true doses below 0.40 mSv and 36.33% for true doses ≥0.40 mSv. For the OSL dosimetry system microStar, the maximum relative overall uncertainties, in absolute value, are 52.17% for true doses below 0.40 mSv and 37.43% for true doses ≥0.40 mSv. These results are in good agreement with the requirements for accuracy of the International Commission on Radiological protection. When expressing the uncertainties in terms of response, comparison with the IAEA requirements for overall accuracy showed that the uncertainty results were also acceptable. The values of Hp(10) directly measured by the two dosimetry systems showed a significant underestimation for the Harshaw 6600 system, and a slight overestimation for the microStar system. After correction for linearity of the measured doses, the two dosimetry systems gave better and comparable results. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Quality assurance of proton beams using a multilayer ionization chamber system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dhanesar, Sandeep; Sahoo, Narayan; Kerr, Matthew

2013-09-15

Purpose: The measurement of percentage depth-dose (PDD) distributions for the quality assurance of clinical proton beams is most commonly performed with a computerized water tank dosimetry system with ionization chamber, commonly referred to as water tank. Although the accuracy and reproducibility of this method is well established, it can be time-consuming if a large number of measurements are required. In this work the authors evaluate the linearity, reproducibility, sensitivity to field size, accuracy, and time-savings of another system: the Zebra, a multilayer ionization chamber system.Methods: The Zebra, consisting of 180 parallel-plate ionization chambers with 2 mm resolution, was used tomore » measure depth-dose distributions. The measurements were performed for scattered and scanned proton pencil beams of multiple energies delivered by the Hitachi PROBEAT synchrotron-based delivery system. For scattered beams, the Zebra-measured depth-dose distributions were compared with those measured with the water tank. The principal descriptors extracted for comparisons were: range, the depth of the distal 90% dose; spread-out Bragg peak (SOBP) length, the region between the proximal 95% and distal 90% dose; and distal-dose fall off (DDF), the region between the distal 80% and 20% dose. For scanned beams, the Zebra-measured ranges were compared with those acquired using a Bragg peak chamber during commissioning.Results: The Zebra demonstrated better than 1% reproducibility and monitor unit linearity. The response of the Zebra was found to be sensitive to radiation field sizes greater than 12.5 × 12.5 cm; hence, the measurements used to determine accuracy were performed using a field size of 10 × 10 cm. For the scattered proton beams, PDD distributions showed 1.5% agreement within the SOBP, and 3.8% outside. Range values agreed within −0.1 ± 0.4 mm, with a maximum deviation of 1.2 mm. SOBP length values agreed within 0 ± 2 mm, with a maximum deviation of 6 mm. DDF values agreed within 0.3 ± 0.1 mm, with a maximum deviation of 0.6 mm. For the scanned proton pencil beams, Zebra and Bragg peak chamber range values demonstrated agreement of 0.0 ± 0.3 mm with a maximum deviation of 1.3 mm. The setup and measurement time for all Zebra measurements was 3 and 20 times less, respectively, compared to the water tank measurements.Conclusions: Our investigation shows that the Zebra can be useful not only for fast but also for accurate measurements of the depth-dose distributions of both scattered and scanned proton beams. The analysis of a large set of measurements shows that the commonly assessed beam quality parameters obtained with the Zebra are within the acceptable variations specified by the manufacturer for our delivery system.« less

Measurement of radiation dose with BeO dosimeters using optically stimulated luminescence technique in radiotherapy applications.

PubMed

Şahin, Serdar; Güneş Tanır, A; Meriç, Niyazi; Aydınkarahaliloğlu, Ercan

2015-09-01

The radiation dose delivered to the target by using different radiotherapy applications has been measured with the help of beryllium oxide (BeO) dosimeters to be placed inside the rando phantom. Three-Dimensional Conformal Radiotherapy (3DCRT), Intensity-Modulated Radiotherapy (IMRT) and Intensity-Modulated Arc Therapy (IMAT) have been used as radiotherapy application. Individual treatment plans have been made for the three radiotherapy applications of rando phantom. The section 4 on the phantom was selected as target and 200 cGy doses were delivered. After the dosimeters placed on section 4 (target) and the sections 2 and 6 (non-target) were irradiated, the result was read through the OSL technique on the Risø TL/OSL system. This procedure was repeated three times for each radiotherapy application. The doses delivered to the target and the non-target sections as a result of the 3DCRT, IMRT and IMAT plans were analyzed. The doses received by the target were measured as 204.71 cGy, 204.76 cGy and 205.65 cGy, respectively. The dose values obtained from treatment planning system (TPS) were compared to the dose values obtained using the OSL technique. It has been concluded that, the radiation dose can be measured with the OSL technique by using BeO dosimeters in medical practices. Copyright © 2015 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klüter, Sebastian, E-mail: sebastian.klueter@med.uni-heidelberg.de; Schubert, Kai; Lissner, Steffen

Purpose: The dosimetric verification of treatment plans in helical tomotherapy usually is carried out via verification measurements. In this study, a method for independent dose calculation of tomotherapy treatment plans is presented, that uses a conventional treatment planning system with a pencil kernel dose calculation algorithm for generation of verification dose distributions based on patient CT data. Methods: A pencil beam algorithm that directly uses measured beam data was configured for dose calculation for a tomotherapy machine. Tomotherapy treatment plans were converted into a format readable by an in-house treatment planning system by assigning each projection to one static treatmentmore » field and shifting the calculation isocenter for each field in order to account for the couch movement. The modulation of the fluence for each projection is read out of the delivery sinogram, and with the kernel-based dose calculation, this information can directly be used for dose calculation without the need for decomposition of the sinogram. The sinogram values are only corrected for leaf output and leaf latency. Using the converted treatment plans, dose was recalculated with the independent treatment planning system. Multiple treatment plans ranging from simple static fields to real patient treatment plans were calculated using the new approach and either compared to actual measurements or the 3D dose distribution calculated by the tomotherapy treatment planning system. In addition, dose–volume histograms were calculated for the patient plans. Results: Except for minor deviations at the maximum field size, the pencil beam dose calculation for static beams agreed with measurements in a water tank within 2%/2 mm. A mean deviation to point dose measurements in the cheese phantom of 0.89% ± 0.81% was found for unmodulated helical plans. A mean voxel-based deviation of −0.67% ± 1.11% for all voxels in the respective high dose region (dose values >80%), and a mean local voxel-based deviation of −2.41% ± 0.75% for all voxels with dose values >20% were found for 11 modulated plans in the cheese phantom. Averaged over nine patient plans, the deviations amounted to −0.14% ± 1.97% (voxels >80%) and −0.95% ± 2.27% (>20%, local deviations). For a lung case, mean voxel-based deviations of more than 4% were found, while for all other patient plans, all mean voxel-based deviations were within ±2.4%. Conclusions: The presented method is suitable for independent dose calculation for helical tomotherapy within the known limitations of the pencil beam algorithm. It can serve as verification of the primary dose calculation and thereby reduce the need for time-consuming measurements. By using the patient anatomy and generating full 3D dose data, and combined with measurements of additional machine parameters, it can substantially contribute to overall patient safety.« less

SU-E-T-91: Correction Method to Determine Surface Dose for OSL Detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reynolds, T; Higgins, P

Purpose: OSL detectors are commonly used in clinic due to their numerous advantages, such as linear response, negligible energy, angle and temperature dependence in clinical range, for verification of the doses beyond the dmax. Although, due to the bulky shielding envelope, this type of detectors fails to measure skin dose, which is an important assessment of patient ability to finish the treatment on time and possibility of acute side effects. This study aims to optimize the methodology of determination of skin dose for conventional accelerators and a flattening filter free Tomotherapy. Methods: Measurements were done for x-ray beams: 6 MVmore » (Varian Clinac 2300, 10×10 cm{sup 2} open field, SSD = 100 cm) and for 5.5 MV (Tomotherapy, 15×40 cm{sup 2} field, SAD = 85 cm). The detectors were placed at the surface of the solid water phantom and at the reference depth (dref=1.7cm (Varian 2300), dref =1.0 cm (Tomotherapy)). The measurements for OSLs were related to the externally exposed OSLs measurements, and further were corrected to surface dose using an extrapolation method indexed to the baseline Attix ion chamber measurements. A consistent use of the extrapolation method involved: 1) irradiation of three OSLs stacked on top of each other on the surface of the phantom; 2) measurement of the relative dose value for each layer; and, 3) extrapolation of these values to zero thickness. Results: OSL measurements showed an overestimation of surface doses by the factor 2.31 for Varian 2300 and 2.65 for Tomotherapy. The relationships: SD{sup 2300} = 0.68 × M{sup 2300}-12.7 and SDτoμo = 0.73 × Mτoμo-13.1 were found to correct the single OSL measurements to surface doses in agreement with Attix measurements to within 0.1% for both machines. Conclusion: This work provides simple empirical relationships for surface dose measurements using single OSL detectors.« less

Validation of Dosimetric Leaf Gap (DLG) prior to its implementation in Treatment Planning System (TPS): TrueBeam™ millennium 120 leaf MLC.

PubMed

Shende, Ravindra; Patel, Ganesh

2017-01-01

Objective of present study is to determine optimum value of DLG and its validation prior to being incorporated in TPS for Varian TrueBeam™ millennium 120 leaves MLC. Partial transmission through the rounded leaf ends of the Multi Leaf Collimator (MLC) causes a conflict between the edges of the light field and radiation field. Parameter account for this partial transmission is called Dosimetric Leaf Gap (DLG). The complex high precession technique, such as Intensity Modulated Radiation Therapy (IMRT), entails the modeling of optimum value of DLG inside Eclipse Treatment Planning System (TPS) for precise dose calculation. Distinct synchronized uniformed extension of sweeping dynamic MLC leaf gap fields created by Varian MLC shaper software were use to determine DLG. DLG measurements performed with both 0.13 cc semi-flex ionization chamber and 2D-Array I-Matrix were used to validate the DLG; similarly, values of DLG from TPS were estimated from predicted dose. Similar mathematical approaches were employed to determine DLG from delivered and TPS predicted dose. DLG determined from delivered dose measured with both ionization chamber (DLG Ion ) and I-Matrix (DLG I-Matrix ) compared with DLG estimate from TPS predicted dose (DLG TPS ). Measurements were carried out for all available 6MV, 10MV, 15MV, 6MVFFF and 10MVFFF beam energies. Maximum and minimum DLG deviation between measured and TPS calculated DLG was found to be 0.2 mm and 0.1 mm, respectively. Both of the measured DLGs (DLG Ion and DLG I-Matrix ) were found to be in a very good agreement with estimated DLG from TPS (DLG TPS ). Proposed method proved to be helpful in verifying and validating the DLG value prior to its clinical implementation in TPS.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vostrotin, Vadim; Birchall, Alan; Zhdanov, Alexey

The distribution of calculated internal doses was determined for 8043 Mayak Production Associate (Mayak PA) workers according to the epidemiological cohorts and groups of raw data used as well as the type of industrial compounds of inhaled aerosols. Statistical characteristics of point estimates of accumulated doses to 17 different tissues and organs and the uncertainty ranges were calculated. Under the MWDS-2013 dosimetry system, the mean accumulated lung dose was 185585 mGy, with a median value of 31 mGy and a maximum of 8980 mGy maximum. The ranges of relative standard uncertainty were: from 40 to 2200% for accumulated lung dose,more » from 25-90% to 2600-3000% for accumulated dose to different regions of respiratory tract, from 13-18% to 2300-2500% for systemic organs and tissues. The Mayak PA workers accumulated internal plutonium lung dose is shown to be close to lognormal. The accumulated internal plutonium dose to systemic organs was close to a log-triangle. The dependency of uncertainty of accumulated absorbed lung and liver doses on the dose estimates itself is also shown. The accumulated absorbed doses to lung, alveolar-interstitial region, liver, bone surface cells and red bone marrow, calculated both with MWDS-2013 and MWDS-2008 have been compared. In general, the accumulated lung doses increased by a factor of 1.8 in median value, while the accumulated doses to systemic organs decreased by factor of 1.3-1.4 in median value. For the cases with identical initial data, accumulated lung doses increased by a factor of 2.1 in median value, while accumulated doses to systemic organs decreased by 8-13% in median value. For the cases with both identical initial data and all of plutonium activity in urine measurements above the decision threshold, accumulated lung doses increased by a factor of 2.8 in median value, while accumulated doses to systemic organs increased by 6-12% in median value.« less

A novel method for patient exit and entrance dose prediction based on water equivalent path length measured with an amorphous silicon electronic portal imaging device.

PubMed

Kavuma, Awusi; Glegg, Martin; Metwaly, Mohamed; Currie, Garry; Elliott, Alex

2010-01-21

In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose delivered to the patient. Electronic portal imaging device (EPID) images for a set of solid water phantoms of varying thicknesses were acquired and the data fitted onto a quadratic equation, which relates the reduction in photon beam intensity to the attenuation coefficient and material thickness at a reference condition. The quadratic model is used to convert the measured grey scale value into water equivalent path length (EPL) at each pixel for any material imaged by the detector. For any other non-reference conditions, scatter, field size and MU variation effects on the image were corrected by relative measurements using an ionization chamber and an EPID. The 2D EPL is linked to the percentage exit dose table, for different thicknesses and field sizes, thereby converting the plane pixel values at each point into a 2D dose map. The off-axis ratio is corrected using envelope and boundary profiles generated from the treatment planning system (TPS). The method requires field size, monitor unit and source-to-surface distance (SSD) as clinical input parameters to predict the exit dose, which is then used to determine the entrance dose. The measured pixel dose maps were compared with calculated doses from TPS for both entrance and exit depth of phantom. The gamma index at 3% dose difference (DD) and 3 mm distance to agreement (DTA) resulted in an average of 97% passing for the square fields of 5, 10, 15 and 20 cm. The exit dose EPID dose distributions predicted by the algorithm were in better agreement with TPS-calculated doses than phantom entrance dose distributions.

A novel method for patient exit and entrance dose prediction based on water equivalent path length measured with an amorphous silicon electronic portal imaging device

NASA Astrophysics Data System (ADS)

Kavuma, Awusi; Glegg, Martin; Metwaly, Mohamed; Currie, Garry; Elliott, Alex

2010-01-01

In vivo dosimetry is one of the quality assurance tools used in radiotherapy to monitor the dose delivered to the patient. Electronic portal imaging device (EPID) images for a set of solid water phantoms of varying thicknesses were acquired and the data fitted onto a quadratic equation, which relates the reduction in photon beam intensity to the attenuation coefficient and material thickness at a reference condition. The quadratic model is used to convert the measured grey scale value into water equivalent path length (EPL) at each pixel for any material imaged by the detector. For any other non-reference conditions, scatter, field size and MU variation effects on the image were corrected by relative measurements using an ionization chamber and an EPID. The 2D EPL is linked to the percentage exit dose table, for different thicknesses and field sizes, thereby converting the plane pixel values at each point into a 2D dose map. The off-axis ratio is corrected using envelope and boundary profiles generated from the treatment planning system (TPS). The method requires field size, monitor unit and source-to-surface distance (SSD) as clinical input parameters to predict the exit dose, which is then used to determine the entrance dose. The measured pixel dose maps were compared with calculated doses from TPS for both entrance and exit depth of phantom. The gamma index at 3% dose difference (DD) and 3 mm distance to agreement (DTA) resulted in an average of 97% passing for the square fields of 5, 10, 15 and 20 cm. The exit dose EPID dose distributions predicted by the algorithm were in better agreement with TPS-calculated doses than phantom entrance dose distributions.

Measuring the incentive value of escalating doses of heroin in heroin-dependent Fischer rats during acute spontaneous withdrawal

PubMed Central

Reed, Brian; Ho, Ann; Kreek, Mary Jeanne

2011-01-01

Rationale/objectives Although continued heroin use and relapse are thought to be motivated, in part, by the positive incentive-motivational value attributed to heroin, little is understood about heroin’s incentive value during the relapse-prone state of withdrawal. This study uses place preference to measure the incentive value attributed to escalating-dose heroin in the context of heroin dependence. Methods Male Fischer rats were exposed chronically to escalating doses of heroin in the homecage and during place preference conditioning sessions. Conditioned preference for the context paired with escalating-dose heroin was tested after homecage exposure was discontinued and rats entered acute spontaneous withdrawal. Individuals’ behavioral and locomotor responses to heroin and somatic withdrawal signs were recorded. Results Conditioned preference for the heroin-paired context was strong in rats that received chronic homecage exposure to escalating-dose heroin and were tested in acute withdrawal. Behavioral responses to heroin (e.g., stereotypy) varied widely across individuals, with rats that expressed stronger heroin preference also expressing stronger behavioral activation in response to heroin. Individual differences in preference were also related to locomotor responses to heroin but not to overt somatic withdrawal signs. Conclusions Escalating doses of heroin evoked place preference in rats, suggesting that positive incentive-motivational value is attributed to this clinically relevant pattern of drug exposure. This study offers an improved preclinical model for studying dependence and withdrawal and provides insight into individual vulnerabilities to addiction-like behavior. PMID:21748254

Simulation of computed tomography dose based on voxel phantom

NASA Astrophysics Data System (ADS)

Liu, Chunyu; Lv, Xiangbo; Li, Zhaojun

2017-01-01

Computed Tomography (CT) is one of the preferred and the most valuable imaging tool used in diagnostic radiology, which provides a high-quality cross-sectional image of the body. It still causes higher doses of radiation to patients comparing to the other radiological procedures. The Monte-Carlo method is appropriate for estimation of the radiation dose during the CT examinations. The simulation of the Computed Tomography Dose Index (CTDI) phantom was developed in this paper. Under a similar conditions used in physical measurements, dose profiles were calculated and compared against the measured values that were reported. The results demonstrate a good agreement between the calculated and the measured doses. From different CT exam simulations using the voxel phantom, the highest absorbed dose was recorded for the lung, the brain, the bone surface. A comparison between the different scan type shows that the effective dose for a chest scan is the highest one, whereas the effective dose values during abdomen and pelvis scan are very close, respectively. The lowest effective dose resulted from the head scan. Although, the dose in CT is related to various parameters, such as the tube current, exposure time, beam energy, slice thickness and patient size, this study demonstrates that the MC simulation is a useful tool to accurately estimate the dose delivered to any specific organs for patients undergoing the CT exams and can be also a valuable technique for the design and the optimization of the CT x-ray source.

Proxy-based reconstruction of erythemal UV doses over Estonia for 1955 2004

NASA Astrophysics Data System (ADS)

Eerme, K.; Veismann, U.; Lätt, S.

2006-08-01

A proxy-based reconstruction of the erythemally-weighted UV doses for 1955-2004 has been performed for the Tartu-Tõravere Meteorological Station (58°16' N, 26°28' E, 70 m a.s.l.) site. The pyrheliometer-measured daily sum of direct irradiance on partly cloudy and clear days, and the pyranometer-measured daily sum of global irradiance on overcast days were used as the cloudiness influence related proxies. The TOMS ozone data have been used for detecting the daily deviations from the climatic value (averaged annual cycle). In 1998-2004, the biases between the measured and reconstructed daily doses in 55.5% of the cases were within ±10% and in 83.5% of the cases within ±20%, on average. In the summer half-year these amounts were 62% and 88%, respectively. In most years the results for longer intervals did not differ significantly, if no correction was made for the daily deviations of total ozone from its climatic value. The annual and summer half-yearly erythemal doses (contributing, on average, 89% of the annual value) agreed within ±2%, except for the years after major volcanic eruptions and one extremely fine weather year (2002). Using the daily relative sunshine duration as a proxy without detailed correction for atmospheric turbidity results in biases of 2-4% in the summer half-yearly dose in the years after major volcanic eruptions and a few other years of high atmospheric turbidity. The year-to-year variations of the summer half-yearly erythemal dose in 1955-2004 were found to be within 92-111% relative to their average value. Exclusion of eight extreme years reduces this range for the remaining to 95-105.5%. Due to the quasi-periodic alternation of wet and dry periods, the interval of cloudy summers 1976-1993 regularly manifests summer half-yearly erythemal dose values lower than the 1955-2004 average. Since 1996/1997 midwinters have been darker than on average.

Commissioning and quality assurance for the treatment delivery components of the AccuBoost system.

PubMed

Iftimia, Ileana; Talmadge, Mike; Ladd, Ron; Halvorsen, Per

2015-03-08

The objective for this work was to develop a commissioning methodology for the treatment delivery components of the AccuBoost system, as well as to establish a routine quality assurance program and appropriate guidance for clinical use based on the commissioning results. Various tests were developed: 1) assessment of the accuracy of the displayed separation value; 2) validation of the dwell positions within each applicator; 3) assessment of the accuracy and precision of the applicator localization system; 4) assessment of the combined dose profile of two opposed applicators to confirm that they are coaxial; 5) measurement of the absolute dose delivered with each applicator to confirm acceptable agreement with dose based on Monte Carlo modeling; 6) measurements of the skin-to-center dose ratio using optically stimulated luminescence dosimeters; and 7) assessment of the mammopad cushion's effect on the center dose. We found that the difference between the measured and the actual paddle separation is < 0.1 cm for the separation range of 3 cm to 7.5 cm. Radiochromic film measurements demonstrated that the number of dwell positions inside the applicators agree with the values from the vendor, for each applicator type and size. The shift needed for a good applicator-grid alignment was within 0.2 cm. The dry-run test using film demonstrated that the shift of the dosimetric center is within 0.15 cm. Dose measurements in water converted to polystyrene agreed within 5.0% with the Monte Carlo data in polystyrene for the same applicator type, size, and depth. A solid water-to-water (phantom) factor was obtained for each applicator, and all future annual quality assurance tests will be performed in solid water using an average value of 1.07 for the solid water-to-water factor. The skin-to-center dose ratio measurements support the Monte Carlo-based values within 5.0% agreement. For the treatment separation range of 4 cm to 8cm, the change in center dose would be < 1.0% for all applicators when using a compressed pad of 0.2 cm to 0.3 cm. The tests performed ensured that all treatment components of the AccuBoost system are functional and that a treatment plan can be delivered with acceptable accuracy. Based on the commissioning results, a quality assurance manual and guidance documents for clinical use were developed.

Reconstruction of the erythemal UV radiation data in Novi Sad (Serbia) using the NEOPLANTA parametric model

NASA Astrophysics Data System (ADS)

Malinovic-Milicevic, S.; Mihailovic, D. T.; Radovanovic, M. M.

2015-07-01

This paper focuses on the development and application of a technique for filling the daily erythemal UV dose data gaps and the reconstruction of the past daily erythemal UV doses in Novi Sad, Serbia. The technique implies developing the empirical equation for estimation of daily erythemal UV doses by means of relative daily sunshine duration under all sky conditions. A good agreement was found between modeled and measured values of erythemal UV doses. This technique was used for filling the short gaps in the erythemal UV dose measurement series (2003-2009) as well as for the reconstruction of the past time-series values (1981-2002). Statistically significant positive erythemal UV dose trend of 6.9 J m-2 per year was found during the period 1981-2009. In relation to the reference period 1981-1989, an increase in the erythemal UV dose of 6.92 % is visible in the period 1990-1999 and the increase of 9.67 % can be seen in the period 2000-2009. The strongest increase in erythemal UV doses has been found for winter and spring seasons.

Comparative dosimetric characterization for different types of detectors in high-energy electron beams

NASA Astrophysics Data System (ADS)

Lee, Chang Yeol; Kim, Woo Chul; Kim, Hun Jeong; Huh, Hyun Do; Park, Seungwoo; Choi, Sang Hyoun; Kim, Kum Bae; Min, Chul Kee; Kim, Seong Hoon; Shin, Dong Oh

2017-02-01

The purpose of this study is to perform a comparison and on analysis of measured dose factor values by using various commercially available high-energy electron beam detectors to measure dose profiles and energy property data. By analyzing the high-energy electron beam data from each detector, we determined the optimal detector for measuring electron beams in clinical applications. The dose linearity, dose-rate dependence, percentage depth dose, and dose profile of each detector were measured to evaluate the dosimetry characteristics of high-energy electron beams. The dose profile and the energy characteristics of high-energy electron beams were found to be different when measured by different detectors. Through comparison with other detectors based on the analyzed data, the microdiamond detector was found to have outstanding dose linearity, a low dose-rate dependency, and a small effective volume. Thus, this detector has outstanding spatial resolution and is the optimal detector for measuring electron beams. Radiation therapy results can be improved and related medical accidents can be prevented by using the procedure developed in this research in clinical practice for all beam detectors when measuring the electron beam dose.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Devic, Slobodan; Tomic, Nada; Aldelaijan, Saad

Purpose: Despite numerous advantages of radiochromic film dosimeter (high spatial resolution, near tissue equivalence, low energy dependence) to measure a relative dose distribution with film, one needs to first measure an absolute dose (following previously established reference dosimetry protocol) and then convert measured absolute dose values into relative doses. In this work, we present result of our efforts to obtain a functional form that would linearize the inherently nonlinear dose-response curve of the radiochromic film dosimetry system. Methods: Functional form [{zeta}= (-1){center_dot}netOD{sup (2/3)}/ln(netOD)] was derived from calibration curves of various previously established radiochromic film dosimetry systems. In order to testmore » the invariance of the proposed functional form with respect to the film model used we tested it with three different GAFCHROMIC Trade-Mark-Sign film models (EBT, EBT2, and EBT3) irradiated to various doses and scanned on a same scanner. For one of the film models (EBT2), we tested the invariance of the functional form to the scanner model used by scanning irradiated film pieces with three different flatbed scanner models (Epson V700, 1680, and 10000XL). To test our hypothesis that the proposed functional argument linearizes the response of the radiochromic film dosimetry system, verification tests have been performed in clinical applications: percent depth dose measurements, IMRT quality assurance (QA), and brachytherapy QA. Results: Obtained R{sup 2} values indicate that the choice of the functional form of the new argument appropriately linearizes the dose response of the radiochromic film dosimetry system we used. The linear behavior was insensitive to both film model and flatbed scanner model used. Measured PDD values using the green channel response of the GAFCHROMIC Trade-Mark-Sign EBT3 film model are well within {+-}2% window of the local relative dose value when compared to the tabulated Cobalt-60 data. It was also found that criteria of 3%/3 mm for an IMRT QA plan and 3%/2 mm for a brachytherapy QA plan are passing 95% gamma function points. Conclusions: In this paper, we demonstrate the use of functional argument to linearize the inherently nonlinear response of a radiochromic film based reference dosimetry system. In this way, relative dosimetry can be conveniently performed using radiochromic film dosimetry system without the need of establishing calibration curve.« less

Validation of Monte Carlo simulation of mammography with TLD measurement and depth dose calculation with a detailed breast model

NASA Astrophysics Data System (ADS)

Wang, Wenjing; Qiu, Rui; Ren, Li; Liu, Huan; Wu, Zhen; Li, Chunyan; Li, Junli

2017-09-01

Mean glandular dose (MGD) is not only determined by the compressed breast thickness (CBT) and the glandular content, but also by the distribution of glandular tissues in breast. Depth dose inside the breast in mammography has been widely concerned as glandular dose decreases rapidly with increasing depth. In this study, an experiment using thermo luminescent dosimeters (TLDs) was carried out to validate Monte Carlo simulations of mammography. Percent depth doses (PDDs) at different depth values were measured inside simple breast phantoms of different thicknesses. The experimental values were well consistent with the values calculated by Geant4. Then a detailed breast model with a CBT of 4 cm and a glandular content of 50%, which has been constructed in previous work, was used to study the effects of the distribution of glandular tissues in breast with Geant4. The breast model was reversed in direction of compression to get a reverse model with a different distribution of glandular tissues. Depth dose distributions and glandular tissue dose conversion coefficients were calculated. It revealed that the conversion coefficients were about 10% larger when the breast model was reversed, for glandular tissues in the reverse model are concentrated in the upper part of the model.

Ion recombination and polarity correction factors for a plane-parallel ionization chamber in a proton scanning beam.

PubMed

Liszka, Małgorzata; Stolarczyk, Liliana; Kłodowska, Magdalena; Kozera, Anna; Krzempek, Dawid; Mojżeszek, Natalia; Pędracka, Anna; Waligórski, Michael Patrick Russell; Olko, Paweł

2018-01-01

To evaluate the effect on charge collection in the ionization chamber (IC) in proton pencil beam scanning (PBS), where the local dose rate may exceed the dose rates encountered in conventional MV therapy by up to three orders of magnitude. We measured values of the ion recombination (k s ) and polarity (k pol ) correction factors in water, for a plane-parallel Markus TM23343 IC, using the cyclotron-based Proteus-235 therapy system with an active proton PBS of energies 30-230 MeV. Values of k s were determined from extrapolation of the saturation curve and the Two-Voltage Method (TVM), for planar fields. We compared our experimental results with those obtained from theoretical calculations. The PBS dose rates were estimated by combining direct IC measurements with results of simulations performed using the FLUKA MC code. Values of k s were also determined by the TVM for uniformly irradiated volumes over different ranges and modulation depths of the proton PBS, with or without range shifter. By measuring charge collection efficiency versus applied IC voltage, we confirmed that, with respect to ion recombination, our proton PBS represents a continuous beam. For a given chamber parameter, e.g., nominal voltage, the value of k s depends on the energy and the dose rate of the proton PBS, reaching c. 0.5% for the TVM, at the dose rate of 13.4 Gy/s. For uniformly irradiated regular volumes, the k s value was significantly smaller, within 0.2% or 0.3% for irradiations with or without range shifter, respectively. Within measurement uncertainty, the average value of k pol , for the Markus TM23343 IC, was close to unity over the whole investigated range of clinical proton beam energies. While no polarity effect was observed for the Markus TM23343 IC in our pencil scanning proton beam system, the effect of volume recombination cannot be ignored. © 2017 American Association of Physicists in Medicine.

Analysis of uncertainties in Monte Carlo simulated organ dose for chest CT

NASA Astrophysics Data System (ADS)

Muryn, John S.; Morgan, Ashraf G.; Segars, W. P.; Liptak, Chris L.; Dong, Frank F.; Primak, Andrew N.; Li, Xiang

2015-03-01

In Monte Carlo simulation of organ dose for a chest CT scan, many input parameters are required (e.g., half-value layer of the x-ray energy spectrum, effective beam width, and anatomical coverage of the scan). The input parameter values are provided by the manufacturer, measured experimentally, or determined based on typical clinical practices. The goal of this study was to assess the uncertainties in Monte Carlo simulated organ dose as a result of using input parameter values that deviate from the truth (clinical reality). Organ dose from a chest CT scan was simulated for a standard-size female phantom using a set of reference input parameter values (treated as the truth). To emulate the situation in which the input parameter values used by the researcher may deviate from the truth, additional simulations were performed in which errors were purposefully introduced into the input parameter values, the effects of which on organ dose per CTDIvol were analyzed. Our study showed that when errors in half value layer were within ± 0.5 mm Al, the errors in organ dose per CTDIvol were less than 6%. Errors in effective beam width of up to 3 mm had negligible effect (< 2.5%) on organ dose. In contrast, when the assumed anatomical center of the patient deviated from the true anatomical center by 5 cm, organ dose errors of up to 20% were introduced. Lastly, when the assumed extra scan length was longer by 4 cm than the true value, dose errors of up to 160% were found. The results answer the important question: to what level of accuracy each input parameter needs to be determined in order to obtain accurate organ dose results.

Measurement-based model of a wide-bore CT scanner for Monte Carlo dosimetric calculations with GMCTdospp software.

PubMed

Skrzyński, Witold

2014-11-01

The aim of this work was to create a model of a wide-bore Siemens Somatom Sensation Open CT scanner for use with GMCTdospp, which is an EGSnrc-based software tool dedicated for Monte Carlo calculations of dose in CT examinations. The method was based on matching spectrum and filtration to half value layer and dose profile, and thus was similar to the method of Turner et al. (Med. Phys. 36, pp. 2154-2164). Input data on unfiltered beam spectra were taken from two sources: the TASMIP model and IPEM Report 78. Two sources of HVL data were also used, namely measurements and documentation. Dose profile along the fan-beam was measured with Gafchromic RTQA-1010 (QA+) film. Two-component model of filtration was assumed: bow-tie filter made of aluminum with 0.5 mm thickness on central axis, and flat filter made of one of four materials: aluminum, graphite, lead, or titanium. Good agreement between calculations and measurements was obtained for models based on the measured values of HVL. Doses calculated with GMCTdospp differed from the doses measured with pencil ion chamber placed in PMMA phantom by less than 5%, and root mean square difference for four tube potentials and three positions in the phantom did not exceed 2.5%. The differences for models based on HVL values from documentation exceeded 10%. Models based on TASMIP spectra and IPEM78 spectra performed equally well. Copyright © 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

A correlation study of eye lens dose and personal dose equivalent for interventional cardiologists.

PubMed

Farah, J; Struelens, L; Dabin, J; Koukorava, C; Donadille, L; Jacob, S; Schnelzer, M; Auvinen, A; Vanhavere, F; Clairand, I

2013-12-01

This paper presents the dosimetry part of the European ELDO project, funded by the DoReMi Network of Excellence, in which a method was developed to estimate cumulative eye lens doses for past practices based on personal dose equivalent values, H(p)(10), measured above the lead apron at several positions at the collar, chest and waist levels. Measurement campaigns on anthropomorphic phantoms were carried out in typical interventional settings considering different tube projections and configurations, beam energies and filtration, operator positions and access routes and using both mono-tube and biplane X-ray systems. Measurements showed that eye lens dose correlates best with H(p)(10) measured on the left side of the phantom at the level of the collar, although this correlation implicates high spreads (41 %). Nonetheless, for retrospective dose assessment, H(p)(10) records are often the only option for eye dose estimates and the typically used chest left whole-body dose measurement remains useful.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moura, Eduardo S., E-mail: emoura@wisc.edu; Micka, John A.; Hammer, Cliff G.

Purpose: This work presents the development of a phantom to verify the treatment planning system (TPS) algorithms used for high-dose-rate (HDR) brachytherapy. It is designed to measure the relative dose in a heterogeneous media. The experimental details used, simulation methods, and comparisons with a commercial TPS are also provided. Methods: To simulate heterogeneous conditions, four materials were used: Virtual Water™ (VM), BR50/50™, cork, and aluminum. The materials were arranged in 11 heterogeneity configurations. Three dosimeters were used to measure the relative response from a HDR {sup 192}Ir source: TLD-100™, Gafchromic{sup ®} EBT3 film, and an Exradin™ A1SL ionization chamber. Tomore » compare the results from the experimental measurements, the various configurations were modeled in the PENELOPE/penEasy Monte Carlo code. Images of each setup geometry were acquired from a CT scanner and imported into BrachyVision™ TPS software, which includes a grid-based Boltzmann solver Acuros™. The results of the measurements performed in the heterogeneous setups were normalized to the dose values measured in the homogeneous Virtual Water™ setup and the respective differences due to the heterogeneities were considered. Additionally, dose values calculated based on the American Association of Physicists in Medicine-Task Group 43 formalism were compared to dose values calculated with the Acuros™ algorithm in the phantom. Calculated doses were compared at the same points, where measurements have been performed. Results: Differences in the relative response as high as 11.5% were found from the homogeneous setup when the heterogeneous materials were inserted into the experimental phantom. The aluminum and cork materials produced larger differences than the plastic materials, with the BR50/50™ material producing results similar to the Virtual Water™ results. Our experimental methods agree with the PENELOPE/penEasy simulations for most setups and dosimeters. The TPS relative differences with the Acuros™ algorithm were similar in both experimental and simulated setups. The discrepancy between the BrachyVision™, Acuros™, and TG-43 dose responses in the phantom described by this work exceeded 12% for certain setups. Conclusions: The results derived from the phantom measurements show good agreement with the simulations and TPS calculations, using Acuros™ algorithm. Differences in the dose responses were evident in the experimental results when heterogeneous materials were introduced. These measurements prove the usefulness of the heterogeneous phantom for verification of HDR treatment planning systems based on model-based dose calculation algorithms.« less

Dose reduction and cost-benefit analysis at Japan`s Tokai No. 2 Plant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humamoto, Hisao; Suzuki, Seishiro; Taniguchi, Kazufumi

1995-03-01

In the Tokai No. 2 power plant of the Japan Atomic Power Company, about 80% of the annual dose equivalent is received during periodic maintenance outages. A project group for dose reduction was organized at the company`s headquarters in 1986; in 1988, they proposed a five-year program to reduce by half the collective dose of 4 person-Sv per normal outage work. To achieve the target dose value, some dose-reduction measures were undertaken, namely, permanent radiation shielding, decontamination, automatic, operating machines, and ALARA organization. As the result, the collective dose from normal outage work was 1.6 person-Sv in 1992, which wasmore » less than the initial target value.« less

Evaluation of six TPS algorithms in computing entrance and exit doses.

PubMed

Tan, Yun I; Metwaly, Mohamed; Glegg, Martin; Baggarley, Shaun; Elliott, Alex

2014-05-08

Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measured doses to within 2%-3%. Meanwhile, Eclipse PBC and Eclipse AAA computed exit doses were higher than the IC measured doses by up to 5.3% and 4.8%, respectively. Both algorithms assume that full backscatter exists even at the exit level, leading to an overestimation of exit doses. Despite good agreements at the central axis for Eclipse AXB and Monaco MC, 1D relative comparisons showed profiles mismatched at depths beyond 11.5 cm. Overall, the 2D absolute gamma (3%/3 mm) pass rates were better for Monaco MC, while Eclipse AXB failed mostly at the outer 20% of the field area. The findings of this study serve as a useful baseline for the implementation of entrance and exit in vivo dosimetry in clinical departments utilizing any of these six common TPS algorithms for reference comparison.

Lens of Eye Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mallett, Michael Wesley

An analysis of LANL occupational dose measurements was made with respect to lens of eye dose (LOE), in particular, for plutonium workers. Table 1 shows the reported LOE as a ratio of the “deep” (photon only) and “deep+neutron” dose for routine monitored workers at LANL for the past ten years. The data compares the mean and range of these values for plutonium workers* and non-routine plutonium workers. All doses were reported based on measurements with the LANL Model 8823 TLD.

A Measurement and Analysis of Buildup Region Dose for Open Field Photon Beams (Cobalt-60 through 24 MV)

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCullough, Edwin C.

2015-01-15

The central axis depth dose in the build-up region (surface to d{sub max}) of single open field photon beams (cobalt-60 through 24 MV) has been measured utilizing parallel plate and extrapolation chamber methodology. These data were used to derive, for a prescription dose of 100 cGy, values of surface dose, the maximum value of dose along the central axis (D{sub max}) and the depth (nearest the surface) at which 90% of the prescription dose occurs (d{sub 90}). For both single and parallel opposed pair (POP) open field configurations, data are presented at field sizes of 5 × 5, 15 ×more » 15 and 25 × 25 cm{sup 2} for prescription depths of 10, 15 and 20 cm (midplane for POP). For the treatment machines, field sizes, and prescription depths studied, it is possible to conclude that: for single open field irradiation, surface dose values (as a percentage of the prescription dose) can be either low (<10%) or comparable to the prescription dose itself; for POP open fields, surface dose values are relatively independent of photon energy and midplane depth, and range between 30% and 70% of prescription dose, being principally dependent on field size; the depth of the initial 90 cGy point for a prescription dose of 100 cGy, d{sub 90}, was larger for POP fields. For either single or POP open field treatments, d{sub 90} was always less than 22 mm, while for 6 MV or less, values of d{sub 90} were less than 4 mm; D{sub max} values can be very large (e.g., above 300 cGy) for certain treatment situations and are reduced significantly for POP treatments; for open field POP treatments, the percent reduction in D{sub max} with each increment in beam energy above 10 MV is reduced over that seen at 10 MV or less and, possibly, this further reduction may be clinically insignificant; for open field POP treatments, changes in surface dose, d{sub 90} and D{sub max} with beam energy above 10 MV do not suggest, with regard to these specific build-up curve parameters, any obvious advantage for treatment with beam energies greater than 10 MV for the specific machines and situations studied.« less

UV index experimental values during the years 2000 and 2001 from the Spanish broadband UV-B radiometric network.

PubMed

Martínez-Lozano, José A; Marín, María J; Tena, Fernando; Utrillas, María P; Sánchez-Muniosguren, Luis; González-Frías, Carlos; Cuevas, Emilio; Redondas, Alberto; Lorente, Jerónimo; de Cabo, Xavier; Cachorro, Victoria; Vergaz, Ricardo; de Frutos, Angel; Díaz, Juan P; Expósito, Francisco J; de la Morena, Benito; Vilaplana, José M

2002-08-01

An analysis is made of experimental ultraviolet erythemal solar radiation data measured during the years 2000 and 2001 by the Spanish UV-B radiation evaluation and prediction network. This network consists of 16 Robertson-Berger type pyranometers for evaluating solar erythemal radiation and five Brewer spectroradiometers for evaluating the stratospheric ozone. On the basis of these data the Ultraviolet Index (UVI) was evaluated for the measuring stations that are located either in coastal regions or in the more densely populated regions inland on the Iberian Peninsula. It has been checked that in most cases the maximum irradiance values corresponded to solar noon, although there were exceptions that could be explained by cloudiness. The maximum experimental values of the UVI were around 9 during the summer, though frequently passing this value at the inland measurement stations. The annual accumulated dose of irradiation on a horizontal plane has also been studied, as well as the evolution through the year in units of energy, standard erythemal doses and minimum erythemal doses, according to different phototypes.

Dosimetric verification of lung cancer treatment using the CBCTs estimated from limited-angle on-board projections.

PubMed

Zhang, You; Yin, Fang-Fang; Ren, Lei

2015-08-01

Lung cancer treatment is susceptible to treatment errors caused by interfractional anatomical and respirational variations of the patient. On-board treatment dose verification is especially critical for the lung stereotactic body radiation therapy due to its high fractional dose. This study investigates the feasibility of using cone-beam (CB)CT images estimated by a motion modeling and free-form deformation (MM-FD) technique for on-board dose verification. Both digital and physical phantom studies were performed. Various interfractional variations featuring patient motion pattern change, tumor size change, and tumor average position change were simulated from planning CT to on-board images. The doses calculated on the planning CT (planned doses), the on-board CBCT estimated by MM-FD (MM-FD doses), and the on-board CBCT reconstructed by the conventional Feldkamp-Davis-Kress (FDK) algorithm (FDK doses) were compared to the on-board dose calculated on the "gold-standard" on-board images (gold-standard doses). The absolute deviations of minimum dose (ΔDmin), maximum dose (ΔDmax), and mean dose (ΔDmean), and the absolute deviations of prescription dose coverage (ΔV100%) were evaluated for the planning target volume (PTV). In addition, 4D on-board treatment dose accumulations were performed using 4D-CBCT images estimated by MM-FD in the physical phantom study. The accumulated doses were compared to those measured using optically stimulated luminescence (OSL) detectors and radiochromic films. Compared with the planned doses and the FDK doses, the MM-FD doses matched much better with the gold-standard doses. For the digital phantom study, the average (± standard deviation) ΔDmin, ΔDmax, ΔDmean, and ΔV100% (values normalized by the prescription dose or the total PTV) between the planned and the gold-standard PTV doses were 32.9% (±28.6%), 3.0% (±2.9%), 3.8% (±4.0%), and 15.4% (±12.4%), respectively. The corresponding values of FDK PTV doses were 1.6% (±1.9%), 1.2% (±0.6%), 2.2% (±0.8%), and 17.4% (±15.3%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.3% (±0.2%), 0.9% (±0.6%), 0.6% (±0.4%), and 1.0% (±0.8%), respectively. Similarly, for the physical phantom study, the average ΔDmin, ΔDmax, ΔDmean, and ΔV100% of planned PTV doses were 38.1% (±30.8%), 3.5% (±5.1%), 3.0% (±2.6%), and 8.8% (±8.0%), respectively. The corresponding values of FDK PTV doses were 5.8% (±4.5%), 1.6% (±1.6%), 2.0% (±0.9%), and 9.3% (±10.5%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.4% (±0.8%), 0.8% (±1.0%), 0.5% (±0.4%), and 0.8% (±0.8%), respectively. For the 4D dose accumulation study, the average (± standard deviation) absolute dose deviation (normalized by local doses) between the accumulated doses and the OSL measured doses was 3.3% (±2.7%). The average gamma index (3%/3 mm) between the accumulated doses and the radiochromic film measured doses was 94.5% (±2.5%). MM-FD estimated 4D-CBCT enables accurate on-board dose calculation and accumulation for lung radiation therapy. It can potentially be valuable for treatment quality assessment and adaptive radiation therapy.

Experimental verification of a commercial Monte Carlo-based dose calculation module for high-energy photon beams.

PubMed

Künzler, Thomas; Fotina, Irina; Stock, Markus; Georg, Dietmar

2009-12-21

The dosimetric performance of a Monte Carlo algorithm as implemented in a commercial treatment planning system (iPlan, BrainLAB) was investigated. After commissioning and basic beam data tests in homogenous phantoms, a variety of single regular beams and clinical field arrangements were tested in heterogeneous conditions (conformal therapy, arc therapy and intensity-modulated radiotherapy including simultaneous integrated boosts). More specifically, a cork phantom containing a concave-shaped target was designed to challenge the Monte Carlo algorithm in more complex treatment cases. All test irradiations were performed on an Elekta linac providing 6, 10 and 18 MV photon beams. Absolute and relative dose measurements were performed with ion chambers and near tissue equivalent radiochromic films which were placed within a transverse plane of the cork phantom. For simple fields, a 1D gamma (gamma) procedure with a 2% dose difference and a 2 mm distance to agreement (DTA) was applied to depth dose curves, as well as to inplane and crossplane profiles. The average gamma value was 0.21 for all energies of simple test cases. For depth dose curves in asymmetric beams similar gamma results as for symmetric beams were obtained. Simple regular fields showed excellent absolute dosimetric agreement to measurement values with a dose difference of 0.1% +/- 0.9% (1 standard deviation) at the dose prescription point. A more detailed analysis at tissue interfaces revealed dose discrepancies of 2.9% for an 18 MV energy 10 x 10 cm(2) field at the first density interface from tissue to lung equivalent material. Small fields (2 x 2 cm(2)) have their largest discrepancy in the re-build-up at the second interface (from lung to tissue equivalent material), with a local dose difference of about 9% and a DTA of 1.1 mm for 18 MV. Conformal field arrangements, arc therapy, as well as IMRT beams and simultaneous integrated boosts were in good agreement with absolute dose measurements in the heterogeneous phantom. For the clinical test cases, the average dose discrepancy was 0.5% +/- 1.1%. Relative dose investigations of the transverse plane for clinical beam arrangements were performed with a 2D gamma-evaluation procedure. For 3% dose difference and 3 mm DTA criteria, the average value for gamma(>1) was 4.7% +/- 3.7%, the average gamma(1%) value was 1.19 +/- 0.16 and the mean 2D gamma-value was 0.44 +/- 0.07 in the heterogeneous phantom. The iPlan MC algorithm leads to accurate dosimetric results under clinical test conditions.

Dosimetric validation and clinical implementation of two 3D dose verification systems for quality assurance in volumetric-modulated arc therapy techniques.

PubMed

Clemente-Gutiérrez, Francisco; Pérez-Vara, Consuelo

2015-03-08

A pretreatment quality assurance program for volumetric techniques should include redundant calculations and measurement-based verifications. The patient-specific quality assurance process must be based in clinically relevant metrics. The aim of this study was to show the commission, clinical implementation, and comparison of two systems that allow performing a 3D redundant dose calculation. In addition, one of them is capable of reconstructing the dose on patient anatomy from measurements taken with a 2D ion chamber array. Both systems were compared in terms of reference calibration data (absolute dose, output factors, percentage depth-dose curves, and profiles). Results were in good agreement for absolute dose values (discrepancies were below 0.5%) and output factors (mean differences were below 1%). Maximum mean discrepancies were located between 10 and 20 cm of depth for PDDs (-2.7%) and in the penumbra region for profiles (mean DTA of 1.5 mm). Validation of the systems was performed by comparing point-dose measurements with values obtained by the two systems for static, dynamic fields from AAPM TG-119 report, and 12 real VMAT plans for different anatomical sites (differences better than 1.2%). Comparisons between measurements taken with a 2D ion chamber array and results obtained by both systems for real VMAT plans were also performed (mean global gamma passing rates better than 87.0% and 97.9% for the 2%/2 mm and 3%/3 mm criteria). Clinical implementation of the systems was evaluated by comparing dose-volume parameters for all TG-119 tests and real VMAT plans with TPS values (mean differences were below 1%). In addition, comparisons between dose distributions calculated by TPS and those extracted by the two systems for real VMAT plans were also performed (mean global gamma passing rates better than 86.0% and 93.0% for the 2%/2 mm and 3%/ 3 mm criteria). The clinical use of both systems was successfully evaluated.

Capture of complexity of specialty care in pediatric cardiology by work RVU measures.

PubMed

Bergersen, Lisa; Gauvreau, Kimberlee; McElhinney, Doff; Fenwick, Sandra; Kirshner, David; Harding, Julie; Hickey, Patricia; Mayer, John; Marshall, Audrey

2013-02-01

We sought to determine the relationship between relative value units (RVUs) and intended measures of work in catheterization for congenital heart disease. RVU was determined by matching RVU values to Current Procedural Terminology codes generated for cases performed at a single institution. Differences in median case duration, radiation exposure, adverse events, and RVU values by risk category and cases were assessed. Interventional case types were ranked from lowest to highest median RVU value, and correlations with case duration, radiation dose, and a cases-predicted probability of an adverse event were quantified with the Spearman rank correlation coefficient. Between January 2008 and December 2010, 3557 of 4011 cases were identified with an RVU and risk category designation, of which 2982 were assigned a case type. Median RVU values, radiation dose, and case duration increased with procedure risk category. Although all diagnostic cases had similar RVU values (median 10), adverse event rates ranged from 6% to 21% by age group (P < .001). Median RVU values ranged from 9 to 54 with the lowest in diagnostic and biopsy cases and increasing with isolated and then multiple interventions. Among interventional cases, no correlation existed between ranked RVU value and case duration, radiation dose, or adverse event probability (P = .13, P = .62, and P = .43, respectively). Time, skill, and stress inherent to performing catheterization procedures for congenital heart disease are not captured by measurement of RVU alone.

Radiochromic film calibration for the RQT9 quality beam

NASA Astrophysics Data System (ADS)

Costa, K. C.; Gomez, A. M. L.; Alonso, T. C.; Mourao, A. P.

2017-11-01

When ionizing radiation interacts with matter it generates energy deposition. Radiation dosimetry is important for medical applications of ionizing radiation due to the increasing demand for diagnostic radiology and radiotherapy. Different dosimetry methods are used and each one has its advantages and disadvantages. The film is a dose measurement method that records the energy deposition by the darkening of its emulsion. Radiochromic films have a little visible light sensitivity and respond better to ionizing radiation exposure. The aim of this study is to obtain the resulting calibration curve by the irradiation of radiochromic film strips, making it possible to relate the darkening of the film with the absorbed dose, in order to measure doses in experiments with X-ray beam of 120 kV, in computed tomography (CT). Film strips of GAFCHROMIC XR-QA2 were exposed according to RQT9 reference radiation, which defines an X-ray beam generated from a voltage of 120 kV. Strips were irradiated in "Laboratório de Calibração de Dosímetros do Centro de Desenvolvimento da Tecnologia Nuclear" (LCD / CDTN) at a dose range of 5-30 mGy, corresponding to the range values commonly used in CT scans. Digital images of the irradiated films were analyzed by using the ImageJ software. The darkening responses on film strips according to the doses were observed and they allowed obtaining the corresponding numeric values to the darkening for each specific dose value. From the numerical values of darkening, a calibration curve was obtained, which correlates the darkening of the film strip with dose values in mGy. The calibration curve equation is a simplified method for obtaining absorbed dose values using digital images of radiochromic films irradiated. With the calibration curve, radiochromic films may be applied on dosimetry in experiments on CT scans using X-ray beam of 120 kV, in order to improve CT acquisition image processes.

Test Operations Procedure (TOP) 1-2-612 Nuclear Environment Survivability

DTIC Science & Technology

2008-10-24

measurements. The area equal to the area of gamma dose sensitive electronics will be mapped using CaF2 (Mn) TLDs . The selection of each STT...October 2008 8 2.3.3 HEMP / SREMP Instrumentation / Dosimetry . Measurement Parameter Preferred Device Measurement Accuracy Current...Calcium Fluoride Manganese CaF2 (Mn) Thermoluminescent Dosimeter ( TLDs ) and Compton diodes, respectively. The measured gamma dose values will be

Organ dose conversion coefficients for pediatric reference computational phantoms in external photon radiation fields

NASA Astrophysics Data System (ADS)

Chang, Lienard A.

In the event of a radiological accident or attack, it is important to estimate the organ doses to those exposed. In general, it is difficult to measure organ dose directly in the field and therefore dose conversion coefficients (DCC) are needed to convert measurable values such as air kerma to organ dose. Previous work on these coefficients has been conducted mainly for adults with a focus on radiation protection workers. Hence, there is a large gap in the literature for pediatric values. This study coupled a Monte Carlo N-Particle eXtended (MCNPX) code with International Council of Radiological Protection (ICRP)-adopted University of Florida and National Cancer Institute pediatric reference phantoms to calculate a comprehensive list of dose conversion coefficients (mGy/mGy) to convert air-kerma to organ dose. Parameters included ten phantoms (newborn, 1-year, 5-year, 10-year, 15-year old male and female), 28 organs over 33 energies between 0.01 and 20 MeV in six (6) irradiation geometries relevant to a child who might be exposed to a radiological release: anterior-posterior (AP), posterior-anterior (PA), right-lateral (RLAT), left-lateral (LLAT), rotational (ROT), and isotropic (ISO). Dose conversion coefficients to the red bone marrow over 36 skeletal sites were also calculated. It was hypothesized that the pediatric organ dose conversion coefficients would follow similar trends to the published adult values as dictated by human anatomy, but be of a higher magnitude. It was found that while the pediatric coefficients did yield similar patterns to that of the adult coefficients, depending on the organ and irradiation geometry, the pediatric values could be lower or higher than that of the adult coefficients.

Cranial CT with adaptive statistical iterative reconstruction: improved image quality with concomitant radiation dose reduction.

PubMed

Rapalino, O; Kamalian, Shervin; Kamalian, Shahmir; Payabvash, S; Souza, L C S; Zhang, D; Mukta, J; Sahani, D V; Lev, M H; Pomerantz, S R

2012-04-01

To safeguard patient health, there is great interest in CT radiation-dose reduction. The purpose of this study was to evaluate the impact of an iterative-reconstruction algorithm, ASIR, on image-quality measures in reduced-dose head CT scans for adult patients. Using a 64-section scanner, we analyzed 100 reduced-dose adult head CT scans at 6 predefined levels of ASIR blended with FBP reconstruction. These scans were compared with 50 CT scans previously obtained at a higher routine dose without ASIR reconstruction. SNR and CNR were computed from Hounsfield unit measurements of normal GM and WM of brain parenchyma. A blinded qualitative analysis was performed in 10 lower-dose CT datasets compared with higher-dose ones without ASIR. Phantom data analysis was also performed. Lower-dose scans without ASIR had significantly lower mean GM and WM SNR (P = .003) and similar GM-WM CNR values compared with higher routine-dose scans. However, at ASIR levels of 20%-40%, there was no statistically significant difference in SNR, and at ASIR levels of ≥60%, the SNR values of the reduced-dose scans were significantly higher (P < .01). CNR values were also significantly higher at ASIR levels of ≥40% (P < .01). Blinded qualitative review demonstrated significant improvements in perceived image noise, artifacts, and GM-WM differentiation at ASIR levels ≥60% (P < .01). These results demonstrate that the use of ASIR in adult head CT scans reduces image noise and increases low-contrast resolution, while allowing lower radiation doses without affecting spatial resolution.

Toward an organ based dose prescription method for the improved accuracy of murine dose in orthovoltage x-ray irradiators.

PubMed

Belley, Matthew D; Wang, Chu; Nguyen, Giao; Gunasingha, Rathnayaka; Chao, Nelson J; Chen, Benny J; Dewhirst, Mark W; Yoshizumi, Terry T

2014-03-01

Accurate dosimetry is essential when irradiating mice to ensure that functional and molecular endpoints are well understood for the radiation dose delivered. Conventional methods of prescribing dose in mice involve the use of a single dose rate measurement and assume a uniform average dose throughout all organs of the entire mouse. Here, the authors report the individual average organ dose values for the irradiation of a 12, 23, and 33 g mouse on a 320 kVp x-ray irradiator and calculate the resulting error from using conventional dose prescription methods. Organ doses were simulated in the Geant4 application for tomographic emission toolkit using the MOBY mouse whole-body phantom. Dosimetry was performed for three beams utilizing filters A (1.65 mm Al), B (2.0 mm Al), and C (0.1 mm Cu + 2.5 mm Al), respectively. In addition, simulated x-ray spectra were validated with physical half-value layer measurements. Average doses in soft-tissue organs were found to vary by as much as 23%-32% depending on the filter. Compared to filters A and B, filter C provided the hardest beam and had the lowest variation in soft-tissue average organ doses across all mouse sizes, with a difference of 23% for the median mouse size of 23 g. This work suggests a new dose prescription method in small animal dosimetry: it presents a departure from the conventional approach of assigninga single dose value for irradiation of mice to a more comprehensive approach of characterizing individual organ doses to minimize the error and uncertainty. In human radiation therapy, clinical treatment planning establishes the target dose as well as the dose distribution, however, this has generally not been done in small animal research. These results suggest that organ dose errors will be minimized by calibrating the dose rates for all filters, and using different dose rates for different organs.

Toward an organ based dose prescription method for the improved accuracy of murine dose in orthovoltage x-ray irradiators

PubMed Central

Belley, Matthew D.; Wang, Chu; Nguyen, Giao; Gunasingha, Rathnayaka; Chao, Nelson J.; Chen, Benny J.; Dewhirst, Mark W.; Yoshizumi, Terry T.

2014-01-01

Purpose: Accurate dosimetry is essential when irradiating mice to ensure that functional and molecular endpoints are well understood for the radiation dose delivered. Conventional methods of prescribing dose in mice involve the use of a single dose rate measurement and assume a uniform average dose throughout all organs of the entire mouse. Here, the authors report the individual average organ dose values for the irradiation of a 12, 23, and 33 g mouse on a 320 kVp x-ray irradiator and calculate the resulting error from using conventional dose prescription methods. Methods: Organ doses were simulated in the Geant4 application for tomographic emission toolkit using the MOBY mouse whole-body phantom. Dosimetry was performed for three beams utilizing filters A (1.65 mm Al), B (2.0 mm Al), and C (0.1 mm Cu + 2.5 mm Al), respectively. In addition, simulated x-ray spectra were validated with physical half-value layer measurements. Results: Average doses in soft-tissue organs were found to vary by as much as 23%–32% depending on the filter. Compared to filters A and B, filter C provided the hardest beam and had the lowest variation in soft-tissue average organ doses across all mouse sizes, with a difference of 23% for the median mouse size of 23 g. Conclusions: This work suggests a new dose prescription method in small animal dosimetry: it presents a departure from the conventional approach of assigning a single dose value for irradiation of mice to a more comprehensive approach of characterizing individual organ doses to minimize the error and uncertainty. In human radiation therapy, clinical treatment planning establishes the target dose as well as the dose distribution, however, this has generally not been done in small animal research. These results suggest that organ dose errors will be minimized by calibrating the dose rates for all filters, and using different dose rates for different organs. PMID:24593746

Toward an organ based dose prescription method for the improved accuracy of murine dose in orthovoltage x-ray irradiators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belley, Matthew D.; Wang, Chu; Nguyen, Giao

2014-03-15

Purpose: Accurate dosimetry is essential when irradiating mice to ensure that functional and molecular endpoints are well understood for the radiation dose delivered. Conventional methods of prescribing dose in mice involve the use of a single dose rate measurement and assume a uniform average dose throughout all organs of the entire mouse. Here, the authors report the individual average organ dose values for the irradiation of a 12, 23, and 33 g mouse on a 320 kVp x-ray irradiator and calculate the resulting error from using conventional dose prescription methods. Methods: Organ doses were simulated in the Geant4 application formore » tomographic emission toolkit using the MOBY mouse whole-body phantom. Dosimetry was performed for three beams utilizing filters A (1.65 mm Al), B (2.0 mm Al), and C (0.1 mm Cu + 2.5 mm Al), respectively. In addition, simulated x-ray spectra were validated with physical half-value layer measurements. Results: Average doses in soft-tissue organs were found to vary by as much as 23%–32% depending on the filter. Compared to filters A and B, filter C provided the hardest beam and had the lowest variation in soft-tissue average organ doses across all mouse sizes, with a difference of 23% for the median mouse size of 23 g. Conclusions: This work suggests a new dose prescription method in small animal dosimetry: it presents a departure from the conventional approach of assigninga single dose value for irradiation of mice to a more comprehensive approach of characterizing individual organ doses to minimize the error and uncertainty. In human radiation therapy, clinical treatment planning establishes the target dose as well as the dose distribution, however, this has generally not been done in small animal research. These results suggest that organ dose errors will be minimized by calibrating the dose rates for all filters, and using different dose rates for different organs.« less

Dose uniformity analysis among ten 16-slice same-model CT scanners.

PubMed

Erdi, Yusuf Emre

2012-01-01

With the introduction of multislice scanners, computed tomographic (CT) dose optimization has become important. The patient-absorbed dose may differ among the scanners although they are the same type and model. To investigate the dose output variation of the CT scanners, we designed the study to analyze dose outputs of 10 same-model CT scanners using 3 clinical protocols. Ten GE Lightspeed (GE Healthcare, Waukesha, Wis) 16-slice scanners located at main campus and various satellite locations of our institution have been included in this study. All dose measurements were performed using poly (methyl methacrylate) (PMMA) head (diameter, 16 cm) and body (diameter, 32 cm) phantoms manufactured by Radcal (RadCal Corp, Monrovia, Calif) using a 9095 multipurpose analyzer with 10 × 9-3CT ion chamber both from the same manufacturer. Ion chamber is inserted into the peripheral and central axis locations and volume CT dose index (CTDIvol) is calculated as weighted average of doses at those locations. Three clinical protocol settings for adult head, high-resolution chest, and adult abdomen are used for dose measurements. We have observed up to 9.4% CTDIvol variation for the adult head protocol in which the largest variation occurred among the protocols. However, head protocol uses higher milliampere second values than the other 2 protocols. Most of the measured values were less than the system-stored CTDIvol values. It is important to note that reduction in dose output from tubes as they age is expected in addition to the intrinsic radiation output fluctuations of the same scanner. Although the same model CT scanners were used in this study, it is possible to see CTDIvol variation in standard patient scanning protocols of head, chest, and abdomen. The compound effect of the dose variation may be larger with higher milliampere and multiphase and multilocation CT scans.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Therriault-Proulx, F; Wootton, L; Beddar, S

Purpose: To evaluate a measurement method that renders plastic scintillation detectors temperature independent and capable of recovering dose and temperature information simultaneously. Methods: A novel approach was developed to account for the temperature dependence of plastic scintillation detectors (PSDs) without prior knowledge of the temperature. To enable this, the optical response of the scintillating element is separated into two sub-components, one being the response at a given temperature and the other accounting for the change in the optical emission spectrum with temperature. Using a previously demonstrated hyperspectral approach and following the proper calibration protocol, the contribution to scintillator emission andmore » physical value of both dose and temperature can be obtained in real-time. To validate the method, dose and temperature were measured under cobalt irradiation in a temperature controlled water tank developed for this study. The temperature was varied from 22°C to 42°C. Depth-dose curves were also obtained during irradiations from a linear accelerator, first maintaining the water at room temperature and then warming it to 40°C and letting it cool down naturally over the course of the second measurement. Results: Dose measurements delivered with the Co-60 unit showed an average relative difference to the expected value of (1.0±0.8)%, with a maximum difference of 2.3% over the entire range of temperatures. The measured temperatures using the PSD were all within 1°C of the expected values. The difference between room temperature and warmer depth dose measurements differed by only (1.2±0.4)%. The dosimeter showed to be accurate for temporal resolution down to 0.1s. Conclusion: The proposed method was shown to reliably correct for the temperature dependence of a PSD. Additionally, it makes it possible to assess the temperature at the point of measurement. These are significant advances in PSD technology, particularly in relation to real-time in vivo dosimetry. Part of this research was supported by the Odyssey Program at The University of Texas MD Anderson Cancer Center.« less

Medical and occupational dose reduction in pediatric barium meal procedures

NASA Astrophysics Data System (ADS)

Filipov, D.; Schelin, H. R.; Denyak, V.; Paschuk, S. A.; Ledesma, J. A.; Legnani, A.; Bunick, A. P.; Sauzen, J.; Yagui, A.; Vosiak, P.

2017-11-01

Doses received in pediatric Barium Meal procedure can be rather high. It is possible to reduce dose values following the recommendations of the European Communities (EC) and the International Commission on Radiological Protection (ICRP). In the present work, the modifications of radiographic techniques made in a Brazilian hospital according to the EC and the ICRP recommendations and their influence on medical and occupational exposure are reported. The procedures of 49 patients before and 44 after the optimization were studied and air kerma-area product (PK,A) values and the effective doses were evaluated. The occupational equivalent doses were measured next to the eyes, under the thyroid shield and on each hand of both professionals who remained inside the examination room. The implemented modifications reduced by 70% and 60% the PK,A and the patient effective dose, respectively. The obtained dose values are lower than approximately 75% of the results from similar studies. The occupational annual equivalent doses for all studied organs became lower than the limits set by the ICRP. The equivalent doses in one examination were on average below than 75% of similar studies.

SU-G-IeP2-04: Dosimetric Accuracy of a Monte Carlo-Based Tool for Cone-Beam CT Organ Dose Calculation: Validation Against OSL and XRQA2 Film Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesneau, H; Lazaro, D; Blideanu, V

Purpose: The intensive use of Cone-Beam Computed Tomography (CBCT) during radiotherapy treatments raise some questions about the dose to healthy tissues delivered during image acquisitions. We hence developed a Monte Carlo (MC)-based tool to predict doses to organs delivered by the Elekta XVI kV-CBCT. This work aims at assessing the dosimetric accuracy of the MC tool, in all tissue types. Methods: The kV-CBCT MC model was developed using the PENELOPE code. The beam properties were validated against measured lateral and depth dose profiles in water, and energy spectra measured with a CdTe detector. The CBCT simulator accuracy then required verificationmore » in clinical conditions. For this, we compared calculated and experimental dose values obtained with OSL nanoDots and XRQA2 films inserted in CIRS anthropomorphic phantoms (male, female, and 5-year old child). Measurements were performed at different locations, including bone and lung structures, and for several acquisition protocols: lung, head-and-neck, and pelvis. OSLs and film measurements were corrected when possible for energy dependence, by taking into account for spectral variations between calibration and measurement conditions. Results: Comparisons between measured and MC dose values are summarized in table 1. A mean difference of 8.6% was achieved for OSLs when the energy correction was applied, and 89.3% of the 84 dose points were within uncertainty intervals, including those in bones and lungs. Results with XRQA2 are not as good, because incomplete information about electronic equilibrium in film layers hampered the application of a simple energy correction procedure. Furthermore, measured and calculated doses (Fig.1) are in agreement with the literature. Conclusion: The MC-based tool developed was validated with an extensive set of measurements, and enables the organ dose calculation with accuracy. It can now be used to compute and report doses to organs for clinical cases, and also to drive strategies to optimize imaging protocols.« less

Dose Distribution in Cone-Beam Breast Computed Tomography: An Experimental Phantom Study

NASA Astrophysics Data System (ADS)

Russo, Paolo; Lauria, Adele; Mettivier, Giovanni; Montesi, Maria Cristina; Villani, Natalia

2010-02-01

We measured the spatial distribution of absorbed dose in a 14 cm diameter PMMA half-ellipsoid phantom simulating the uncompressed breast, using an X-ray cone-beam breast computed tomography apparatus, assembled for laboratory tests. Thermoluminescent dosimeters (TLD-100) were placed inside the phantom in six positions, both axially and at the phantom periphery. To study the dose distribution inside the PMMA phantom two experimental setups were adopted with effective energies in the range 28.7-44.4 keV. Different values of effective energies were obtained by combining different configurations of added Cu filtration (0.05 mm or 0.2 mm) and tube voltages (from 50 kVp to 80 kVp). Dose values obtained by TLDs in different positions inside the PMMA are reported. To evaluate the dose distribution in the breast shaped volume, the values measured were normalized to the one obtained in the inner position inside the phantom. Measurements with a low energy setup show a gradual increment of dose going from the "chest wall" to the "nipple" (63% more at the "nipple" compared to the central position). Likewise, a gradual increment is observed going from the breast axis toward the periphery (82% more at the "skin" compared to the central position). A more uniform distribution of dose inside the PMMA was obtained with a high energy setup (the maximum variation was 33% at 35.5 keV effective energy in the radial direction). The most uniform distribution is obtained at 44.4 keV. The results of this study show how the dose is distributed: it varies as a function of effective energy of the incident X-ray beam and as a function of the position inside the volume (axial or peripheral position).

Antipsychotic dose equivalents and dose-years: a standardized method for comparing exposure to different drugs.

PubMed

Andreasen, Nancy C; Pressler, Marcus; Nopoulos, Peg; Miller, Del; Ho, Beng-Choon

2010-02-01

A standardized quantitative method for comparing dosages of different drugs is a useful tool for designing clinical trials and for examining the effects of long-term medication side effects such as tardive dyskinesia. Such a method requires establishing dose equivalents. An expert consensus group has published charts of equivalent doses for various antipsychotic medications for first- and second-generation medications. These charts were used in this study. Regression was used to compare each drug in the experts' charts to chlorpromazine and haloperidol and to create formulas for each relationship. The formulas were solved for chlorpromazine 100 mg and haloperidol 2 mg to derive new chlorpromazine and haloperidol equivalents. The formulas were incorporated into our definition of dose-years such that 100 mg/day of chlorpromazine equivalent or 2 mg/day of haloperidol equivalent taken for 1 year is equal to one dose-year. All comparisons to chlorpromazine and haloperidol were highly linear with R(2) values greater than .9. A power transformation further improved linearity. By deriving a unique formula that converts doses to chlorpromazine or haloperidol equivalents, we can compare otherwise dissimilar drugs. These equivalents can be multiplied by the time an individual has been on a given dose to derive a cumulative value measured in dose-years in the form of (chlorpromazine equivalent in mg) x (time on dose measured in years). After each dose has been converted to dose-years, the results can be summed to provide a cumulative quantitative measure of lifetime exposure. Copyright 2010 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Estimation of computed tomography dose index in cone beam computed tomography: MOSFET measurements and Monte Carlo simulations.

PubMed

Kim, Sangroh; Yoshizumi, Terry; Toncheva, Greta; Yoo, Sua; Yin, Fang-Fang; Frush, Donald

2010-05-01

To address the lack of accurate dose estimation method in cone beam computed tomography (CBCT), we performed point dose metal oxide semiconductor field-effect transistor (MOSFET) measurements and Monte Carlo (MC) simulations. A Varian On-Board Imager (OBI) was employed to measure point doses in the polymethyl methacrylate (PMMA) CT phantoms with MOSFETs for standard and low dose modes. A MC model of the OBI x-ray tube was developed using BEAMnrc/EGSnrc MC system and validated by the half value layer, x-ray spectrum and lateral and depth dose profiles. We compared the weighted computed tomography dose index (CTDIw) between MOSFET measurements and MC simulations. The CTDIw was found to be 8.39 cGy for the head scan and 4.58 cGy for the body scan from the MOSFET measurements in standard dose mode, and 1.89 cGy for the head and 1.11 cGy for the body in low dose mode, respectively. The CTDIw from MC compared well to the MOSFET measurements within 5% differences. In conclusion, a MC model for Varian CBCT has been established and this approach may be easily extended from the CBCT geometry to multi-detector CT geometry.

A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system.

PubMed

Rana, V K; Rudin, S; Bednarek, D R

2016-09-01

Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, a data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries.

A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system

PubMed Central

Rana, V. K.; Rudin, S.; Bednarek, D. R.

2016-01-01

Purpose: Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. Methods: The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, a data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. Results: The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. Conclusions: The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries. PMID:27587043

A tracking system to calculate patient skin dose in real-time during neurointerventional procedures using a biplane x-ray imaging system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rana, V. K., E-mail: vkrana@buffalo.edu

Purpose: Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. Methods: The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, amore » data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. Results: The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. Conclusions: The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries.« less

In vivo TLD dose measurements in catheter-based high-dose-rate brachytherapy.

PubMed

Adlienė, Diana; Jakštas, Karolis; Urbonavičius, Benas Gabrielis

2015-07-01

Routine in vivo dosimetry is well established in external beam radiotherapy; however, it is restricted mainly to detection of gross errors in high-dose-rate (HDR) brachytherapy due to complicated measurements in the field of steep dose gradients in the vicinity of radioactive source and high uncertainties. The results of in vivo dose measurements using TLD 100 mini rods and TLD 'pin worms' in catheter-based HDR brachytherapy are provided in this paper alongside with their comparison with corresponding dose values obtained using calculation algorithm of the treatment planning system. Possibility to perform independent verification of treatment delivery in HDR brachytherapy using TLDs is discussed. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Monte Carlo simulation and film dosimetry for electron therapy in vicinity of a titanium mesh

PubMed Central

Rostampour, Masoumeh; Roayaei, Mahnaz

2014-01-01

Titanium (Ti) mesh plates are used as a bone replacement in brain tumor surgeries. In the case of radiotherapy, these plates might interfere with the beam path. The purpose of this study is to evaluate the effect of titanium mesh on the dose distribution of electron fields. Simulations were performed using Monte Carlo BEAMnrc and DOSXYZnrc codes for 6 and 10 MeV electron beams. In Monte Carlo simulation, the shape of the titanium mesh was simulated. The simulated titanium mesh was considered as the one which is used in head and neck surgery with a thickness of 0.055 cm. First, by simulation, the percentage depth dose was obtained while the titanium mesh was present, and these values were then compared with the depth dose of homogeneous phantom with no titanium mesh. In the experimental measurements, the values of depth dose with titanium mesh and without titanium mesh in various depths were measured. The experiments were performed using a RW3 phantom with GAFCHROMIC EBT2 film. The results of experimental measurements were compared with values of depth dose obtained by simulation. In Monte Carlo simulation, as well as experimental measurements, for the voxels immediately beyond the titanium mesh, the change of the dose were evaluated. For this purpose the ratio of the dose for the case with titanium to the case without titanium was calculated as a function of titanium depth. For the voxels before the titanium mesh there was always an increase of the dose up to 13% with respect to the same voxel with no titanium mesh. This is because of the increased back scattering effect of the titanium mesh. The results also showed that for the voxel right beyond the titanium mesh, there is an increased or decreased dose to soft tissues, depending on the depth of the titanium mesh. For the regions before the depth of maximum dose, there is an increase of the dose up to 10% compared to the dose of the same depth in homogeneous phantom. Beyond the depth of maximum dose, there was a 16% decrease in dose. For both 6 and 10 MeV, before the titanium mesh, there was always an increase in dose. If titanium mesh is placed in buildup region, it causes an increase of the dose and could lead to overdose of the adjacent tissue, whereas if titanium mesh is placed beyond the buildup region, it would lead to a decrease in dose compared to the homogenous tissue. PACS number: 87.53.Bn PMID:25207397

Measurements of occupational exposure for a technologist performing 18F FDG PET scans.

PubMed

Biran, Talma; Weininger, Jolie; Malchi, Shalom; Marciano, Rami; Chisin, Roland

2004-11-01

Radiation doses to one PET technologist performing 100 18F FDG (18F fluorodeoxyglucose) imaging procedures were measured in a clinical setting using two types of thermoluminescent dosimeter (TLD) badges, one finger-ring TLD and one electronic pocket dosimeter (EPD). 18F FDG was handled either with unshielded or with viewing window tungsten shielded syringes. The resulting doses using unshielded syringes were 13.8 +/- 0.8 microSv/370 MBq and 14.3 +/- 0.4 microSv/370 MBq, measured with TLD 100 and with TLD 700H/600H, respectively. For the same series of measurements, the doses obtained using shielded syringes were 10.7 +/- 0.4 microSv/370 MBq and 7.2 +/- 2.1 microSv/370 MBq with TLD700H/600H and with EPD, respectively. The dose to the right hand from shielded syringes was 69.3 +/- 5.5 microSv/370 MBq. All these values are within the ICRP recommended dose limits. Extrapolated to 725 examinations per year, the resulting effective dose measured with TLD would be 10 mSv with unshielded and 7.5 mSv with shielded syringes, respectively (25% dose reduction). The doses measured by TLD were consistently higher than those measured by EPD, suggesting that EPD measurements might underestimate occupational doses.

Dose measurement using Al2O3 dosimeter in comparison to LiF:Mg,Ti dosimeter and ionization chamber at low and high energy x-ray

NASA Astrophysics Data System (ADS)

Yusof, Mohd Fahmi Mohd; Yahya, Muhammad Hadzmi; Rosnan, Muhammad Syazwan; Abdullah, Reduan; Kadir, Ahmad Bazlie Abdul

2017-01-01

The dose measurement using Al2O3 OSL dosimeter (OSLD) was carried out at low and high energy x-ray. The dose at low energy x-ray was measured at 40, 71 and 125 kVp x-ray energies. The dose ar high energy x-ray was measured at 6 and 10 MV x-ray energies measured at the depth of maximum dose (Zmax). The results were compared to that in ionization chamber and LiF: Mg,Ti thermoluminescent dosimeters (TLD100). The results showed that the dose of OSLD were less in agreement to ionization chamber compared to that in TLD100. The dose of OSLD however was in good agreement to that in ionization chamber at high energy x-ray. The dose measured using OSLD were found to be more consistence at high energy x-ray shown by the standard deviation of the readings. The measurement of x2 showed that the readings of OSLD were close to that in ionization chamber with values of 2.21 and 4.63 for 6 and 10 MV respectively. The results indicated that OSLD is more suitable for dose measurement at high energy x-ray.

In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity.

PubMed

Kohno, Ryosuke; Hotta, Kenji; Matsubara, Kana; Nishioka, Shie; Matsuura, Taeko; Kawashima, Mitsuhiko

2012-03-08

When in vivo proton dosimetry is performed with a metal-oxide semiconductor field-effect transistor (MOSFET) detector, the response of the detector depends strongly on the linear energy transfer. The present study reports a practical method to correct the MOSFET response for linear energy transfer dependence by using a simplified Monte Carlo dose calculation method (SMC). A depth-output curve for a mono-energetic proton beam in polyethylene was measured with the MOSFET detector. This curve was used to calculate MOSFET output distributions with the SMC (SMC(MOSFET)). The SMC(MOSFET) output value at an arbitrary point was compared with the value obtained by the conventional SMC(PPIC), which calculates proton dose distributions by using the depth-dose curve determined by a parallel-plate ionization chamber (PPIC). The ratio of the two values was used to calculate the correction factor of the MOSFET response at an arbitrary point. The dose obtained by the MOSFET detector was determined from the product of the correction factor and the MOSFET raw dose. When in vivo proton dosimetry was performed with the MOSFET detector in an anthropomorphic phantom, the corrected MOSFET doses agreed with the SMC(PPIC) results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector.

THE UNIQUE VALUE OF BREATH BIOMARKERS FOR ESTIMATING PHAMACOKINETIC RATE CONSTANTS AND BODY BURDEN FROM RANDOM/INTERMITTENT DOSE

EPA Science Inventory

Biomarker measurements are used in three ways: 1) evaluating the time course and distribution of a chemical in the body, 2) estimating previous exposure or dose, and 3) assessing disease state. Blood and urine measurements are the primary methods employed. Of late, it has been ...

Determination of dosimetric quantities in pediatric abdominal computed tomography scans*

PubMed Central

Jornada, Tiago da Silva; da Silva, Teógenes Augusto

2014-01-01

Objective Aiming at contributing to the knowledge on doses in computed tomography (CT), this study has the objective of determining dosimetric quantities associated with pediatric abdominal CT scans, comparing the data with diagnostic reference levels (DRL). Materials and methods The study was developed with a Toshiba Asteion single-slice CT scanner and a GE BrightSpeed multi-slice CT unit in two hospitals. Measurements were performed with a pencil-type ionization chamber and a 16 cm-diameter polymethylmethacrylate trunk phantom. Results No significant difference was observed in the values for weighted air kerma index (CW), but the differences were relevant in values for volumetric air kerma index (CVOL), air kerma-length product (PKL,CT) and effective dose. Conclusion Only the CW values were lower than the DRL, suggesting that dose optimization might not be necessary. However, PKL,CT and effective dose values stressed that there still is room for reducing pediatric radiation doses. The present study emphasizes the importance of determining all dosimetric quantities associated with CT scans. PMID:25741103

Dosimetric evaluation of the staff working in a PET/CT department

NASA Astrophysics Data System (ADS)

Dalianis, K.; Malamitsi, J.; Gogou, L.; Pagou, M.; Efthimiadou, R.; Andreou, J.; Louizï, A.; Georgiou, E.

2006-12-01

The dosimetric literature data concerning the medical personnel working in positron emission tomography/computed tomography (PET/CT) departments are limited. Therefore, we measured the radiation dose of the staff working in the first PET/CT department in Greece at the Diagnostic and Therapeutic Center of Athens HYGEIA—Harvard Medical International. As, for the time being, only 2-deoxy-2-[ 18F]fluoro-d-glucose (FDG) PET studies are performed, radiation dose measurements concern those derived from dispensing of the radiopharmaceutical as well as from the patients undergoing FDG-PET imaging. Our aim is to develop more effective protective measures against radionuclide exposure. To estimate the effective dose from external exposure, all seven members of the staff (two nurses, two medical physicists, two technologists, one secretary) had TLD badges worn at the upper pocket of their overall, TLD rings on the right hand and digital dosimeters at their upper side pocket. In addition, isodose curves were measured with thermoluminescence detectors for distances of 20, 50, 70 and 100 cm away from patients who had been injected with 18F-FDG. Dose values of the PET/CT staff were measured with digital detectors, TLD badges and TLD rings over the first 8 months for a total of 160 working days of the department's operation, consisting of a workload of about 10-15 patients/week who received 250-420 MBq of 18F-FDG each. Whole - body collective doses and hand doses for the staff were the following: Nurse #1 received 1.6 mSv as a whole body dose and 2,1 as a hand dose, Nurse #2 received 1.9 and 2.4 mSv respectively. For medical physicist #1 the dose values were 1.45 mSv whole body and 1.7 mSv hand dose, for medical physicist #2 1.67 mSv wholebody dose and 1.55 mSv hand dose and for technologists #1 & #2 the whole body doses were 0.7 and 0.64 mSv respectively. Lastly, the secretary received 0.1 mSv whole body dose. These preliminary data have shown that the dose levels of our PET/CT staff are within acceptable limits.

Assessment of an organ-based tube current modulation in thoracic computed tomography.

PubMed

Matsubara, Kosuke; Sugai, Mai; Toyoda, Asami; Koshida, Haruka; Sakuta, Keita; Takata, Tadanori; Koshida, Kichiro; Iida, Hiroji; Matsui, Osamu

2012-03-08

Recently, specific computed tomography (CT) scanners have been equipped with organ-based tube current modulation (TCM) technology. It is possible that organ-based TCM will replace the conventional dose-reduction technique of reducing the effective milliampere-second. The aim of this study was to determine if organ-based TCM could reduce radiation exposure to the breasts without compromising the image uniformity and beam hardening effect in thoracic CT examinations. Breast and skin radiation doses and the absorbed radiation dose distribution within a single section were measured with an anthropomorphic phantom and radiophotoluminescent glass dosimeters using four approaches to thoracic CT (reference, organ-based TCM, copper shielding, and the combination of the above two techniques, hereafter referred to as the combination technique). The CT value and noise level were measured using the same calibration phantom. Organ-based TCM and copper shielding reduced radiation doses to the breast by 23.7% and 21.8%, respectively. However, the CT value increased, especially in the anterior region, using copper shielding. In contrast, the CT value and noise level barely increased using organ-based TCM. The combination technique reduced the radiation dose to the breast by 38.2%, but greatly increased the absorbed radiation dose from the central to the posterior regions. Moreover, the CT value increased in the anterior region and the noise level increased by more than 10% in the entire region. Therefore, organ-based TCM can reduce radiation doses to breasts with only small increases in noise levels, making it preferable for specific groups of patients, such as children and young women.

Evaluation of the peripheral dose to uterus in breast carcinoma radiotherapy.

PubMed

Martín Rincón, C; Jerez Sainz, I; Modolell Farré, I; España López, M L; López Franco, P; Muñiz, J L; Romero, A M; Rodríguez, R

2002-01-01

The absorbed dose outside of the direct fields of radiotherapy treatment (or peripheral dose, PD) is responsible for radiation exposure of the fetus in pregnant women. Because the radiological protection of the unborn child is of particular concern in the early period of the pregnancy, the aim of this study is to estimate the PD in order to assess the absorbed dose in the uterus in a pregnant patient irradiated for breast carcinoma therapy. The treatment was simulated on an Alderson-Rando anthropomorphic phantom, and the radiation dose to the fetus was measured using an ionisation chamber and thermoluminescence dosemeters. Two similar treatments plans with and without wedges were delivered, using a 6 MV photon beam with two isocentric opposite tangential fields with a total dose of 50 Gy, in accordance with common established procedures. Average field parameters for more than 300 patients were studied. Measurements showed the fetal dose to be slightly lower than 50 mGy, a level at which the risk to the fetus is uncertain, although several authors consider this value as the dose threshold for deterministic effects. The planning system (PS) underestimated PD values and no significant influence was found with the use of wedge filters.

Dependence of normal brain integral dose and normal tissue complication probability on the prescription isodose values for γ-knife radiosurgery

NASA Astrophysics Data System (ADS)

Ma, Lijun

2001-11-01

A recent multi-institutional clinical study suggested possible benefits of lowering the prescription isodose lines for stereotactic radiosurgery procedures. In this study, we investigate the dependence of the normal brain integral dose and the normal tissue complication probability (NTCP) on the prescription isodose values for γ-knife radiosurgery. An analytical dose model was developed for γ-knife treatment planning. The dose model was commissioned by fitting the measured dose profiles for each helmet size. The dose model was validated by comparing its results with the Leksell gamma plan (LGP, version 5.30) calculations. The normal brain integral dose and the NTCP were computed and analysed for an ensemble of treatment cases. The functional dependence of the normal brain integral dose and the NCTP versus the prescribing isodose values was studied for these cases. We found that the normal brain integral dose and the NTCP increase significantly when lowering the prescription isodose lines from 50% to 35% of the maximum tumour dose. Alternatively, the normal brain integral dose and the NTCP decrease significantly when raising the prescribing isodose lines from 50% to 65% of the maximum tumour dose. The results may be used as a guideline for designing future dose escalation studies for γ-knife applications.

Measurements of eye lens doses in interventional cardiology using OSL and electronic dosemeters†.

PubMed

Sanchez, R M; Vano, E; Fernandez, J M; Ginjaume, M; Duch, M A

2014-12-01

The purpose of this paper is to test the appropriateness of OSL and electronic dosemeters to estimate eye lens doses at interventional cardiology environment. Using TLD as reference detectors, personal dose equivalent was measured in phantoms and during clinical procedures. For phantom measurements, OSL dose values resulted in an average difference of -15 % vs. TLD. Tests carried out with other electronic dosemeters revealed differences up to ±20 % versus TLD. With dosemeters positioned outside the goggles and when TLD doses were >20 μSv, the average difference OSL vs. TLD was -9 %. Eye lens doses of almost 700 μSv per procedure were measured in two cases out of a sample of 33 measurements in individual clinical procedures, thus showing the risk of high exposure to the lenses of the eye when protection rules are not followed. The differences found between OSL and TLD are acceptable for the purpose and range of doses measured in the survey. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Pharmacokinetics, pharmacodynamics, and dose-response relationship of repaglinide in type 2 diabetes.

PubMed

Strange, P; Schwartz, S L; Graf, R J; Polvino, W; Weston, I; Marbury, T C; Huang, W C; Goldberg, R B

1999-01-01

The pharmacodynamics and dose-response relationship of repaglinide, a novel oral hypoglycemic agent, were evaluated in steady-state treatment of patients with type 2 diabetes. Efficacy of repaglinide (0.25 mg, 0.5 mg, 1 mg, 2 mg, and 4 mg) was compared to that of placebo in a double-blind, randomized, parallel-group, 4-week dose-response clinical trial in 143 patients. Repaglinide was administered 15 minutes before meals (breakfast, lunch, and dinner). Efficacy of repaglinide therapy was assessed by measuring changes from baseline in mean levels of blood glucose (BGmean), fasting serum glucose (FSG), and mean levels of serum insulin (INSmean). Blood concentrations of repaglinide were proportional to the dose administered. INSmean values increased in all repaglinide treatment groups (by 6.7 to 12.9 microU/mL). All doses of repaglinide significantly decreased values of BGmean and FSG as compared with the placebo group. BGmean values stabilized between the second and third week of repaglinide treatment. A well-defined dose-response relationship was observed for BGmean and FSG values. All doses of repaglinide were well tolerated, and there were no serious adverse events. These findings show that the therapeutic reduction of serum glucose levels produced by repaglinide is dose-dependent for the 0.25- to 4-mg dose range. All doses of repaglinide tested were effective and well tolerated in patients with type 2 diabetes.

Commissioning and quality assurance for the treatment delivery components of the AccuBoost system

PubMed Central

Talmadge, Mike; Ladd, Ron; Halvorsen, Per

2015-01-01

The objective for this work was to develop a commissioning methodology for the treatment delivery components of the AccuBoost system, as well as to establish a routine quality assurance program and appropriate guidance for clinical use based on the commissioning results. Various tests were developed: 1) assessment of the accuracy of the displayed separation value; 2) validation of the dwell positions within each applicator; 3) assessment of the accuracy and precision of the applicator localization system; 4) assessment of the combined dose profile of two opposed applicators to confirm that they are coaxial; 5) measurement of the absolute dose delivered with each applicator to confirm acceptable agreement with dose based on Monte Carlo modeling; 6) measurements of the skin‐to‐center dose ratio using optically stimulated luminescence dosimeters; and 7) assessment of the mammopad cushion's effect on the center dose. We found that the difference between the measured and the actual paddle separation is <0.1 cm for the separation range of 3 cm to 7.5 cm. Radiochromic film measurements demonstrated that the number of dwell positions inside the applicators agree with the values from the vendor, for each applicator type and size. The shift needed for a good applicator‐grid alignment was within 0.2 cm. The dry‐run test using film demonstrated that the shift of the dosimetric center is within 0.15 cm. Dose measurements in water converted to polystyrene agreed within 5.0% with the Monte Carlo data in polystyrene for the same applicator type, size, and depth. A solid water‐to‐water (phantom) factor was obtained for each applicator, and all future annual quality assurance tests will be performed in solid water using an average value of 1.07 for the solid water‐to‐water factor. The skin‐to‐center dose ratio measurements support the Monte Carlo‐based values within 5.0% agreement. For the treatment separation range of 4 cm to 8 cm, the change in center dose would be <1.0% for all applicators when using a compressed pad of 0.2 cm to 0.3 cm. The tests performed ensured that all treatment components of the AccuBoost system are functional and that a treatment plan can be delivered with acceptable accuracy. Based on the commissioning results, a quality assurance manual and guidance documents for clinical use were developed. PACS numbers: 87.55.Qr, 87.56.Da, 87.90.+y PMID:26103184

Experimental validation of a Monte Carlo proton therapy nozzle model incorporating magnetically steered protons.

PubMed

Peterson, S W; Polf, J; Bues, M; Ciangaru, G; Archambault, L; Beddar, S; Smith, A

2009-05-21

The purpose of this study is to validate the accuracy of a Monte Carlo calculation model of a proton magnetic beam scanning delivery nozzle developed using the Geant4 toolkit. The Monte Carlo model was used to produce depth dose and lateral profiles, which were compared to data measured in the clinical scanning treatment nozzle at several energies. Comparisons were also made between measured and simulated off-axis profiles to test the accuracy of the model's magnetic steering. Comparison of the 80% distal dose fall-off values for the measured and simulated depth dose profiles agreed to within 1 mm for the beam energies evaluated. Agreement of the full width at half maximum values for the measured and simulated lateral fluence profiles was within 1.3 mm for all energies. The position of measured and simulated spot positions for the magnetically steered beams agreed to within 0.7 mm of each other. Based on these results, we found that the Geant4 Monte Carlo model of the beam scanning nozzle has the ability to accurately predict depth dose profiles, lateral profiles perpendicular to the beam axis and magnetic steering of a proton beam during beam scanning proton therapy.

SU-G-BRC-16: Theory and Clinical Implications of the Constant Dosimetric Leaf Gap (DLG) Approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaraswamy, L; Xu, Z; Podgorsak, M

Purpose: Commercial dose calculation algorithms incorporate a single DLG value for a given beam energy that is applied across an entire treatment field. However, the physical processes associated with beam generation and dose delivery suggest that the DLG is not constant. The aim of this study is to evaluate the variation of DLG among all leaf pairs, to quantify how this variation impacts delivered dose, and to establish a novel method to correct dose distributions calculated using the approximation of constant DLG. Methods: A 2D diode array was used to measure the DLG for all 60 leaf pairs at severalmore » points along each leaf pair travel direction. This approach was validated by comparison to DLG values measured at select points using a 0.6 cc ion chamber with the standard formalism. In-house software was developed to enable incorporation of position dependent DLG values into dose distribution optimization and calculation. The accuracy of beam delivery of both the corrected and uncorrected treatment plans was studied through gamma pass rate evaluation. A comparison of DVH statistics in corrected and uncorrected treatment plans was made. Results: The outer 20 MLC leaf pairs (1.0 cm width) have DLG values that are 0.32 mm (mean) to 0.65 mm (maximum) lower than the central leaf-pair. VMAT plans using a large number of 1 cm wide leaves were more accurately delivered (gamma pass rate increased by 5%) and dose coverage was higher (D100 increased by 3%) when the 2D DLG was modeled. Conclusion: Using a constant DLG value for a given beam energy will result in dose optimization, dose calculation and treatment delivery inaccuracies that become significant for treatment plans with high modulation complexity scores delivered with 1 cm wide leaves.« less

Evaluation of external and internal irradiation on uranium mining enterprise staff by tooth enamel EPR spectroscopy

NASA Astrophysics Data System (ADS)

Zhumadilov, Kassym; Ivannikov, Alexander; Khailov, Artem; Orlenko, Sergei; Skvortsov, Valeriy; Stepanenko, Valeriy; Kuterbekov, Kairat; Toyoda, Shin; Kazymbet, Polat; Hoshi, Masaharu

2017-11-01

In order to estimate radiation effects on uranium enterprise staff and population teeth samples were collected for EPR tooth enamel dosimetry from population of Stepnogorsk city and staff of uranium mining enterprise in Shantobe settlment (Akmola region, North of Kazakhstan). By measurements of tooth enamel EPR spectra, the total absorbed dose in the enamel samples and added doses after subtraction of the contribution of natural background radiation are determined. For the population of Stepnogorsk city average added dose value of 4 +/- 11 mGy with variation of 51 mGy was obtained. For the staff of uranium mining enterprise in Shantobe settlment average value of added dose 95 +/- 20 mGy, with 85 mGy variation was obtained. Higher doses and the average value and a large variation for the staff, probably is due to the contribution of occupational exposure.

MO-AB-BRA-03: Calorimetry-Based Absorbed Dose to Water Measurements Using Interferometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flores-Martinez, E; Malin, M; DeWerd, L

2015-06-15

Purpose: Interferometry-based calorimetry is a novel technique to measure radiation-induced temperature changes allowing the measurement of absorbed dose to water (ADW). There are no mechanical components in the field. This technique also has the possibility of obtaining 2D dose distributions. The goal of this investigation is to calorimetrically-measure doses between 2.5 and 5 Gy over a single projection in a photon beam using interferometry and compare the results with doses calculated using the TG-51 linac calibration. Methods: ADW was determined by measuring radiation-induced phase shifts (PSs) of light passing through water irradiated with a 6 MV photon beam. A 9×9×9more » cm{sup 3} glass phantom filled with water and placed in an arm of a Michelson interferometer was irradiated with 300, 400, 500 and 600 monitor units. The whole system was thermally insulated to achieve sufficient passive temperature control. The depth of measurement was 4.5 cm with a field size of 7×7 cm{sup 2}. The intensity of the fringe pattern was monitored with a photodiode and used to calculate the time-dependent PS curve. Data was acquired 60 s before and after the irradiation. The radiation-induced PS was calculated by taking the difference in the pre- and post-irradiation drifts extrapolated to the midpoint of the irradiation. Results were compared to computed doses. Results: Average comparison of calculated ADW values with interferometry-measured values showed an agreement to within 9.5%. k=1 uncertainties were 4.3% for calculations and 14.7% for measurements. The dominant source of uncertainty for the measurements was a temperature drift of about 30 µK/s caused by heat conduction from the interferometer’s surroundings. Conclusion: This work presented the first absolute ADW measurements using interferometry in the dose range of linac-based radiotherapy. Future work to improve measurements’ reproducibility includes the implementation of active thermal control techniques.« less

On the Use of Optically Stimulated Luminescent Dosimeter for Surface Dose Measurement during Radiotherapy

PubMed Central

Yusof, Fasihah Hanum; Ung, Ngie Min; Wong, Jeannie Hsiu Ding; Jong, Wei Loong; Ath, Vannyat; Phua, Vincent Chee Ee; Heng, Siew Ping; Ng, Kwan Hoong

2015-01-01

This study was carried out to investigate the suitability of using the optically stimulated luminescence dosimeter (OSLD) in measuring surface dose during radiotherapy. The water equivalent depth (WED) of the OSLD was first determined by comparing the surface dose measured using the OSLD with the percentage depth dose at the buildup region measured using a Markus ionization chamber. Surface doses were measured on a solid water phantom using the OSLD and compared against the Markus ionization chamber and Gafchromic EBT3 film measurements. The effect of incident beam angles on surface dose was also studied. The OSLD was subsequently used to measure surface dose during tangential breast radiotherapy treatments in a phantom study and in the clinical measurement of 10 patients. Surface dose to the treated breast or chest wall, and on the contralateral breast were measured. The WED of the OSLD was found to be at 0.4 mm. For surface dose measurement on a solid water phantom, the Markus ionization chamber measured 15.95% for 6 MV photon beam and 12.64% for 10 MV photon beam followed by EBT3 film (23.79% and 17.14%) and OSLD (37.77% and 25.38%). Surface dose increased with the increase of the incident beam angle. For phantom and patient breast surface dose measurement, the response of the OSLD was higher than EBT3 film. The in-vivo measurements were also compared with the treatment planning system predicted dose. The OSLD measured higher dose values compared to dose at the surface (Hp(0.0)) by a factor of 2.37 for 6 MV and 2.01 for 10 MV photon beams, respectively. The measurement of absorbed dose at the skin depth of 0.4 mm by the OSLD can still be a useful tool to assess radiation effects on the skin dermis layer. This knowledge can be used to prevent and manage potential acute skin reaction and late skin toxicity from radiotherapy treatments. PMID:26052690

The influence of particle size distribution on dose conversion factors for radon progeny in the underground excavations of hard coal mine.

PubMed

Skubacz, Krystian; Wojtecki, Łukasz; Urban, Paweł

2016-10-01

In Polish underground mines, hazards caused by enhanced natural radioactivity occur. The sources of radiation exposure are short-lived radon decay products, mine waters containing radium 226 Ra and 228 Ra and the radioactive sediments that can precipitate out of these waters. For miners, the greatest exposure is usually due to short-lived radon decay products. The risk assessment is based on the measurement of the total potential alpha energy concentration (PAEC) and the evaluation of the related dose by using the dose conversion factor as recommended by relevant legal requirements. This paper presents the results of measurements of particle size distributions of ambient aerosols in an underground hard coal mine, the assessment of the radioactive particle size distribution of the short-lived radon decay products and the corresponding values of dose conversion factors. The measurements of the ambient airborne particle size distribution were performed in the range from a few nanometers to about 20 μm. The study therefore included practically the whole class of respirable particles. The results showed that the high concentration of ultrafine and fine aerosols measured can significantly affect the value of the dose conversion factors, and consequently the corresponding committed effective dose, to which the miners can be exposed. Copyright © 2016 Elsevier Ltd. All rights reserved.

SU-E-T-44: Angular Dependence of Surface Dose Enhancement Measured On Several Inhomogeneities Using Radiochromic EBT3 Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jansen, A; Schoenfeld, A; Poppinga, D

Purpose: The quantification of the relative surface dose enhancement in dependence on the angle of incidence and the atomic number Z of the surface material. Methods: Experiments were performed with slabs made of aluminum, titanium, copper, silver, dental gold and lead. The metal slabs with equal sizes of 1.0×8.0×8.8mm{sup 3} were embedded in an Octavius 4D phantom (PTW Freiburg, Germany). Radiochromic EBT3 films were used to measure the surface dose for angles of incidence ranging from 0° to 90°. The setup with the metals slabs at the isocenter was irradiated with acceleration voltages of 6MV and 10MV. Water reference measurementsmore » were taken under equal conditions. Results: The surface dose enhancement is highest for angles of incidence below 30° and drops significantly for higher. The surface dose enhancement produced by lead and dental gold at 6MV showed a peak of 65%. At 90°, the surface dose enhancement dropped to 15% for both materials. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 32%, 22% and 12% at 0°, respectively. At an angle of incidence of 80°, the values dropped to 22%, 18%, 12% und 6%. The values for 10MV were very similar. Lead and dental gold showed peaks of 65% und 60%. Their values dropped to 18% at an angle of 90°. The surface dose enhancements for silver, copper, titanium and aluminum were 45%, 30%, 20% and 8% at 0°. At 80° the values dropped to 30%, 20%, 12% and 5%. A dependence of the magnitude of the surface dose enhancement on the atomic number of the surface material can be seen, which is in consistence with literature. Conclusion: The results show that the surface dose enhancements near implant materials with high Z-values should be taken into consideration in radio therapy, even when the angle of incidence is flat.« less

Total body irradiation, toward optimal individual delivery: dose evaluation with metal oxide field effect transistors, thermoluminescence detectors, and a treatment planning system.

PubMed

Bloemen-van Gurp, Esther J; Mijnheer, Ben J; Verschueren, Tom A M; Lambin, Philippe

2007-11-15

To predict the three-dimensional dose distribution of our total body irradiation technique, using a commercial treatment planning system (TPS). In vivo dosimetry, using metal oxide field effect transistors (MOSFETs) and thermoluminescence detectors (TLDs), was used to verify the calculated dose distributions. A total body computed tomography scan was performed and loaded into our TPS, and a three-dimensional-dose distribution was generated. In vivo dosimetry was performed at five locations on the patient. Entrance and exit dose values were converted to midline doses using conversion factors, previously determined with phantom measurements. The TPS-predicted dose values were compared with the MOSFET and TLD in vivo dose values. The MOSFET and TLD dose values agreed within 3.0% and the MOSFET and TPS data within 0.5%. The convolution algorithm of the TPS, which is routinely applied in the clinic, overestimated the dose in the lung region. Using a superposition algorithm reduced the calculated lung dose by approximately 3%. The dose inhomogeneity, as predicted by the TPS, can be reduced using a simple intensity-modulated radiotherapy technique. The use of a TPS to calculate the dose distributions in individual patients during total body irradiation is strongly recommended. Using a TPS gives good insight of the over- and underdosage in a patient and the influence of patient positioning on dose homogeneity. MOSFETs are suitable for in vivo dosimetry purposes during total body irradiation, when using appropriate conversion factors. The MOSFET, TLD, and TPS results agreed within acceptable margins.

High dose-per-pulse electron beam dosimetry - A model to correct for the ion recombination in the Advanced Markus ionization chamber.

PubMed

Petersson, Kristoffer; Jaccard, Maud; Germond, Jean-François; Buchillier, Thierry; Bochud, François; Bourhis, Jean; Vozenin, Marie-Catherine; Bailat, Claude

2017-03-01

The purpose of this work was to establish an empirical model of the ion recombination in the Advanced Markus ionization chamber for measurements in high dose rate/dose-per-pulse electron beams. In addition, we compared the observed ion recombination to calculations using the standard Boag two-voltage-analysis method, the more general theoretical Boag models, and the semiempirical general equation presented by Burns and McEwen. Two independent methods were used to investigate the ion recombination: (a) Varying the grid tension of the linear accelerator (linac) gun (controls the linac output) and measuring the relative effect the grid tension has on the chamber response at different source-to-surface distances (SSD). (b) Performing simultaneous dose measurements and comparing the dose-response, in beams with varying dose rate/dose-per-pulse, with the chamber together with dose rate/dose-per-pulse independent Gafchromic™ EBT3 film. Three individual Advanced Markus chambers were used for the measurements with both methods. All measurements were performed in electron beams with varying mean dose rate, dose rate within pulse, and dose-per-pulse (10 -2  ≤ mean dose rate ≤ 10 3 Gy/s, 10 2  ≤ mean dose rate within pulse ≤ 10 7  Gy/s, 10 -4  ≤ dose-per-pulse ≤ 10 1  Gy), which was achieved by independently varying the linac gun grid tension, and the SSD. The results demonstrate how the ion collection efficiency of the chamber decreased as the dose-per-pulse increased, and that the ion recombination was dependent on the dose-per-pulse rather than the dose rate, a behavior predicted by Boag theory. The general theoretical Boag models agreed well with the data over the entire investigated dose-per-pulse range, but only for a low polarizing chamber voltage (50 V). However, the two-voltage-analysis method and the Burns & McEwen equation only agreed with the data at low dose-per-pulse values (≤ 10 -2 and ≤ 10 -1  Gy, respectively). An empirical model of the ion recombination in the chamber was found by fitting a logistic function to the data. The ion collection efficiency of the Advanced Markus ionization chamber decreases for measurements in electron beams with increasingly higher dose-per-pulse. However, this chamber is still functional for dose measurements in beams with dose-per-pulse values up toward and above 10 Gy, if the ion recombination is taken into account. Our results show that existing models give a less-than-accurate description of the observed ion recombination. This motivates the use of the presented empirical model for measurements with the Advanced Markus chamber in high dose-per-pulse electron beams, as it enables accurate absorbed dose measurements (uncertainty estimation: 2.8-4.0%, k = 1). The model depends on the dose-per-pulse in the beam, and it is also influenced by the polarizing chamber voltage, with increasing ion recombination with a lowering of the voltage. © 2017 American Association of Physicists in Medicine.

Comparison of intensity-modulated radiotherapy and volumetric-modulated arc therapy dose measurement for head and neck cancer using optical stimulated luminescence dosimeter

NASA Astrophysics Data System (ADS)

Lai, Lu-Han; Chuang, Keh-Shih; Lin, Hsin-Hon; Liu, Yi-Chi; Kuo, Chiung-Wen; Lin, Jao-Perng

2017-11-01

The in-vivo dose distributions of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), a newly developed technique, for head and neck cancer have been investigated for several years. The present study used a head-and-neck RANDO phantom to simulate the clinical conditions of nasopharyngeal carcinoma and compare the radiation doses between VMAT and IMRT. Three types of planning target volume (PTV) profiles were targeted by reducing the PTV surface margin by 0, 3, and 5 mm. An optically stimulated luminescence dosimeter was used to measure the surface doses. The results revealed that VMAT provided on average 16.8-13.8% lower surface doses within the PTV target areas than IMRT. When the PTV margin was reduced by 0 mm, the surface doses for IMRT reached their maximum value, accounting for 75.1% of its prescribed dose (Dp); however, the Dp value of VMAT was only 61.1%. When the PTV margin was reduced by 3 or 5 mm, the surface doses decreased considerably. The observed surface doses were insufficient when the tumours invaded the body surface; however, VMAT exerted larger skin-sparing effects than IMRT when the tumours away from the skin. These results suggest that the skin doses for these two techniques are insufficient for surface tumours. Notably, VMAT can provide lower skin doses for deep tumours.

Estimating peak skin and eye lens dose from neuroperfusion examinations: use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM Report No. 111, and ImPACT dosimetry tool values.

PubMed

Zhang, Di; Cagnon, Chris H; Villablanca, J Pablo; McCollough, Cynthia H; Cody, Dianna D; Zankl, Maria; Demarco, John J; McNitt-Gray, Michael F

2013-09-01

CT neuroperfusion examinations are capable of delivering high radiation dose to the skin or lens of the eyes of a patient and can possibly cause deterministic radiation injury. The purpose of this study is to: (a) estimate peak skin dose and eye lens dose from CT neuroperfusion examinations based on several voxelized adult patient models of different head size and (b) investigate how well those doses can be approximated by some commonly used CT dose metrics or tools, such as CTDIvol, American Association of Physicists in Medicine (AAPM) Report No. 111 style peak dose measurements, and the ImPACT organ dose calculator spreadsheet. Monte Carlo simulation methods were used to estimate peak skin and eye lens dose on voxelized patient models, including GSF's Irene, Frank, Donna, and Golem, on four scanners from the major manufacturers at the widest collimation under all available tube potentials. Doses were reported on a per 100 mAs basis. CTDIvol measurements for a 16 cm CTDI phantom, AAPM Report No. 111 style peak dose measurements, and ImPACT calculations were performed for available scanners at all tube potentials. These were then compared with results from Monte Carlo simulations. The dose variations across the different voxelized patient models were small. Dependent on the tube potential and scanner and patient model, CTDIvol values overestimated peak skin dose by 26%-65%, and overestimated eye lens dose by 33%-106%, when compared to Monte Carlo simulations. AAPM Report No. 111 style measurements were much closer to peak skin estimates ranging from a 14% underestimate to a 33% overestimate, and with eye lens dose estimates ranging from a 9% underestimate to a 66% overestimate. The ImPACT spreadsheet overestimated eye lens dose by 2%-82% relative to voxelized model simulations. CTDIvol consistently overestimates dose to eye lens and skin. The ImPACT tool also overestimated dose to eye lenses. As such they are still useful as a conservative predictor of dose for CT neuroperfusion studies. AAPM Report No. 111 style measurements are a better predictor of both peak skin and eye lens dose than CTDIvol and ImPACT for the patient models used in this study. It should be remembered that both the AAPM Report No. 111 peak dose metric and CTDIvol dose metric are dose indices and were not intended to represent actual organ doses.

Estimating peak skin and eye lens dose from neuroperfusion examinations: Use of Monte Carlo based simulations and comparisons to CTDIvol, AAPM Report No. 111, and ImPACT dosimetry tool values

PubMed Central

Zhang, Di; Cagnon, Chris H.; Villablanca, J. Pablo; McCollough, Cynthia H.; Cody, Dianna D.; Zankl, Maria; Demarco, John J.; McNitt-Gray, Michael F.

2013-01-01

Purpose: CT neuroperfusion examinations are capable of delivering high radiation dose to the skin or lens of the eyes of a patient and can possibly cause deterministic radiation injury. The purpose of this study is to: (a) estimate peak skin dose and eye lens dose from CT neuroperfusion examinations based on several voxelized adult patient models of different head size and (b) investigate how well those doses can be approximated by some commonly used CT dose metrics or tools, such as CTDIvol, American Association of Physicists in Medicine (AAPM) Report No. 111 style peak dose measurements, and the ImPACT organ dose calculator spreadsheet. Methods: Monte Carlo simulation methods were used to estimate peak skin and eye lens dose on voxelized patient models, including GSF's Irene, Frank, Donna, and Golem, on four scanners from the major manufacturers at the widest collimation under all available tube potentials. Doses were reported on a per 100 mAs basis. CTDIvol measurements for a 16 cm CTDI phantom, AAPM Report No. 111 style peak dose measurements, and ImPACT calculations were performed for available scanners at all tube potentials. These were then compared with results from Monte Carlo simulations. Results: The dose variations across the different voxelized patient models were small. Dependent on the tube potential and scanner and patient model, CTDIvol values overestimated peak skin dose by 26%–65%, and overestimated eye lens dose by 33%–106%, when compared to Monte Carlo simulations. AAPM Report No. 111 style measurements were much closer to peak skin estimates ranging from a 14% underestimate to a 33% overestimate, and with eye lens dose estimates ranging from a 9% underestimate to a 66% overestimate. The ImPACT spreadsheet overestimated eye lens dose by 2%–82% relative to voxelized model simulations. Conclusions: CTDIvol consistently overestimates dose to eye lens and skin. The ImPACT tool also overestimated dose to eye lenses. As such they are still useful as a conservative predictor of dose for CT neuroperfusion studies. AAPM Report No. 111 style measurements are a better predictor of both peak skin and eye lens dose than CTDIvol and ImPACT for the patient models used in this study. It should be remembered that both the AAPM Report No. 111 peak dose metric and CTDIvol dose metric are dose indices and were not intended to represent actual organ doses. PMID:24007152

Experimental benchmarking of a Monte Carlo dose simulation code for pediatric CT

NASA Astrophysics Data System (ADS)

Li, Xiang; Samei, Ehsan; Yoshizumi, Terry; Colsher, James G.; Jones, Robert P.; Frush, Donald P.

2007-03-01

In recent years, there has been a desire to reduce CT radiation dose to children because of their susceptibility and prolonged risk for cancer induction. Concerns arise, however, as to the impact of dose reduction on image quality and thus potentially on diagnostic accuracy. To study the dose and image quality relationship, we are developing a simulation code to calculate organ dose in pediatric CT patients. To benchmark this code, a cylindrical phantom was built to represent a pediatric torso, which allows measurements of dose distributions from its center to its periphery. Dose distributions for axial CT scans were measured on a 64-slice multidetector CT (MDCT) scanner (GE Healthcare, Chalfont St. Giles, UK). The same measurements were simulated using a Monte Carlo code (PENELOPE, Universitat de Barcelona) with the applicable CT geometry including bowtie filter. The deviations between simulated and measured dose values were generally within 5%. To our knowledge, this work is one of the first attempts to compare measured radial dose distributions on a cylindrical phantom with Monte Carlo simulated results. It provides a simple and effective method for benchmarking organ dose simulation codes and demonstrates the potential of Monte Carlo simulation for investigating the relationship between dose and image quality for pediatric CT patients.

Estimating the dose response relationship for occupational radiation exposure measured with minimum detection level.

PubMed

Xue, Xiaonan; Shore, Roy E; Ye, Xiangyang; Kim, Mimi Y

2004-10-01

Occupational exposures are often recorded as zero when the exposure is below the minimum detection level (BMDL). This can lead to an underestimation of the doses received by individuals and can lead to biased estimates of risk in occupational epidemiologic studies. The extent of the exposure underestimation is increased with the magnitude of the minimum detection level (MDL) and the frequency of monitoring. This paper uses multiple imputation methods to impute values for the missing doses due to BMDL. A Gibbs sampling algorithm is developed to implement the method, which is applied to two distinct scenarios: when dose information is available for each measurement (but BMDL is recorded as zero or some other arbitrary value), or when the dose information available represents the summation of a series of measurements (e.g., only yearly cumulative exposure is available but based on, say, weekly measurements). Then the average of the multiple imputed exposure realizations for each individual is used to obtain an unbiased estimate of the relative risk associated with exposure. Simulation studies are used to evaluate the performance of the estimators. As an illustration, the method is applied to a sample of historical occupational radiation exposure data from the Oak Ridge National Laboratory.

Monte Carlo simulations to replace film dosimetry in IMRT verification.

PubMed

Goetzfried, Thomas; Rickhey, Mark; Treutwein, Marius; Koelbl, Oliver; Bogner, Ludwig

2011-01-01

Patient-specific verification of intensity-modulated radiation therapy (IMRT) plans can be done by dosimetric measurements or by independent dose or monitor unit calculations. The aim of this study was the clinical evaluation of IMRT verification based on a fast Monte Carlo (MC) program with regard to possible benefits compared to commonly used film dosimetry. 25 head-and-neck IMRT plans were recalculated by a pencil beam based treatment planning system (TPS) using an appropriate quality assurance (QA) phantom. All plans were verified both by film and diode dosimetry and compared to MC simulations. The irradiated films, the results of diode measurements and the computed dose distributions were evaluated, and the data were compared on the basis of gamma maps and dose-difference histograms. Average deviations in the high-dose region between diode measurements and point dose calculations performed with the TPS and MC program were 0.7 ± 2.7% and 1.2 ± 3.1%, respectively. For film measurements, the mean gamma values with 3% dose difference and 3mm distance-to-agreement were 0.74 ± 0.28 (TPS as reference) with dose deviations up to 10%. Corresponding values were significantly reduced to 0.34 ± 0.09 for MC dose calculation. The total time needed for both verification procedures is comparable, however, by far less labor intensive in the case of MC simulations. The presented study showed that independent dose calculation verification of IMRT plans with a fast MC program has the potential to eclipse film dosimetry more and more in the near future. Thus, the linac-specific QA part will necessarily become more important. In combination with MC simulations and due to the simple set-up, point-dose measurements for dosimetric plausibility checks are recommended at least in the IMRT introduction phase. Copyright © 2010. Published by Elsevier GmbH.

SU-E-T-275: Dose Build Up and Bolusing Characteristics for Total Body Irradiation Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butson, M; Pope, D; Whitaker, M

2015-06-15

Purpose: Total Body Irradiation (TBI) treatments are mainly used in a preparative regimen for haematopoietic stem cell (or bone marrow) transplantation. Our standard regimen is a 12 Gy / 6 fraction bi-daily technique. To evaluate the delivered dose homogeneity to the patient, EBT3 Gafchromic film is positioned at the head, neck, chest, pelvis and groin for all fractions. This work investigates and quantifies the build-up dose characteristics at TBI distances and requirements for in-vivo dosimetry bolusing. Methods: Percentage dose build up characteristics of photon beams have been investigated at large extended SSD’s using parallel plate ionisations chambers (Attix) and EBT3more » Gafchromic film. Measurements were made to open fields at different field sizes as well as large 40cm × 40cm fields with differing scatter conditions such as the introduction of standard Perspex scattering plates at different distances to the measurement point. Results: Percentage surface dose measured values for open fields at 300 cm SSD were found to range from 20 % up to 65.5 % for fields of 5 cm × 5 cm to 40 cm × 40 cm. With the introduction of 1cm Perspex scattering plates used in TBI treatments the surface dose values increased up to 83% to 90%, depending on the position of the Perspex scattering plate compared to the measurement point. Our work showed that at least 3mm water equivalent bolus / scatter material should be placed over the EBT3 for accurate dose assessment for TBI treatments. Conclusion: Build up dose characteristics exist at long (300cm) SSD’s including treatments using Perspex scattering plates placed at various distances form the patient during TBI treatment. Top accurately assess the applied dose during treatment, in-vivo dosimeters such as Gafchromic EBT3 should have at least 3mm bolus / scatter material placed over them to measure actual applied doses.« less

Evaluation of six TPS algorithms in computing entrance and exit doses

PubMed Central

Metwaly, Mohamed; Glegg, Martin; Baggarley, Shaun P.; Elliott, Alex

2014-01-01

Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measured doses to within 2%‐3%. Meanwhile, Eclipse PBC and Eclipse AAA computed exit doses were higher than the IC measured doses by up to 5.3% and 4.8%, respectively. Both algorithms assume that full backscatter exists even at the exit level, leading to an overestimation of exit doses. Despite good agreements at the central axis for Eclipse AXB and Monaco MC, 1D relative comparisons showed profiles mismatched at depths beyond 11.5 cm. Overall, the 2D absolute gamma (3%/3 mm) pass rates were better for Monaco MC, while Eclipse AXB failed mostly at the outer 20% of the field area. The findings of this study serve as a useful baseline for the implementation of entrance and exit in vivo dosimetry in clinical departments utilizing any of these six common TPS algorithms for reference comparison. PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.N‐, 87.53.Bn PMID:24892349

Investigation of Presage 3D Dosimetry as a Method of Clinically Intuitive Quality Assurance and Comparison to a Semi-3D Delta4 System

NASA Astrophysics Data System (ADS)

Crockett, Ethan Van

The need for clinically intuitive metrics for patient-specific quality assurance in radiation therapy has been well-documented (Zhen, Nelms et al. 2011). A novel transform method has shown to be effective at converting full-density 3D dose measurements made in a phantom to dose values in the patient geometry, enabling comparisons using clinically intuitive metrics such as dose-volume histograms (Oldham et al. 2011). This work investigates the transform method and compares its calculated dose-volume histograms (DVHs) to DVH values calculated by a Delta4 QA device (Scandidos), marking the first comparison of a true 3D system to a semi-3D device using clinical metrics. Measurements were made using Presage 3D dosimeters, which were readout by an in-house optical-CT scanner. Three patient cases were chosen for the study: one head-and-neck VMAT treatment and two spine IMRT treatments. The transform method showed good agreement with the planned dose values for all three cases. Furthermore, the transformed DVHs adhered to the planned dose with more accuracy than the Delta4 DVHs. The similarity between the Delta4 DVHs and the transformed DVHs, however, was greater for one of the spine cases than it was for the head-and-neck case, implying that the accuracy of the Delta4 Anatomy software may vary from one treatment site to another. Overall, the transform method, which incorporates data from full-density 3D dose measurements, provides clinically intuitive results that are more accurate and consistent than the corresponding results from a semi-3D Delta 4 system.

Output calculation of electron therapy at extended SSD using an improved LBR method.

PubMed

Alkhatib, Hassaan A; Gebreamlak, Wondesen T; Tedeschi, David J; Mihailidis, Dimitris; Wright, Ben W; Neglia, William J; Sobash, Philip T; Fontenot, Jonas D

2015-02-01

To calculate the output factor (OPF) of any irregularly shaped electron beam at extended SSD. Circular cutouts were prepared from 2.0 cm diameter to the maximum possible size for 15 × 15 applicator cone. In addition, two irregular cutouts were prepared. For each cutout, percentage depth dose (PDD) at the standard SSD and doses at different SSD values were measured using 6, 9, 12, and 16 MeV electron beam energies on a Varian 2100C LINAC and the distance at which the central axis electron fluence becomes independent of cutout size was determined. The measurements were repeated with an ELEKTA Synergy LINAC using 14 × 14 applicator cone and electron beam energies of 6, 9, 12, and 15 MeV. The PDD measurements were performed using a scanning system and two diodes-one for the signal and the other a stationary reference outside the tank. The doses of the circular cutouts at different SSDs were measured using PTW 0.125 cm(3) Semiflex ion-chamber and EDR2 films. The electron fluence was measured using EDR2 films. For each circular cutout, the lateral buildup ratio (LBR) was calculated from the measured PDD curve using the open applicator cone as the reference field. The effective SSD (SSDeff) of each circular cutout was calculated from the measured doses at different SSD values. Using the LBR value and the radius of the circular cutout, the corresponding lateral spread parameter [σR(z)] was calculated. Taking the cutout size dependence of σR(z) into account, the PDD curves of the irregularly shaped cutouts at the standard SSD were calculated. Using the calculated PDD curve of the irregularly shaped cutout along with the LBR and SSDeff values of the circular cutouts, the output factor of the irregularly shaped cutout at extended SSD was calculated. Finally, both the calculated PDD curves and output factor values were compared with the measured values. The improved LBR method has been generalized to calculate the output factor of electron therapy at extended SSD. The percentage difference between the calculated and the measured output factors of irregularly shaped cutouts in a clinical useful SSD region was within 2%. Similar results were obtained for all available electron energies of both Varian 2100C and ELEKTA Synergy machines.

Evaluation of forest decontamination using radiometric measurements.

PubMed

Cresswell, Alan J; Kato, Hiroaki; Onda, Yuichi; Nanba, Kenji

2016-11-01

An experiment has been conducted to evaluate the additional dose reduction by clear felling contaminated forestry in Fukushima Prefecture, Japan, and using the timber to cover the areas with wood chips. A portable gamma spectrometry system, comprising a backpack containing a 3 × 3″ NaI(Tl) detector with digital spectrometer and GPS receiver, has been used to map dose rate and radionuclide activity concentrations before, after and at stages during this experiment. The data show the effect of the different stages of the experiment on dose rate at different locations around the site. The spectrometric data have allowed the assessment of the contributions of natural and anthropogenic radionuclides to the dose rate at different parts of the site before and after the experiment. This has clearly demonstrated the value of radiometric methods in evaluating remediation, and the effect of other environmental processes. The value of spectrometric methods which directly measure radionuclide concentrations has also been shown, especially through the identification of the contribution of natural and anthropogenic activity to the measured dose rate. The experiment has shown that clearing trees and applying wood chips can reduce dose rates by 10-15% beyond that achieved by just clearing the forest litter and natural redistribution of radiocaesium. Copyright © 2016 Elsevier Ltd. All rights reserved.

A Novel Simple Phantom for Verifying the Dose of Radiation Therapy

PubMed Central

Lee, J. H.; Chang, L. T.; Shiau, A. C.; Chen, C. W.; Liao, Y. J.; Li, W. J.; Lee, M. S.; Hsu, S. M.

2015-01-01

A standard protocol of dosimetric measurements is used by the organizations responsible for verifying that the doses delivered in radiation-therapy institutions are within authorized limits. This study evaluated a self-designed simple auditing phantom for use in verifying the dose of radiation therapy; the phantom design, dose audit system, and clinical tests are described. Thermoluminescent dosimeters (TLDs) were used as postal dosimeters, and mailable phantoms were produced for use in postal audits. Correction factors are important for converting TLD readout values from phantoms into the absorbed dose in water. The phantom scatter correction factor was used to quantify the difference in the scattered dose between a solid water phantom and homemade phantoms; its value ranged from 1.084 to 1.031. The energy-dependence correction factor was used to compare the TLD readout of the unit dose irradiated by audit beam energies with 60Co in the solid water phantom; its value was 0.99 to 1.01. The setup-condition factor was used to correct for differences in dose-output calibration conditions. Clinical tests of the device calibrating the dose output revealed that the dose deviation was within 3%. Therefore, our homemade phantoms and dosimetric system can be applied for accurately verifying the doses applied in radiation-therapy institutions. PMID:25883980

SU-G-206-05: A Comparison of Head Phantoms Used for Dose Determination in Imaging Procedures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiong, Z; Vijayan, S; Kilian-Meneghin, J

Purpose: To determine similarities and differences between various head phantoms that might be used for dose measurements in diagnostic imaging procedures. Methods: We chose four frequently used anthropomorphic head phantoms (SK-150, PBU-50, RS-240T and Alderson Rando), a computational patient phantom (Zubal) and the CTDI head phantom for comparison in our study. We did a CT scan of the head phantoms using the same protocol and compared their dimensions and CT numbers. The scan data was used to calculate dose values for each of the phantoms using EGSnrc Monte Carlo software. An .egsphant file was constructed to describe these phantoms usingmore » a Visual C++ program for DOSXYZnrc/EGSnrc simulation. The lens dose was calculated for a simulated CBCT scan using DOSXYZnrc/EGSnrc and the calculated doses were validated with measurements using Gafchromic film and an ionization chamber. Similar calculations and measurements were made for PA radiography to investigate the attenuation and backscatter differences between these phantoms. We used the Zubal phantom as the standard for comparison since it was developed based on a CT scan of a patient. Results: The lens dose for the Alderson Rando phantom is around 9% different than the Zubal phantom, while the lens dose for the PBU-50 phantom was about 50% higher, possibly because its skull thickness and the density of bone and soft tissue are lower than anthropometric values. The lens dose for the CTDI phantom is about 500% higher because of its totally different structure. The entrance dose profiles are similar for the five anthropomorphic phantoms, while that for the CTDI phantom was distinctly different. Conclusion: The CTDI and PBU-50 head phantoms have substantially larger lens dose estimates in CBCT. The other four head phantoms have similar entrance dose with backscatter hence should be preferred for dose measurement in imaging procedures of the head. Partial support from NIH Grant R01-EB002873 and Toshiba Medical Systems Corp.« less

[Dose and image quality in intraoral radiography].

PubMed

Hjardemaal, O

1991-11-01

The technique factors when performing intraoral X-ray exposures must be selected in such a way that sufficient diagnostic information is obtained at a reasonable patient dose. The Danish National Institute of Radiation Hygiene has performed a study comprising 32 dental X-ray sets. The mean value of the skin dose for a maxillary molar was 9.6 mGy and the value for the dental colleges 7.0 mGy. For a mandibular incisor the corresponding doses were 7.7 mGy and 3.6 mGy. After the conclusion of the mentioned study it has been part of the institute's inspection procedure for dental X-ray sets to measure patient skin doses. 243 measurements were performed and the mean value of the entrance skin dose was 6.5 mGy and the dose interval was 0.7-57 mGy. All doses are normalised to speed class D film. At 16% of the inspected sets films of speed class E were used. The remainder used class D films. The spread in doses cannot be explained by variation in equipment parameters alone but is to a high degree due to a combination of inappropriate film processing and exposure time. Interviews with staff in dental clinics confirm that films are frequently processed until the desired density is obtained by visual estimation. It is shown that the skin dose when using film of speed class D can be kept below 7 mGy for a mandibular incisor. Concluding is stated that film processing shall be performed in accordance with specifications from the manufacturer of the developer. Film of speed class E must be used. Finally must the exposure time be graduated according to the object exposed.

Is multidetector CT-based bone mineral density and quantitative bone microstructure assessment at the spine still feasible using ultra-low tube current and sparse sampling?

PubMed

Mei, Kai; Kopp, Felix K; Bippus, Rolf; Köhler, Thomas; Schwaiger, Benedikt J; Gersing, Alexandra S; Fehringer, Andreas; Sauter, Andreas; Münzel, Daniela; Pfeiffer, Franz; Rummeny, Ernst J; Kirschke, Jan S; Noël, Peter B; Baum, Thomas

2017-12-01

Osteoporosis diagnosis using multidetector CT (MDCT) is limited to relatively high radiation exposure. We investigated the effect of simulated ultra-low-dose protocols on in-vivo bone mineral density (BMD) and quantitative trabecular bone assessment. Institutional review board approval was obtained. Twelve subjects with osteoporotic vertebral fractures and 12 age- and gender-matched controls undergoing routine thoracic and abdominal MDCT were included (average effective dose: 10 mSv). Ultra-low radiation examinations were achieved by simulating lower tube currents and sparse samplings at 50%, 25% and 10% of the original dose. BMD and trabecular bone parameters were extracted in T10-L5. Except for BMD measurements in sparse sampling data, absolute values of all parameters derived from ultra-low-dose data were significantly different from those derived from original dose images (p<0.05). BMD, apparent bone fraction and trabecular thickness were still consistently lower in subjects with than in those without fractures (p<0.05). In ultra-low-dose scans, BMD and microstructure parameters were able to differentiate subjects with and without vertebral fractures, suggesting osteoporosis diagnosis is feasible. However, absolute values differed from original values. BMD from sparse sampling appeared to be more robust. This dose-dependency of parameters should be considered for future clinical use. • BMD and quantitative bone parameters are assessable in ultra-low-dose in vivo MDCT scans. • Bone mineral density does not change significantly when sparse sampling is applied. • Quantitative trabecular bone microstructure measurements are sensitive to dose reduction. • Osteoporosis subjects could be differentiated even at 10% of original dose. • Radiation exposure should be considered when comparing quantitative bone parameters.

A point kernel algorithm for microbeam radiation therapy

NASA Astrophysics Data System (ADS)

Debus, Charlotte; Oelfke, Uwe; Bartzsch, Stefan

2017-11-01

Microbeam radiation therapy (MRT) is a treatment approach in radiation therapy where the treatment field is spatially fractionated into arrays of a few tens of micrometre wide planar beams of unusually high peak doses separated by low dose regions of several hundred micrometre width. In preclinical studies, this treatment approach has proven to spare normal tissue more effectively than conventional radiation therapy, while being equally efficient in tumour control. So far dose calculations in MRT, a prerequisite for future clinical applications are based on Monte Carlo simulations. However, they are computationally expensive, since scoring volumes have to be small. In this article a kernel based dose calculation algorithm is presented that splits the calculation into photon and electron mediated energy transport, and performs the calculation of peak and valley doses in typical MRT treatment fields within a few minutes. Kernels are analytically calculated depending on the energy spectrum and material composition. In various homogeneous materials peak, valley doses and microbeam profiles are calculated and compared to Monte Carlo simulations. For a microbeam exposure of an anthropomorphic head phantom calculated dose values are compared to measurements and Monte Carlo calculations. Except for regions close to material interfaces calculated peak dose values match Monte Carlo results within 4% and valley dose values within 8% deviation. No significant differences are observed between profiles calculated by the kernel algorithm and Monte Carlo simulations. Measurements in the head phantom agree within 4% in the peak and within 10% in the valley region. The presented algorithm is attached to the treatment planning platform VIRTUOS. It was and is used for dose calculations in preclinical and pet-clinical trials at the biomedical beamline ID17 of the European synchrotron radiation facility in Grenoble, France.

An analytical model of leakage neutron equivalent dose for passively-scattered proton radiotherapy and validation with measurements.

PubMed

Schneider, Christopher; Newhauser, Wayne; Farah, Jad

2015-05-18

Exposure to stray neutrons increases the risk of second cancer development after proton therapy. Previously reported analytical models of this exposure were difficult to configure and had not been investigated below 100 MeV proton energy. The purposes of this study were to test an analytical model of neutron equivalent dose per therapeutic absorbed dose  at 75 MeV and to improve the model by reducing the number of configuration parameters and making it continuous in proton energy from 100 to 250 MeV. To develop the analytical model, we used previously published H/D values in water from Monte Carlo simulations of a general-purpose beamline for proton energies from 100 to 250 MeV. We also configured and tested the model on in-air neutron equivalent doses measured for a 75 MeV ocular beamline. Predicted H/D values from the analytical model and Monte Carlo agreed well from 100 to 250 MeV (10% average difference). Predicted H/D values from the analytical model also agreed well with measurements at 75 MeV (15% average difference). The results indicate that analytical models can give fast, reliable calculations of neutron exposure after proton therapy. This ability is absent in treatment planning systems but vital to second cancer risk estimation.

Biological Effectiveness of Accelerated Particles for the Induction of Chromosome Damage Measured in Metaphase and Interphase Human Lymphocytes

NASA Technical Reports Server (NTRS)

George, Kerry; Durante, Marco; Willingham, Veronica; Wu, Honglu; Yang, Tracy C.; Cucinotta, Francis A.

2003-01-01

Chromosome aberrations were investigated in human lymphocytes after in vitro exposure to 1H-, 3He-, 12C-, 40Ar-, 28Si-, 56Fe-, or 197Au-ion beams, with LET ranging from approximately 0.4-1393 keV/microm in the dose range of 0.075-3 Gy. Dose-response curves for chromosome exchanges, measured at the first mitosis postirradiation using fluorescence in situ hybridization (FISH) with whole-chromosome probes, were fitted with linear or linear-quadratic functions. The relative biological effectiveness (RBE) was estimated from the initial slope of the dose-response curve for chromosomal damage with respect to low- or high-dose-rate gamma rays. Estimates of RBEmax values for mitotic spreads, which ranged from near 0.7 to 11.1 for total exchanges, increased with LET, reaching a maximum at about 150 keV/microm, and decreased with further increase in LET. RBEs for complex aberrations are undefined due to the lack of an initial slope for gamma rays. Additionally, the effect of mitotic delay on RBE values was investigated by measuring chromosome aberrations in interphase after chemically induced premature chromosome condensation (PCC), and values were up to threefold higher than for metaphase analysis.

Dosimetric verification of lung cancer treatment using the CBCTs estimated from limited-angle on-board projections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, You; Yin, Fang-Fang; Ren, Lei, E-mail: lei.ren@duke.edu

2015-08-15

Purpose: Lung cancer treatment is susceptible to treatment errors caused by interfractional anatomical and respirational variations of the patient. On-board treatment dose verification is especially critical for the lung stereotactic body radiation therapy due to its high fractional dose. This study investigates the feasibility of using cone-beam (CB)CT images estimated by a motion modeling and free-form deformation (MM-FD) technique for on-board dose verification. Methods: Both digital and physical phantom studies were performed. Various interfractional variations featuring patient motion pattern change, tumor size change, and tumor average position change were simulated from planning CT to on-board images. The doses calculated onmore » the planning CT (planned doses), the on-board CBCT estimated by MM-FD (MM-FD doses), and the on-board CBCT reconstructed by the conventional Feldkamp-Davis-Kress (FDK) algorithm (FDK doses) were compared to the on-board dose calculated on the “gold-standard” on-board images (gold-standard doses). The absolute deviations of minimum dose (ΔD{sub min}), maximum dose (ΔD{sub max}), and mean dose (ΔD{sub mean}), and the absolute deviations of prescription dose coverage (ΔV{sub 100%}) were evaluated for the planning target volume (PTV). In addition, 4D on-board treatment dose accumulations were performed using 4D-CBCT images estimated by MM-FD in the physical phantom study. The accumulated doses were compared to those measured using optically stimulated luminescence (OSL) detectors and radiochromic films. Results: Compared with the planned doses and the FDK doses, the MM-FD doses matched much better with the gold-standard doses. For the digital phantom study, the average (± standard deviation) ΔD{sub min}, ΔD{sub max}, ΔD{sub mean}, and ΔV{sub 100%} (values normalized by the prescription dose or the total PTV) between the planned and the gold-standard PTV doses were 32.9% (±28.6%), 3.0% (±2.9%), 3.8% (±4.0%), and 15.4% (±12.4%), respectively. The corresponding values of FDK PTV doses were 1.6% (±1.9%), 1.2% (±0.6%), 2.2% (±0.8%), and 17.4% (±15.3%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.3% (±0.2%), 0.9% (±0.6%), 0.6% (±0.4%), and 1.0% (±0.8%), respectively. Similarly, for the physical phantom study, the average ΔD{sub min}, ΔD{sub max}, ΔD{sub mean}, and ΔV{sub 100%} of planned PTV doses were 38.1% (±30.8%), 3.5% (±5.1%), 3.0% (±2.6%), and 8.8% (±8.0%), respectively. The corresponding values of FDK PTV doses were 5.8% (±4.5%), 1.6% (±1.6%), 2.0% (±0.9%), and 9.3% (±10.5%), respectively. In contrast, the corresponding values of MM-FD PTV doses were 0.4% (±0.8%), 0.8% (±1.0%), 0.5% (±0.4%), and 0.8% (±0.8%), respectively. For the 4D dose accumulation study, the average (± standard deviation) absolute dose deviation (normalized by local doses) between the accumulated doses and the OSL measured doses was 3.3% (±2.7%). The average gamma index (3%/3 mm) between the accumulated doses and the radiochromic film measured doses was 94.5% (±2.5%). Conclusions: MM-FD estimated 4D-CBCT enables accurate on-board dose calculation and accumulation for lung radiation therapy. It can potentially be valuable for treatment quality assessment and adaptive radiation therapy.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, S; Yuen, C; Huang, V

Purpose: In this abstract we implement and validate a 4D VMAT Acuros XB dose calculation using Gafchromic film. Special attention is paid to the physical material assignment in the CT dataset and to reported dose to water and dose to medium. Methods: A QUASAR phantom with a 3 cm sinusoidal tumor motion and 5 second period was scanned using 4D computed tomography. A CT was also obtained of the static QUASAR phantom with the tumor at the central position. A VMAT plan was created on the average CT dataset and was delivered on a Varian TrueBeam linear accelerator. The trajectorymore » log file from this treatment was acquired and used to create 10 VMAT subplans (one for each portion of the breathing cycle). Motion for each subplan was simulated by moving the beam isocentre in the superior/inferior direction in the Treatment Planning System on the static CT scan. The 10 plans were calculated (both dose to medium and dose to water) and summed for 1) the original HU values from the static CT scan and 2) the correct physical material assignment in the CT dataset. To acquire a breathing phase synchronized film measurements the trajectory log was used to create a VMAT delivery plan which includes dynamic couch motion using the Developer Mode. Three different treatment start phases were investigated (mid inhalation, full inhalation and full exhalation). Results: For each scenario the coronal dose distributions were measured using Gafchromic film and compared to the corresponding calculation with Film QA Pro Software using a Gamma test with a 3%/3mm distance to agreement criteria. Good agreement was found between calculation and measurement. No statistically significant difference in agreement was found between calculations to original HU values vs calculations to over-written (material-assigned) HU values. Conclusion: The investigated 4D dose calculation method agrees well with measurement.« less

Measurement of X-ray intensity in mammography by a ferroelectric dosimeter

NASA Astrophysics Data System (ADS)

Alter, Albert J.

2005-07-01

Each year in the US over 20 million women undergo mammography, a relatively high dose x-ray examination of the breast, which is relatively sensitive to the carcinogenic effect of ionizing radiation. The radiation risk from mammography is usually expressed in terms of mean glandular dose (MGD) which is calculated as the product of measured entrance exposure (ESE) and a dose conversion factor which is a function of anode material, peak tube voltage (23 to 35 kVp), half-value layer, filtration, compressed breast thickness and breast composition. Mammographic units may have anodes made of molybdenum, rhodium or tungsten and filters of molybdenum, rhodium, or aluminum. In order to accommodate all these parameters, multiple extensive tables of conversion factors are required to cover the range of possibilities. Energy fluence and energy imparted are alternative measures of radiation hazard, which have been used in situations where geometry or filtration is unconventional such as computed tomography or fluoroscopy. Unfortunately, at the present there is no way to directly measure these quantities clinically. In radiation therapy applications, calorimetry has been used to measure energy absorbed. A ferroelectric-based detector has been described that measures energy fluence rate (x-ray intensity) for diagnostic x-ray, 50 to 140 kVp, aluminum filtered tungsten spectrum [Carvalho & Alter: IEEE Transactions 44(6) 1997]. This work explores use of ferroelectric detectors to measure energy fluence, energy fluence rate and energy imparted in mammography. A detector interfaced with a laptop computer was developed to allow measurements on clinical units of five different manufactures having targets of molybdenum, rhodium and tungsten and filters of molybdenum, rhodium, and aluminum of various thicknesses. The measurements provide the first values of energy fluence and energy imparted in mammography. These measurements are compared with conventional parameters such as entrance exposure and mean glandular dose as well as published values of energy imparted for other types of x-ray examinations. Advantage of measuring dose in terms of energy imparted in mammography are simplicity of comparison with other sources of radiation exposure and potential (relative ease) of measurement across a variety of anode and filter combinations.

Evaluation of variations in absorbed dose and image noise according to patient forms in X-ray computed tomography.

PubMed

Matsubara, Kosuke; Koshida, Kichiro; Suzuki, Masayuki; Hayakawa, Mayumi; Tsujii, Hideo; Yamamoto, Tomoyuki

2005-12-20

Excessive radiation exposure in pediatric computed tomography (CT) scanning has become a serious problem, and it is difficult to select scan parameters for the scanning of small patients such as children. We investigated differences in absorbed dose and standard deviation (SD) in Hounsfield unit (HU) caused by differences in the form of the subject using a body-type phantom with removable body parts. Using four X-ray CT scanners, measurements were made with values from 50 mAs to 300 mAs, with slices of 50 mAs, using scan protocols that were assumed to perform thorough examinations. The results showed that the mAs values and absorbed doses were almost proportional, and the absorbed doses in the phantom without body parts were about 1.1-2.2-fold higher than those of the phantom with body parts at the same points. The SD values obtained indicated that the absorbed doses in the phantom with body parts were 0.3-0.6 times those of the phantom without body parts when the mAs values used were adjusted so that both SD values were the same. The absorbed doses in various patient forms can be estimated from these results, and they will become critical data for the selection of appropriate scan protocols.

SU-F-19A-05: Experimental and Monte Carlo Characterization of the 1 Cm CivaString 103Pd Brachytherapy Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reed, J; Micka, J; Culberson, W

Purpose: To determine the in-air azimuthal anisotropy and in-water dose distribution for the 1 cm length of the CivaString {sup 103}Pd brachytherapy source through measurements and Monte Carlo (MC) simulations. American Association of Physicists in Medicine Task Group No. 43 (TG-43) dosimetry parameters were also determined for this source. Methods: The in-air azimuthal anisotropy of the source was measured with a NaI scintillation detector and simulated with the MCNP5 radiation transport code. Measured and simulated results were normalized to their respective mean values and compared. The TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function for this sourcemore » were determined from LiF:Mg,Ti thermoluminescent dosimeter (TLD) measurements and MC simulations. The impact of {sup 103}Pd well-loading variability on the in-water dose distribution was investigated using MC simulations by comparing the dose distribution for a source model with four wells of equal strength to that for a source model with strengths increased by 1% for two of the four wells. Results: NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy showed that ≥95% of the normalized data were within 1.2% of the mean value. TLD measurements and MC simulations of the TG-43 dose-rate constant, line-source radial dose function, and 2D anisotropy function agreed to within the experimental TLD uncertainties (k=2). MC simulations showed that a 1% variability in {sup 103}Pd well-loading resulted in changes of <0.1%, <0.1%, and <0.3% in the TG-43 dose-rate constant, radial dose distribution, and polar dose distribution, respectively. Conclusion: The CivaString source has a high degree of azimuthal symmetry as indicated by the NaI scintillation detector measurements and MC simulations of the in-air azimuthal anisotropy. TG-43 dosimetry parameters for this source were determined from TLD measurements and MC simulations. {sup 103}Pd well-loading variability results in minimal variations in the in-water dose distribution according to MC simulations. This work was partially supported by CivaTech Oncology, Inc. through an educational grant for Joshua Reed, John Micka, Wesley Culberson, and Larry DeWerd and through research support for Mark Rivard.« less

SU-E-J-19: An Intra-Institutional Study of Cone-Beam CT Dose for Image-Guided Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knutson, N; Present Address: Mount Sinai Roosevelt Hospital, New York, NY; Rankine, L

2015-06-15

Purpose: To determine the variability of Cone-Beam CT Dose Index (CB-CTDI) across multiple on-board imaging (OBI) systems within a single institution, and compare this to manufacturer provided data. Methods: The CB-CTDI was measured on three Trilogy and three TrueBeam Varian OBI systems, for six different clinically used scan protocols. Measurements were taken using a 10 cm long CT ionization chamber in either a 16 cm (head-simulating) or 32 cm (body-simulating) diameter, acrylic, cylindrical, 15 cm long CTDI phantom. We assessed the variation in CB-CTDI between the OBI systems and compared our measured values to the data provided by the manufacturer.more » Results: The standard error in the CB-CTDI measured for all protocols was found to be within ±2% and ±5% of the mean for TrueBeam and Trilogy, respectively. For all head scan protocols, the measured TrueBeam values were lower than the manufacturer’s reported values, with a maximum difference of 13.9% and an average difference of 11%. For the body scan protocols, the TrueBeam measured values were 3% and 13% greater than the manufacturer’s reported values for two out of three protocols, and 38% lower than reported for the third protocol. In total, 7/18 CB-CTDI measurements fell within the manufacturers specified range (±10%). Across all scans the Truebeam machines were found to have a lower CB-CTDI than Trilogy, particularly the head scan protocols, which show decreases of up to 30% . Conclusion: The intra-institutional variation of CB-CTDI was found to be clinically acceptable at less than 5%. For the TrueBeam OBI system, over half of the measured scans failed to fall with in the manufactured quoted range of 10%, however, all measured values were within 15% of the manufacturer’s reported values. For accurate assessment and reporting of imaging dose to radiotherapy patients, our results indicate a need for standardization in CB-CTDI measurement technique.« less

Contralateral breast dose from chest wall and breast irradiation: local experience.

PubMed

Alzoubi, A S; Kandaiya, S; Shukri, A; Elsherbieny, E

2010-06-01

Second cancer induction in the contralateral breast (CB) is an issue of some concern in breast radiotherapy especially for women under the age of 45 years at the time of treatment. The CB dose from 2-field and 3-field techniques in post-mastectomy chest wall irradiations in an anthropomorphic phantom as well as in patients were measured using thermoluminescent dosimeters (TLDs) at the local radiotherapy center. Breast and chest wall radiotherapy treatments were planned conformally (3D-CRT) and delivered using 6-MV photons. The measured CB dose at the surface fell sharply with distance from the field edge. However, the average ratio of the measured to the calculated CB dose using the pencil beam algorithm at the surface was approximately 53%. The mean and median measured internal dose at the posterior border of CB in a phantom was 5.47+/-0.22 cGy and 5.44 cGy, respectively. The internal CB dose was relatively independent of depth. In the present study the internal CB dose is 2.1-4.1% of the prescribed dose which is comparable to the values reported by other authors.

SU-E-I-59: Image Quality and Dose Measurement for Partial Cone-Beam CT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abouei, E; Ford, N

Purpose: To characterize performance of cone beam CT (CBCT) used in dentistry investigating quantitatively the image quality and radiation dose during dental CBCT over different settings for partial rotation of the x-ray tube. Methods: Image quality and dose measurements were done on a variable field of view (FOV) dental CBCT (Carestream 9300). X-ray parameters for clinical settings were adjustable for 2–10 mA, 60–90 kVp, and two optional voxel size values, but time was fixed for each FOV. Image quality was assessed by scanning cylindrical poly-methyl methacrylate (PMMA) image quality phantom (SEDENTEXCT IQ), and then the images were analyzed using ImageJmore » to calculate image quality parameters such as noise, uniformity, and contrast to noise ratio (CNR). A protocol proposed by SEDENTEXCT, dose index 1 (DI1), was applied to dose measurements obtained using a thimble ionization chamber and cylindrical PMMA dose index phantom (SEDENTEXCT DI). Dose distributions were obtained using Gafchromic film. The phantoms were positioned in the FOV to imitate a clinical positioning. Results: The image noise was 6–12.5% which, when normalized to the difference of mean voxel value of PMMA and air, was comparable between different FOVs. Uniformity was 93.5ß 99.7% across the images. CNR was 1.7–4.2 and 6.3–14.3 for LDPE and Aluminum, respectively. Dose distributions were symmetric about the rotation angle's bisector. For large and medium FOVs at 4 mA and 80–90 kVp, DI1 values were in the range of 1.26–3.23 mGy. DI1 values were between 1.01–1.93 mGy for small FOV (5×5 cm{sup 2}) at 4–5 mA and 75–84 kVp. Conclusion: Noise decreased by increasing kVp, and the CNR increased for each FOV. When FOV size increased, image noise increased and CNR decreased. DI1 values were increased by increasing tube current (mA), tube voltage (kVp), and/or FOV. Funding for this project from NSERC Discovery grant, UBC Faculty of Dentistry Research Equipment Grant and UBC Faculty of Dentistry S. Wah Leung Endowment Fund.« less

Absorbed Dose Determination Using Experimental and Analytical Predictions of X-Ray Spectra

NASA Technical Reports Server (NTRS)

Edwards, D. L.; Carruth, Ralph (Technical Monitor)

2001-01-01

Electron beam welding in a vacuum is a technology that NASA is investigating as a joining technique for manufacture of space structures. This investigation characterizes the x-ray environment due to operation of an in-vacuum electron beam welding tool and provides recommendations for adequate shielding for astronauts performing the in-vacuum electron beam welding. NASA, in a joint venture with the Russian Space Agency, was scheduled to perform a series of welding in space experiments on board the U.S. Space Shuttle. This series of experiments was named the international space welding experiment (ISWE). The hardware associated with the ISWE was leased to NASA by the Paton Welding Institute (PWI) in Ukraine for ground-based welding experiments in preparation for flight. Two ground tests were scheduled, using the ISWE electron beam welding tool, to characterize the radiation exposure to an astronaut during the operation of the ISWE. These radiation exposure tests used thermoluminescence dosimeters (TLD's) shielded with material currently used by astronauts during extravehicular activities to measure the radiation dose. The TLD's were exposed to x-ray radiation generated by operation of the ISWE in-vacuum electron beam welding tool. This investigation was the first known application of TLD's to measure absorbed dose from x rays of energy less than 10 keV. The ISWE hardware was returned to Ukraine before the issue of adequate shielding for the astronauts was completely verified. Therefore, alternate experimental and analytical methods were developed to measure and predict the x-ray spectral and intensity distribution generated by ISWE electron beam impact with metal. These x-ray spectra were normalized to an equivalent ISWE exposure, then used to calculate the absorbed radiation dose to astronauts. These absorbed dose values were compared to TLD measurements obtained during actual operation of the ISWE in-vacuum electron beam welding tool. The calculated absorbed dose values were found to be in agreement with the measured TLD values.

SU-F-18C-09: Assessment of OSL Dosimeter Technology in the Validation of a Monte Carlo Radiation Transport Code for CT Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carver, D; Kost, S; Pickens, D

Purpose: To assess the utility of optically stimulated luminescent (OSL) dosimeter technology in calibrating and validating a Monte Carlo radiation transport code for computed tomography (CT). Methods: Exposure data were taken using both a standard CT 100-mm pencil ionization chamber and a series of 150-mm OSL CT dosimeters. Measurements were made at system isocenter in air as well as in standard 16-cm (head) and 32-cm (body) CTDI phantoms at isocenter and at the 12 o'clock positions. Scans were performed on a Philips Brilliance 64 CT scanner for 100 and 120 kVp at 300 mAs with a nominal beam width ofmore » 40 mm. A radiation transport code to simulate the CT scanner conditions was developed using the GEANT4 physics toolkit. The imaging geometry and associated parameters were simulated for each ionization chamber and phantom combination. Simulated absorbed doses were compared to both CTDI{sub 100} values determined from the ion chamber and to CTDI{sub 100} values reported from the OSLs. The dose profiles from each simulation were also compared to the physical OSL dose profiles. Results: CTDI{sub 100} values reported by the ion chamber and OSLs are generally in good agreement (average percent difference of 9%), and provide a suitable way to calibrate doses obtained from simulation to real absorbed doses. Simulated and real CTDI{sub 100} values agree to within 10% or less, and the simulated dose profiles also predict the physical profiles reported by the OSLs. Conclusion: Ionization chambers are generally considered the standard for absolute dose measurements. However, OSL dosimeters may also serve as a useful tool with the significant benefit of also assessing the radiation dose profile. This may offer an advantage to those developing simulations for assessing radiation dosimetry such as verification of spatial dose distribution and beam width.« less

In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity

PubMed Central

Hotta, Kenji; Matsubara, Kana; Nishioka, Shie; Matsuura, Taeko; Kawashima, Mitsuhiko

2012-01-01

When in vivo proton dosimetry is performed with a metal‐oxide semiconductor field‐effect transistor (MOSFET) detector, the response of the detector depends strongly on the linear energy transfer. The present study reports a practical method to correct the MOSFET response for linear energy transfer dependence by using a simplified Monte Carlo dose calculation method (SMC). A depth‐output curve for a mono‐energetic proton beam in polyethylene was measured with the MOSFET detector. This curve was used to calculate MOSFET output distributions with the SMC (SMCMOSFET). The SMCMOSFET output value at an arbitrary point was compared with the value obtained by the conventional SMCPPIC, which calculates proton dose distributions by using the depth‐dose curve determined by a parallel‐plate ionization chamber (PPIC). The ratio of the two values was used to calculate the correction factor of the MOSFET response at an arbitrary point. The dose obtained by the MOSFET detector was determined from the product of the correction factor and the MOSFET raw dose. When in vivo proton dosimetry was performed with the MOSFET detector in an anthropomorphic phantom, the corrected MOSFET doses agreed with the SMCPPIC results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector. PACS number: 87.56.‐v PMID:22402385

SU-F-T-220: Validation of Hounsfield Unit-To-Stopping Power Ratio Calibration Used for Dose Calculation in Proton Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Polf, J; Chung, H; Langen, K

Purpose: To validate the stoichiometric calibration of the Hounsfield Unit (HU) to Stopping Power Ratio (SPR) calibration used to commission a commercial treatment planning system (TPS) for proton radiotherapy dose calculation. Methods and Materials: The water equivalent thickness (WET) of several individual pig tissues (lung, fat, muscle, liver, intestine, rib, femur), mixed tissue samples (muscle/rib, ice/femur, rib/air cavity/muscle), and an intact pig head were measured with a multi-layer ionization chamber (MLIC). A CT scan of each sample was obtained and imported into a commercial TPS. The WET calculated by the TPS for each tissue sample was compared to the measuredmore » WET value to determine the accuracy of the HU-to-SPR calibration curve used by the TPS to calculate dose. Results: The WET values calculated by the TPS showed good agreement (< 2.0%) with the measured values for bone and all soft tissues except fat (3.1% difference). For the mixed tissue samples and the intact pig head measurements, the difference in the TPS and measured WET values all agreed to within 3.5%. In addition, SPR values were calculated from the measured WET of each tissue, and compared to SPR values of reference tissues from ICRU 46 used to generate the HU-to-SPR calibration for the TPS. Conclusion: For clinical scenarios where the beam passes through multiple tissue types and its path is dominated by soft tissues, we believe using an uncertainty of 3.5% of the planned beam range is acceptable to account for uncertainties in the TPS WET determination.« less

RESPONSE OF THE GREEK EARLY WARNING SYSTEM REUTER-STOKES IONIZATION CHAMBERS TO TERRESTRIAL AND COSMIC RADIATION EVALUATED IN COMPARISON WITH SPECTROSCOPIC DATA AND TIME SERIES ANALYSIS.

PubMed

Leontaris, F; Clouvas, A; Xanthos, S; Maltezos, A; Potiriadis, C; Kiriakopoulos, E; Guilhot, J

2018-02-01

The Telemetric Early Warning System Network of the Greek Atomic Energy Commission consists mainly of a network of 24 Reuter-Stokes high-pressure ionization chambers (HPIC) for gamma dose rate measurements and covers all Greece. In the present work, the response of the Reuter-Stokes HPIC to terrestrial and cosmic radiation was evaluated in comparison with spectroscopic data obtained by in situ gamma spectrometry measurements with portable hyper pure Germanium detectors (HPGe), near the Reuter-Stokes detectors and time series analysis. For the HPIC detectors, a conversion factor for the measured absorbed dose rate in air (in nGy h-1) to the total ambient dose equivalent rate Ḣ*(10), due to terrestrial and cosmic component, was deduced by the field measurements. Time series analysis of the mean monthly dose rate (measured by the Reuter-Stokes detector in Thessaloniki, northern Greece, from 2001 to 2016) was performed with advanced statistical methods (Fast Fourier Analysis and Zhao Atlas Marks Transform). Fourier analysis reveals several periodicities (periodogram). The periodogram of the absorbed dose rate in air values was compared with the periodogram of the values measured for the same period (2001-16) and in the same location with a NaI (Tl) detector which in principle is not sensitive to cosmic radiation. The obtained results are presented and discussed. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

The effect of dose heterogeneity on radiation risk in medical imaging.

PubMed

Samei, Ehsan; Li, Xiang; Chen, Baiyu; Reiman, Robert

2013-06-01

The current estimations of risk associated with medical imaging procedures rely on assessing the organ dose via direct measurements or simulation. The dose to each organ is assumed to be homogeneous. To take into account the differences in radiation sensitivities, the mean organ doses are weighted by a corresponding tissue-weighting coefficients provided by ICRP to calculate the effective dose, which has been used as a surrogate of radiation risk. However, those coefficients were derived under the assumption of a homogeneous dose distribution within each organ. That assumption is significantly violated in most medical-imaging procedures. In helical chest CT, for example, superficial organs (e.g. breasts) demonstrate a heterogeneous dose distribution, whereas organs on the peripheries of the irradiation field (e.g. liver) might possess a discontinuous dose profile. Projection radiography and mammography involve an even higher level of organ dose heterogeneity spanning up to two orders of magnitude. As such, mean dose or point measured dose values do not reflect the maximum energy deposited per unit volume of the organ. In this paper, the magnitude of the dose heterogeneity in both CT and projection X-ray imaging was reported, using Monte Carlo methods. The lung dose demonstrated factors of 1.7 and 2.2 difference between the mean and maximum dose for chest CT and radiography, respectively. The corresponding values for the liver were 1.9 and 3.5. For mammography and breast tomosynthesis, the difference between mean glandular dose and maximum glandular dose was 3.1. Risk models based on the mean dose were found to provide a reasonable reflection of cancer risk. However, for leukaemia, they were found to significantly under-represent the risk when the organ dose distribution is heterogeneous. A systematic study is needed to develop a risk model for heterogeneous dose distributions.

SU-E-I-28: Evaluating the Organ Dose From Computed Tomography Using Monte Carlo Calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ono, T; Araki, F

Purpose: To evaluate organ doses from computed tomography (CT) using Monte Carlo (MC) calculations. Methods: A Philips Brilliance CT scanner (64 slice) was simulated using the GMctdospp (IMPS, Germany) based on the EGSnrc user code. The X-ray spectra and a bowtie filter for MC simulations were determined to coincide with measurements of half-value layer (HVL) and off-center ratio (OCR) profile in air. The MC dose was calibrated from absorbed dose measurements using a Farmer chamber and a cylindrical water phantom. The dose distribution from CT was calculated using patient CT images and organ doses were evaluated from dose volume histograms.more » Results: The HVLs of Al at 80, 100, and 120 kV were 6.3, 7.7, and 8.7 mm, respectively. The calculated HVLs agreed with measurements within 0.3%. The calculated and measured OCR profiles agreed within 3%. For adult head scans (CTDIvol) =51.4 mGy), mean doses for brain stem, eye, and eye lens were 23.2, 34.2, and 37.6 mGy, respectively. For pediatric head scans (CTDIvol =35.6 mGy), mean doses for brain stem, eye, and eye lens were 19.3, 24.5, and 26.8 mGy, respectively. For adult chest scans (CTDIvol=19.0 mGy), mean doses for lung, heart, and spinal cord were 21.1, 22.0, and 15.5 mGy, respectively. For adult abdominal scans (CTDIvol=14.4 mGy), the mean doses for kidney, liver, pancreas, spleen, and spinal cord were 17.4, 16.5, 16.8, 16.8, and 13.1 mGy, respectively. For pediatric abdominal scans (CTDIvol=6.76 mGy), mean doses for kidney, liver, pancreas, spleen, and spinal cord were 8.24, 8.90, 8.17, 8.31, and 6.73 mGy, respectively. In head scan, organ doses were considerably different from CTDIvol values. Conclusion: MC dose distributions calculated by using patient CT images are useful to evaluate organ doses absorbed to individual patients.« less

Dental radiography: tooth enamel EPR dose assessment from Rando phantom measurements

NASA Astrophysics Data System (ADS)

Aragno, D.; Fattibene, P.; Onori, S.; Aragno, D.; Fattibene, P.

2000-09-01

Electron paramagnetic resonance dosimetry of tooth enamel is now established as a suitable method for individual dose reconstruction following radiation accidents. The accuracy of the method is limited by some confounding factors, among which is the dose received due to medical x-ray irradiation. In the present paper the EPR response of tooth enamel to endoral examination was experimentally evaluated using an anthropomorphic phantom. The dose to enamel for a single exposure of a typical dental examination performed with a new x-ray generation unit working at 65 kVp gave rise to a CO2- signal of intensity similar to that induced by a dose of about 2 mGy of 60Co. EPR measurements were performed on the entire tooth with no attempt to separate buccal and lingual components. Also the dose to enamel for an orthopantomography exam was estimated. It was derived from TLD measurements as equivalent to 0.2 mGy of 60Co. In view of application to risk assessment analysis, in the present work the value for the ratio of the reference dose at the phantom surface measured with TLD to the dose at the tooth measured with EPR was determined.

Calibration of helical tomotherapy machine using EPR/alanine dosimetry.

PubMed

Perichon, Nicolas; Garcia, Tristan; François, Pascal; Lourenço, Valérie; Lesven, Caroline; Bordy, Jean-Marc

2011-03-01

Current codes of practice for clinical reference dosimetry of high-energy photon beams in conventional radiotherapy recommend using a 10 x 10 cm2 square field, with the detector at a reference depth of 10 cm in water and 100 cm source to surface distance (SSD) (AAPM TG-51) or 100 cm source-to-axis distance (SAD) (IAEA TRS-398). However, the maximum field size of a helical tomotherapy (HT) machine is 40 x 5 cm2 defined at 85 cm SAD. These nonstandard conditions prevent a direct implementation of these protocols. The purpose of this study is twofold: To check the absorbed dose in water and dose rate calibration of a tomotherapy unit as well as the accuracy of the tomotherapy treatment planning system (TPS) calculations for a specific test case. Both topics are based on the use of electron paramagnetic resonance (EPR) using alanine as transfer dosimeter between the Laboratoire National Henri Becquerel (LNHB) 60Co-gamma-ray reference beam and the Institut Curie's HT beam. Irradiations performed in the LNHB reference 60Co-gamma-ray beam allowed setting up the calibration method, which was then implemented and tested at the LNHB 6 MV linac x-ray beam, resulting in a deviation of 1.6% (at a 1% standard uncertainty) relative to the reference value determined with the standard IAEA TRS-398 protocol. HT beam dose rate estimation shows a difference of 2% with the value stated by the manufacturer at a 2% standard uncertainty. A 4% deviation between measured dose and the calculation from the tomotherapy TPS was found. The latter was originated by an inadequate representation of the phantom CT-scan values and, consequently, mass densities within the phantom. This difference has been explained by the mass density values given by the CT-scan and used by the TPS which were not the true ones. Once corrected using Monte Carlo N-Particle simulations to validate the accuracy of this process, the difference between corrected TPS calculations and alanine measured dose values was then found to be around 2% (with 2% standard uncertainty on TPS doses and 1.5% standard uncertainty on EPR measurements). Beam dose rate estimation results were found to be in good agreement with the reference value given by the manufacturer at 2% standard uncertainty. Moreover, the dose determination method was set up with a deviation around 2% (at a 2% standard uncertainty).

Effect of gamma-irradiation on the occurrence of pathogenic microorganisms and nutritive value of four principal cereal grains.

PubMed

Aziz, N H; Souzan, R M; Shahin Azza, A

2006-12-01

The effects of (60)Co gamma-photon-irradiation on the natural occurrence of pathogenic microorganisms in four principal cereal grains and on amino acids and vitamins in these cereals were investigated. The total numbers of aerobic bacteria were reduced by three logarithmic decades when grains were given a dose of 10kGy. Coliforms and "coagulase- positive" staphylococci were inhibited by a dose of 1kGy, whereas fungi were inhibited by a dose of 5kGy. The 15kGy dose eliminated viable microorganisms in cereal grains, and about 10-30 colony-forming units of Clostridium sp. per gram of grain survived after this dose. The dose of 10kGy did not cause any measurable destruction of total amino acids. Thiamin was reduced by 22-33% and riboflavin by 10-16% after a dose of 10kGy. Irradiation did not increase the acid values significantly, but did increase the peroxide values, which was not accompanied by the off-odors of cereals. We conclude that the overall dose of 10kGy is very effective for microbial decontamination of cereal grains, and does not adversely affect the nutritional quality of cereal grains.

SU-E-T-339: Dosimetric Verification of Acuros XB Dose Calculation Algorithm On An Air Cavity for 6-MV Flattening Filter-Free Beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, S; Suh, T; Chung, J

Purpose: This study was to verify the accuracy of Acuros XB (AXB) dose calculation algorithm on an air cavity for a single radiation field using 6-MV flattening filter-free (FFF) beam. Methods: A rectangular slab phantom containing an air cavity was made for this study. The CT images of the phantom for dose calculation were scanned with and without film at measurement depths (4.5, 5.5, 6.5 and 7.5 cm). The central axis doses (CADs) and the off-axis doses (OADs) were measured by film and calculated with Analytical Anisotropic Algorithm (AAA) and AXB for field sizes ranging from 2 Χ 2 tomore » 5 Χ 5 cm{sup 2} of 6-MV FFF beams. Both algorithms were divided into AXB-w and AAA -w when included the film in phantom for dose calculation, and AXB-w/o and AAA-w/o in calculation without film. The calculated OADs for both algorithms were compared with the measured OADs and difference values were determined using root means squares error (RMSE) and gamma evaluation. Results: The percentage differences (%Diffs) between the measured and calculated CAD for AXB-w was most agreement than others. Compared to the %Diff with and without film, the %Diffs with film were decreased than without within both algorithms. The %Diffs for both algorithms were reduced with increasing field size and increased relative to the depth increment. RMSEs of CAD for AXB-w were within 10.32% for both inner-profile and penumbra, while the corresponding values of AAA-w appeared to 96.50%. Conclusion: This study demonstrated that the dose calculation with AXB within air cavity shows more accurate than with AAA compared to the measured dose. Furthermore, we found that the AXB-w was superior to AXB-w/o in this region when compared against the measurements.« less

Occupational dose constraints in interventional cardiology procedures: the DIMOND approach

NASA Astrophysics Data System (ADS)

Tsapaki, Virginia; Kottou, Sophia; Vano, Eliseo; Komppa, Tuomo; Padovani, Renato; Dowling, Annita; Molfetas, Michael; Neofotistou, Vassiliki

2004-03-01

Radiation fields involved in angiographic suites are most uneven with intensity and gradient varying widely with projection geometry. The European Commission DIMOND III project addressed among others, the issues regarding optimization of staff doses with an attempt to propose preliminary occupational dose constraints. Two thermoluminescent dosemeters (TLD) were used to assess operators' extremity doses (left shoulder and left foot) during 20 coronary angiographies (CAs) and 20 percutaneous transluminal coronary angioplasties (PTCAs) in five European centres. X-ray equipment, radiation protection measures used and the dose delivered to the patient in terms of dose-area product (DAP) were recorded so as to subsequently associate them with operator's dose. The range of staff doses noted for the same TLD position, centre and procedure type emphasizes the importance of protective measures and technical characteristics of x-ray equipment. Correlation of patient's DAP with staff shoulder dose is moderate whereas correlation of patient's DAP with staff foot dose is poor in both CA and PTCA. Therefore, it is difficult to predict operator's dose from patient's DAP mainly due to the different use of protective measures. A preliminary occupational dose constraint value was defined by calculating cardiologists' annual effective dose and found to be 0.6 mSv.

In vivo dosimetry for external photon treatments of head and neck cancers by diodes and TLDS.

PubMed

Tung, C J; Wang, H C; Lo, S H; Wu, J M; Wang, C J

2004-01-01

In vivo dosimetry was implemented for treatments of head and neck cancers in the large fields. Diode and thermoluminescence dosemeter (TLD) measurements were carried out for the linear accelerators of 6 MV photon beams. ESTRO in vivo dosimetry protocols were followed in the determination of midline doses from measurements of entrance and exit doses. Of the fields monitored by diodes, the maximum absolute deviation of measured midline doses from planned target doses was 8%, with the mean value and the standard deviation of -1.0 and 2.7%. If planned target doses were calculated using radiological water equivalent thicknesses rather than patient geometric thicknesses, the maximum absolute deviation dropped to 4%, with the mean and the standard deviation of 0.7 and 1.8%. For in vivo dosimetry monitored by TLDs, the shift in mean dose remained small but the statistical precision became poor.

Dose in x-ray computed tomography

NASA Astrophysics Data System (ADS)

Kalender, Willi A.

2014-02-01

Radiation dose in x-ray computed tomography (CT) has become a topic of high interest due to the increasing numbers of CT examinations performed worldwide. This review aims to present an overview of current concepts for both scanner output metrics and for patient dosimetry and will comment on their strengths and weaknesses. Controversial issues such as the appropriateness of the CT dose index (CTDI) are discussed in detail. A review of approaches to patient dose assessment presently in practice, of the dose levels encountered and options for further dose optimization are also given and discussed. Patient dose assessment remains a topic for further improvement and for international consensus. All approaches presently in use are based on Monte Carlo (MC) simulations. Estimates for effective dose are established, but they are crude and not patient-specific; organ dose estimates are rarely available. Patient- and organ-specific dose estimates can be provided with adequate accuracy and independent of CTDI phantom measurements by fast MC simulations. Such information, in particular on 3D dose distributions, is important and helpful in optimization efforts. Dose optimization has been performed very successfully in recent years and even resulted in applications with effective dose values of below 1 mSv. In general, a trend towards lower dose values based on technical innovations has to be acknowledged. Effective dose values are down to clearly below 10 mSv on average, and there are a number of applications such as cardiac and pediatric CT which are performed routinely below 1 mSv on modern equipment.

SU-F-19A-02: Comparison of Absorbed Dose to Water Standards for HDR Ir-192 Brachytherapy Between the LCR, Brazil and NRC, Canada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Salata, C; David, M; Almeida, C de

2014-06-15

Purpose: To compare absorbed dose to water standards for HDR brachytherapy dosimetry developed by the Radiological Science Laboratory of Rio de Janeiro State University (LCR) and the National Research Council, Canada (NRC). Methods: The two institutions have separately developed absorbed dose standards based on the Fricke dosimetry system. There are important differences between the two standards, including: preparation and read-out of the Fricke solution, irradiation geometry of the Fricke holder in relation to the Ir-192 source, and determination of the G-value to be used at Ir-192 energies. All measurements for both standards were made directly at the NRC laboratory (i.e.,more » no transfer instrument was used) using a single Ir-192 source (microSelectron v2). In addition, the NRC group has established a self-consistent method to determine the G-value for Ir-192, based on an interpolation between G-values obtained at Co-60 and 250kVp X-rays, and this measurement was repeated using the LCR Fricke solution to investigate possible systematic uncertainties. Results: G-values for Co-60 and 250 kVp x-rays, obtained using the LCR Fricke system, agreed with the NRC values within 0.5 % and 1 % respectively, indicating that the general assumption of universal G-values is appropriate in this case. The standard uncertainty in the determination of G for Ir-192 is estimated to be 0.6 %. For the comparison of absorbed dose measurements at the reference point for Ir-192 (1 cm depth in water, perpendicular to the seed long-axis), the ratio Dw(NRC)/Dw(LCR) was found to be 1.011 with a combined standard uncertainty of 1.7 %, k=1. Conclusion: The agreement in the absorbed dose to water values for the LCR and NRC systems is very encouraging. Combined with the lower uncertainty in this approach compared to the present air-kerma approach, these results reaffirm the use of Fricke solution as a potential primary standard for HDR Ir-192 brachytherapy.« less

SU-E-I-49: Influence of Scanner Output Measurement Technique on KERMA Ratios in CT.

PubMed

Ogden, K; Roskopf, M; Scalzetti, E

2012-06-01

KERMA ratios (RK) are defined as the ratio of KERMA measured at a specific phantom location (K) to in-air isocenter CT scanner output (KCT). In this work we investigate the impact of measurement methodology on KCT values. OSL dosimeter chips were used to measure KCT for a GE VCT scanner (GE Medical Systems, Waukesha WI), using the 40 mm nominal beam width. Methods included a single point measurement at the center of the beam (1 tube rotation), and extended z-axis measurements using multiple adjacent OSL's (7.5 cm extent), with single tube rotation, multiple contiguous axial scans, and helical scans (pitch of 1.375). Measurements were made in air and on the scan table at 80 and 120 kV. Averaged single point measurements were consistent, with a mean coefficient of variation of 2.5%. For extended measurements with a single tube rotation, the mean value was equivalent to the single point measurements. For multiple contiguous axial scans, the in-air KCT values were higher than the single rotation mean value and single point measurements by 13% and 10.3% at 120 and 80 kV, respectively, and for the on-table measurements the values were 14.9% and 8.1% higher at 120 and 80 kV, respectively. The increase is due to beam overlap caused by z- axis over-beaming. Extended measurements using helical scanning were equivalent to the multiple rotation axial measurements when corrected for the helical pitch. For all methodologies, the in-air values exceeded the on- table measurements by an average of 23% and 19.4% at 80 and 120 kV, respectively. Scanner KCT values must be measured to allow organ dose estimation using published RK values. It is imperative that the KCT measurement methodology is the same as for the published values, or large errors may be introduced into the resulting organ dose estimates. © 2012 American Association of Physicists in Medicine.

RCT: Module 2.06, Air Sampling Program and Methods, Course 8772

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hillmer, Kurt T.

The inhalation of radioactive particles is the largest cause of an internal radiation dose. Airborne radioactivity measurements are necessary to ensure that the control measures are and continue to be effective. Regulations govern the allowable effective dose equivalent to an individual. The effective dose equivalent is determined by combining the external and internal dose equivalent values. Typically, airborne radioactivity levels are maintained well below allowable levels to keep the total effective dose equivalent small. This course will prepare the student with the skills necessary for RCT qualification by passing quizzes, tests, and the RCT Comprehensive Phase 1, Unit 2 Examinationmore » (TEST 27566) and will provide in-the-field skills.« less

Investigation of the Entrance Surface Dose and Dose to Different Organs in Lumbar Spine Imaging

PubMed Central

Sina, S; Zeinali, B; Karimipoorfard, M; Lotfalizadeh, F; Sadeghi, M; Zamani, E; Faghihi, R

2014-01-01

Background: Dose assessment using proper dosimeters is especially important in radiation protection optimization and imaging justification in diagnostic radiology. Objective: The aim of this study is to obtain the Entrance Skin Dose (ESD) of patients undergoing lumbar spine imaging using two thermoluminescence dosimeters TLD-100 (LiF: Mg, Ti) and GR-200 (LiF: Mg, Cu, P) and also to obtain the absorbed dose to different organs in lumbar spine imaging with several views. Methods: To measure the ESD values of the patients undergoing lumbar spine imaging, the two TLD types were put on their skin surface. The ESD values for different views of lumbar spine imaging were also measured by putting the TLDs at the surface of the Rando phantom. Several TLD chips were inserted inside different organs of Rando phantom to measure the absorbed dose to different organs in lumbar spine imaging. Results: The results indicate that there is a close agreement between the results of the two dosimeters. Based on the results of this experiment, the ESD dose of the 16 patients included in this study varied between 2.71 mGy and 26.29 mGy with the average of 11.89 mGy for TLD-100, and between 2.55 mGy and 27.41 mGy with the average of 12.32 mGy for GR-200 measurements. The ESDs obtained by putting the two types of TLDs at the surface of Rando phantom are in close agreement. Conclusion: According to the results, the GR200 has greater sensitivity than the TLD-100. PMID:25599058

Determination of absorbed dose to water around a clinical HDR {sup 192}Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlsson Tedgren, Aasa; Elia, Rouba; Hedtjaern, Haakan

2012-02-15

Purpose: Experimental radiation dosimetry with thermoluminescent dosimeters (TLDs), calibrated in a {sup 60}Co or megavoltage (MV) photon beam, is recommended by AAPM TG-43U1for verification of Monte Carlo calculated absorbed doses around brachytherapy sources. However, it has been shown by Carlsson Tedgren et al.[Med. Phys. 38, 5539-5550 (2011)] that for TLDs of LiF:Mg,Ti, detector response was 4% higher in a {sup 137}Cs beam than in a {sup 60}Co one. The aim of this work was to investigate if similar over-response exists when measuring absorbed dose to water around {sup 192}Ir sources, using LiF:Mg,Ti dosimeters calibrated in a 6 MV photon beam.more » Methods: LiF dosimeters were calibrated to measure absorbed dose to water in a 6 MV photon beam and used to measure absorbed dose to water at distances of 3, 5, and 7 cm from a clinical high dose rate (HDR) {sup 192}Ir source in a polymethylmethacrylate (PMMA) phantom. Measured values were compared to values of absorbed dose to water calculated using a treatment planning system (TPS) including corrections for the difference in energy absorption properties between calibration quality and the quality in the users'{sup 192}Ir beam and for the use of a PMMA phantom instead of the water phantom underlying dose calculations in the TPS. Results: Measured absorbed doses to water around the {sup 192}Ir source were overestimated by 5% compared to those calculated by the TPS. Corresponding absorbed doses to water measured in a previous work with lithium formate electron paramagnetic resonance (EPR) dosimeters by Antonovic et al. [Med. Phys. 36, 2236-2247 (2009)], using the same irradiation setup and calibration procedure as in this work, were 2% lower than those calculated by the TPS. The results obtained in the measurements in this work and those obtained using the EPR lithium formate dosimeters were, within the expanded (k = 2) uncertainty, in agreement with the values derived by the TPS. The discrepancy between the results using LiF:Mg,Ti TLDs and the EPR lithium formate dosimeters was, however, statistically significant and in agreement with the difference in relative detector responses found for the two detector systems by Carlsson Tedgren et al. [Med. Phys. 38, 5539-5550 (2011)] and by Adolfsson et al.[Med. Phys. 37, 4946-4959 (2010)]. Conclusions: When calibrated in {sup 60}Co or MV photon beams, correction for the linear energy transfer (LET) dependence of LiF:Mg,Ti detector response will be needed as to measure absorbed doses to water in a {sup 192}Ir beam with highest accuracy. Such corrections will depend on the manufacturing process (MTS-N Poland or Harshaw TLD-100) and details of the annealing and read-out schemes used.« less

Determination of absorbed dose to water around a clinical HDR (192)Ir source using LiF:Mg,Ti TLDs demonstrates an LET dependence of detector response.

PubMed

Carlsson Tedgren, Asa; Elia, Rouba; Hedtjarn, Hakan; Olsson, Sara; Alm Carlsson, Gudrun

2012-02-01

Experimental radiation dosimetry with thermoluminescent dosimeters (TLDs), calibrated in a (60)Co or megavoltage (MV) photon beam, is recommended by AAPM TG-43U1for verification of Monte Carlo calculated absorbed doses around brachytherapy sources. However, it has been shown by Carlsson Tedgren et al. [Med. Phys. 38, 5539-5550 (2011)] that for TLDs of LiF:Mg,Ti, detector response was 4% higher in a (137)Cs beam than in a (60)Co one. The aim of this work was to investigate if similar over-response exists when measuring absorbed dose to water around (192)Ir sources, using LiF:Mg,Ti dosimeters calibrated in a 6 MV photon beam. LiF dosimeters were calibrated to measure absorbed dose to water in a 6 MV photon beam and used to measure absorbed dose to water at distances of 3, 5, and 7 cm from a clinical high dose rate (HDR) (192)Ir source in a polymethylmethacrylate (PMMA) phantom. Measured values were compared to values of absorbed dose to water calculated using a treatment planning system (TPS) including corrections for the difference in energy absorption properties between calibration quality and the quality in the users' (192)Ir beam and for the use of a PMMA phantom instead of the water phantom underlying dose calculations in the TPS. Measured absorbed doses to water around the (192)Ir source were overestimated by 5% compared to those calculated by the TPS. Corresponding absorbed doses to water measured in a previous work with lithium formate electron paramagnetic resonance (EPR) dosimeters by Antonovic et al. [Med. Phys. 36, 2236-2247 (2009)], using the same irradiation setup and calibration procedure as in this work, were 2% lower than those calculated by the TPS. The results obtained in the measurements in this work and those obtained using the EPR lithium formate dosimeters were, within the expanded (k = 2) uncertainty, in agreement with the values derived by the TPS. The discrepancy between the results using LiF:Mg,Ti TLDs and the EPR lithium formate dosimeters was, however, statistically significant and in agreement with the difference in relative detector responses found for the two detector systems by Carlsson Tedgren et al. [Med. Phys. 38, 5539-5550 (2011)] and by Adolfsson et al. [Med. Phys. 37, 4946-4959 (2010)]. When calibrated in (60)Co or MV photon beams, correction for the linear energy transfer (LET) dependence of LiF:Mg,Ti detector response will be needed as to measure absorbed doses to water in a (192)Ir beam with highest accuracy. Such corrections will depend on the manufacturing process (MTS-N Poland or Harshaw TLD-100) and details of the annealing and read-out schemes used.

Measurement of 131I activity in thyroid of nuclear medical staff and internal dose assessment in a Polish nuclear medical hospital.

PubMed

Brudecki, K; Kowalska, A; Zagrodzki, P; Szczodry, A; Mroz, T; Janowski, P; Mietelski, J W

2017-03-01

This paper presents results of 131 I thyroid activity measurements in 30 members of the nuclear medicine personnel of the Department of Endocrinology and Nuclear Medicine Holy Cross Cancer Centre in Kielce, Poland. A whole-body spectrometer equipped with two semiconductor gamma radiation detectors served as the basic research instrument. In ten out of 30 examined staff members, the determined 131 I activity was found to be above the detection limit (DL = 5 Bq of 131 I in the thyroid). The measured activities ranged from (5 ± 2) Bq to (217 ± 56) Bq. The highest activities in thyroids were detected for technical and cleaning personnel, whereas the lowest values were recorded for medical doctors. Having measured the activities, an attempt has been made to estimate the corresponding annual effective doses, which were found to range from 0.02 to 0.8 mSv. The highest annual equivalent doses have been found for thyroid, ranging from 0.4 to 15.4 mSv, detected for a cleaner and a technician, respectively. The maximum estimated effective dose corresponds to 32% of the annual background dose in Poland, and to circa 4% of the annual limit for the effective dose due to occupational exposure of 20 mSv per year, which is in compliance with the value recommended by the International Commission on Radiological Protection.

Assessing doses to interventional radiologists using a personal dosimeter worn over a protective apron.

PubMed

Stranden, E; Widmark, A; Sekse, T

2008-05-01

Interventional radiologists receive significant radiation doses, and it is important to have simple methods for routine monitoring of their exposure. To evaluate the usefulness of a dosimeter worn outside the protective apron for assessments of dose to interventional radiologists. Assessments of effective dose versus dose to dosimeters worn outside the protective apron were achieved by phantom measurements. Doses outside and under the apron were assessed by phantom measurements and measurements on eight radiologists wearing two routine dosimeters for a 2-month period during ordinary working conditions. Finger doses for the same radiologists were recorded using thermoluminescent dosimeters (TLD; DXT-RAD Extremity dosimeters). Typical values for the ratio between effective dose and dosimeter dose were found to be about 0.02 when the radiologist used a thyroid shield and about 0.03 without. The ratio between the dose to the dosimeter under and outside a protective apron was found to be less than 0.04. There was very good correlation between finger dose and dosimeter dose. A personal dosimeter worn outside a protective apron is a good screening device for dose to the eyes and fingers as well as for effective dose, even though the effective dose is grossly overestimated. Relatively high dose to the fingers and eyes remains undetected by a dosimeter worn under the apron.

SU-E-T-607: Performance Quantification of the Nine Detectors Used for Dosimetry Measurements in Advanced Radiation Therapy Treatments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Markovic, M; Stathakis, S; Jurkovic, I

2015-06-15

Purpose: The purpose of this study was to quantify performance of the nine detectors used for dosimetry measurements in advanced radiation therapy treatments. Methods: The 6 MV beam was utilized for measurements of the field sizes with the lack of lateral charge particle equilibrium. For dose fidelity aspect, energy dependence was studied by measuring PDD and profiles at different depths. The volume effect and its influence on the measured dose profiles have been observed by measuring detector’s response function. Output factor measurements with respect to change in energy spectrum have been performed and collected data has been analyzed. The linearitymore » of the measurements with the dose delivered has been evaluated and relevant comparisons were done. Results: The measured values of the output factors with respect to change in energy spectrum indicated presence of the energy dependence. The detectors with active volume size ≤ 0.3 mm3 maximum deviation from the mean is 5.6% for the field size 0.5 x 0.5 cm2 while detectors with active volume size > 0.3 mm3 have maximum deviation from the mean 7.1%. Linearity with dose at highest dose rate examined for diode detectors showed maximum deviation of 4% while ion chambers showed maximum deviation of 2.2%. Dose profiles showed energy dependence at shallow depths (surface to dmax) influenced by low energy particles with 12 % maximum deviation from the mean for 5 mm2 field size. In relation to Monte Carlo calculation, the detector’s response function σ values were between (0.42±0.25) mm and (1.2±0.25) mm. Conclusion: All the detectors are appropriate for the dosimetry measurements in advanced radiation therapy treatments. The choice of the detectors has to be determined by the application and the scope of the measurements in respect to energy dependence and ability to accurately resolve dose profiles as well as to it’s intrinsic characteristics.« less

Vitamin A status of Filipino preschool children given a massive oral dose.

PubMed

Perlas, L A; Florentino, R F; Fuertes, R T; Madriaga, J R; Cheong, R L; Desnacido, J A; Marcos, J M; Cabrera, M I

1996-12-01

The protection period of a 200,000 IU of vitamin A on Filipino children was determined. Subjects were 105 children aged 1-5 years given a single massive dose during the "Araw ng Sangkap Pinoy" (ASAP) in March 1995. Serum retinol was measured by HPLC at baseline, one, two, four and six months after the administration of the dose. Results showed that baseline serum retinol levels were significantly lower than all follow-up values. Serum retinol values were maintained at levels higher than pre-supplementation values although the values decreased on the second month after supplementation. The proportions of deficient and low (< 20 microg/dl) levels were significantly lower one and six months after supplementation. All follow-up serum retinol levels of children with deficient and low values at baseline were significantly lower (p < 0.001) than those with normal values. The WHO recommendation of 200,000 IU was effective in increasing serum retinol concentrations and maintaining it above pre-supplementation levels up to 6 months after administration of the dose. It also replenished organic vitamin A reserves as shown by the dose response (S30DR) approach. Incidence of infection also decreased among the children. Supplementation with vitamin A has likewise resulted in an increase in hemoglobin values and a decrease in the proportion of anemics (Hb < 11.0 g/dl) among the children.

Measurement of the natural radioactivity in building materials used in Ankara and assessment of external doses.

PubMed

Turhan, S; Baykan, U N; Sen, K

2008-03-01

A total of 183 samples of 20 different commonly used structural and covering building materials were collected from housing and other building construction sites and from suppliers in Ankara to measure the natural radioactivity due to the presence of (226)Ra, (232)Th and (40)K. The measurements were carried out using gamma-ray spectrometry with two HPGe detectors. The specific activities of the different building materials studied varied from 0.5 +/- 0.1 to 144.9 +/- 4.9 Bq kg(-1), 0.6 +/- 0.2 to 169.9 +/- 6.6 Bq kg(-1) and 2.0 +/- 0.1 to 1792.3 +/- 60.8 Bq kg(-1) for (226)Ra, (232)Th and (40)K, respectively. The results show that the lowest mean values of the specific activity of (226)Ra, (232)Th and (40)K are 0.8 +/- 0.5, 0.9 +/- 0.4 and 4.1 +/- 1.4 Bq kg(-1), respectively, measured in travertine tile while the highest mean values of the specific activity of the same radionuclides are 78.5 +/- 18.1 (ceramic wall tile), 77.4 +/- 53.0 (granite tile) and 923.4 +/- 161.0 (white brick), respectively. The radium equivalent activity (Ra(eq)), the gamma-index, the indoor absorbed dose rate and the corresponding annual effective dose were evaluated to assess the potential radiological hazard associated with these building materials. The mean values of the gamma-index and the estimated annual effective dose due to external gamma radiation inside the room for structural building materials ranged from 0.15 to 0.89 and 0.2 to 1.1 mSv, respectively. Applying criteria recently recommended for building materials in the literature, four materials meet the exemption annual dose criterion of 0.3 mSv, five materials meet the annual dose limit of 1 mSv and only one material slightly exceeds this limit. The mean values of the gamma-index for all building materials were lower than the upper limit of 1.

Occupational radiation exposure in nuclear medicine department in Kuwait

NASA Astrophysics Data System (ADS)

Alnaaimi, M.; Alkhorayef, M.; Omar, M.; Abughaith, N.; Alduaij, M.; Salahudin, T.; Alkandri, F.; Sulieman, A.; Bradley, D. A.

2017-11-01

Ionizing radiation exposure is associated with eye lens opacities and cataracts. Radiation workers with heavy workloads and poor protection measures are at risk for vision impairment or cataracts if suitable protection measures are not implemented. The aim of this study was to measure and evaluate the occupational radiation exposure in a nuclear medicine (NM) department. The annual average effective doses (Hp[10] and Hp[0.07]) were measured using calibrated thermos-luminescent dosimeters (TLDs; MCP-N [LiF:Mg,Cu,P]). Five categories of staff (hot lab staff, PET physicians, NM physicians, technologists, and nurses) were included. The average annual eye dose (Hp[3]) for NM staff, based on measurements for a typical yearly workload of >7000 patients, was 4.5 mSv. The annual whole body radiation (Hp[10]) and skin doses (Hp[0.07]) were 4.0 and 120 mSv, respectively. The measured Hp(3), Hp(10), and Hp(0.07) doses for all NM staff categories were below the dose limits described in ICRP 2014 in light of the current practice. The results provide baseline data for staff exposure in NM in Kuwait. Radiation dose optimization measures are recommended to reduce NM staff exposure to its minimal value.

Assessment of dose and DNA damages in individuals exposed to low dose and low dose rate ionizing radiations during computed tomography imaging.

PubMed

Kanagaraj, Karthik; Abdul Syed Basheerudeen, Safa; Tamizh Selvan, G; Jose, M T; Ozhimuthu, Annalakshmi; Panneer Selvam, S; Pattan, Sudha; Perumal, Venkatachalam

2015-08-01

Computed tomography (CT) is a frequently used imaging modality that contributes to a tenfold increase in radiation exposure to the public when compared to other medical imaging modalities. The use of radiation for therapeutic need is always rationalized on the basis of risk versus benefit thereby increasing concerns on the dose received by patients undergoing CT imaging. Therefore, it was of interest to us to investigate the effects of low dose and low dose-rate X-irradiation in patients who underwent CT imaging by recording the doses received by the eye, forehead and thyroid, and to study the levels of damages in the lymphocytes in vivo. Lithium manganese borate doped with terbium (LMB:Tb) thermo luminescence dosimeters (TLD) were used to record the doses in the patient's (n = 27) eye, forehead, and thyroid and compared with the dose length product (DLP) values. The in vivo DNA damages measured were compared before and after CT imaging using chromosomal aberration (CA) and micronucleus (MN) assays. The overall measured organ dose ranged between 2 ± 0.29 and 520 ± 41.63 mGy for the eye, 0.84 ± 0.29 and 210 ± 20.50 mGy for the forehead, and 1.79 ± 0.43 and 185 ± 0.70 mGy for the thyroid. The in vivo damages measured from the blood lymphocytes of the subjects showed an extremely significant (p < 0.0001) increase in CA frequency and significant (p < 0.001) increase in MN frequency after exposure, compared to before exposure. The results suggest that CT imaging delivers a considerable amount of radiation dose to the eye, forehead, and thyroid, and the observed increase in the CA and MN frequencies show low dose radiation effects calling for protective regulatory measures to increase patient's safety. This study is the first attempt to indicate the trend of doses received by the patient's eye, forehead and thyroid and measured directly in contrast to earlier values obtained by extrapolation from phantoms, and to assess the in vivo low dose effects in an Indian patient population undergoing CT procedures. Copyright © 2015 Elsevier B.V. All rights reserved.

Dexmedetomidine reduces pain associated with rocuronium injection without causing a decrease in BIS values: a dose-response study.

PubMed

Joo, Jin; Baek, Jungwon; Lee, Jaemin

2014-09-01

To examine whether dexmedetomidine reduces the injection pain of propofol and rocuronium and to investigate whether the decrease in injection pain is associated with the known sedative action of dexmedetomidine. Randomized, double-blind, placebo-controlled clinical comparison study. Patients undergoing general anesthesia with intubation received 40 mg of 1% lidocaine (lidocaine group; n = 28), 0.25 μg/kg of dexmedetomidine (low-dose group; n = 27), 0.5 μg/kg of dexmedetomidine (subclinical dose group; n = 28), 1.0 μg/kg of dexmedetomidine (clinical dose group, n = 27), or normal saline (saline group; n = 28) before anesthetic induction. Pain associated with propofol and rocuronium injection was assessed using a 10-point verbal analog scale (VAS) and a 4-point withdrawal movement scale, respectively. The BIS value was measured 60 seconds after administration of the study drug, and at the time of rocuronium injection and intubation. The overall incidence of withdrawal movements due to rocuronium decreased significantly as the dose of dexmedetomidine increased (92.8%, 85.2%, 78.6%, and 51.9% in the saline, low-dose, subclinical dose, and clinical dose groups, respectively; P = 0.001). There was no significant difference in BIS values among the groups 60 seconds after study drug administration or at the time of rocuronium injection. Dexmedetomidine reduced pain associated with rocuronium injection in a dose-dependent manner. This effect was not associated with the decrease in BIS value. Copyright © 2014 Elsevier Inc. All rights reserved.

Nuclear emulsion measurements of the dose contribution from tissue disintegration stars on the Apollo-Soyuz mission

NASA Technical Reports Server (NTRS)

Schaefer, H. J.

1977-01-01

A total of 996 disintegration stars were prong-counted in two 100 micron llford K.2 emulsions from the dosimeter of the Docking Pilot on Apollo-Soyuz. The change of slope of the distribution at a prong number of about 6 or 7 indicates 219 stars as originating in gelatin. Applying the QF values set forth in official regulations to the energy spectra of the proton and a alpha prongs of the gelatin stars leads to a tissue star dose of 7.8 millirad or 45 millirem. The quoted values do not include the dose contribution from star-produced neutrons since neutrons do not leave visible prongs in emulsion. Nuclear theory, in good agreement with measurements of galactic radiation in the earth's atmosphere, indicates that the dose equivalent from neutrons is about equal to the one from all ionizing secondaries of stars. Application of this proposition to the star prong spectrum found on Apollo-Soyuz would set the total tissue star dose for the mission at approximately 90 millirem.

SU-E-T-643: Pure Alanine Dosimeter for Verification Dosimetry in IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Karmi, Anan M.; Zraiqat, Fadi

Purpose: The objective of this study was evaluation of accuracy of pure alanine dosimeters measuring intensity-modulated radiation therapy (IMRT) dose distributions in a thorax phantom. Methods: Alanine dosimeters were prepared in the form of 110 mg pure L-α-alanine powder filled into clear tissue-equivalent polymethylmethacrylate (PMMA) plastic tubes with the dimensions 25 mm length, 3 mm inner diameter, and 1 mm wall thickness. A dose-response calibration curve was established for the alanine by placing the dosimeters at 1.5 cm depth in a 30×30×30 cm{sup 3} solid water phantom and then irradiating on a linac with 6 MV photon beam at 10×10more » cm{sup 2} field size to doses ranging from 1 to 5 Gy. Electron paramagnetic resonance (EPR) spectroscopy was used to determine the absorbed dose in alanine. An IMRT treatment plan was designed for a commercial heterogeneous CIRS thorax phantom and the dose values were calculated at three different points located in tissue, lung, and bone equivalent materials. A set of dose measurements was carried out to compare measured and calculated dose values by placing the alanine dosimeters at those selected locations inside the thorax phantom and delivering the IMRT to the phantom. Results: The alanine dose measurements and the IMRT plan dose calculations were found to be in agreement within ±2%. Specifically, the deviations were −0.5%, 1.3%, and −1.7% for tissue, lung, and bone; respectively. The slightly large deviations observed for lung and bone may be attributed to tissue inhomogeneity, steep dose gradients in these regions, and uncontrollable changes in spectrometer conditions. Conclusion: The results described herein confirmed that pure alanine dosimeter was suitable for in-phantom dosimetry of IMRT beams because of its high sensitivity and acceptable accuracy. This makes the dosimeter a promising option for quality control of the therapeutic beams, complementing the commonly used ionization chambers, TLDs, and films.« less

Study on the Dose Uncertainties in the Lung during Passive Proton Irradiation with a Proton Beam Range Compensator

NASA Astrophysics Data System (ADS)

Yoo, Seung Hoon; Son, Jae Man; Yoon, Myonggeun; Park, Sung Yong; Shin, Dongho; Min, Byung Jun

2018-06-01

A moving phantom is manufactured for mimicking lung model to study the dose uncertainty from CT number-stopping power conversion and dose calculation in the soft tissue, light lung tissue and bone regions during passive proton irradiation with compensator smearing value. The phantom is scanned with a CT system, and a proton beam irradiation plan is carried out with the use of a treatment planning system (Eclipse). In the case of the moving phantom, a RPM system is used for respiratory gating. The uncertainties in the dose distribution between the measured data and the planned data are investigated by a gamma analysis with 3%-3 mm acceptance criteria. To investigate smearing effect, three smearing values (0.3 cm, 0.7 cm, 1.2 cm) are used to for fixed and moving phantom system. For both fixed and moving phantom, uncertainties in the light lung tissue are severe than those in soft tissue region in which the dose uncertainties are within clinically tolerable ranges. As the smearing value increases, the uncertainty in the proton dose distribution decreases.

UVER and UV index at high altitude in Northwestern Argentina.

PubMed

Utrillas, M P; Marín, M J; Esteve, A R; Salazar, G; Suarez, H; Castillo, J; Martínez-Lozano, J A

2016-10-01

Measurements of ultraviolet erythemal radiation (UVER) made during two years at three sites located at altitudes over 1000ma.s.l. in Northwestern Argentina (Salta, San Carlos, and El Rosal) have been used to estimate and analyze the UV Index (UVI) and the cumulative doses at these locations. For the UVER irradiance, data of January (maximum values) and June (minimum values) have been analyzed as representative of the year for all locations. The UVI reaches extreme (>11) values in >20% of the analyzed days in Salta (1190ma.s.l.), while these are reached in San Carlos (1611ma.s.l.) and El Rosal (3355ma.s.l.) in >40% of the analyzed days. Finally, the cumulative doses over an average year have also been studied for each location. The doses received during austral summer and autumn are of the same order, and represent one third of the annual dose, while the doses received during austral winter and spring represent one sixth of the annual dose approximately. Copyright © 2016 Elsevier B.V. All rights reserved.

In vivo skin dose measurement in breast conformal radiotherapy.

PubMed

Soleymanifard, Shokouhozaman; Aledavood, Seyed Amir; Noghreiyan, Atefeh Vejdani; Ghorbani, Mahdi; Jamali, Farideh; Davenport, David

2016-01-01

Accurate skin dose assessment is necessary during breast radiotherapy to assure that the skin dose is below the tolerance level and is sufficient to prevent tumour recurrence. The aim of the current study is to measure the skin dose and to evaluate the geometrical/anatomical parameters that affect it. Forty patients were simulated by TIGRT treatment planning system and treated with two tangential fields of 6 MV photon beam. Wedge filters were used to homogenise dose distribution for 11 patients. Skin dose was measured by thermoluminescent dosimeters (TLD-100) and the effects of beam incident angle, thickness of irradiated region, and beam entry separation on the skin dose were analysed. Average skin dose in treatment course of 50 Gy to the clinical target volume (CTV) was 36.65 Gy. The corresponding dose values for patients who were treated with and without wedge filter were 35.65 and 37.20 Gy, respectively. It was determined that the beam angle affected the average skin dose while the thickness of the irradiated region and the beam entry separation did not affect dose. Since the skin dose measured in this study was lower than the amount required to prevent tumour recurrence, application of bolus material in part of the treatment course is suggested for post-mastectomy advanced breast radiotherapy. It is more important when wedge filters are applied to homogenize dose distribution.

SU-F-T-300: Impact of Electron Density Modeling of ArcCHECK Cylindricaldiode Array On 3DVH Patient Specific QA Software Tool Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patwe, P; Mhatre, V; Dandekar, P

Purpose: 3DVH software is a patient specific quality assurance tool which estimates the 3D dose to the patient specific geometry with the help of Planned Dose Perturbation algorithm. The purpose of this study is to evaluate the impact of HU value of ArcCHECK phantom entered in Eclipse TPS on 3D dose & DVH QA analysis. Methods: Manufacturer of ArcCHECK phantom provides CT data set of phantom & recommends considering it as a homogeneous phantom with electron density (1.19 gm/cc or 282 HU) close to PMMA. We performed this study on Eclipse TPS (V13, VMS) & trueBEAM STx VMS Linac &more » ArcCHECK phantom (SNC). Plans were generated for 6MV photon beam, 20cm×20cm field size at isocentre & SPD (Source to phantom distance) of 86.7 cm to deliver 100cGy at isocentre. 3DVH software requires patients DICOM data generated by TPS & plan delivered on ArcCHECK phantom. Plans were generated in TPS by assigning different HU values to phantom. We analyzed gamma index & the dose profile for all plans along vertical down direction of beam’s central axis for Entry, Exit & Isocentre dose. Results: The global gamma passing rate (2% & 2mm) for manufacturer recommended HU value 282 was 96.3%. Detector entry, Isocentre & detector exit Doses were 1.9048 (1.9270), 1.00(1.0199) & 0.5078(0.527) Gy for TPS (Measured) respectively.The global gamma passing rate for electron density 1.1302 gm/cc was 98.6%. Detector entry, Isocentre & detector exit Doses were 1.8714 (1.8873), 1.00(0.9988) & 0.5211(0.516) Gy for TPS (Measured) respectively. Conclusion: Electron density value assigned by manufacturer does not hold true for every user. Proper modeling of electron density of ArcCHECK in TPS is essential to avoid systematic error in dose calculation of patient specific QA.« less

Predicting terrestrial gamma dose rate based on geological and soil information: case study of Perak state, Malaysia.

PubMed

Ramli, A T; Apriantoro, N H; Heryansyah, A; Basri, N A; Sanusi, M S M; Abu Hanifah, N Z H

2016-03-01

An extensive terrestrial gamma radiation dose (TGRD) rate survey has been conducted in Perak State, Peninsular Malaysia. The survey has been carried out taking into account geological and soil information, involving 2930 in situ surveys. Based on geological and soil information collected during TGRD rate measurements, TGRD rates have been predicted in Perak State using a statistical regression analysis which would be helpful to focus surveys in areas that are difficult to access. An equation was formulated according to a linear relationship between TGRD rates, geological contexts and soil types. The comparison of in situ measurements and predicted TGRD dose rates was tabulated and showed good agreement with the linear regression equation. The TGRD rates in the study area ranged from 38 nGy h(-1) to 1039 nGy h(-1) with a mean value of 224  ±  138 nGy h(-1). This value is higher than the world average as reported in UNSCEAR 2000. The TGRD rates contribute an average dose rate of 1.37 mSv per year. An isodose map for the study area was developed using a Kriging method based on predicted and in situ TGRD rate values.

Dosimetric changes with computed tomography automatic tube-current modulation techniques.

PubMed

Spampinato, Sofia; Gueli, Anna Maria; Milone, Pietro; Raffaele, Luigi Angelo

2018-04-06

The study is aimed at a verification of dose changes for a computed tomography automatic tube-current modulation (ATCM) technique. For this purpose, anthropomorphic phantom and Gafchromic ® XR-QA2 films were used. Radiochromic films were cut according to the shape of two thorax regions. The ATCM algorithm is based on noise index (NI) and three exam protocols with different NI were chosen, of which one was a reference. Results were compared with dose values displayed by the console and with Poisson statistics. The information obtained with radiochromic films has been normalized with respect to the NI reference value to compare dose percentage variations. Results showed that, on average, the information reported by the CT console and calculated values coincide with measurements. The study allowed verification of the dose information reported by the CT console for an ATCM technique. Although this evaluation represents an estimate, the method can be a starting point for further studies.

[ESTIMATION OF IONIZING RADIATION EFFECTIVE DOSES IN THE INTERNATIONAL SPACE STATION CREWS BY THE METHOD OF CALCULATION MODELING].

PubMed

Mitrikas, V G

2015-01-01

Monitoring of the radiation loading on cosmonauts requires calculation of absorbed dose dynamics with regard to the stay of cosmonauts in specific compartments of the space vehicle that differ in shielding properties and lack means of radiation measurement. The paper discusses different aspects of calculation modeling of radiation effects on human body organs and tissues and reviews the effective dose estimates for cosmonauts working in one or another compartment over the previous period of the International space station operation. It was demonstrated that doses measured by a real or personal dosimeters can be used to calculate effective dose values. Correct estimation of accumulated effective dose can be ensured by consideration for time course of the space radiation quality factor.

SU-E-I-57: Estimating the Occupational Eye Lens Dose in Interventional Radiology Using Active Personal Dosimeters Worn On the Chest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Omar, A; Marteinsdottir, M; Kadesjo, N

Purpose: To provide a general formalism for determination of occupational eye lens dose based on the response of an active personal dosimeter (APD) worn at chest level above the radiation protection apron. Methods: The formalism consists of three factors: (1) APD conversion factor converting the reading at chest level (APDchest) to the corresponding personal dose equivalent at eye level, (2) Dose conversion factor transferring the measured dose quantity, Hp(10), into a dose quantity relevant for the eye lens dose, (3) Correction factor accounting for differences in exposure of the eye(s) compared to the exposure at chest level (e.g., due tomore » protective lead glasses).The different factors were investigated and evaluated based on phantom and clinical measurements performed in an x-ray angiography suite for interventional cardiology. Results: The eye lens dose can be conservatively estimated by assigning an appropriate numerical value to each factor entering the formalism that in most circumstances overestimates the dose. Doing so, the eye lens dose to the primary operator and assisting staff was estimated in this work as D-eye,primary = 2.0 APDchest and D-eye,assisting = 1.0 APDchest, respectively.The annual eye lens dose to three nurses and one cardiologist was estimated to be 2, 2, 2, and 13 mSv (Hp(0.07)), respectively, using a TLD dosimeter worn at eye level. In comparison, using the formalism and APDchest measurements, the respective doses were 2, 2, 2, and 16 mSv (Hp(3)). Conclusion: The formalism outlined in this work can be used to estimate the occupational eye lens dose from the response of an APD worn on the chest. The formalism is general and could be applied also to other types of dosimeters. However, the numerical value of the different factors may differ from those obtained with the APD’s used in this work due to differences in dosimeter properties.« less

Preclinical dose number and its application in understanding drug absorption risk and formulation design for preclinical species.

PubMed

Wuelfing, W Peter; Daublain, Pierre; Kesisoglou, Filippos; Templeton, Allen; McGregor, Caroline

2015-04-06

In the drug discovery setting, the ability to rapidly identify drug absorption risk in preclinical species at high doses from easily measured physical properties is desired. This is due to the large number of molecules being evaluated and their high attrition rate, which make resource-intensive in vitro and in silico evaluation unattractive. High-dose in vivo data from rat, dog, and monkey are analyzed here, using a preclinical dose number (PDo) concept based on the dose number described by Amidon and other authors (Pharm. Res., 1993, 10, 264-270). PDo, as described in this article, is simply calculated as dose (mg/kg) divided by compound solubility in FaSSIF (mg/mL) and approximates the volume of biorelevant media per kilogram of animal that would be needed to fully dissolve the dose. High PDo values were found to be predictive of difficulty in achieving drug exposure (AUC)-dose proportionality in in vivo studies, as could be expected; however, this work analyzes a large data set (>900 data points) and provides quantitative guidance to identify drug absorption risk in preclinical species based on a single solubility measurement commonly carried out in drug discovery. Above the PDo values defined, >50% of all in vivo studies exhibited poor AUC-dose proportionality in rat, dog, and monkey, and these values can be utilized as general guidelines in discovery and early development to rapidly assess risk of solubility-limited absorption for a given compound. A preclinical dose number generated by biorelevant dilutions of formulated compounds (formulated PDo) was also evaluated and defines solubility targets predictive of suitable AUC-dose proportionality in formulation development efforts. Application of these guidelines can serve to efficiently identify compounds in discovery that are likely to present extreme challenges with respect to solubility-limited absorption in preclinical species as well as reduce the testing of poor formulations in vivo, which is a key ethical and resource matter.

SU-F-T-322: A Comparison of Two Si Detectors for in Vivo Dosimetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Talarico, O; Krylova, T; Lebedenko, I

Purpose: To compare two types of semiconductor detectors for in vivo dosimetry by their dependence from various parameters in different conditions. Methods: QED yellow (Sun Nuclear) and EDP (Scanditronix) Si detectors were radiated by a Varian Clinac 2300 ix with 6 and 18 MV energies. 10 cm thickness water equivalent phantom consisted of 30×30 cm{sup 2} squared plates was used for experiments. Dose dependencies for different beam angles (0 – 180°), field size (3–40 cm), dose (50 – 300 MU), and dose rates (50 – 300 MU/min) were obtained and calibrated with Standard Farmer chamber (PTW). Results: Reproducibility, linearity, dosemore » rate, angular dependence, and field size dependence were obtained for QED and EDP. They show no dose-rate dependence in available clinical dose rate range (100–600 MU/min). Both diodes have linear dependence with increasing the dose. Therefore even in case of high radiation therapy (including total body irradiation) it is not necessary to apply an additional correction during in vivo dosimetry. The diodes have different behavior for angular and field size dependencies. QED diode showed that dose value is stable for beam angles from 0 to 60°, for 60–180° correction factor has to be applied for each beam angle during in vivo measurements. For EDP diode dose value is sensitive to beam angle in whole range of angles. Conclusion: The study shows that QED diode is more suitable for in vivo dosimetry due to dose value independence from incident beam angle in the range 0–60°. There is no need in correction factors for increasing of dose and dose rate for both diodes. The next step will be to carry out measurements in non-standard conditions of total body irradiation. After this modeling of these experiments with Monte Carlo simulation for comparison calculated and obtained data is planned.« less

Evaluation of dose-area product of common radiographic examinations towards establishing a preliminary diagnostic reference levels (PDRLs) in Southwestern Nigeria.

PubMed

Jibiri, Nnamdi N; Olowookere, Christopher J

2016-11-08

In Nigeria, a large number of radiographic examinations are conducted yearly for various diagnostic purposes. However, most examinations carried out do not have records of doses received by the patients, and the employed exposure parameters used are not documented; therefore, adequate radiation dose management is hin-dered. The aim of the present study was to estimate the dose-area product (DAP) of patients examined in Nigeria, and to propose regional reference dose levels for nine common examinations (chest PA, abdomen AP, pelvis AP, lumbar AP, skull AP, leg AP, knee AP, hand AP, and thigh AP) undertaken in Nigeria. Measurement of entrance surface dose (ESD) was carried out using thermoluminescent dosimeter (TLD). Measured ESDS were converted into DAP using the beam area of patients in 12 purposely selected hospitals. Results of the study show that the maximum/ minimum ratio ranged from 3 for thigh AP to 57 in abdomen AP. The range of determined mean and 75th percentile DAPs were 0.18-17.16, and 0.25-28.59 Gy cm2, respectively. Data available for comparison show that 75th percentile DAPs in this study (in chest PA, abdomen AP, pelvis AP, lumbar AP) are higher than NRPB-HPE reference values. The DAP in this study is higher by factor of 31.4 (chest PA), 9.9 (abdomen AP), 2.2 (pelvis AP), and 2.1 (lumbar AP) than NRPB-HPE values. The relative higher dose found in this study shows nonoptimization of practice in Nigeria. It is expected that regular dose auditing and dose optimization implementation in Nigeria would lead to lower DAP value, especially in abdomen AP. The 75th percentile DAP distribution reported in this study could be taken as regional diagnostic reference level in the Southwestern Nigeria; however, a more extensive nationwide dose survey is required to establish national reference dose. © 2016 The Authors.

An evaluation of some pertinent parameters that influence the dosimetric performance of synthetic diamond detectors

NASA Astrophysics Data System (ADS)

Ade, N.; Nam, T. L.; Mhlanga, S. H.

2013-05-01

Although the near-tissue equivalence of diamond allows the direct measurement of dose for clinical applications without the need for energy-corrections, it is often cited that diamond detectors require pre-irradiation, a procedure necessary to stabilize the response or sensitivity of a diamond detector before dose measurements. In addition it has been pointed out that the relative dose measured with a diamond detector requires dose rate dependence correction and that the angular dependence of a detector could be due to its mechanical design or to the intrinsic angular sensitivity of the detection process. While the cause of instability of response has not been meticulously investigated, the issue of dose rate dependence correction is uncertain as some studies ignored it but reported good results. The aims of this study were therefore to investigate, in particular (1) the major cause of the unstable response of diamond detectors requiring pre-irradiation; (2) the influence of dose rate dependence correction in relative dose measurements; and (3) the angular dependence of the diamond detectors. The study was conducted with low-energy X-rays and electron therapy beams on HPHT and CVD synthesized diamonds. Ionization chambers were used for comparative measurements. Through systematic investigations, the major cause of the unstable response of diamond detectors requiring the recommended pre-irradiation step was isolated and attributed to the presence and effects of ambient light. The variation in detector's response between measurements in light and dark conditions could be as high as 63% for a CVD diamond. Dose rate dependence parameters (Δ values) of 0.950 and 1.035 were found for the HPHT and CVD diamond detectors, respectively. Without corrections based on dose rate dependence, the relative differences between depth-doses measured with the diamond detectors and a Markus chamber for exposures to 7 and 14 MeV electron beams were within 2.5%. A dose rate dependence correction using the Δ values obtained seemed to worsen the performance of the HPHT sample (up to about 3.3%) but it had a marginal effect on the performance of the CVD sample. In addition, the angular response of the CVD diamond detector was shown to be comparable with that of a cylindrical chamber. This study concludes that once the responses of the diamond detectors have been stabilised and they are properly shielded from ambient light, pre-irradiation prior to each measurement is not required. Also, the relative dose measured with the diamond detectors do not require dose rate dependence corrections as the required correction is only marginal and could have no dosimetric significance.

Initial experience of ArcCHECK and 3DVH software for RapidArc treatment plan verification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Infusino, Erminia; Mameli, Alessandra, E-mail: e.infusino@unicampus.it; Conti, Roberto

2014-10-01

The purpose of this study was to perform delivery quality assurance with ArcCHECK and 3DVH system (Sun Nuclear, FL) and to evaluate the suitability of this system for volumetric-modulated arc therapy (VMAT) (RapidArc [RA]) verification. This software calculates the delivered dose distributions in patients by perturbing the calculated dose using errors detected in fluence or planar dose measurements. The device is tested to correlate the gamma passing rate (%GP) and the composite dose predicted by 3DVH software. A total of 28 patients with prostate cancer who were treated with RA were analyzed. RA treatments were delivered to a diode arraymore » phantom (ArcCHECK), which was used to create a planned dose perturbation (PDP) file. The 3DVH analysis used the dose differences derived from comparing the measured dose with the treatment planning system (TPS)-calculated doses to perturb the initial TPS-calculated dose. The 3DVH then overlays the resultant dose on the patient's structures using the resultant “PDP” beams. Measured dose distributions were compared with the calculated ones using the gamma index (GI) method by applying the global (Van Dyk) normalization and acceptance criteria, i.e., 3%/3 mm. Paired differences tests were used to estimate statistical significance of the differences between the composite dose calculated using 3DVH and %GP. Also, statistical correlation by means of logistic regression analysis has been analyzed. Dose-volume histogram (DVH) analysis for patient plans revealed small differences between treatment plan calculations and 3DVH results for organ at risk (OAR), whereas planning target volume (PTV) of the measured plan was systematically higher than that predicted by the TPS. The t-test results between the planned and the estimated DVH values showed that mean values were incomparable (p < 0.05). The quality assurance (QA) gamma analysis 3%/3 mm showed that in all cases there were only weak-to-moderate correlations (Pearson r: 0.12 to 0.74). Moreover, clinically relevant differences increased with increasing QA passing rate, indicating that some of the largest dose differences occurred in the cases of high QA passing rates, which may be called “false negatives.” The clinical importance of any disagreement between the measured and the calculated dose is often difficult to interpret; however, beam errors (either in delivery or in TPS calculation) can affect the effectiveness of the patient dose. Further research is needed to determinate the role of a PDP-type algorithm to accurately estimate patient dose effect.« less

A novel method for the evaluation of uncertainty in dose-volume histogram computation.

PubMed

Henríquez, Francisco Cutanda; Castrillón, Silvia Vargas

2008-03-15

Dose-volume histograms (DVHs) are a useful tool in state-of-the-art radiotherapy treatment planning, and it is essential to recognize their limitations. Even after a specific dose-calculation model is optimized, dose distributions computed by using treatment-planning systems are affected by several sources of uncertainty, such as algorithm limitations, measurement uncertainty in the data used to model the beam, and residual differences between measured and computed dose. This report presents a novel method to take them into account. To take into account the effect of associated uncertainties, a probabilistic approach using a new kind of histogram, a dose-expected volume histogram, is introduced. The expected value of the volume in the region of interest receiving an absorbed dose equal to or greater than a certain value is found by using the probability distribution of the dose at each point. A rectangular probability distribution is assumed for this point dose, and a formulation that accounts for uncertainties associated with point dose is presented for practical computations. This method is applied to a set of DVHs for different regions of interest, including 6 brain patients, 8 lung patients, 8 pelvis patients, and 6 prostate patients planned for intensity-modulated radiation therapy. Results show a greater effect on planning target volume coverage than in organs at risk. In cases of steep DVH gradients, such as planning target volumes, this new method shows the largest differences with the corresponding DVH; thus, the effect of the uncertainty is larger.

A Comparison of Four Indices for Combining Distance and Dose Differences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, Simon J., E-mail: simon.thomas@addenbrookes.nhs.uk; Cowley, Ian R.

2012-04-01

Purpose: When one is comparing two dose distributions, a number of methods have been published to combine dose difference and distance to agreement into a single measure. Some have been defined as pass/fail indices and some as numeric indices. We show that the pass/fail indices can all be used to derive numeric indices, and we compare the results of using these indices to evaluate one-dimensional (1D) and three-dimensional (3D) dose distributions, with the aim of selecting the most appropriate index for use in different circumstances. Methods and Materials: The indices compared are the gamma index, the kappa index, the indexmore » in International Commission on Radiation Units and Measurements Report 83, and a box index. Comparisons are made for 1D and 3D distributions. The 1D distribution is chosen to have a variety of dose gradients. The 3D distribution is taken from a clinical treatment plan. The effect of offsetting distributions by known distances and doses is studied. Results: The International Commission on Radiation Units and Measurements Report 83 index causes large discontinuities unless the dose gradient cutoff is set to equal the ratio of the dose tolerance to the distance tolerance. If it is so set, it returns identical results to the kappa index. Where the gradient is very high or very low, all the indices studied in this article give similar results for the same tolerance values. For moderate gradients, they differ, with the box index being the least strict, followed by the gamma index, and with the kappa index being the most strict. Conclusions: If the clinical tolerances are much greater than the uncertainties of the measuring system, the kappa index should be used, with tolerance values determined by the clinical tolerances. In cases where the uncertainties of the measuring system dominate, the box index will be best able to determine errors in the delivery system.« less

A simplified approach for exit dose in vivo measurements in radiotherapy and its clinical application.

PubMed

Banjade, D P; Shrestha, S L; Shukri, A; Tajuddin, A A; Bhat, M

2002-09-01

This is a study using LiF:Mg;Ti thermoluminescent dosimeter (TLD) rods in phantoms to investigate the effect of lack of backscatter on exit dose. Comparing the measured dose with anticipated dose calculated using tissue maximum ratio (TMR) or percentage depth dose (PDD) gives rise to a correction factor. This correction factor may be applied to in-vivo dosimetry results to derive true dose to a point within the patient. Measurements in a specially designed humanoid breast phantom as well as patients undergoing radiotherapy treatment were also been done. TLDs with reproducibility of within +/- 3% (1 SD) are irradiated in a series of measurements for 6 and 10 MV photon beams from a medical linear accelerator. The measured exit doses for the different phantom thickness for 6 MV beams are found to be lowered by 10.9 to 14.0% compared to the dose derived from theoretical estimation (normalized dose at dmax). The same measurements for 10 MV beams are lowered by 9.0 to 13.5%. The variations of measured exit dose for different field sizes are found to be within 2.5%. The exit doses with added backscatter material from 2 mm up to 15 cm, shows gradual increase and the saturated values agreed within 1.5% with the expected results for both beams. The measured exit doses in humanoid breast phantom as well as in the clinical trial on patients undergoing radiotherapy also agreed with the predicted results based on phantom measurements. The authors' viewpoint is that this technique provides sufficient information to design exit surface bolus to restore build down effect in cases where part of the exit surface is being considered as a target volume. It indicates that the technique could be translated for in vivo dose measurements, which may be a conspicuous step of quality assurance in clinical practice.

Assessment of an organ‐based tube current modulation in thoracic computed tomography

PubMed Central

Sugai, Mai; Toyoda, Asami; Koshida, Haruka; Sakuta, Keita; Takata, Tadanori; Koshida, Kichiro; Iida, Hiroji; Matsui, Osamu

2012-01-01

Recently, specific computed tomography (CT) scanners have been equipped with organ‐based tube current modulation (TCM) technology. It is possible that organ‐based TCM will replace the conventional dose‐reduction technique of reducing the effective milliampere‐second. The aim of this study was to determine if organ‐based TCM could reduce radiation exposure to the breasts without compromising the image uniformity and beam hardening effect in thoracic CT examinations. Breast and skin radiation doses and the absorbed radiation dose distribution within a single section were measured with an anthropomorphic phantom and radiophotoluminescent glass dosimeters using four approaches to thoracic CT (reference, organ‐based TCM, copper shielding, and the combination of the above two techniques, hereafter referred to as the combination technique). The CT value and noise level were measured using the same calibration phantom. Organ‐based TCM and copper shielding reduced radiation doses to the breast by 23.7% and 21.8%, respectively. However, the CT value increased, especially in the anterior region, using copper shielding. In contrast, the CT value and noise level barely increased using organ‐based TCM. The combination technique reduced the radiation dose to the breast by 38.2%, but greatly increased the absorbed radiation dose from the central to the posterior regions. Moreover, the CT value increased in the anterior region and the noise level increased by more than 10% in the entire region. Therefore, organ‐based TCM can reduce radiation doses to breasts with only small increases in noise levels, making it preferable for specific groups of patients, such as children and young women. PACS numbers: 87.53.Bn; 87.57.Q‐; 87.57.qp PMID:22402390

Serotonin transporter occupancy by escitalopram and citalopram in the non-human primate brain: a [(11)C]MADAM PET study.

PubMed

Finnema, Sjoerd J; Halldin, Christer; Bang-Andersen, Benny; Bundgaard, Christoffer; Farde, Lars

2015-11-01

A number of serotonin receptor positron emission tomography (PET) radioligands have been shown to be sensitive to changes in extracellular serotonin concentration, in a generalization of the well-known dopamine competition model. High doses of selective serotonin reuptake inhibitors (SSRIs) decrease serotonin receptor availability in monkey brain, consistent with increased serotonin concentrations. However, two recent studies on healthy human subjects, using a single, lower and clinically relevant SSRI dose, showed increased cortical serotonin receptor radioligand binding, suggesting potential decreases in serotonin concentration in projection regions when initiating treatment. The cross-species differential SSRI effect may be partly explained by serotonin transporter (SERT) occupancy in monkey brain being higher than is clinically relevant. We here determine SERT occupancy after single doses of escitalopram or citalopram by conducting PET measurements with [(11)C]MADAM in monkeys. Relationships between dose, plasma concentration and SERT occupancy were estimated by one-site binding analyses. Binding affinity was expressed as dose (ID50) or plasma concentration (K i) where 50 % SERT occupancy was achieved. Estimated ID50 and K i values were 0.020 mg/kg and 9.6 nmol/L for escitalopram and 0.059 mg/kg and 9.7 nmol/L for citalopram, respectively. Obtained K i values are comparable to values reported in humans. Escitalopram or citalopram doses nearly saturated SERT in previous monkey studies which examined serotonin sensitivity of receptor radioligands. PET-measured cross-species differential effects of SSRI on cortical serotonin concentration may thus be related to SSRI dose. Future monkey studies using SSRI doses inducing clinically relevant SERT occupancy may further illuminate the delayed onset of SSRI therapeutic effects.

A gradient of radioactive contamination in Dolon village near the SNTS and comparison of computed dose values with instrumental estimates for the 29 August, 1949 nuclear test.

PubMed

Stepanenko, Valeriy F; Hoshi, Masaharu; Dubasov, Yuriy V; Sakaguchi, Aya; Yamamoto, Masayoshi; Orlov, Mark Y; Bailiff, Ian K; Ivannikov, Alexander I; Skvortsov, Valeriy G; Iaskova, Elena K; Kryukova, Irina G; Zhumadilov, Kassym S; Endo, Satoru; Tanaka, Kenichi; Apsalikov, Kazbek N; Gusev, Boris I

2006-02-01

Spatial distributions of soil contamination by 137Cs (89 sampling points) and 239+240Pu (76 points) near and within Dolon village were analyzed. An essential exponential decrease of contamination was found in Dolon village: the distance of a half reduction in contamination is about 0.87-1.25 km (in a northwest-southeast direction from the supposed centerline of the radioactive trace). This fact is in agreement with the available exposure rate measurements near Dolon (September 1949 archive data): on the basis of a few measurements the pattern of the trace was estimated to comprise a narrow 2 km corridor of maximum exposure rate. To compare computed external doses in air with local dose estimates by retrospective luminescence dosimetry (RLD) the gradient of radioactive soil contamination within the village was accounted for. The computed dose associated with the central axis of the trace was found to be equal to 2260 mGy (calculations based on archive exposure rate data). Local doses near the RLD sampling points (southeast of the village) were calculated to be in the range 466-780 mGy (averaged value: 645+/-70 mGy), which is comparable with RLD data (averaged value 460+/-92 mGy with range 380-618 mGy). A comparison of the computed mean dose in the settlement with dose estimates by ESR tooth enamel dosimetry makes it possible to estimate the "upper level" of the "shielding and behavior" factor in dose reduction for inhabitants of Dolon village which was found to be 0.28+/-0.068.

SU-E-T-161: Characterization and Validation of CT Simulator Hounsfield Units to Relative Stopping Power Values for Proton Treatment Planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnell, E; Ahmad, S; De La Fuente Herman, T

2015-06-15

Purpose: To develop a calibration curve that includes and minimizes the variations of Hounsfield Unit (HU) from a CT scanner to Relative Stopping Power (RSP) of tissues along the proton beam path. The variations are due to scanner and proton energy, technique, phantom size and placement, and tissue arrangement. Methods: A CIRS 062 M phantom with 10 plugs of known relative electron density (RED) was scanned through a 16 slice GE Discovery CT Simulator scanner. Three setup combinations of plug distributions and techniques clinically implemented for five treatment regions were scanned with energies of 100, 120, and 140 kV. Volumetricmore » HU values were measured for each plug and scan. The RSP values derived through the Bethe-Bloch formula are currently being verified with parallel-plate ionization chamber measurements in water using 80, 150, and 225 MeV proton beam. Typical treatment plans for treatment regions of brain, head-&-neck, chest, abdomen, and pelvis are being planned and dose delivered will be compared with film and Optically Stimulated Luminescence (OSL) measurements. Results: Percentage variations were determined for each variable. For tissues close to water, variations were <1% from any given parameter. Tissues far from water equivalence (lung and bone) showed the greatest sensitivity to change (7.4% maximum) with scanner energy and up to 5.3% with positioning of the phantom. No major variations were observed for proton energies within the treatment range. Conclusion: When deriving a calibration curve, attention should be placed to low and high HU values. A thorough verification process of calculated vs. water-phantom measured RSP values at different proton energies, followed by dose validation of planned vs. measured doses in phantom with film and OSL detectors are currently being undertaken.« less

The Impact of Monte Carlo Dose Calculations on Intensity-Modulated Radiation Therapy

NASA Astrophysics Data System (ADS)

Siebers, J. V.; Keall, P. J.; Mohan, R.

The effect of dose calculation accuracy for IMRT was studied by comparing different dose calculation algorithms. A head and neck IMRT plan was optimized using a superposition dose calculation algorithm. Dose was re-computed for the optimized plan using both Monte Carlo and pencil beam dose calculation algorithms to generate patient and phantom dose distributions. Tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP) were computed to estimate the plan outcome. For the treatment plan studied, Monte Carlo best reproduces phantom dose measurements, the TCP was slightly lower than the superposition and pencil beam results, and the NTCP values differed little.

SU-E-T-196: Comparative Analysis of Surface Dose Measurements Using MOSFET Detector and Dose Predicted by Eclipse - AAA with Varying Dose Calculation Grid Size

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badkul, R; Nejaiman, S; Pokhrel, D

2015-06-15

Purpose: Skin dose can be the limiting factor and fairly common reason to interrupt the treatment, especially for treating head-and-neck with Intensity-modulated-radiation-therapy(IMRT) or Volumetrically-modulated - arc-therapy (VMAT) and breast with tangentially-directed-beams. Aim of this study was to investigate accuracy of near-surface dose predicted by Eclipse treatment-planning-system (TPS) using Anisotropic-Analytic Algorithm (AAA)with varying calculation grid-size and comparing with metal-oxide-semiconductor-field-effect-transistors(MOSFETs)measurements for a range of clinical-conditions (open-field,dynamic-wedge, physical-wedge, IMRT,VMAT). Methods: QUASAR™-Body-Phantom was used in this study with oval curved-surfaces to mimic breast, chest wall and head-and-neck sites.A CT-scan was obtained with five radio-opaque markers(ROM) placed on the surface of phantom to mimic themore » range of incident angles for measurements and dose prediction using 2mm slice thickness.At each ROM, small structure(1mmx2mm) were contoured to obtain mean-doses from TPS.Calculations were performed for open-field,dynamic-wedge,physical-wedge,IMRT and VMAT using Varian-21EX,6&15MV photons using twogrid-sizes:2.5mm and 1mm.Calibration checks were performed to ensure that MOSFETs response were within ±5%.Surface-doses were measured at five locations and compared with TPS calculations. Results: For 6MV: 2.5mm grid-size,mean calculated doses(MCD)were higher by 10%(±7.6),10%(±7.6),20%(±8.5),40%(±7.5),30%(±6.9) and for 1mm grid-size MCD were higher by 0%(±5.7),0%(±4.2),0%(±5.5),1.2%(±5.0),1.1% (±7.8) for open-field,dynamic-wedge,physical-wedge,IMRT,VMAT respectively.For 15MV: 2.5mm grid-size,MCD were higher by 30%(±14.6),30%(±14.6),30%(±14.0),40%(±11.0),30%(±3.5)and for 1mm grid-size MCD were higher by 10% (±10.6), 10%(±9.8),10%(±8.0),30%(±7.8),10%(±3.8) for open-field, dynamic-wedge, physical-wedge, IMRT, VMAT respectively.For 6MV, 86% and 56% of all measured values agreed better than ±20% for 1mm and 2.5mm grid-sizes respectively. For 18MV, 56% and 18% of all measured-values agreed better than ±20% for 1mm and 2.5mm grid-sizes respectively. Conclusion: Reliable Skin-dose calculations by TPS can be very difficult due to steep dose-gradient and inaccurate beam-modelling in buildup region.Our results showed that Eclipse over-estimates surface-dose.Impact of grid-size is also significant,surface-dose increased up to 40% from 1mm to 2.5mm,however, 1mm calculated-values closely agrees with measurements. Due to large uncertnities in skin-dose predictions from TPS, outmost caution must be exercised when skin dose is evaluated,a sufficiently smaller grid-size(1mm)can improve the accuracy and MOSFETs can be used for verification.« less

SU-F-T-441: Dose Calculation Accuracy in CT Images Reconstructed with Artifact Reduction Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ng, C; Chan, S; Lee, F

Purpose: Accuracy of radiotherapy dose calculation in patients with surgical implants is complicated by two factors. First is the accuracy of CT number, second is the dose calculation accuracy. We compared measured dose with dose calculated on CT images reconstructed with FBP and an artifact reduction algorithm (OMAR, Philips) for a phantom with high density inserts. Dose calculation were done with Varian AAA and AcurosXB. Methods: A phantom was constructed with solid water in which 2 titanium or stainless steel rods could be inserted. The phantom was scanned with the Philips Brillance Big Bore CT. Image reconstruction was done withmore » FBP and OMAR. Two 6 MV single field photon plans were constructed for each phantom. Radiochromic films were placed at different locations to measure the dose deposited. One plan has normal incidence on the titanium/steel rods. In the second plan, the beam is at almost glancing incidence on the metal rods. Measurements were then compared with dose calculated with AAA and AcurosXB. Results: The use of OMAR images slightly improved the dose calculation accuracy. The agreement between measured and calculated dose was best with AXB and image reconstructed with OMAR. Dose calculated on titanium phantom has better agreement with measurement. Large discrepancies were seen at points directly above and below the high density inserts. Both AAA and AXB underestimated the dose directly above the metal surface, while overestimated the dose below the metal surface. Doses measured downstream of metal were all within 3% of calculated values. Conclusion: When doing treatment planning for patients with metal implants, care must be taken to acquire correct CT images to improve dose calculation accuracy. Moreover, great discrepancies in measured and calculated dose were observed at metal/tissue interface. Care must be taken in estimating the dose in critical structures that come into contact with metals.« less

Validation of calculation algorithms for organ doses in CT by measurements on a 5 year old paediatric phantom

NASA Astrophysics Data System (ADS)

Dabin, Jérémie; Mencarelli, Alessandra; McMillan, Dayton; Romanyukha, Anna; Struelens, Lara; Lee, Choonsik

2016-06-01

Many organ dose calculation tools for computed tomography (CT) scans rely on the assumptions: (1) organ doses estimated for one CT scanner can be converted into organ doses for another CT scanner using the ratio of the Computed Tomography Dose Index (CTDI) between two CT scanners; and (2) helical scans can be approximated as the summation of axial slices covering the same scan range. The current study aims to validate experimentally these two assumptions. We performed organ dose measurements in a 5 year-old physical anthropomorphic phantom for five different CT scanners from four manufacturers. Absorbed doses to 22 organs were measured using thermoluminescent dosimeters for head-to-torso scans. We then compared the measured organ doses with the values calculated from the National Cancer Institute dosimetry system for CT (NCICT) computer program, developed at the National Cancer Institute. Whereas the measured organ doses showed significant variability (coefficient of variation (CoV) up to 53% at 80 kV) across different scanner models, the CoV of organ doses normalised to CTDIvol substantially decreased (12% CoV on average at 80 kV). For most organs, the difference between measured and simulated organ doses was within  ±20% except for the bone marrow, breasts and ovaries. The discrepancies were further explained by additional Monte Carlo calculations of organ doses using a voxel phantom developed from CT images of the physical phantom. The results demonstrate that organ doses calculated for one CT scanner can be used to assess organ doses from other CT scanners with 20% uncertainty (k  =  1), for the scan settings considered in the study.

Radiation Dose to the Lens of the Eye from Computed Tomography Scans of the Head

NASA Astrophysics Data System (ADS)

Januzis, Natalie Ann

While it is well known that exposure to radiation can result in cataract formation, questions still remain about the presence of a dose threshold in radiation cataractogenesis. Since the exposure history from diagnostic CT exams is well documented in a patient's medical record, the population of patients chronically exposed to radiation from head CT exams may be an interesting area to explore for further research in this area. However, there are some challenges in estimating lens dose from head CT exams. An accurate lens dosimetry model would have to account for differences in imaging protocols, differences in head size, and the use of any dose reduction methods. The overall objective of this dissertation was to develop a comprehensive method to estimate radiation dose to the lens of the eye for patients receiving CT scans of the head. This research is comprised of a physics component, in which a lens dosimetry model was derived for head CT, and a clinical component, which involved the application of that dosimetry model to patient data. The physics component includes experiments related to the physical measurement of the radiation dose to the lens by various types of dosimeters placed within anthropomorphic phantoms. These dosimeters include high-sensitivity MOSFETs, TLDs, and radiochromic film. The six anthropomorphic phantoms used in these experiments range in age from newborn to adult. First, the lens dose from five clinically relevant head CT protocols was measured in the anthropomorphic phantoms with MOSFET dosimeters on two state-of-the-art CT scanners. The volume CT dose index (CTDIvol), which is a standard CT output index, was compared to the measured lens doses. Phantom age-specific CTDIvol-to-lens dose conversion factors were derived using linear regression analysis. Since head size can vary among individuals of the same age, a method was derived to estimate the CTDIvol-to-lens dose conversion factor using the effective head diameter. These conversion factors were derived for each scanner individually, but also were derived with the combined data from the two scanners as a means to investigate the feasibility of a scanner-independent method. Using the scanner-independent method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter, most of the fitted lens dose values fell within 10-15% of the measured values from the phantom study, suggesting that this is a fairly accurate method of estimating lens dose from the CTDIvol with knowledge of the patient's head size. Second, the dose reduction potential of organ-based tube current modulation (OB-TCM) and its effect on the CTDIvol-to-lens dose estimation method was investigated. The lens dose was measured with MOSFET dosimeters placed within the same six anthropomorphic phantoms. The phantoms were scanned with the five clinical head CT protocols with OB-TCM enabled on the one scanner model at our institution equipped with this software. The average decrease in lens dose with OB-TCM ranged from 13.5 to 26.0%. Using the size-specific method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter for protocols with OB-TCM, the majority of the fitted lens dose values fell within 15-18% of the measured values from the phantom study. Third, the effect of gantry angulation on lens dose was investigated by measuring the lens dose with TLDs placed within the six anthropomorphic phantoms. The 2-dimensional spatial distribution of dose within the areas of the phantoms containing the orbit was measured with radiochromic film. A method was derived to determine the CTDIvol-to-lens dose conversion factor based upon distance from the primary beam scan range to the lens. The average dose to the lens region decreased substantially for almost all the phantoms (ranging from 67 to 92%) when the orbit was exposed to scattered radiation compared to the primary beam. The effectiveness of this method to reduce lens dose is highly dependent upon the shape and size of the head, which influences whether or not the angled scan range coverage can include the entire brain volume and still avoid the orbit. The clinical component of this dissertation involved performing retrospective patient studies in the pediatric and adult populations, and reconstructing the lens doses from head CT examinations with the methods derived in the physics component. The cumulative lens doses in the patients selected for the retrospective study ranged from 40 to 1020 mGy in the pediatric group, and 53 to 2900 mGy in the adult group. This dissertation represents a comprehensive approach to lens of the eye dosimetry in CT imaging of the head. The collected data and derived formulas can be used in future studies on radiation-induced cataracts from repeated CT imaging of the head. Additionally, it can be used in the areas of personalized patient dose management, and protocol optimization and clinician training.

Radiation exposure levels within timber industries in Calabar, Nigeria

PubMed Central

Inyang, S. O.; Inyang, I. S.; Egbe, N. O.

2009-01-01

The UNSCEAR (2000) observed that there could be some exposure at work which would require regulatory control but is not really considered. This study was, therefore, set up to evaluate the effective dose in timber industries in Calabar, Nigeria to determine if the evaluated dose levels could lead to any radiological health effect in the workers, and also determine if the industries require regulatory control. The gamma ray exposure at four timber industries measured using an exposure meter were converted to effective dose and compared with the public and occupational values. The evaluated effective dose values in the timber industries were below public and occupational exposure limits and may not necessarily result in any radiological health hazard. Therefore, they may not require regulatory control. PMID:20098544

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellefson, S; Department of Human Oncology, University of Wisconsin, Madison, WI; Culberson, W

Purpose: Discrepancies in absolute dose values have been detected between the ViewRay treatment planning system and ArcCHECK readings when performing delivery quality assurance on the ViewRay system with the ArcCHECK-MR diode array (SunNuclear Corporation). In this work, we investigate whether these discrepancies are due to errors in the ViewRay planning and/or delivery system or due to errors in the ArcCHECK’s readings. Methods: Gamma analysis was performed on 19 ViewRay patient plans using the ArcCHECK. Frequency analysis on the dose differences was performed. To investigate whether discrepancies were due to measurement or delivery error, 10 diodes in low-gradient dose regions weremore » chosen to compare with ion chamber measurements in a PMMA phantom with the same size and shape as the ArcCHECK, provided by SunNuclear. The diodes chosen all had significant discrepancies in absolute dose values compared to the ViewRay TPS. Absolute doses to PMMA were compared between the ViewRay TPS calculations, ArcCHECK measurements, and measurements in the PMMA phantom. Results: Three of the 19 patient plans had 3%/3mm gamma passing rates less than 95%, and ten of the 19 plans had 2%/2mm passing rates less than 95%. Frequency analysis implied a non-random error process. Out of the 10 diode locations measured, ion chamber measurements were all within 2.2% error relative to the TPS and had a mean error of 1.2%. ArcCHECK measurements ranged from 4.5% to over 15% error relative to the TPS and had a mean error of 8.0%. Conclusion: The ArcCHECK performs well for quality assurance on the ViewRay under most circumstances. However, under certain conditions the absolute dose readings are significantly higher compared to the planned doses. As the ion chamber measurements consistently agree with the TPS, it can be concluded that the discrepancies are due to ArcCHECK measurement error and not TPS or delivery system error. This work was funded by the Bhudatt Paliwal Professorship and the University of Wisconsin Medical Radiation Research Center.« less

SU-C-201-04: Noise and Temporal Resolution in a Near Real-Time 3D Dosimeter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rilling, M; Centre de recherche sur le cancer, Universite Laval, Quebec City, QC; Radiation oncology department, CHU de Quebec, Quebec City, QC

Purpose: To characterize the performance of a real-time three-dimensional scintillation dosimeter in terms of signal-to-noise ratio (SNR) and temporal resolution of 3D dose measurements. This study quantifies its efficiency in measuring low dose levels characteristic of EBRT dynamic treatments, and in reproducing field profiles for varying multileaf collimator (MLC) speeds. Methods: The dosimeter prototype uses a plenoptic camera to acquire continuous images of the light field emitted by a 10×10×10 cm{sup 3} plastic scintillator. Using EPID acquisitions, ray tracing-based iterative tomographic algorithms allow millimeter-sized reconstruction of relative 3D dose distributions. Measurements were taken at 6MV, 400 MU/min with the scintillatormore » centered at the isocenter, first receiving doses from 1.4 to 30.6 cGy. Dynamic measurements were then performed by closing half of the MLCs at speeds of 0.67 to 2.5 cm/s, at 0° and 90° collimator angles. A reference static half-field was obtained for measured profile comparison. Results: The SNR steadily increases as a function of dose and reaches a clinically adequate plateau of 80 at 10 cGy. Below this, the decrease in light collected and increase in pixel noise diminishes the SNR; nonetheless, the EPID acquisitions and the voxel correlation employed in the reconstruction algorithms result in suitable SNR values (>75) even at low doses. For dynamic measurements at varying MLC speeds, central relative dose profiles are characterized by gradients at %D{sub 50} of 8.48 to 22.7 %/mm. These values converge towards the 32.8 %/mm-gradient measured for the static reference field profile, but are limited by the dosimeter’s current acquisition rate of 1Hz. Conclusion: This study emphasizes the efficiency of the 3D dose distribution reconstructions, while identifying limits of the current prototype’s temporal resolution in terms of dynamic EBRT parameters. This work paves the way for providing an optimized, second-generational real-time 3D scintillation dosimeter capable of highly efficient and precise dose measurements. The presenting author is financially supported by an Alexander-Graham Bell doctoral scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC).« less

SU-E-T-77: Comparison of 2D and 3D Gamma Analysis in Patient-Specific QA for Prostate VMAT Plans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clemente, F; Perez, C

2014-06-01

Purpose: Patient-specific QA procedures for IMRT and VMAT are traditionally performed by comparing TPS calculations with measured single point values and plane dose distributions by means of gamma analysis. New QA devices permit us to calculate 3D dose distributions on patient anatomy as redundant secondary check and reconstruct it from measurements taken with 2D and 3D detector arrays. 3D dose calculations allow us to perform DVH-based comparisons with clinical relevance, as well as 3D gamma analysis. One of these systems (Compass, IBA Dosimetry) combines traditional 2D with new anatomical-based 3D gamma analysis. This work shows the ability of this systemmore » by comparing 2D and 3D gamma analysis in pre-treatment QA for several VMAT prostate plans. Methods: Compass is capable of calculating dose as secondary check from DICOM TPS data and reconstructing it from measurements taken by a 2D ion chamber array (MatriXX Evolution, IBA Dosimetry). Both 2D and 3D gamma tests are available to compare calculated and reconstructed dose in Compass with TPS RT Dose. Results: 15 VMAT prostate plans have been measured with Compass. Dose is reconstructed with Compass for these plans. 2D gamma comparisons can be done for any plane from dose matrix. Mean gamma passing rates for isocenter planes (axial, coronal, sagittal) are (99.7±0.2)%, (99.9±0.1)%, (99.9±0.1)% for reconstructed dose planes. 3D mean gamma passing rates are (98.5±1.7)% for PTVs, (99.1±1.5)% for rectum, (100.0±0.0)% for bladder, (99.6±0.7)% for femoral heads and (98.1±4.1)% for penile bulb. Conclusion: Compass is a powerful tool to perform a complete pre-treatment QA analysis, from 2D techniques to 3D DVH-based techniques with clinical relevance. All reported values for VMAT prostate plans are in good agreement with TPS values. This system permits us to ensure the accuracy in the delivery of VMAT treatments completing a full patient-specific QA program.« less

Comparison of measured and estimated maximum skin doses during CT fluoroscopy lung biopsies.

PubMed

Zanca, F; Jacobs, A; Crijns, W; De Wever, W

2014-07-01

To measure patient-specific maximum skin dose (MSD) associated with CT fluoroscopy (CTF) lung biopsies and to compare measured MSD with the MSD estimated from phantom measurements, as well as with the CTDIvol of patient examinations. Data from 50 patients with lung lesions who underwent a CT fluoroscopy-guided biopsy were collected. The CT protocol consisted of a low-kilovoltage (80 kV) protocol used in combination with an algorithm for dose reduction to the radiology staff during the interventional procedure, HandCare (HC). MSD was assessed during each intervention using EBT2 gafchromic films positioned on patient skin. Lesion size, position, total fluoroscopy time, and patient-effective diameter were registered for each patient. Dose rates were also estimated at the surface of a normal-size anthropomorphic thorax phantom using a 10 cm pencil ionization chamber placed at every 30°, for a full rotation, with and without HC. Measured MSD was compared with MSD values estimated from the phantom measurements and with the cumulative CTDIvol of the procedure. The median measured MSD was 141 mGy (range 38-410 mGy) while the median cumulative CTDIvol was 72 mGy (range 24-262 mGy). The ratio between the MSD estimated from phantom measurements and the measured MSD was 0.87 (range 0.12-4.1) on average. In 72% of cases the estimated MSD underestimated the measured MSD, while in 28% of the cases it overestimated it. The same trend was observed for the ratio of cumulative CTDIvol and measured MSD. No trend was observed as a function of patient size. On average, estimated MSD from dose rate measurements on phantom as well as from CTDIvol of patient examinations underestimates the measured value of MSD. This can be attributed to deviations of the patient's body habitus from the standard phantom size and to patient positioning in the gantry during the procedure.

Public exposure due to external gamma background radiation in boundary areas of Iran.

PubMed

Pooya, S M Hosseini; Dashtipour, M R; Enferadi, A; Orouji, T

2015-09-01

A monitoring program in boundary areas of a country is an appropriate way to indicate the level of public exposure. In this research, gamma background radiation was measured using TL dosimeters at 12 boundary areas as well as in the capital city of Iran during the period 2010 to 2011. The measurements were carried out in semi-annual time intervals from January to June and July to December in each year. The maximum average dose equivalent value measured was approximately 70 μSv/month for Tehran city. Also, the average dose values obtained were less than 40 μSv/month for all the cities located at the sea level except that of high level natural radiation area of Ramsar, and more than 55 μSv/month for the higher elevation cities. The public exposure due to ambient gamma dose equivalent in Iran is within the levels reported by UNSCEAR. Copyright © 2015 Elsevier Ltd. All rights reserved.

Out-of-field doses and neutron dose equivalents for electron beams from modern Varian and Elekta linear accelerators.

PubMed

Cardenas, Carlos E; Nitsch, Paige L; Kudchadker, Rajat J; Howell, Rebecca M; Kry, Stephen F

2016-07-08

Out-of-field doses from radiotherapy can cause harmful side effects or eventually lead to secondary cancers. Scattered doses outside the applicator field, neutron source strength values, and neutron dose equivalents have not been broadly investigated for high-energy electron beams. To better understand the extent of these exposures, we measured out-of-field dose characteristics of electron applicators for high-energy electron beams on two Varian 21iXs, a Varian TrueBeam, and an Elekta Versa HD operating at various energy levels. Out-of-field dose profiles and percent depth-dose curves were measured in a Wellhofer water phantom using a Farmer ion chamber. Neutron dose was assessed using a combination of moderator buckets and gold activation foils placed on the treatment couch at various locations in the patient plane on both the Varian 21iX and Elekta Versa HD linear accelerators. Our findings showed that out-of-field electron doses were highest for the highest electron energies. These doses typically decreased with increasing distance from the field edge but showed substantial increases over some distance ranges. The Elekta linear accelerator had higher electron out-of-field doses than the Varian units examined, and the Elekta dose profiles exhibited a second dose peak about 20 to 30 cm from central-axis, which was found to be higher than typical out-of-field doses from photon beams. Electron doses decreased sharply with depth before becoming nearly constant; the dose was found to decrease to a depth of approximately E(MeV)/4 in cm. With respect to neutron dosimetry, Q values and neutron dose equivalents increased with electron beam energy. Neutron contamination from electron beams was found to be much lower than that from photon beams. Even though the neutron dose equivalent for electron beams represented a small portion of neutron doses observed under photon beams, neutron doses from electron beams may need to be considered for special cases.

In vivo dosimetry with TLD in conservative treatment of breast cancer patients treated with the EORTC protocol 22881.

PubMed

Hamers, H P; Johansson, K A; Venselaar, J L; de Brouwer, P; Hansson, U; Moudi, C

1993-01-01

Two anthropomorphic phantom breasts and six patients with breast carcinoma were irradiated according the prescriptions of the EORTC protocol 22881 on the conservative management of breast carcinoma by tumorectomy and radiotherapy. During the implantation procedure for an iridium-192 boost, three tubes were implanted, enabling the measurement with TLD rods of the dose within the breasts of the phantom and the patients during one fraction of the external x-ray therapy and during the interstitial therapy. Measured doses were compared with calculated values from a 2-D dose planning system. In general a fair agreement was found between the measured and calculated doses in points within the breast for the external beam therapy as well as for the interstitial treatment.

Radiation measurements aboard the fourth Gemini flight.

PubMed

Janni, J F; Schneider, M F

1967-01-01

Two special tissue-equivalent ionization chambers and 5 highly sensitive passive dosimetry packages were flown aboard the recent Gemini 4 flight for the purpose of obtaining precise values of instantaneous dose rate, accumulated dose. and shielding effectiveness. This experiment marked the first time that well-defined tissue dose and radiation survey measurements have been carried out in manned spaceflight operations. Since all measurements were accomplished under normal spacecraft environmental conditions, the biological dose resulted primarily from trapped inner Van Allen Belt radiation encountered by the spacecraft in the South Atlantic Anomaly. The experiment determined the particle type, ionizing and penetrating power, and variation with time and position within the Gemini spacecraft. Measured dose rates ranged from 100 mrad/hr for passes penetrating deeply into the South Atlantic Anomaly to less than 0.1 mrad/hr from lower latitude cosmic radiation. The accumulated tissue dose measured by the active ionization chambers, shielded by 0.4 gm/cm2 for the 4-day mission, was 82 mrad. Since the 5 passive dosimetry packages were each located in different positions within the spacecraft, the total mission surface dose measured by these detectors varied from 73 to 27 mrad, depending upon location and shielding. The particles within the spacecraft were recorded in nuclear emulsion, which established that over 90% of the tissue dose was attributable to penetrating protons. This experiment indicates that the radiation environment under shielded conditions at Gemini altitudes was not hazardous.

Empirical determination of collimator scatter data for use in Radcalc commercial monitor unit calculation software: Implication for prostate volumetric modulated-arc therapy calculations.

PubMed

Richmond, Neil; Tulip, Rachael; Walker, Chris

2016-01-01

The aim of this work was to determine, by measurement and independent monitor unit (MU) check, the optimum method for determining collimator scatter for an Elekta Synergy linac with an Agility multileaf collimator (MLC) within Radcalc, a commercial MU calculation software package. The collimator scatter factors were measured for 13 field shapes defined by an Elekta Agility MLC on a Synergy linac with 6MV photons. The value of the collimator scatter associated with each field was also calculated according to the equation Sc=Sc(mlc)+Sc(corr)(Sc(open)-Sc(mlc)) with Sc(corr) varied between 0 and 1, where Sc(open) is the value of collimator scatter calculated from the rectangular collimator-defined field and Sc(mlc) the value using only the MLC-defined field shape by applying sector integration. From this the optimum value of the correction was determined as that which gives the minimum difference between measured and calculated Sc. Single (simple fluence modulation) and dual-arc (complex fluence modulation) treatment plans were generated on the Monaco system for prostate volumetric modulated-arc therapy (VMAT) delivery. The planned MUs were verified by absolute dose measurement in phantom and by an independent MU calculation. The MU calculations were repeated with values of Sc(corr) between 0 and 1. The values of the correction yielding the minimum MU difference between treatment planning system (TPS) and check MU were established. The empirically derived value of Sc(corr) giving the best fit to the measured collimator scatter factors was 0.49. This figure however was not found to be optimal for either the single- or dual-arc prostate VMAT plans, which required 0.80 and 0.34, respectively, to minimize the differences between the TPS and independent-check MU. Point dose measurement of the VMAT plans demonstrated that the TPS MUs were appropriate for the delivered dose. Although the value of Sc(corr) may be obtained by direct comparison of calculation with measurement, the efficacy of the value determined for VMAT-MU calculations are very much dependent on the complexity of the MLC delivery. Copyright © 2016 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.

Evaluation of organ doses in CT examinations with an infant anthropomorphic phantom.

PubMed

Fujii, K; Akahane, K; Miyazaki, O; Horiuchi, T; Shimada, A; Nagmatsu, H; Yamauchi, M; Yamauchi-Kawaura, C; Kawasaki, T

2011-09-01

The aim of this study is to evaluate organ doses in infant CT examinations with multi-detector row CT scanners. Radiation doses were measured with radiophotoluminescence glass dosemeters set in various organ positions within a 1-y-old child anthropomorphic phantom and organ doses were evaluated from the measurement values. Doses for tissues or organs within the scan range were 28-36 mGy in an infant head CT, 3-11 mGy in a chest CT, 5-11 mGy in an abdominal-pelvic CT and 2-14 mGy in a cardiac CT. The doses varied by the differences in the types of CT scanners and scan parameters used at each medical facility. Compared with those for children of various ages, the doses in an infant CT protocol were found to be similar to or slightly smaller than those in a paediatric CT for 5- or 6-y-old children.

Estimation of thyroid equivalent doses during evacuation based on body surface contamination levels in the nuclear accident of FDNPS in 2011

NASA Astrophysics Data System (ADS)

Ohba, Takashi; Hasegawa, Arifumi; Kohayakawa, Yoshitaka; Kondo, Hisayoshi; Suzuki, Gen

2017-09-01

To reduce uncertainty in thyroid dose estimation, residents' radiation protection behavior should be reflected in the estimation. Screening data of body surface contamination provide information on exposure levels during evacuation. Our purpose is to estimate thyroid equivalent doses based on body surface contamination levels using a new methodology. We obtained a record of 7,539 residents/evacuees. Geiger-Mueller survey meter measurement value in cpm was translated into Bq/cm2 according to the nuclides densities obtained by measuring clothing from two persons by germanium γ-spectrometer. The measurement value of body surface contamination on head was adjusted by a natural removal rate of 15 hours and radionuclides' physical half-life. Thyroid equivalent dose of 1-year-old children by inhalation was estimated by two-dimensional Monte Carlo simulation. The proportions of evacuees/residents with measurement value in cpm of Namie and Minamisoma groups were higher than those of other groups during both periods (p<0.01, Kruskal-Wallis). During 12-14 March period, 50 and 95 percentiles of thyroid equivalent doses by inhalation were estimated as 2.7 and 86.0 mSv, respectively, for Namie group, and 4.2 and 17.2 mSv, respectively, for Minamisoma group, 0.1 and 1.0 mSv, respectively, for Tomioka/Okuma/Futaba/Naraha group, and 0.2 and 2.1 mSv, respectively, for the other group. During 15- 17 March period, 50 and 95 percentiles of thyroid equivalent doses by inhalation were 0.8 and 15.7 mSv, respectively, for Namie group, and 1.6 and 8.4 mSv, respectively, for Minamisoma group, 0.2 and 13.2 mSv, respectively, for Tomioka/Okuma/Futaba/Naraha group, and 1.2 and 12.7 mSv, respectively, for the other group. It was indicated that inhalation dose was generally higher in Namie and Minamisoma groups during 12-14 March than those during 15-17 March might reflect different self-protective behavior to radioactive plumes from other groups.

Estimation of staff lens doses during interventional procedures. Comparing cardiology, neuroradiology and interventional radiology.

PubMed

Vano, E; Sanchez, R M; Fernandez, J M

2015-07-01

The purpose of this article is to estimate lens doses using over apron active personal dosemeters in interventional catheterisation laboratories (cardiology IC, neuroradiology IN and radiology IR) and to investigate correlations between occupational lens doses and patient doses. Active electronic personal dosemeters placed over the lead apron were used on a sample of 204 IC procedures, 274 IN and 220 IR (all performed at the same university hospital). Patient dose values (kerma area product) were also recorded to evaluate correlations with occupational doses. Operators used the ceiling-suspended screen in most cases. The median and third quartile values of equivalent dose Hp(10) per procedure measured over the apron for IC, IN and IR resulted, respectively, in 21/67, 19/44 and 24/54 µSv. Patient dose values (median/third quartile) were 75/128, 83/176 and 61/159 Gy cm(2), respectively. The median ratios for dosemeters worn over the apron by operators (protected by the ceiling-suspended screen) and patient doses were 0.36; 0.21 and 0.46 µSv Gy(-1) cm(-2), respectively. With the conservative approach used (lens doses estimated from the over apron chest dosemeter) we came to the conclusion that more than 800 procedures y(-1) and per operator were necessary to reach the new lens dose limit for the three interventional specialties. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Estimation of organ and effective doses from newborn radiography of the chest and abdomen.

PubMed

Ma, Hillgan; Elbakri, Idris A; Reed, Martin

2013-09-01

Neonatal intensive care patients undergo frequent chest and abdomen radiographic imaging. In this study, the organ doses and the effective dose resulting from combined chest-abdomen radiography of the newborn child are determined. These values are calculated using the Monte Carlo simulation software PCXCM 2.0 and compared with direct dose measurements obtained from thermoluminescent detectors (TLDs) in a physical phantom. The effective dose obtained from PCXMC is 21.2 ± 0.7 μSv and that obtained from TLD measurements is 22.0 ± 0.5 μSv. While the two methods are in close agreement with regard to the effective dose, there is a wide range of variation in organ doses, ranging from 85 % difference for the testes to 1.4 % for the lungs. Large organ dose variations are attributed to organs at the edge of the field of view, or organs with large experimental error or simulation uncertainty. This study suggests that PCXMC can be used to estimate organ and effective doses for newborn patients.

Relative dosimetry with an MR-linac: Response of ion chambers, diamond, and diode detectors for off-axis, depth dose, and output factor measurements.

PubMed

O'Brien, Daniel J; Dolan, James; Pencea, Stefan; Schupp, Nicholas; Sawakuchi, Gabriel O

2018-02-01

The purpose of this study was to acquire beam data for an MR-linac, with and without a 1.5 T magnetic field, by using a variety of commercially available detectors to assess their relative response in the magnetic field. The impact of the magnetic field on the measured dose distribution was also assessed. An MR-safe 3D scanning water phantom was used to measure output factors, depth dose curves, and off-axis profiles for various depths and for field sizes between 2 × 2 cm 2 and 22 × 22 cm 2 for an Elekta MR-linac beam with the orthogonal 1.5 T magnetic field on or off. An on-board MV portal imaging system was used to ensure that the reproducibility of the detector position, both with and without the magnetic field, was within 0.1 mm. The detectors used included ionization chambers with large, medium, and small sensitive volumes; a diamond detector; a shielded diode; and an unshielded diode. The offset of the effective point of measurement of the ionization chambers was found to be reduced by at least half for each chamber in the direction parallel with the beam. A lateral shift of similar magnitude was also introduced to the chambers' effective point of measurement toward the average direction of the Lorentz force. A similar lateral shift (but in the opposite direction) was also observed for the diamond and diode detectors. The measured lateral shift in the dose distribution was independent of depth and field size for each detector for fields between 2 × 2 cm 2 and 10 × 10 cm 2 . The shielded diode significantly misrepresented the dose distribution in the lateral direction perpendicular to the magnetic field, making it seem more symmetric. The percentage depth dose was generally found to be lower with the magnetic field than without, but this difference was reduced as field size increased. The depth of maximum dose showed little dependence on field size in the presence of the magnetic field, with values from 1.2 cm to 1.3 cm between the 2 × 2 cm 2 and 22 × 22 cm 2 fields. Output factors measured in the magnetic field at the center of the beam profile produced a larger spread of values between detectors for fields smaller than 10 × 10 cm 2 (with a spread of 2% at 3 × 3 cm 2 ). The spread of values was more consistent when the output factors were measured at the point of peak intensity of the lateral dose distribution instead (except for the shielded diode which differed by up to 2% depending on field size). The magnetic field of the MR-linac alters the effective point of measurement of ionization chambers, shifting it both downstream and laterally. Shielded diodes produce incorrect and misleading dose profiles. The output factor measured at the point of peak intensity in the lateral dose distribution is more robust than the conventional output factor (measured at central axis). Diodes are not recommended for output factor measurements in the magnetic field. © 2017 American Association of Physicists in Medicine.

Method for measuring dose-equivalent in a neutron flux with an unknown energy spectra and means for carrying out that method

DOEpatents

Distenfeld, Carl H.

1978-01-01

A method for measuring the dose-equivalent for exposure to an unknown and/or time varing neutron flux which comprises simultaneously exposing a plurality of neutron detecting elements of different types to a neutron flux and combining the measured responses of the various detecting elements by means of a function, whose value is an approximate measure of the dose-equivalent, which is substantially independent of the energy spectra of the flux. Also, a personnel neutron dosimeter, which is useful in carrying out the above method, comprising a plurality of various neutron detecting elements in a single housing suitable for personnel to wear while working in a radiation area.

SU-E-T-01: 2-D Characterization of DLG Among All MLC Leaf Pairs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaraswamy, L; Xu, Z; Podgorsak, M

Purpose: The aim of this study is to evaluate the variation of dosimetric leaf-gap (DLG) along the travel path of each MLC leaf pair. This study evaluates whether the spatial variations in DLG could cause dose differences between TPS-calculated and measured dose. Methods: The 6MV DLG values were measured for all leaf pairs in the direction of leaf motion using a 2-D diode array and 0.6cc ion chamber. These measurements were performed on two Varian Linacs, employing the Millennium 120-leaf MLC and a 2-D-DLG variation map was created via in-house software. Several test plans were created with sweeping MLC fieldsmore » using constant gaps from 2mm to 10mm and corrected for 2-D variation utilizing in-house software. Measurements were performed utilizing the MapCHECK at 5.0cm depth for plans with and without the 2-D DLG correction and compared to the TPS calculated dose via gamma analysis (3%/3mm). Results: The measured DLGs for the middle 40 MLC leaf pairs (0.5cm width) were very similar along the central superior-inferior axis, with maximum variation of 0.2mm. The outer 20 MLC leaf pairs (1.0cm width) have DLG values from 0.32mm (mean) to 0.65mm (maximum) lower than the central leaf-pair, depending on off-axis distance. Gamma pass rates for the 2mm, 4mm, and 6mm sweep plans increased by 23.2%, 28.7%, and 26.0% respectively using the 2-D-DLG correction. The most improved dose points occur in areas modulated by the 1.0cm leaf-pairs. The gamma pass rate for the 10mm sweep plan increased by only 7.7%, indicating that the 2D variation becomes less significant for dynamic plans with larger MLC gaps. Conclusion: Fluences residing significantly off-axis with narrow sweeping gaps may exhibit significant variations from planned dose due to large differences between the true DLG exhibited by the 1.0cm leaf-pairs versus the constant DLG value utilized by the TPS for dose calculation.« less

Absorbed dose determination using experimental and analytical predictions of x-ray spectra

NASA Astrophysics Data System (ADS)

Edwards, David Lee

1999-10-01

Electron beam welding in a vacuum is a technology that NASA is investigating as a joining technique for manufacture of space structures. The interaction of energetic electrons with metal produces x-rays. This investigation characterizes the x-ray environment due to operation of an in-vacuum electron beam welding tool and provides recommendations for adequate radiation shielding for astronauts performing the in-vacuum electron beam welding. NASA, in a joint venture with the Russian Space Agency, was scheduled to perform a series of welding in space experiments on board the United States Space Shuttle. This series of experiments was named the International Space Welding Experiment (ISWE). The hardware associated with the ISWE was leased to NASA, by the Paton Welding Institute (PWI) in Ukraine, for ground based welding experiments in preparation for flight. Two ground tests were scheduled, using the ISWE electron beam welding tool, to characterize the radiation exposure to an astronaut during the operation of the ISWE. These radiation exposure tests used Thermoluminescence Dosimeters (TLD's) shielded with material currently used by astronauts during Extra Vehicular Activities (EVA) to measure the radiation dose. The TLD's were exposed to x- ray radiation generated by operation of the ISWE in- vacuum electron beam welding tool. This investigation was the first known application of TLD's to measure absorbed dose from x-rays of energy less than 10 keV. The ISWE hardware was returned to Ukraine before the issue of adequate shielding for the astronauts was completely verified. Therefore alternate experimental and analytical methods were developed to measure and predict the x-ray spectral and intensity distribution generated by ISWE electron beam impact with metal. These x-ray spectra were normalized to an equivalent ISWE exposure then used to calculate the absorbed radiation dose to astronauts. These absorbed dose values were compared to TLD measurements obtained during actual operation of the ISWE in-vacuum electron beam welding tool. The calculated absorbed dose values were found to be in good agreement with the measured TLD values.

Medical personnel and patient dosimetry during coronary angiography and intervention

NASA Astrophysics Data System (ADS)

Efstathopoulos, Efstathios P.; Makrygiannis, Stamatis S.; Kottou, Sofia; Karvouni, Evangelia; Giazitzoglou, Eleftherios; Korovesis, Socrates; Tzanalaridou, Efthalia; Raptou, Panagiota D.; Katritsis, Demosthenes G.

2003-09-01

Percutaneous coronary interventions are associated with increased radiation exposure compared to most radiological examinations. This prospective study aimed at (1) measuring entrance doses for all in-room personnel, (2) performing an assessment of patient effective dose and intracoronary doses, (3) investigating the contribution of each projection to kerma-area product (KAP) and irradiation time, (4) comparing results with established DRL values in this clinical setting and (5) estimating the risk for fatal cancer to patients and operators. Measurements were performed during 40 consecutive procedures of coronary angiography (CA), half of which were followed by ad hoc coronary angioplasty (PTCA). KAP measurements were used for patients and thermoluminescent dosimetry for the in-room personnel. The mean KAP value per procedure for CA was 29 +/- 9 Gy cm2. Thirty four per cent of KAP was due to fluoroscopy, whereas the remainder (66%) was due to digital cine. Accordingly, the mean KAP value per PTCA procedure was 75 +/- 30 Gy cm2, and contribution of fluoroscopy is 57%. Effective dose per year was estimated to be 0.04-0.05 mSv y-1 for the primary operator, and 0.03-0.04 mSv y-1 for those assisting. Corresponding measurements for radiographer and nurse were below detectable level, implying minimal radiation hazards for them. Regarding radiation exposure, coronary intervention is considered a quite safe procedure for both patients and personnel in laboratories with modern equipment and experienced operators as long as standard safety precautions are considered. Exposure optimization though should be constantly sought through continuous review of procedures.

SU-E-P-57: Radiation Doses Assessment to Paediatric Patients for Some Digital Diagnostic Radiology Examination in Emergency Department in Qatar

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abdallah, I; Aly, A; Al Naemi, H

Purpose: The aim of this study was to evaluate radiation doses to pediatric patients undergoing standard radiographic examinations using Direct Digital Radiography (DDR) in Paediatric emergency center of Hamad General Hospital (HGH) in state of Qatar and compared with regional and international Dose Reference Levels (DRLs). Methods: Entrance Skin Dose (ESD) was measured for 2739 patients for two common X-ray examinations namely: Chest AP/PA, Abdomen. Exposure factors such as kV, mAs and Focal to Skin Distance (FSD) were recorded for each patient. Tube Output was measured for a range of selected kV values. ESD for each individual patient was calculatedmore » using the tube output and the technical exposure factors for each examination. The ESD values were compared with the some international Dose Reference Levels (DRL) for all types of examinations. Results: The most performed procedure during the time of this study was chest PA/PA (85%). The mean ESD values obtained from AP chest, PA chest and AP abdomen ranged 91–120, 80–84 and 209 – 659 µGy per radiograph for different age’s groups respectively. Two protocols have been used for chest AP and PA using different radiological parameters, and the different of ESD values for chest PA and were 41% for 1 years old child, 57% for 5 years old for chest AP. Conclusion: The mean ESD were compared with those found in literature and were found to be comparable. The radiation dose can be reduced more for Chest AP and PA examination by optimization of each investigation and hence more studies are required for this task. The results presented will serve as a baseline data needed for deriving local reference doses for pediatric X-ray examinations in this local department and hence it can be applied in the whole Qatar.« less

Clinical in vivo dosimetry using optical fibers.

PubMed

Gripp, S; Haesing, F W; Bueker, H; Schmitt, G

1998-01-01

Discoloring of glass due to ionizing radiation depends on the absorbed dose. The radiation-induced light attenuation in optical fibers may be used as a measure of the dose. In high-energy photon beams (6 MV X rays), a lead-doped silica fiber can be calibrated. A dosimeter based on an optical fiber was developed for applications in radiation therapy. The diameter of the mounted fiber is 0.25 mm, whereas the length depends on the sensitivity required. To demonstrate the applicability, a customized fiber device was used to determine scattered radiation close to the lens of the eye. Measurements were compared with TLDs (LiF) in an anthropomorphic phantom. The comparison with TLD measurements shows good agreement. In contrast to TLD, optical fibers provide immediate dose values, and the readout procedure is much easier. Owing to its small size and diameter, interesting invasive dose measurements are feasible.

Potential uncertainty reduction in model-averaged benchmark dose estimates informed by an additional dose study.

PubMed

Shao, Kan; Small, Mitchell J

2011-10-01

A methodology is presented for assessing the information value of an additional dosage experiment in existing bioassay studies. The analysis demonstrates the potential reduction in the uncertainty of toxicity metrics derived from expanded studies, providing insights for future studies. Bayesian methods are used to fit alternative dose-response models using Markov chain Monte Carlo (MCMC) simulation for parameter estimation and Bayesian model averaging (BMA) is used to compare and combine the alternative models. BMA predictions for benchmark dose (BMD) are developed, with uncertainty in these predictions used to derive the lower bound BMDL. The MCMC and BMA results provide a basis for a subsequent Monte Carlo analysis that backcasts the dosage where an additional test group would have been most beneficial in reducing the uncertainty in the BMD prediction, along with the magnitude of the expected uncertainty reduction. Uncertainty reductions are measured in terms of reduced interval widths of predicted BMD values and increases in BMDL values that occur as a result of this reduced uncertainty. The methodology is illustrated using two existing data sets for TCDD carcinogenicity, fitted with two alternative dose-response models (logistic and quantal-linear). The example shows that an additional dose at a relatively high value would have been most effective for reducing the uncertainty in BMA BMD estimates, with predicted reductions in the widths of uncertainty intervals of approximately 30%, and expected increases in BMDL values of 5-10%. The results demonstrate that dose selection for studies that subsequently inform dose-response models can benefit from consideration of how these models will be fit, combined, and interpreted. © 2011 Society for Risk Analysis.

Influence of CT automatic tube current modulation on uncertainty in effective dose.

PubMed

Sookpeng, S; Martin, C J; Gentle, D J

2016-01-01

Computed tomography (CT) scanners are equipped with automatic tube current modulation (ATCM) systems that adjust the current to compensate for variations in patient attenuation. CT dosimetry variables are not defined for ATCM situations and, thus, only the averaged values are displayed and analysed. The patient effective dose (E), which is derived from a weighted sum of organ equivalent doses, will be modified by the ATCM. Values for E for chest-abdomen-pelvis CT scans have been calculated using the ImPACT spreadsheet for patients on five CT scanners. Values for E resulting from the z-axis modulation under ATCM have been compared with results assessed using the same effective mAs values with constant tube currents. Mean values for E under ATCM were within ±10 % of those for fixed tube currents for all scanners. Cumulative dose distributions under ATCM have been simulated for two patient scans using single-slice dose profiles measured in elliptical and cylindrical phantoms on one scanner. Contributions to the effective dose from organs in the upper thorax under ATCM are 30-35 % lower for superficial tissues (e.g. breast) and 15-20 % lower for deeper organs (e.g. lungs). The effect on doses to organs in the abdomen depends on body shape, and they can be 10-22 % higher for larger patients. Results indicate that scan dosimetry parameters, dose-length product and effective mAs averaged over the whole scan can provide an assessment in terms of E that is sufficiently accurate to quantify relative risk for routine patient exposures under ATCM. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

A phantom study on bladder and rectum dose measurements in brachytherapy of cervix cancer using FBX aqueous chemical dosimeter.

PubMed

Bansal, Anil K; Semwal, Manoj K; Arora, Deepak; Sharma, D N; Julka, P K; Rath, G K

2013-06-01

The ferrous sulphate-benzoic acid-xylenol orange (FBX) chemical dosimeter, due to its aqueous form can measure average volume doses and hence may overcome the limitations of point dosimetry. The present study was undertaken to validate the use of FBX dosimeter for rectum and bladder dose measurement during intracavitary brachytherapy (ICBT) and transperineal interstitial brachytherapy (TIB). We filled cylindrical polypropylene tubes (PT) and Foley balloons (FB) with FBX solution and used them as substitutes for rectum and bladder dose measurements respectively. A water phantom was fabricated with provision to place the Fletcher-type ICBT and MUPIT template applicators, and FBX filled PT and FB within the phantom. The phantom was then CT scanned for treatment planning and subsequent irradiation. Our results show that the average difference between DVH derived dose value and FBX measured dose is 3.5% (PT) and 13.7% (FB) for ICBT, and 9% (PT) and 9.9% (FB) for TIB. We believe that the FBX system should be able to provide accuracy and precision sufficient for routine quality assurance purposes. The advantage of the FBX system is its water equivalent composition, average volume dose measuring capability, and energy and temperature independent response as compared to TLD or semiconductor dosimeters. However, detailed studies will be needed with regards to its safety before actual in-vivo dose measurements are possible with the FBX dosimeter. Copyright © 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Verification of eye lens dose in IMRT by MOSFET measurement.

PubMed

Wang, Xuetao; Li, Guangjun; Zhao, Jianling; Song, Ying; Xiao, Jianghong; Bai, Sen

2018-04-17

The eye lens is recognized as one of the most radiosensitive structures in the human body. The widespread use of intensity-modulated radiotherapy (IMRT) complicates dose verification and necessitates high standards of dose computation. The purpose of this work was to assess the computed dose accuracy of eye lens through measurements using a metal-oxide-semiconductor field-effect transistor (MOSFET) dosimetry system. Sixteen clinical IMRT plans of head and neck patients were copied to an anthropomorphic head phantom. Measurements were performed using the MOSFET dosimetry system based on the head phantom. Two MOSFET detectors were imbedded in the eyes of the head phantom as the left and the right lens, covered by approximately 5-mm-thick paraffin wax. The measurement results were compared with the calculated values with a dose grid size of 1 mm. Sixteen IMRT plans were delivered, and 32 measured lens doses were obtained for analysis. The MOSFET dosimetry system can be used to verify the lens dose, and our measurements showed that the treatment planning system used in our clinic can provide adequate dose assessment in eye lenses. The average discrepancy between measurement and calculation was 6.7 ± 3.4%, and the largest discrepancy was 14.3%, which met the acceptability criterion set by the American Association of Physicists in Medicine Task Group 53 for external beam calculation for multileaf collimator-shaped fields in buildup regions. Copyright © 2018 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.

Measurements of environmental terrestrial gamma radiation dose rate in three mountainous locations in the western region of Saudi Arabia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Ghorabie, Fayez H.H.

2005-06-01

This paper describes measurements of external gamma radiation dose rate from terrestrial gamma-rays 1 m above the ground in three different mountainous locations in the western region of the Kingdom of Saudi Arabia. These locations are At-Taif city, Al-Hada village, and Ash-Shafa village. CaSO{sub 4}:Dy (TLD-900) thermoluminescent dosimeters were used for the detection of terrestrial gamma radiation at 40 different places in the three locations. The values of terrestrial gamma radiation dose rate measured ranged between 14 and 279 nGy h{sup -1} for the time interval from June 2001 to June 2002. The measured dose rate varied with the seasonmore » of the year. The average gamma radiation dose rates were 468, 541, and 781 {mu}Gy y{sup -1} for At-Taif city, Al-Hada village, and Ash-Shafa village, respectively. The corresponding average absorbed doses to the population of the three locations were 328, 379, and 547 {mu}Sv y{sup -1}, respectively. The quality factor of 0.7 Sv Gy{sup -1} was applied in the calculations of the absorbed dose to humans.« less

Measurement of Absorbed Dose from Radionuclide Solutions Mixed Intimately with the Fbx Dosimeter.

NASA Astrophysics Data System (ADS)

Benedetto, Anthony Richard

Chemical dosimeters are used widely for accurate measurement of large radiation doses due to external beam irradiation from radioisotope sources and from particle accelerators. Their use for measurement of absorbed doses from radioactive solutions mixed in the dosimeter solution was reported as early as 1952, but the large activities needed to produce suitable absorbance values in the relatively insensitive dosimeters of that time discouraged further work. This manuscript reports the results of an investigation into the suitability of the ferrous sulfate-benzoic acid -xylenol orange (FBX) dosimeter for measurement of small absorbed doses caused by radionuclide solutions dissolved in the dosimeter solution. The FBX dosimeter exhibited a linear dose response as a function of activity for two common radiopharmaceuticals, technetium-99m sodium pertechnetate and iodine-131 sodium iodide. Conditions under which the FBX dosimeter may be used with radionuclide solutions were studied and were found to be amenable to routine use by laboratories possessing relatively unsophisticated instrumentation. It appears likely that any radionuclide could be studied using this dosimeter. Finally, potential applications and future research work are suggested, including measurement of absorbed dose from radiopharmaceuticals using realistic human-like phantoms to assess the risk from clinical nuclear medicine studies.

Thermoluminescence dosimetry applied to in vivo dose measurements for total body irradiation techniques.

PubMed

Duch, M A; Ginjaume, M; Chakkor, H; Ortega, X; Jornet, N; Ribas, M

1998-06-01

In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure the accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to bone marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. Irradiations were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Different TLD calibration experiments were set up to optimize in vivo dose assessment and to analyze the influence on dose measurement of shielding blocks. An algorithm to estimate midplane doses from entrance and exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthropomorphic phantom. The predictions of the dose algorithm, even in heterogeneous zones of the body such as the lungs, are in good agreement with the experimental results obtained with and without shielding blocks. The differences between measured and predicted values are in all cases lower than 2%. The TLD system described in this work has been proven to be appropriate for in vivo dosimetry in TBI irradiations. The described calibration experiments point out the difficulty of calibrating an in vivo dosimetry system when lung shielding blocks are used.

Gamma Radiation Doses In Sweden

NASA Astrophysics Data System (ADS)

Almgren, Sara; Barregârd, Lars; Isaksson, Mats

2008-08-01

Gamma dose rate measurements were performed in one urban and one rural area using thermoluminescence dosimeters (TLD) worn by 46 participants and placed in their dwellings. The personal effective dose rates were 0.096±0.019(1 SD) and 0.092±0.016(1 SD)μSv/h in the urban and rural area, respectively. The corresponding dose rates in the dwellings were 0.11±0.042(1 SD) and 0.091±0.026(1 SD)μSv/h. However, the differences between the areas were not significant. The values were higher in buildings made of concrete than of wood and higher in apartments than in detached houses. Also, 222Rn measurements were performed in each dwelling, which showed no correlation with the gamma dose rates in the dwellings.

Radiation-induced change of optical property of hydroxypropyl cellulose hydrogel containing methacrylate compounds: As a basis for development of a new type of radiation dosimeter

NASA Astrophysics Data System (ADS)

Yamashita, Shinichi; Hiroki, Akihiro; Taguchi, Mitsumasa

2014-08-01

Hydrogels with matrix of a cellulose derivative, hydrogel of hydroxpropyl cellulose (HPC), containing two of methacrylate compounds (2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) dimethacrylate (9G)) were irradiated with 60Co γ-rays. The gels become white with irradiation, and thus, could be candidates of a new type of radiation dosimeter utilized in radiation therapy because the gels become white with irradiation and can be confirmed directly by human eyes even at low doses of 1-2 Gy. Radiation-induced change of optical properties, haze value and UV-vis absorption spectrum, of the irradiated gels was measured. Dose response of the white turbidity appearance was different for different compositions of the methacrylate compounds as well as for different dose rates. The degree of the radiation-induced white turbidity was quantified by measuring haze value, showing linear dose response in low dose region (<2 Gy). We also analyzed the gels with a UV-vis spectrometer and HEMA- and 9G-rich gels gave different spectral shapes, indicating that there are at least two mechanisms leading to the white turbidity. In addition, dose rate dependence was smaller for 9G-rich gels than HEMA-rich gels in the range of 0.015-1.5 Gy/min.

Effects of high doses of oxytetracycline on metacarpophalangeal joint kinematics in neonatal foals.

PubMed

Kasper, C A; Clayton, H M; Wright, A K; Skuba, E V; Petrie, L

1995-07-01

Thirteen clinically normal Belgian-type foals were used to study the effects of high doses of oxytetracycline on metacarpophalangeal joint kinematics. Seven foals (treatment group) received 2 doses of oxytetracycline (3 g, IV). The first dose was given when foals were 4 days old; the second dose was given 24 hours later. Six foals (control group) received 2 doses of saline (0.9% NaCl) solution (15 ml, IV) at equivalent time periods. All foals were videotaped at a walk twice: immediately prior to the first treatment and 24 hours after the second treatment. The tapes were digitized, and metacarpophalangeal joint angle was measured along the palmar surface of the limb during 3 strides. The angular data were normalized for time, and data from the 3 strides were averaged to describe a representative stride. Repeated measures ANOVA was used to test for differences between groups and within groups over time. Values for stride duration, stance phase percentage, and minimum metacarpophalangeal joint angle obtained before treatment were not significantly different from values obtained after treatment. Maximum metacarpophalangeal joint angle, which occurred during the stance phase of the stride, and range of joint motion were significantly increased for foals in the treatment group, compared with foals in the control group.

Radiation dosimetry measurements during U.S. Space Shuttle missions with the RME-III.

PubMed

Golightly, M J; Hardy, K; Quam, W

1994-01-01

Time-resolved radiation dosimetry measurements inside the crew compartment have been made during recent Shuttle missions with the U.S. Air Force Radiation Monitoring Equipment-III (RME-III), a portable battery-powered four-channel tissue equivalent proportional counter. Results from the first six missions are presented and discussed. Half of the missions had orbital inclinations of 28.5 degrees with the remainder at inclinations of 57 degrees or greater; altitudes ranged from 300 to 600 km. The determined dose equivalent rates ranged from 70 to 5300 microSv/day. The RME-III measurements are in good agreement with other dosimetry measurements made aboard the vehicles. Measurements indicate that medium- and high-LET particles contribute less than 2% of the particle fluence for all missions, but up to 50% of the dose equivalent, depending on the spacecraft's altitude and orbital inclination. Isocontours of fluence, dose and dose equivalent rate have been developed from measurements made during the STS-28 mission. The drift rate of the South Atlantic Anomaly is estimated to be 0.49 degrees W/yr and 0.12 degrees N/yr. The calculated trapped proton and GCR dose for the STS-28 mission was significantly lower than the measured values.

TU-EF-204-03: Task-Based KV and MAs Optimization for Radiation Dose Reduction in CT: From FBP to Statistical Model-Based Iterative Reconstruction (MBIR)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gomez-Cardona, D; Li, K; Lubner, M G

Purpose: The introduction of the highly nonlinear MBIR algorithm to clinical CT systems has made CNR an invalid metric for kV optimization. The purpose of this work was to develop a task-based framework to unify kV and mAs optimization for both FBP- and MBIR-based CT systems. Methods: The kV-mAs optimization was formulated as a constrained minimization problem: to select kV and mAs to minimize dose under the constraint of maintaining the detection performance as clinically prescribed. To experimentally solve this optimization problem, exhaustive measurements of detectability index (d’) for a hepatic lesion detection task were performed at 15 different mAmore » levels and 4 kV levels using an anthropomorphic phantom. The measured d’ values were used to generate an iso-detectability map; similarly, dose levels recorded at different kV-mAs combinations were used to generate an iso-dose map. The iso-detectability map was overlaid on top of the iso-dose map so that for a prescribed detectability level d’, the optimal kV-mA can be determined from the crossing between the d’ contour and the dose contour that corresponds to the minimum dose. Results: Taking d’=16 as an example: the kV-mAs combinations on the measured iso-d’ line of MBIR are 80–150 (3.8), 100–140 (6.6), 120–150 (11.3), and 140–160 (17.2), where values in the parentheses are measured dose values. As a Result, the optimal kV was 80 and optimal mA was 150. In comparison, the optimal kV and mA for FBP were 100 and 500, which corresponded to a dose level of 24 mGy. Results of in vivo animal experiments were consistent with the phantom results. Conclusion: A new method to optimize kV and mAs selection has been developed. This method is applicable to both linear and nonlinear CT systems such as those using MBIR. Additional dose savings can be achieved by combining MBIR with this method. This work was partially supported by an NIH grant R01CA169331 and GE Healthcare. K. Li, D. Gomez-Cardona, M. G. Lubner: Nothing to disclose. P. J. Pickhardt: Co-founder, VirtuoCTC, LLC Stockholder, Cellectar Biosciences, Inc. G.-H. Chen: Research funded, GE Healthcare; Research funded, Siemens AX.« less

Development of Monte Carlo simulations to provide scanner-specific organ dose coefficients for contemporary CT

NASA Astrophysics Data System (ADS)

Jansen, Jan T. M.; Shrimpton, Paul C.

2016-07-01

The ImPACT (imaging performance assessment of CT scanners) CT patient dosimetry calculator is still used world-wide to estimate organ and effective doses (E) for computed tomography (CT) examinations, although the tool is based on Monte Carlo calculations reflecting practice in the early 1990’s. Subsequent developments in CT scanners, definitions of E, anthropomorphic phantoms, computers and radiation transport codes, have all fuelled an urgent need for updated organ dose conversion factors for contemporary CT. A new system for such simulations has been developed and satisfactorily tested. Benchmark comparisons of normalised organ doses presently derived for three old scanners (General Electric 9800, Philips Tomoscan LX and Siemens Somatom DRH) are within 5% of published values. Moreover, calculated normalised values of CT Dose Index for these scanners are in reasonable agreement (within measurement and computational uncertainties of  ±6% and  ±1%, respectively) with reported standard measurements. Organ dose coefficients calculated for a contemporary CT scanner (Siemens Somatom Sensation 16) demonstrate potential deviations by up to around 30% from the surrogate values presently assumed (through a scanner matching process) when using the ImPACT CT Dosimetry tool for newer scanners. Also, illustrative estimates of E for some typical examinations and a range of anthropomorphic phantoms demonstrate the significant differences (by some 10’s of percent) that can arise when changing from the previously adopted stylised mathematical phantom to the voxel phantoms presently recommended by the International Commission on Radiological Protection (ICRP), and when following the 2007 ICRP recommendations (updated from 1990) concerning tissue weighting factors. Further simulations with the validated dosimetry system will provide updated series of dose coefficients for a wide range of contemporary scanners.

Methods for estimation of radiation risk in epidemiological studies accounting for classical and Berkson errors in doses.

PubMed

Kukush, Alexander; Shklyar, Sergiy; Masiuk, Sergii; Likhtarov, Illya; Kovgan, Lina; Carroll, Raymond J; Bouville, Andre

2011-02-16

With a binary response Y, the dose-response model under consideration is logistic in flavor with pr(Y=1 | D) = R (1+R)(-1), R = λ(0) + EAR D, where λ(0) is the baseline incidence rate and EAR is the excess absolute risk per gray. The calculated thyroid dose of a person i is expressed as Dimes=fiQi(mes)/Mi(mes). Here, Qi(mes) is the measured content of radioiodine in the thyroid gland of person i at time t(mes), Mi(mes) is the estimate of the thyroid mass, and f(i) is the normalizing multiplier. The Q(i) and M(i) are measured with multiplicative errors Vi(Q) and ViM, so that Qi(mes)=Qi(tr)Vi(Q) (this is classical measurement error model) and Mi(tr)=Mi(mes)Vi(M) (this is Berkson measurement error model). Here, Qi(tr) is the true content of radioactivity in the thyroid gland, and Mi(tr) is the true value of the thyroid mass. The error in f(i) is much smaller than the errors in ( Qi(mes), Mi(mes)) and ignored in the analysis. By means of Parametric Full Maximum Likelihood and Regression Calibration (under the assumption that the data set of true doses has lognormal distribution), Nonparametric Full Maximum Likelihood, Nonparametric Regression Calibration, and by properly tuned SIMEX method we study the influence of measurement errors in thyroid dose on the estimates of λ(0) and EAR. The simulation study is presented based on a real sample from the epidemiological studies. The doses were reconstructed in the framework of the Ukrainian-American project on the investigation of Post-Chernobyl thyroid cancers in Ukraine, and the underlying subpolulation was artificially enlarged in order to increase the statistical power. The true risk parameters were given by the values to earlier epidemiological studies, and then the binary response was simulated according to the dose-response model.

SU-F-T-477: Investigation of DEFGEL Dosimetry Using MRI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matrosic, C; McMillan, A; Bednarz, B

Purpose: The DEFGEL dosimeter/phantom allows for the measurement of 3D dose distributions while maintaining tissue equivalence and deformability. Although DEFGEL is traditionally read out with optical CT, the use of MRI would permit the measurement of 3D dose distributions in optically interfering configurations, like while embedded in a phantom. To the knowledge of the authors, this work is the first investigation that uses MRI to measure dose distributions in DEFGEL dosimeters. Methods: The DEFGEL (6%T) formula was used to create 1 cm thick, 4.5 cm diameter cylindrical dosimeters. The dosimeters were irradiated using a Varian Clinac 21EX linac. The MRImore » based transverse relaxation rate (R2) of the gel was measured in a central slice of the dosimeter with a Spin-Echo (SE) pulse sequence on a 3T GE SIGNA PET/MR scanner. The R2 values were fit to a monoexponential dose response equation using in-house software (MATLAB). Results: The data was well fit using a monoexponential fit for R2 as a function of absorbed dose (R{sup 2} = 0.9997). The fitting parameters of the monoexponential fit resulted in a 0.1229 Gy{sub −1}s{sub −1} slope. The data also resulted in an average standard deviation of 1.8% for the R2 values within the evaluated ROI. Conclusion: The close fit for the dose response curve shows that a DEFGEL based dosimeter can be paired with a SE MRI acquisition. The Type A uncertainty of the MRI method shows adequate precision, while the slope of the fit curve is large enough that R2 differences between different gel doses are distinguishable. These results suggest that the gel could potentially be used in configurations where an optical readout is not viable, such as measurements with the gel dosimeter positioned inside larger or optically opaque phantoms. This work is partially funded by NIH grant R01CA190298.« less

Estimation of external dose by car-borne survey in Kerala, India.

PubMed

Hosoda, Masahiro; Tokonami, Shinji; Omori, Yasutaka; Sahoo, Sarata Kumar; Akiba, Suminori; Sorimachi, Atsuyuki; Ishikawa, Tetsuo; Nair, Raghu Ram; Jayalekshmi, Padmavathy Amma; Sebastian, Paul; Iwaoka, Kazuki; Akata, Naofumi; Kudo, Hiromi

2015-01-01

A car-borne survey was carried out in Kerala, India to estimate external dose. Measurements were made with a 3-in × 3-in NaI(Tl) scintillation spectrometer from September 23 to 27, 2013. The routes were selected from 12 Panchayats in Karunagappally Taluk which were classified into high level, mid-level and low level high background radiation (HBR) areas. A heterogeneous distribution of air kerma rates was seen in the dose rate distribution map. The maximum air kerma rate, 2.1 μGy/h, was observed on a beach sand surface. 232Th activity concentration for the beach sand was higher than that for soil and grass surfaces, and the range of activity concentration was estimated to be 0.7-2.3 kBq/kg. The contribution of 232Th to air kerma rate was over 70% at the measurement points with values larger than 0.34 μGy/h. The maximum value of the annual effective dose in Karunagappally Taluk was observed around coastal areas, and it was estimated to be 13 mSv/y. More than 30% of all the annual effective doses obtained in this survey exceeded 1 mSv/y.

Measurement of the terrestrial and anthropogenic radionuclide concentrations in Bafra Kizilirmak delta (bird sanctuary) in Turkey.

PubMed

Mutuk, Halil; Gümüs, Hasan; Turhan, Seref

2014-01-01

In this study, the activity concentrations of terrestrial and anthropogenic radionuclides in the soil samples collected from Bafra Kızılırmak Delta were measured by using gamma spectrometry with an NaI(Tl) detector. The average values of activity concentrations of (238)U, (232)Th and (40)K were found to be 37.2±2.8, 33.7±3.1 and 413.0±59.8 Bq kg(-1), respectively. (137)Cs was also measured in some samples. It has a mean value of 13.8±1.0 Bq kg(-1). From the activity concentrations, the absorbed gamma dose rates in outdoor and the corresponding annual effective dose rates and external hazard index (Hex) were estimated.

SU-E-T-86: A Systematic Method for GammaKnife SRS Fetal Dose Estimation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Geneser, S; Paulsson, A; Sneed, P

Purpose: Estimating fetal dose is critical to the decision-making process when radiation treatment is indicated during pregnancy. Fetal doses less than 5cGy confer no measurable non-cancer developmental risks but can produce a threefold increase in developing childhood cancer. In this study, we estimate fetal dose for a patient receiving Gamma Knife stereotactic radiosurgery (GKSRS) treatment and develop a method to estimate dose directly from plan details. Methods: A patient underwent GKSRS on a Perfexion unit for eight brain metastases (two infratentorial and one brainstem). Dose measurements were performed using a CC13, head phantom, and solid water. Superficial doses to themore » thyroid, sternum, and pelvis were measured using MOSFETs during treatment. Because the fetal dose was too low to accurately measure, we obtained measurements proximally to the isocenter, fitted to an exponential function, and extrapolated dose to the fundus of the uterus, uterine midpoint, and pubic synthesis for both the preliminary and delivered plans. Results: The R-squared fit for the delivered doses was 0.995. The estimated fetal doses for the 72 minute preliminary and 138 minute delivered plans range from 0.0014 to 0.028cGy and 0.07 to 0.38cGy, respectively. MOSFET readings during treatment were just above background for the thyroid and negligible for all inferior positions. The method for estimating fetal dose from plan shot information was within 0.2cGy of the measured values at 14cm cranial to the fetal location. Conclusion: Estimated fetal doses for both the preliminary and delivered plan were well below the 5cGy recommended limit. Due to Pefexion shielding, internal dose is primarily governed by attenuation and drops off exponentially. This is the first work that reports fetal dose for a GK Perfexion unit. Although multiple lesions were treated and the duration of treatment was long, the estimated fetal dose remained very low.« less

It's All Relative: A Validation of Radiation Quality Comparison Metrics

NASA Technical Reports Server (NTRS)

Chappell, Lori J.; Milder, Caitlin M.; Elgart, S. Robin; Semones, Edward J.

2017-01-01

The difference between high-LET and low-LET radiation is quantified by a measure called relative biological effectiveness (RBE). RBE is defined as the ratio of the dose of a reference radiation to that of a test radiation to achieve the same effect level, and thus, is described either as an iso-effector dose-to-dose ratio. A single dose point is not sufficient to calculate an RBE value; therefore, studies with only one dose point usually calculate an effect-to-effect ratio. While not formally used in radiation protection, these iso-dose values may still be informative. Shuryak, et al 2017 investigated the use of an iso-dose metric termed "radiation effects ratio" (RER) and used both RBE and RER to estimate high-LET risks. To apply RBE or RER to risk prediction, the selected metric must be uniquely defined. That is, the calculated value must be consistent within a model given a constant set of constraints and assumptions, regardless of how effects are defined using statistical transformations from raw endpoint data. We first test the RBE and the RER to determine whether they are uniquely defined using transformations applied to raw data. Then, we test whether both metrics can predict heavy ion response data after simulated effect size scaling between human populations or when converting animal to human endpoints.

Evaluation of dose‐area product of common radiographic examinations towards establishing a preliminary diagnostic reference levels (PDRLs) in Southwestern Nigeria

PubMed Central

Jibiri, Nnamdi N.

2016-01-01

In Nigeria, a large number of radiographic examinations are conducted yearly for various diagnostic purposes. However, most examinations carried out do not have records of doses received by the patients, and the employed exposure parameters used are not documented; therefore, adequate radiation dose management is hindered. The aim of the present study was to estimate the dose‐area product (DAP) of patients examined in Nigeria, and to propose regional reference dose levels for nine common examinations (chest PA, abdomen AP, pelvis AP, lumbar AP, skull AP, leg AP, knee AP, hand AP, and thigh AP) undertaken in Nigeria. Measurement of entrance surface dose (ESD) was carried out using thermoluminescent dosimeter (TLD). Measured ESDS were converted into DAP using the beam area of patients in 12 purposely selected hospitals. Results of the study show that the maximum/minimum ratio ranged from 3 for thigh AP to 57 in abdomen AP. The range of determined mean and 75th percentile DAPs were 0.18–17.16, and 0.25–28.59 Gy cm2, respectively. Data available for comparison show that 75th percentile DAPs in this study (in chest PA, abdomen AP, pelvis AP, lumbar AP) are higher than NRPB‐HPE reference values. The DAP in this study is higher by factor of 31.4 (chest PA), 9.9 (abdomen AP), 2.2 (pelvis AP), and 2.1 (lumbar AP) than NRPB‐HPE values. The relative higher dose found in this study shows nonoptimization of practice in Nigeria. It is expected that regular dose auditing and dose optimization implementation in Nigeria would lead to lower DAP value, especially in abdomen AP. The 75th percentile DAP distribution reported in this study could be taken as regional diagnostic reference level in the Southwestern Nigeria; however, a more extensive nationwide dose survey is required to establish national reference dose. PACS number(s): 87.53.Bn, 87.59.B PMID:27929511

Using physiologically based pharmacokinetic modeling to address nonlinear kinetics and changes in rodent physiology and metabolism due to aging and adaptation in deriving reference values for propylene glycol methyl ether and propylene glycol methyl ether acetate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirman, C R.; Sweeney, Lisa M.; Corley, Rick A.

2005-04-01

Reference values, including an oral reference dose (RfD) and an inhalation reference concentration (RfC), were derived for propylene glycol methyl ether (PGME), and an oral RfD was derived for its acetate (PGMEA). These values were based upon transient sedation observed in F344 rats and B6C3F1 mice during a two-year inhalation study. The dose-response relationship for sedation was characterized using internal dose measures as predicted by a physiologically based pharmacokinetic (PBPK) model for PGME and its acetate. PBPK modeling was used to account for changes in rodent physiology and metabolism due to aging and adaptation, based on data collected during weeksmore » 1, 2, 26, 52, and 78 of a chronic inhalation study. The peak concentration of PGME in richly perfused tissues was selected as the most appropriate internal dose measure based upon a consideration of the mode of action for sedation and similarities in tissue partitioning between brain and other richly perfused tissues. Internal doses (peak tissue concentrations of PGME) were designated as either no-observed-adverse-effect levels (NOAELs) or lowest-observed-adverse-effect levels (LOAELs) based upon the presence or absence of sedation at each time-point, species, and sex in the two year study. Distributions of the NOAEL and LOAEL values expressed in terms of internal dose were characterized using an arithmetic mean and standard deviation, with the mean internal NOAEL serving as the basis for the reference values, which was then divided by appropriate uncertainty factors. Where data were permitting, chemical-specific adjustment factors were derived to replace default uncertainty factor values of ten. Nonlinear kinetics are were predicted by the model in all species at PGME concentrations exceeding 100 ppm, which complicates interspecies and low-dose extrapolations. To address this complication, reference values were derived using two approaches which differ with respect to the order in which these extrapolations were performed: (1) uncertainty factor application followed by interspecies extrapolation (PBPK modeling); and (2) interspecies extrapolation followed by uncertainty factor application. The resulting reference values for these two approaches are substantially different, with values from the former approach being 7-fold higher than those from the latter approach. Such a striking difference between the two approaches reveals an underlying issue that has received little attention in the literature regarding the application of uncertainty factors and interspecies extrapolations to compounds where saturable kinetics occur in the range of the NOAEL. Until such discussions have taken place, reference values based on the latter approach are recommended for risk assessments involving human exposures to PGME and PGMEA.« less

SU-G-IeP3-04: Effective Dose Measurements in Fast Kvp Switch Dual Energy Computed Tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raudabaugh, J; Moore, B; Nguyen, G

2016-06-15

Purpose: The objective of this study was two-fold: (a) to test a new approach to approximating organ dose by using the effective energy of the combined 80kV/140kV beam in dual-energy (DE) computed tomography (CT), and (b) to derive the effective dose (ED) in the abdomen-pelvis protocol in DECT. Methods: A commercial dual energy CT scanner was employed using a fast-kV switch abdomen/pelvis protocol alternating between 80 kV and 140 kV. MOSFET detectors were used for organ dose measurements. First, an experimental validation of the dose equivalency between MOSFET and ion chamber (as a gold standard) was performed using a CTDImore » phantom. Second, the ED of DECT scans was measured using MOSFET detectors and an anthropomorphic phantom. For ED calculations, an abdomen/pelvis scan was used using ICRP 103 tissue weighting factors; ED was also computed using the AAPM Dose Length Product (DLP) method and compared to the MOSFET value. Results: The effective energy was determined as 42.9 kV under the combined beam from half-value layer (HVL) measurement. ED for the dual-energy scan was calculated as 16.49 ± 0.04 mSv by the MOSFET method and 14.62 mSv by the DLP method. Conclusion: Tissue dose in the center of the CTDI body phantom was 1.71 ± 0.01 cGy (ion chamber) and 1.71 ± 0.06 (MOSFET) respectively; this validated the use of effective energy method for organ dose estimation. ED from the abdomen-pelvis scan was calculated as 16.49 ± 0.04 mSv by MOSFET and 14.62 mSv by the DLP method; this suggests that the DLP method provides a reasonable approximation to the ED.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, R; Bai, W

Purpose: Because of statistical noise in Monte Carlo dose calculations, effective point doses may not be accurate. Volume spheres are useful for evaluating dose in Monte Carlo plans, which have an inherent statistical uncertainty.We use a user-defined sphere volume instead of a point, take sphere sampling around effective point make the dose statistics to decrease the stochastic errors. Methods: Direct dose measurements were made using a 0.125cc Semiflex ion chamber (IC) 31010 isocentrically placed in the center of a homogeneous Cylindric sliced RW3 phantom (PTW, Germany).In the scanned CT phantom series the sensitive volume length of the IC (6.5mm) weremore » delineated and defined the isocenter as the simulation effective points. All beams were simulated in Monaco in accordance to the measured model. In our simulation using 2mm voxels calculation grid spacing and choose calculate dose to medium and request the relative standard deviation ≤0.5%. Taking three different assigned IC over densities (air electron density(ED) as 0.01g/cm3 default CT scanned ED and Esophageal lumen ED 0.21g/cm3) were tested at different sampling sphere radius (2.5, 2, 1.5 and 1 mm) statistics dose were compared with the measured does. Results: The results show that in the Monaco TPS for the IC using Esophageal lumen ED 0.21g/cm3 and sampling sphere radius 1.5mm the statistical value is the best accordance with the measured value, the absolute average percentage deviation is 0.49%. And when the IC using air electron density(ED) as 0.01g/cm3 and default CT scanned EDthe recommented statistical sampling sphere radius is 2.5mm, the percentage deviation are 0.61% and 0.70%, respectivly. Conclusion: In Monaco treatment planning system for the ionization chamber 31010 recommend air cavity using ED 0.21g/cm3 and sampling 1.5mm sphere volume instead of a point dose to decrease the stochastic errors. Funding Support No.C201505006.« less

Dosimetric validation and clinical implementation of two 3D dose verification systems for quality assurance in volumetric‐modulated arc therapy techniques

PubMed Central

Pérez‐Vara, Consuelo

2015-01-01

A pretreatment quality assurance program for volumetric techniques should include redundant calculations and measurement‐based verifications. The patient‐specific quality assurance process must be based in clinically relevant metrics. The aim of this study was to show the commission, clinical implementation, and comparison of two systems that allow performing a 3D redundant dose calculation. In addition, one of them is capable of reconstructing the dose on patient anatomy from measurements taken with a 2D ion chamber array. Both systems were compared in terms of reference calibration data (absolute dose, output factors, percentage depth‐dose curves, and profiles). Results were in good agreement for absolute dose values (discrepancies were below 0.5%) and output factors (mean differences were below 1%). Maximum mean discrepancies were located between 10 and 20 cm of depth for PDDs (‐2.7%) and in the penumbra region for profiles (mean DTA of 1.5 mm). Validation of the systems was performed by comparing point‐dose measurements with values obtained by the two systems for static, dynamic fields from AAPM TG‐119 report, and 12 real VMAT plans for different anatomical sites (differences better than 1.2%). Comparisons between measurements taken with a 2D ion chamber array and results obtained by both systems for real VMAT plans were also performed (mean global gamma passing rates better than 87.0% and 97.9% for the 2%/2 mm and 3%/3 mm criteria). Clinical implementation of the systems was evaluated by comparing dose‐volume parameters for all TG‐119 tests and real VMAT plans with TPS values (mean differences were below 1%). In addition, comparisons between dose distributions calculated by TPS and those extracted by the two systems for real VMAT plans were also performed (mean global gamma passing rates better than 86.0% and 93.0% for the 2%/2 mm and 3%/3 mm criteria). The clinical use of both systems was successfully evaluated. PACS numbers: 87.56.Fc, 87.56.‐v, 87.55.dk, 87.55.Qr, 87.55.‐x, 07.57.Kp, 85.25.Pb PMID:26103189

Measurement of the stochastic radial dose distribution for a 30-MeV proton beam using a wall-less tissue-equivalent proportional counter

PubMed Central

Tsuda, S.; Sato, T.; Ogawa, T.

2016-01-01

The frequency distribution of the lineal energy, y, of a 30-MeV proton beam was measured as a function of the radial distance from the beam path, and the dosed mean of y,y¯D, was obtained to investigate the radial dependence of y¯D. A wall-less tissue-equivalent proportional counter, in a cylindrical volume with simulated diameters of 0.36, 0.72 and 1.44 µm was used for the measurement of y distributions, yf(y). The measured values of yf(y) summed in the radial direction agreed fairly well with the corresponding data taken from the microdosimetric calculations using the PHITS code. The y¯D value of the 30-MeV proton beam presented its smallest value at r = 0.0 and gradually increased with radial distance, and the y¯D values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrated that the stochastic deposited energy distribution of high-energy protons in the microscopic region is rather constant in the core as well as in the penumbra region of the track structure. PMID:25956785

Patient doses from chest radiography in Victoria.

PubMed

Cardillo, I; Boal, T J; Einsiedel, P F

1997-06-01

This survey examines doses from PA chest radiography at radiology practices, private hospitals and public hospitals throughout metropolitan and country Victoria. Data were collected from 111 individual X-ray units at 86 different practices. Entrance skin doses in air were measured for exposure factors used by the centre for a 23 cm thick male chest. A CDRH LucA1 chest phantom was used when making these measurements. About half of the centres used grid technique and half used non-grid technique. There was a factor of greater than 10 difference in the entrance dose delivered between the highest dose centre and the lowest dose centre for non-grid centres; and a factor of about 5 for centres using grids. Factors contributing to the high doses recorded at some centres were identified. Guidance levels for chest radiography based on the third quartile value of the entrance doses from this survey have been recommended and compared with guidance levels recommended in other countries.

Double-blind evaluation of the safety and pharmacokinetics of multiple oral once-daily 750-milligram and 1-gram doses of levofloxacin in healthy volunteers.

PubMed

Chien, S C; Wong, F A; Fowler, C L; Callery-D'Amico, S V; Williams, R R; Nayak, R; Chow, A T

1998-04-01

The safety and pharmacokinetics of once-daily oral levofloxacin in 16 healthy male volunteers were investigated in a randomized, double-blind, placebo-controlled study. Subjects were randomly assigned to the treatment (n = 10) or placebo group (n = 6). In study period 1, 750 mg of levofloxacin or a placebo was administered orally as a single dose on day 1, followed by a washout period on days 2 and 3; dosing resumed for days 4 to 10. Following a 3-day washout period, 1 g of levofloxacin or a placebo was administered in a similar fashion in period 2. Plasma and urine levofloxacin concentrations were measured by high-pressure liquid chromatography. Pharmacokinetic parameters were estimated by model-independent methods. Levofloxacin was rapidly absorbed after single and multiple once-daily 750-mg and 1-g doses with an apparently large volume of distribution. Peak plasma levofloxacin concentration (Cmax) values were generally attained within 2 h postdose. The mean values of Cmax and area under the concentration-time curve from 0 to 24 h (AUC0-24) following a single 750-mg dose were 7.1 microg/ml and 71.3 microg x h/ml, respectively, compared to 8.6 microg/ml and 90.7 microg x h/ml, respectively, at steady state. Following the single 1-g dose, mean Cmax and AUC0-24 values were 8.9 microg/ml and 95.4 microg x h/ml, respectively; corresponding values at steady state were 11.8 microg/ml and 118 microg x h/ml. These Cmax and AUC0-24 values indicate modest and similar degrees of accumulation upon multiple dosing at the two dose levels. Values of apparent total body clearance (CL/F), apparent volume of distribution (Vss/F), half-life (t1/2), and renal clearance (CL[R]) were similar for the two dose levels and did not vary from single to multiple dosing. Mean steady-state values for CL/F, Vss/F, t1/2, and CL(R) following 750 mg of levofloxacin were 143 ml/min, 100 liters, 8.8 h, and 116 ml/min, respectively; corresponding values for the 1-g dose were 146 ml/min, 105 liters, 8.9 h, and 105 ml/min. In general, the pharmacokinetics of levofloxacin in healthy subjects following 750-mg and 1-g single and multiple once-daily oral doses appear to be consistent with those found in previous studies of healthy volunteers given 500-mg doses. Levofloxacin was well tolerated at either high dose level. The most frequently reported drug-related adverse events were nausea and headache.

Double-Blind Evaluation of the Safety and Pharmacokinetics of Multiple Oral Once-Daily 750-Milligram and 1-Gram Doses of Levofloxacin in Healthy Volunteers

PubMed Central

Chien, Shu-Chean; Wong, Frank A.; Fowler, Cynthia L.; Callery-D’Amico, Susan V.; Williams, R. Rex; Nayak, Ramchandra; Chow, Andrew T.

1998-01-01

The safety and pharmacokinetics of once-daily oral levofloxacin in 16 healthy male volunteers were investigated in a randomized, double-blind, placebo-controlled study. Subjects were randomly assigned to the treatment (n = 10) or placebo group (n = 6). In study period 1, 750 mg of levofloxacin or a placebo was administered orally as a single dose on day 1, followed by a washout period on days 2 and 3; dosing resumed for days 4 to 10. Following a 3-day washout period, 1 g of levofloxacin or a placebo was administered in a similar fashion in period 2. Plasma and urine levofloxacin concentrations were measured by high-pressure liquid chromatography. Pharmacokinetic parameters were estimated by model-independent methods. Levofloxacin was rapidly absorbed after single and multiple once-daily 750-mg and 1-g doses with an apparently large volume of distribution. Peak plasma levofloxacin concentration (Cmax) values were generally attained within 2 h postdose. The mean values of Cmax and area under the concentration-time curve from 0 to 24 h (AUC0–24) following a single 750-mg dose were 7.1 μg/ml and 71.3 μg · h/ml, respectively, compared to 8.6 μg/ml and 90.7 μg · h/ml, respectively, at steady state. Following the single 1-g dose, mean Cmax and AUC0–24 values were 8.9 μg/ml and 95.4 μg · h/ml, respectively; corresponding values at steady state were 11.8 μg/ml and 118 μg · h/ml. These Cmax and AUC0–24 values indicate modest and similar degrees of accumulation upon multiple dosing at the two dose levels. Values of apparent total body clearance (CL/F), apparent volume of distribution (Vss/F), half-life (t1/2), and renal clearance (CLR) were similar for the two dose levels and did not vary from single to multiple dosing. Mean steady-state values for CL/F, Vss/F, t1/2, and CLR following 750 mg of levofloxacin were 143 ml/min, 100 liters, 8.8 h, and 116 ml/min, respectively; corresponding values for the 1-g dose were 146 ml/min, 105 liters, 8.9 h, and 105 ml/min. In general, the pharmacokinetics of levofloxacin in healthy subjects following 750-mg and 1-g single and multiple once-daily oral doses appear to be consistent with those found in previous studies of healthy volunteers given 500-mg doses. Levofloxacin was well tolerated at either high dose level. The most frequently reported drug-related adverse events were nausea and headache. PMID:9559801

Absorbed dose thresholds and absorbed dose rate limitations for studies of electron radiation effects on polyetherimides

NASA Technical Reports Server (NTRS)

Long, Edward R., Jr.; Long, Sheila Ann T.; Gray, Stephanie L.; Collins, William D.

1989-01-01

The threshold values of total absorbed dose for causing changes in tensile properties of a polyetherimide film and the limitations of the absorbed dose rate for accelerated-exposure evaluation of the effects of electron radiation in geosynchronous orbit were studied. Total absorbed doses from 1 kGy to 100 MGy and absorbed dose rates from 0.01 MGy/hr to 100 MGy/hr were investigated, where 1 Gy equals 100 rads. Total doses less than 2.5 MGy did not significantly change the tensile properties of the film whereas doses higher than 2.5 MGy significantly reduced elongation-to-failure. There was no measurable effect of the dose rate on the tensile properties for accelerated electron exposures.

Effects of dose scaling on delivery quality assurance in tomotherapy

PubMed Central

Nalichowski, Adrian; Burmeister, Jay

2012-01-01

Delivery quality assurance (DQA) of tomotherapy plans is routinely performed with silver halide film which has a limited range due to the effects of saturation. DQA plans with dose values exceeding this limit require the dose of the entire plan to be scaled downward if film is used, to evaluate the dose distribution in two dimensions. The potential loss of fidelity between scaled and unscaled DQA plans as a function of dose scaling is investigated. Three treatment plans for 12 Gy fractions designed for SBRT of the lung were used to create DQA procedures that were scaled between 100% and 10%. The dose was measured with an ionization chamber array and compared to values from the tomotherapy treatment planning system. Film and cylindrical ion chamber measurements were also made for one patient for scaling factors of 50% to 10% to compare with the ionization chamber array measurements. The array results show the average gamma pass rate is ≥99% from 100% to 30% scaling. The average gamma pass rate falls to 93.6% and 51.1% at 20% and 10% scaling, respectively. Film analysis yields similar pass rates. Cylindrical ion chambers did not exhibit significant variation with dose scaling, but only represent points in the low gradient region of the dose distribution. Scaling the dose changes the mechanics of the radiation delivery, as well as the signal‐to‐noise ratio. Treatment plans which exhibit parameters that differ significantly from those common to DQA plans studied in this paper may exhibit different behavior. Dose scaling should be limited to the smallest degree possible. Planar information, such as that from film or a detector array, is required. The results show that it is not necessary to perform both a scaled and unscaled DQA plan for the treatment plans considered here. PACS numbers: 87.55.km, 87.55.Qr PMID:22231213

Measurement of microdosimetric spectra with a wall-less tissue-equivalent proportional counter for a 290 MeV/u 12C beam.

PubMed

Tsuda, Shuichi; Sato, Tatsuhiko; Takahashi, Fumiaki; Satoh, Daiki; Endo, Akira; Sasaki, Shinichi; Namito, Yoshihito; Iwase, Hiroshi; Ban, Shuichi; Takada, Masashi

2010-09-07

The frequency distribution of the lineal energy, y, of a 290 MeV/u carbon beam was measured to obtain the dose-weighted mean of y and compare it with the linear energy transfer (LET). In the experiment, a wall-less tissue-equivalent proportional counter (TEPC) in a cylindrical volume with a simulated diameter of 0.72 microm was used. The measured frequency distribution of y as well as its dose-mean value agrees within 10% uncertainty with the corresponding data from microdosimetric calculations using the PHITS code. The ratio of the measured dose-mean lineal energy to the LET of the 290 MeV/u carbon beam is 0.73, which is much smaller than the corresponding data obtained by a wall TEPC. This result demonstrates that a wall-less TEPC is necessary to precisely measure the dose-mean of y for energetic heavy ion beams.

Development of probabilistic internal dosimetry computer code

NASA Astrophysics Data System (ADS)

Noh, Siwan; Kwon, Tae-Eun; Lee, Jai-Ki

2017-02-01

Internal radiation dose assessment involves biokinetic models, the corresponding parameters, measured data, and many assumptions. Every component considered in the internal dose assessment has its own uncertainty, which is propagated in the intake activity and internal dose estimates. For research or scientific purposes, and for retrospective dose reconstruction for accident scenarios occurring in workplaces having a large quantity of unsealed radionuclides, such as nuclear power plants, nuclear fuel cycle facilities, and facilities in which nuclear medicine is practiced, a quantitative uncertainty assessment of the internal dose is often required. However, no calculation tools or computer codes that incorporate all the relevant processes and their corresponding uncertainties, i.e., from the measured data to the committed dose, are available. Thus, the objective of the present study is to develop an integrated probabilistic internal-dose-assessment computer code. First, the uncertainty components in internal dosimetry are identified, and quantitative uncertainty data are collected. Then, an uncertainty database is established for each component. In order to propagate these uncertainties in an internal dose assessment, a probabilistic internal-dose-assessment system that employs the Bayesian and Monte Carlo methods. Based on the developed system, we developed a probabilistic internal-dose-assessment code by using MATLAB so as to estimate the dose distributions from the measured data with uncertainty. Using the developed code, we calculated the internal dose distribution and statistical values ( e.g. the 2.5th, 5th, median, 95th, and 97.5th percentiles) for three sample scenarios. On the basis of the distributions, we performed a sensitivity analysis to determine the influence of each component on the resulting dose in order to identify the major component of the uncertainty in a bioassay. The results of this study can be applied to various situations. In cases of severe internal exposure, the causation probability of a deterministic health effect can be derived from the dose distribution, and a high statistical value ( e.g., the 95th percentile of the distribution) can be used to determine the appropriate intervention. The distribution-based sensitivity analysis can also be used to quantify the contribution of each factor to the dose uncertainty, which is essential information for reducing and optimizing the uncertainty in the internal dose assessment. Therefore, the present study can contribute to retrospective dose assessment for accidental internal exposure scenarios, as well as to internal dose monitoring optimization and uncertainty reduction.

In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans.

PubMed

Zhang, Da; Padole, Atul; Li, Xinhua; Singh, Sarabjeet; Khawaja, Ranish Deedar Ali; Lira, Diego; Liu, Tianyu; Shi, Jim Q; Otrakji, Alexi; Kalra, Mannudeep K; Xu, X George; Liu, Bob

2014-09-01

To present a study of radiation dose measurements with a human cadaver scanned on a clinical CT scanner. Multiple point dose measurements were obtained with high-accuracy Thimble ionization chambers placed inside the stomach, liver, paravertebral gutter, ascending colon, left kidney, and urinary bladder of a human cadaver (183 cm in height and 67.5 kg in weight) whose abdomen/pelvis region was scanned repeatedly with a multidetector row CT. The flat energy response and precision of the dosimeters were verified, and the slight differences in each dosimeter's response were evaluated and corrected to attain high accuracy. In addition, skin doses were measured for radiosensitive organs outside the scanned region with OSL dosimeters: the right eye, thyroid, both nipples, and the right testicle. Three scan protocols were used, which shared most scan parameters but had different kVp and mA settings: 120-kVp automA, 120-kVp 300 mA, and 100-kVp 300 mA. For each protocol three repeated scans were performed. The tube starting angle (TSA) was found to randomly vary around two major conditions, which caused large fluctuations in the repeated point dose measurements: for the 120-kVp 300 mA protocol this angle changed from approximately 110° to 290°, and caused 8%-25% difference in the point dose measured at the stomach, liver, colon, and urinary bladder. When the fluctuations of the TSA were small (within 5°), the maximum coefficient of variance was approximately 3.3%. The soft tissue absorbed doses averaged from four locations near the center of the scanned region were 27.2±3.3 and 16.5±2.7 mGy for the 120 and 100-kVp fixed-mA scans, respectively. These values were consistent with the corresponding size specific dose estimates within 4%. The comparison of the per-100-mAs tissue doses from the three protocols revealed that: (1) dose levels at nonsuperficial locations in the TCM scans could not be accurately deduced by simply scaling the fix-mA doses with local mA values; (2) the general power law relationship between dose and kVp varied from location to location, with the power index ranged between 2.7 and 3.5. The averaged dose measurements at both nipples, which were about 0.6 cm outside the prescribed scan region, ranged from 23 to 27 mGy at the left nipple, and varied from 3 to 20 mGy at the right nipple over the three scan protocols. Large fluctuations over repeated scans were also observed, as a combined result of helical scans of large pitch (1.375) and small active areas of the skin dosimeters. In addition, the averaged skin dose fell off drastically with the distance to the nearest boundary of the scanned region. This study revealed the complexity of CT dose fluctuation and variation with a human cadaver.

Skin entrance dose with and without lead apron in digital panoramic radiography for selected sensitive body regions.

PubMed

Schulze, Ralf Kurt Willy; Cremers, Catrin; Karle, Heiko; de Las Heras Gala, Hugo

2017-05-01

The aim of this study was to compare the dose at skin level at five significant anatomical regions for panoramic radiography devices with and without lead apron by means of a highly sensitive dosimeter. A female RANDO-phantom was exposed in five different digital panoramic radiography systems, and the dose at skin level was assessed tenfold for each measurement region by means of a highly sensitive solid-state-dosimeter. The five measurement regions selected were the thyroid, both female breasts, the gonads, and a central region in the back of the phantom. For each panoramic machine, the measurements were performed in two modes: with and without a commercial lead apron specifically designed for panoramic radiography. Reproducibility of the measurements was expressed by absolute differences and the coefficient of variation. Values between shielded and unshielded doses were pooled for each region and compared by means of the paired Wilcoxon tests (p ≤ 0.05). Reproducibility as represented by the mean CV was 22 ± 52 % (median 2.3 %) with larger variations for small dose values. Doses at skin level ranged between 0.00 μGy at the gonads and 85.39 μGy at the unshielded thyroid (mean ± SD 15 ± 24 μGy). Except for the gonads, the dose in all the other regions was significantly lower (p < 0.001) when a lead apron was applied. Unshielded doses were between 1.02-fold (thyroid) and 112-fold (at the right breast) higher than those with lead apron shielding (mean: 14-fold ± 18-fold). Although the doses were entirely very low, we observed a significant increase in dose in the radiation-sensitive female breast region when no lead apron was used. Future discussions on shielding requirements for panoramic radiography should focus on these differences in the light of the linear non-threshold (LNT) theory which is generally adopted in medical imaging.

Strengths and Weaknesses of a Planar Whole-Body Method of 153Sm Dosimetry for Patients with Metastatic Osteosarcoma and Comparison with Three-Dimensional Dosimetry

PubMed Central

Plyku, Donika; Loeb, David M.; Prideaux, Andrew R.; Baechler, Sébastien; Wahl, Richard L.; Sgouros, George

2015-01-01

Abstract Purpose: Dosimetric accuracy depends directly upon the accuracy of the activity measurements in tumors and organs. The authors present the methods and results of a retrospective tumor dosimetry analysis in 14 patients with a total of 28 tumors treated with high activities of 153Sm-ethylenediaminetetramethylenephosphonate (153Sm-EDTMP) for therapy of metastatic osteosarcoma using planar images and compare the results with three-dimensional dosimetry. Materials and Methods: Analysis of phantom data provided a complete set of parameters for dosimetric calculations, including buildup factor, attenuation coefficient, and camera dead-time compensation. The latter was obtained using a previously developed methodology that accounts for the relative motion of the camera and patient during whole-body (WB) imaging. Tumor activity values calculated from the anterior and posterior views of WB planar images of patients treated with 153Sm-EDTMP for pediatric osteosarcoma were compared with the geometric mean value. The mean activities were integrated over time and tumor-absorbed doses were calculated using the software package OLINDA/EXM. Results: The authors found that it was necessary to employ the dead-time correction algorithm to prevent measured tumor activity half-lives from often exceeding the physical decay half-life of 153Sm. Measured half-lives so long are unquestionably in error. Tumor-absorbed doses varied between 0.0022 and 0.27 cGy/MBq with an average of 0.065 cGy/MBq; however, a comparison with absorbed dose values derived from a three-dimensional analysis for the same tumors showed no correlation; moreover, the ratio of three-dimensional absorbed dose value to planar absorbed dose value was 2.19. From the anterior and posterior activity comparisons, the order of clinical uncertainty for activity and dose calculations from WB planar images, with the present methodology, is hypothesized to be about 70%. Conclusion: The dosimetric results from clinical patient data indicate that absolute planar dosimetry is unreliable and dosimetry using three-dimensional imaging is preferable, particularly for tumors, except perhaps for the most sophisticated planar methods. The relative activity and patient kinetics derived from planar imaging show a greater level of reliability than the dosimetry. PMID:26560193

High-order noise analysis for low dose iterative image reconstruction methods: ASIR, IRIS, and MBAI

NASA Astrophysics Data System (ADS)

Do, Synho; Singh, Sarabjeet; Kalra, Mannudeep K.; Karl, W. Clem; Brady, Thomas J.; Pien, Homer

2011-03-01

Iterative reconstruction techniques (IRTs) has been shown to suppress noise significantly in low dose CT imaging. However, medical doctors hesitate to accept this new technology because visual impression of IRT images are different from full-dose filtered back-projection (FBP) images. Most common noise measurements such as the mean and standard deviation of homogeneous region in the image that do not provide sufficient characterization of noise statistics when probability density function becomes non-Gaussian. In this study, we measure L-moments of intensity values of images acquired at 10% of normal dose and reconstructed by IRT methods of two state-of-art clinical scanners (i.e., GE HDCT and Siemens DSCT flash) by keeping dosage level identical to each other. The high- and low-dose scans (i.e., 10% of high dose) were acquired from each scanner and L-moments of noise patches were calculated for the comparison.

Measurement of the secondary neutron dose distribution from the LET spectrum of recoils using the CR-39 plastic nuclear track detector in 10 MV X-ray medical radiation fields

NASA Astrophysics Data System (ADS)

Fujibuchi, Toshioh; Kodaira, Satoshi; Sawaguchi, Fumiya; Abe, Yasuyuki; Obara, Satoshi; Yamaguchi, Masae; Kawashima, Hajime; Kitamura, Hisashi; Kurano, Mieko; Uchihori, Yukio; Yasuda, Nakahiro; Koguchi, Yasuhiro; Nakajima, Masaru; Kitamura, Nozomi; Sato, Tomoharu

2015-04-01

We measured the recoil charged particles from secondary neutrons produced by the photonuclear reaction in a water phantom from a 10-MV photon beam from medical linacs. The absorbed dose and the dose equivalent were evaluated from the linear energy transfer (LET) spectrum of recoils using the CR-39 plastic nuclear track detector (PNTD) based on well-established methods in the field of space radiation dosimetry. The contributions and spatial distributions of these in the phantom on nominal photon exposures were verified as the secondary neutron dose and neutron dose equivalent. The neutron dose equivalent normalized to the photon-absorbed dose was 0.261 mSv/100 MU at source to chamber distance 90 cm. The dose equivalent at the surface gave the highest value, and was attenuated to less than 10% at 5 cm from the surface. The dose contribution of the high LET component of ⩾100 keV/μm increased with the depth in water, resulting in an increase of the quality factor. The CR-39 PNTD is a powerful tool that can be used to systematically measure secondary neutron dose distributions in a water phantom from an in-field to out-of-field high-intensity photon beam.

Measurement and properties of the dose-area product ratio in external small-beam radiotherapy.

PubMed

Niemelä, Jarkko; Partanen, Mari; Ojala, Jarkko; Sipilä, Petri; Björkqvist, Mikko; Kapanen, Mika; Keyriläinen, Jani

2017-06-21

In small-beam radiation therapy (RT) the measurement of the beam quality parameter, i.e. the tissue-phantom ratio or TPR 20,10 , using a conventional point detector is a challenge. To obtain reliable results, one has to consider potential sources of error, including volume averaging and adjustment of the point detector into the narrow beam. To overcome these challenges, a different type of beam quality parameter in small beams was studied, namely the dose-area product ratio, or DAPR 20,10 . With this method, the measurement of a dose-area product (DAP) using a large-area plane-parallel chamber (LAC) eliminates the uncertainties in detector positioning and volume averaging that are present when using a point detector. In this study, the properties of the DAPR 20,10 of a cone-collimated 6 MV photon beam were investigated using Monte Carlo (MC) calculations and the obtained values were compared to measurements obtained using two LAC detectors, PTW Type 34073 and PTW Type 34070. In addition, the possibility of determining the DAP using EBT3 film and a Razor diode detector was studied. The determination of the DAPR 20,10 value was found to be feasible in external small-beam radiotherapy using cone-collimated beams with diameters from 4-40 mm, based on the results of the two LACs, the MC calculations and the Razor diode. The measurements indicated a constant DAPR 20,10 value for fields 20-40 mm in diameter, with a maximum relative change of 0.6%, but an increase of 7.0% for fields from 20-4 mm in diameter for the PTW Type 34070 chamber. Simulations and measurements showed an increase of DAPR 20,10 with increasing LAC size or dose integral area for the studied 4-40 mm cone-collimated 6 MV photon beams. This has the consequence that there should be a reference to the size of the used LAC active area or the DAP integration area with the reported DAPR 20,10 value.

Verification of BWR Turbine Skyshine Dose with the MCNP5 Code Based on an Experiment Made at SHIMANE Nuclear Power Station

NASA Astrophysics Data System (ADS)

Tayama, Ryuichi; Wakasugi, Kenichi; Kawanaka, Ikunori; Kadota, Yoshinobu; Murakami, Yasuhiro

We measured the skyshine dose from turbine buildings at Shimane Nuclear Power Station Unit 1 (NS-1) and Unit 2 (NS-2), and then compared it with the dose calculated with the Monte Carlo transport code MCNP5. The skyshine dose values calculated with the MCNP5 code agreed with the experimental data within a factor of 2.8, when the roof of the turbine building was precisely modeled. We concluded that our MCNP5 calculation was valid for BWR turbine skyshine dose evaluation.

Nuclear accident dosimetry intercomparison studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sims, C.S.

1989-09-01

Twenty-two nuclear accident dosimetry intercomparison studies utilizing the fast-pulse Health Physics Research Reactor at the Oak Ridge National Laboratory have been conducted since 1965. These studies have provided a total of 62 different organizations a forum for discussion of criticality accident dosimetry, an opportunity to test their neutron and gamma-ray dosimetry systems under a variety of simulated criticality accident conditions, and the experience of comparing results with reference dose values as well as with the measured results obtained by others making measurements under identical conditions. Sixty-nine nuclear accidents (27 with unmoderated neutron energy spectra and 42 with eight different shieldedmore » spectra) have been simulated in the studies. Neutron doses were in the 0.2-8.5 Gy range and gamma doses in the 0.1-2.0 Gy range. A total of 2,289 dose measurements (1,311 neutron, 978 gamma) were made during the intercomparisons. The primary methods of neutron dosimetry were activation foils, thermoluminescent dosimeters, and blood sodium activation. The main methods of gamma dose measurement were thermoluminescent dosimeters, radiophotoluminescent glass, and film. About 68% of the neutron measurements met the accuracy guidelines (+/- 25%) and about 52% of the gamma measurements met the accuracy criterion (+/- 20%) for accident dosimetry.« less

Dose response of alanine detectors irradiated with carbon ion beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrmann, Rochus; Jaekel, Oliver; Palmans, Hugo

Purpose: The dose response of the alanine detector shows a dependence on particle energy and type when irradiated with ion beams. The purpose of this study is to investigate the response behavior of the alanine detector in clinical carbon ion beams and compare the results to model predictions. Methods: Alanine detectors have been irradiated with carbon ions with an energy range of 89-400 MeV/u. The relative effectiveness of alanine has been measured in this regime. Pristine and spread out Bragg peak depth-dose curves have been measured with alanine dosimeters. The track structure based alanine response model developed by Hansen andmore » Olsen has been implemented in the Monte Carlo code FLUKA and calculations were compared to experimental results. Results: Calculations of the relative effectiveness deviate less than 5% from the measured values for monoenergetic beams. Measured depth-dose curves deviate from predictions in the peak region, most pronounced at the distal edge of the peak. Conclusions: The used model and its implementation show a good overall agreement for quasimonoenergetic measurements. Deviations in depth-dose measurements are mainly attributed to uncertainties of the detector geometry implemented in the Monte Carlo simulations.« less

RADON AND PROGENY SOURCED DOSE ASSESSMENT OF SPA EMPLOYEES IN BALNEOLOGICAL SITES.

PubMed

Uzun, Sefa Kemal; Demiröz, Işık

2016-09-01

This study was conducted in the scope of IAEA project with the name 'Establishing a Systematic Radioactivity Survey and Total Effective Dose Assessment in Natural Balneological Sites' (TUR/9/018), at the Health Physics department of Sarayköy Nuclear Research and Training Center (SANAEM). The aim of this study is estimation of radon and progeny sourced effective dose for the people who are working at the spa facilities by measuring radon activity concentration (RAC) at the ambient air of indoor spa pools and dressing rooms. As it is known, the source of the radon gas is the radium content of the earth crust. Therefore, thermal waters coming from ground may contain dissolved radon and the radon can diffuse water to air. So the ambient air of spa pools can contain serious RAC that depends on a lot of parameters. In this regard, RAC measurements were executed at the 70 spa facilities in Turkey. The measurements were done with both active and passive methods at ambient air of spa pools and dressing rooms. Thus, active measurements were carried out by using the Alphaguard(®) with diffusion mode during half an hour, and passive measurements were carried out by using the humidity resistive CR-39 radon detectors during 2 months. Results show that RAC values at ambient air of spa pools varies between 13 Bq m(-3) and 10 kBq m(-3) Because long-term measurements are more reliable, if it is available, for dose calculations passive radon measurements (with CR-39 detectors) at ambient air of spa pools and dressing rooms were used, otherwise active measurement results were used. With the measurement by the conversion coefficients of ICRP 65 and occupational data of the employees has got from questionary forms, effective dose values were calculated. According to the calculations, spa employees are exposed to annual average dose between 0.05 and 29 mSv because of radon and progeny. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

SU-F-T-130: [18F]-FDG Uptake Dose Response in Lung Correlates Linearly with Proton Therapy Dose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, D; Titt, U; Mirkovic, D

2016-06-15

Purpose: Analysis of clinical outcomes in lung cancer patients treated with protons using 18F-FDG uptake in lung as a measure of dose response. Methods: A test case lung cancer patient was selected in an unbiased way. The test patient’s treatment planning and post treatment positron emission tomography (PET) were collected from picture archiving and communication system at the UT M.D. Anderson Cancer Center. Average computerized tomography scan was registered with post PET/CT through both rigid and deformable registrations for selected region of interest (ROI) via VelocityAI imaging informatics software. For the voxels in the ROI, a system that extracts themore » Standard Uptake Value (SUV) from PET was developed, and the corresponding relative biological effectiveness (RBE) weighted (both variable and constant) dose was computed using the Monte Carlo (MC) methods. The treatment planning system (TPS) dose was also obtained. Using histogram analysis, the voxel average normalized SUV vs. 3 different doses was obtained and linear regression fit was performed. Results: From the registration process, there were some regions that showed significant artifacts near the diaphragm and heart region, which yielded poor r-squared values when the linear regression fit was performed on normalized SUV vs. dose. Excluding these values, TPS fit yielded mean r-squared value of 0.79 (range 0.61–0.95), constant RBE fit yielded 0.79 (range 0.52–0.94), and variable RBE fit yielded 0.80 (range 0.52–0.94). Conclusion: A system that extracts SUV from PET to correlate between normalized SUV and various dose calculations was developed. A linear relation between normalized SUV and all three different doses was found.« less

An experimental measurement of galactic cosmic radiation dose in conventional aircraft between San Francisco and London compared to theoretical values for conventional and supersonic aircraft

NASA Technical Reports Server (NTRS)

Wallace, R.; Boyer, M. F.

1972-01-01

These direct measurements are in fair agreement with computations made using a program which considers both basic cosmic ray atmospheric physics and the focusing effect of the earth's magnetic field. These measurements also agree with those made at supersonic jet aircraft altitudes in Rb-57 aircraft. It is concluded that experiments and theory show that the doses received at conventional jet aircraft altitudes are slightly higher than those encountered in supersonic flights at much higher altitudes.

Estimation of background radiation doses for the Peninsular Malaysia's population by ESR dosimetry of tooth enamel.

PubMed

Rodzi, Mohd; Zhumadilov, Kassym; Ohtaki, Megu; Ivannikov, Alexander; Bhattacharjee, Deborshi; Fukumura, Akifumi; Hoshi, Masaharu

2011-08-01

Background radiation dose is used in dosimetry for estimating occupational doses of radiation workers or determining radiation dose of an individual following accidental exposure. In the present study, the absorbed dose and the background radiation level are determined using the electron spin resonance (ESR) method on tooth samples. The effect of using different tooth surfaces and teeth exposed with single medical X-rays on the absorbed dose are also evaluated. A total of 48 molars of position 6-8 were collected from 13 district hospitals in Peninsular Malaysia. Thirty-six teeth had not been exposed to any excessive radiation, and 12 teeth had been directly exposed to a single X-ray dose during medical treatment prior to extraction. There was no significant effect of tooth surfaces and exposure with single X-rays on the measured absorbed dose of an individual. The mean measured absorbed dose of the population is 34 ± 6.2 mGy, with an average tooth enamel age of 39 years. From the slope of a regression line, the estimated annual background dose for Peninsular Malaysia is 0.6 ± 0.3 mGy y(-1). This value is slightly lower than the yearly background dose for Malaysia, and the radiation background dose is established by ESR tooth measurements on samples from India and Russia.

Ambient Dose Equivalent measured at the Instituto Nacional de Cancerología Department of Nuclear Medicine

NASA Astrophysics Data System (ADS)

Ávila, O.; Torres-Ulloa, C. L.; Medina, L. A.; Trujillo-Zamudio, F. E.; de Buen, I. Gamboa; Buenfil, A. E.; Brandan, M. E.

2010-12-01

Ambient dose equivalent values were determined in several sites at the Instituto Nacional de Cancerología, Departmento de Medicina Nuclear, using TLD-100 and TLD-900 thermoluminescent dosemeters. Additionally, ambient dose equivalent was measured at a corridor outside the hospitalization room for patients treated with 137Cs brachytherapy. Dosemeter calibration was performed at the Instituto Nacional de Investigaciones Nucleares, Laboratorio de Metrología, to known 137Cs gamma radiation air kerma. Radionuclides considered for this study are 131I, 18F, 67Ga, 99mTc, 111In, 201Tl and 137Cs, with main gamma energies between 93 and 662 keV. Dosemeters were placed during a five month period in the nuclear medicine rooms (containing gamma-cameras), injection corridor, patient waiting areas, PET/CT study room, hot lab, waste storage room and corridors next to the hospitalization rooms for patients treated with 131I and 137Cs. High dose values were found at the waste storage room, outside corridor of 137Cs brachytherapy patients and PET/CT area. Ambient dose equivalent rate obtained for the 137Cs brachytherapy corridor is equal to (18.51±0.02)×10-3 mSv/h. Sites with minimum doses are the gamma camera rooms, having ambient dose equivalent rates equal to (0.05±0.03)×10-3 mSv/h. Recommendations have been given to the Department authorities so that further actions are taken to reduce doses at high dose sites in order to comply with the ALARA principle (as low as reasonably achievable).

SU-F-T-560: Measurement of Dose Blurring Effect Due to Respiratory Motion for Lung Stereotactic Body Radiation Therapy (SBRT) Using Monte Carlo Based Calculation Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Badkul, R; Pokhrel, D; Jiang, H

2016-06-15

Purpose: Intra-fractional tumor motion due to respiration may potentially compromise dose delivery for SBRT of lung tumors. Even sufficient margins are used to ensure there is no geometric miss of target volume, there is potential dose blurring effect may present due to motion and could impact the tumor coverage if motions are larger. In this study we investigated dose blurring effect of open fields as well as Lung SBRT patients planned using 2 non-coplanar dynamic conformal arcs(NCDCA) and few conformal beams(CB) calculated with Monte Carlo (MC) based algorithm utilizing phantom with 2D-diode array(MapCheck) and ion-chamber. Methods: SBRT lung patients weremore » planned on Brainlab-iPlan system using 4D-CT scan and ITV were contoured on MIP image set and verified on all breathing phase image sets to account for breathing motion and then 5mm margin was applied to generate PTV. Plans were created using two NCDCA and 4-5 CB 6MV photon calculated using XVMC MC-algorithm. 3 SBRT patients plans were transferred to phantom with MapCheck and 0.125cc ion-chamber inserted in the middle of phantom to calculate dose. Also open field 3×3, 5×5 and 10×10 were calculated on this phantom. Phantom was placed on motion platform with varying motion from 5, 10, 20 and 30 mm with duty cycle of 4 second. Measurements were carried out for open fields as well 3 patients plans at static and various degree of motions. MapCheck planar dose and ion-chamber reading were collected and compared with static measurements and computed values to evaluate the dosimetric effect on tumor coverage due to motion. Results: To eliminate complexity of patients plan 3 simple open fields were also measured to see the dose blurring effect with the introduction of motion. All motion measured ionchamber values were normalized to corresponding static value. For open fields 5×5 and 10×10 normalized central axis ion-chamber values were 1.00 for all motions but for 3×3 they were 1 up to 10mm motion and 0.97 and 0.87 for 20 and 30mm motion respectively. For SBRT plans central axis dose values were within 1% upto 10mm motions but decreased to average of 5% for 20mm and 8% for 30mm motion. Mapcheck comparison with static showed penumbra enlargement due to motion blurring at the edges of the field for 3×3,5×5,10×10 pass rates were 88% to 12%, 100% to 43% and 100% to 63% respectively as motion increased from 5 to 30mm. For SBRT plans MapCheck mean pass rate were decreased from 73.8% to 39.5% as motion increased from 5mm to 30mm. Conclusion: Dose blurring effect has been seen in open fields as well as SBRT lung plans using NCDCA with CB which worsens with increasing respiratory motion and decreasing field size(tumor size). To reduce this effect larger margins and appropriate motion reduction techniques should be utilized.« less

Radiation Parameters of High Dose Rate Iridium -192 Sources

NASA Astrophysics Data System (ADS)

Podgorsak, Matthew B.

A lack of physical data for high dose rate (HDR) Ir-192 sources has necessitated the use of basic radiation parameters measured with low dose rate (LDR) Ir-192 seeds and ribbons in HDR dosimetry calculations. A rigorous examination of the radiation parameters of several HDR Ir-192 sources has shown that this extension of physical data from LDR to HDR Ir-192 may be inaccurate. Uncertainty in any of the basic radiation parameters used in dosimetry calculations compromises the accuracy of the calculated dose distribution and the subsequent dose delivery. Dose errors of up to 0.3%, 6%, and 2% can result from the use of currently accepted values for the half-life, exposure rate constant, and dose buildup effect, respectively. Since an accuracy of 5% in the delivered dose is essential to prevent severe complications or tumor regrowth, the use of basic physical constants with uncertainties approaching 6% is unacceptable. A systematic evaluation of the pertinent radiation parameters contributes to a reduction in the overall uncertainty in HDR Ir-192 dose delivery. Moreover, the results of the studies described in this thesis contribute significantly to the establishment of standardized numerical values to be used in HDR Ir-192 dosimetry calculations.

Correlation between the Temperature Dependence of Intrsinsic Mr Parameters and Thermal Dose Measured by a Rapid Chemical Shift Imaging Technique

PubMed Central

Taylor, Brian A.; Elliott, Andrew M.; Hwang, Ken-Pin; Hazle, John D.; Stafford, R. Jason

2011-01-01

In order to investigate simultaneous MR temperature imaging and direct validation of tissue damage during thermal therapy, temperature-dependent signal changes in proton resonance frequency (PRF) shifts, R2* values, and T1-weighted amplitudes are measured from one technique in ex vivo tissue heated with a 980-nm laser at 1.5T and 3.0T. Using a multi-gradient echo acquisition and signal modeling with the Stieglitz-McBride algorithm, the temperature sensitivity coefficient (TSC) values of these parameters are measured in each tissue at high spatiotemporal resolutions (1.6×1.6×4mm3,≤5sec) at the range of 25-61 °C. Non-linear changes in MR parameters are examined and correlated with an Arrhenius rate dose model of thermal damage. Using logistic regression, the probability of changes in these parameters is calculated as a function of thermal dose to determine if changes correspond to thermal damage. Temperature calibrations demonstrate TSC values which are consistent with previous studies. Temperature sensitivity of R2* and, in some cases, T1-weighted amplitudes are statistically different before and after thermal damage occurred. Significant changes in the slopes of R2* as a function of temperature are observed. Logistic regression analysis shows that these changes could be accurately predicted using the Arrhenius rate dose model (Ω=1.01±0.03), thereby showing that the changes in R2* could be direct markers of protein denaturation. Overall, by using a chemical shift imaging technique with simultaneous temperature estimation, R2* mapping and T1-W imaging, it is shown that changes in the sensitivity of R2* and, to a lesser degree, T1-W amplitudes are measured in ex vivo tissue when thermal damage is expected to occur according to Arrhenius rate dose models. These changes could possibly be used for direct validation of thermal damage in contrast to model-based predictions. PMID:21721063

Comparison between Measured and Simulated Radiation Doses in the Matoroshka-R Spherical phantom Experiment#1 and Area Monitoring aboard International Space Station using PADLES from May - Sep. 2012

NASA Astrophysics Data System (ADS)

Nagamatsu, Aiko; Tolochek, Raisa; Shurshakov, Vyacheslav; Nikolaev, Igor; Tawara, Hiroko; Kitajo, Keiichi; Shimada, Ken

The measurement of radiation environmental parameters in space is essential to support radiation risk assessments for astronauts and establish a benchmark for space radiation models for present and future human space activities. Since Japanese Experiment Module ‘KIBO’ was attached to the International Space Station (ISS) in 2008, we have been performing continuous space radiation dosimetery using a PADLES (Passive Dosimeter for Life-Science Experiments in Space) consisting of CR-39 PNTDs (Plastic Nuclear track detectors) and TLD-MSOs (Mg2SiO4:Tb) for various space experiments onboard the ‘KIBO’ part of the ISS. The MATROSHKA-R experiments aims to verify of dose distributions in a human body during space flight. The phantom consists of tissue equivalent material covered by a poncho jacket with 32 pockets on the surface. 20 container rods with dosimeters can be struck into the spherical phantom. Its diameter is 370 mm and it is 32 kg in weight. The first experiment onboard the KIBO at Forward No.2 area (JPM1F2 Rack2) was conducted over 114 days from 21 May to 12 September 2012 (the installation schedule inside the phantom) on the way to solar cycle 24th upward curve. 16 PADLES packages were deployed into 16 poncho pockets on the surface of the spherical phantom. Another 12 PADLES packages were deployed inside 4 rods (3 packages per rod in the outer, middle and inner side). Area monitoring in the KIBO was conducted in the same period (Area PADLES series #8 from 15 May to 16 September, 2012). Absorbed doses were measured at 17 area monitoring points in the KIBO and 28 locations (16 packages in poncho pockets and 12 inside 4 rods) in the phantom. The maximum value measured with the PADLES in the poncho pockets on the surface of the spherical phantom facing the outer wall was 0.43 mGy/day and the minimum value measured with the PADLES in the poncho pockets on the surface of the spherical phantom facing the KIBO interior was 0.30 mGy/day. The maximum absorbed doses measured inside rods was 0.28 mGy/day and the minimum value was 0.19 mGy/day. This indicates doses measured from the dosimeters placed in the outer side of each rod are relatively high compared to the doses placed in the center of rod. At this time, we also would like to show the preliminary results of comparative study between measured and Simulated Radiation Doses using the Particle and Heavy Ion Transport code System (PHITS) calculations with well developed shielding model of the KIBO and numerical spherical phantom inside.

Poster - Thurs Eve-09: Evaluation of a commercial 2D ion-chamber array for intensity modulated radiation therapy dose measurements.

PubMed

Mei, X; Bracken, G; Kerr, A

2008-07-01

Experimental verification of calculated dose from a treatment planning system is often essential for quality assurance (QA) of intensity modulated radiation therapy (IMRT). Film dosimetry and single ion chamber measurements are commonly used for IMRT QA. Film dosimetry has very good spatial resolution, but is labor intensive and absolute dose is not reliable. Ion chamber measurements are still required for absolute dose after measurements using films. Dosimeters based on 2D detector arrays that can measure 2D dose in real-time are gaining wider use. These devices provide a much easier and reliable tool for IMRT QA. We report the evaluation of a commercial 2D ion chamber array, including its basic performance characteristics, such as linearity, reproducibility and uniformity of relative ion chamber sensitivities, and comparisons between measured 2D dose and calculated dose with a commercial treatment planning system. Our analysis shows this matrix has excellent linearity and reproducibility, but relative sensitivities are tilted such that the +Y region is over sensitive, while the -Y region is under sensitive. Despite this behavior, our results show good agreement between measured 2D dose profiles and Eclipse planned data for IMRT test plans and a few verification plans for clinical breast field-in-field plans. The gamma values (3% or 3 mm distance-to-agreement) are all less than 1 except for one or two pixels at the field edge This device provides a fast and reliable stand-alone dosimeter for IMRT QA. © 2008 American Association of Physicists in Medicine.

SU-E-I-06: Measurement of Skin Dose from Dental Cone-Beam CT Scans.

PubMed

Akyalcin, S; English, J; Abramovitch, K; Rong, J

2012-06-01

To directly measure skin dose using point-dosimeters from dental cone-beam CT (CBCT) scans. To compare the results among three different dental CBCT scanners and compare the CBCT results with those from a conventional panoramic and cephalomic dental imaging system. A head anthropomorphic phantom was used with nanoDOT dosimeters attached to specified anatomic landmarks of selected radiosensitive tissues of interest. To ensure reliable measurement results, three dosimeters were used for each location. The phantom was scanned under various modes of operation and scan protocols for typical dental exams on three dental CBCT systems plus a conventional dental imaging system. The Landauer OSL nanoDOT dosimeters were calibrated under the same imaging condition as the head phantom scan protocols, and specifically for each of the imaging systems. Using nanoDOT dosimeters, skin doses at several positions on the surface of an adult head anthropomorphic phantom were measured for clinical dental imaging. The measured skin doses ranged from 0.04 to 4.62mGy depending on dosimeter positions and imaging systems. The highest dose location was at the parotid surface for all three CBCT scanners. The surface doses to the locations of the eyes were ∼4.0mGy, well below the 500mGy threshold for possibly causing cataract development. The results depend on x-ray tube output (kVp and mAs) and also are sensitive to SFOV. Comparing to the conventional dental imaging system operated in panoramic and cephalometric modes, doses from all three CBCT systems were at least an order of magnitude higher. No image artifact was caused by presence of nanoDOT dosimeters in the head phantom images. Direct measurements of skin dose using nanoDOT dosimeters provided accurate skin dose values without any image artifacts. The results of skin dose measurements serve as dose references in guiding future dose optimization efforts in dental CBCT imaging. © 2012 American Association of Physicists in Medicine.

Measuring temporal stability of positron emission tomography standardized uptake value bias using long-lived sources in a multicenter network.

PubMed

Byrd, Darrin; Christopfel, Rebecca; Arabasz, Grae; Catana, Ciprian; Karp, Joel; Lodge, Martin A; Laymon, Charles; Moros, Eduardo G; Budzevich, Mikalai; Nehmeh, Sadek; Scheuermann, Joshua; Sunderland, John; Zhang, Jun; Kinahan, Paul

2018-01-01

Positron emission tomography (PET) is a quantitative imaging modality, but the computation of standardized uptake values (SUVs) requires several instruments to be correctly calibrated. Variability in the calibration process may lead to unreliable quantitation. Sealed source kits containing traceable amounts of [Formula: see text] were used to measure signal stability for 19 PET scanners at nine hospitals in the National Cancer Institute's Quantitative Imaging Network. Repeated measurements of the sources were performed on PET scanners and in dose calibrators. The measured scanner and dose calibrator signal biases were used to compute the bias in SUVs at multiple time points for each site over a 14-month period. Estimation of absolute SUV accuracy was confounded by bias from the solid phantoms' physical properties. On average, the intrascanner coefficient of variation for SUV measurements was 3.5%. Over the entire length of the study, single-scanner SUV values varied over a range of 11%. Dose calibrator bias was not correlated with scanner bias. Calibration factors from the image metadata were nearly as variable as scanner signal, and were correlated with signal for many scanners. SUVs often showed low intrascanner variability between successive measurements but were also prone to shifts in apparent bias, possibly in part due to scanner recalibrations that are part of regular scanner quality control. Biases of key factors in the computation of SUVs were not correlated and their temporal variations did not cancel out of the computation. Long-lived sources and image metadata may provide a check on the recalibration process.

Measurement of ambient dose equivalent rates by walk survey around Fukushima Dai-ichi Nuclear Power Plant using KURAMA-II until 2016.

PubMed

Andoh, Masaki; Yamamoto, Hideaki; Kanno, Takashi; Saito, Kimiaki

2018-05-17

Ambient dose equivalent rates in various environments related to human lives were measured by walk surveys using the KURAMA-II systems from 2013 to 2016 within an 80-km radius of the Fukushima Dai-ichi Nuclear Power Plant. The dose rate of the locations where the walk survey was performed decreased to about 38% of its initial value in the 42 months from June 2013 to the December 2016, which was beyond that attributable to the physical decay of radiocaesium. The ecological half-life of the slow decreasing component was evaluated to be 4.1 ± 0.2 y. The air dose rates decreased depending on the level of the evacuation areas, and the decrease in the dose rates was slightly larger in populated areas where humans are active. The dose rates as measured by walk surveys exhibited a good correlation with those by car-borne surveys, suggesting that car-borne survey data are reflecting the air dose rates in living environments surrounding roads. The comparison of walk survey data with car-borne survey data indicated that the air dose rate varies largely even within a 100 m square area, and the variation is enhanced by human activities. The dose rates measured by the walk surveys were estimated to be medial of those along roads and those of undisturbed flat ground, and they were found to be decreasing quickly compared with the air dose rate from the flat ground fixed-point measurements. Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.

Uranium analysis in some food samples collected from Bathinda area of Punjab, India

NASA Astrophysics Data System (ADS)

Kumar, Mukesh; Prasher, Sangeeta; Singh, Surinder

2009-07-01

To strengthen the radiation protection infrastructure in Bathinda, the uranium concentration in daily diet of the residents has been measured and its associated radiation risks were estimated for the adult population. Food samples were collected from major cancer prone areas of the district, from which daily diets were prepared. These diet samples were analyzed using fission track technique. The measured values of the uranium content were found to vary from 0.38 mBq/g in mustard seeds to 4.60 mBq/g in wheat. In case of milk the uranium content is found to vary from 28.57-213.36 mBq/ℓ with mean concentration of 61.35 mBq/ℓ. This leads to a daily dietary intake of 0.90 Bq/day. The measured value of 0.90 Bq d-1, contributes to 1.12 mSv to the cumulative effective dose to the population. This dose is much large than the International Commission for Radiological Protection (ICRP) annual effective dose limit of 1 mSv for the general public [1]. Therefore, it would pose significant health hazard.

Whole-body to tissue concentration ratios for use in biota dose assessments for animals.

PubMed

Yankovich, Tamara L; Beresford, Nicholas A; Wood, Michael D; Aono, Tasuo; Andersson, Pål; Barnett, Catherine L; Bennett, Pamela; Brown, Justin E; Fesenko, Sergey; Fesenko, J; Hosseini, Ali; Howard, Brenda J; Johansen, Mathew P; Phaneuf, Marcel M; Tagami, Keiko; Takata, Hyoe; Twining, John R; Uchida, Shigeo

2010-11-01

Environmental monitoring programs often measure contaminant concentrations in animal tissues consumed by humans (e.g., muscle). By comparison, demonstration of the protection of biota from the potential effects of radionuclides involves a comparison of whole-body doses to radiological dose benchmarks. Consequently, methods for deriving whole-body concentration ratios based on tissue-specific data are required to make best use of the available information. This paper provides a series of look-up tables with whole-body:tissue-specific concentration ratios for non-human biota. Focus was placed on relatively broad animal categories (including molluscs, crustaceans, freshwater fishes, marine fishes, amphibians, reptiles, birds and mammals) and commonly measured tissues (specifically, bone, muscle, liver and kidney). Depending upon organism, whole-body to tissue concentration ratios were derived for between 12 and 47 elements. The whole-body to tissue concentration ratios can be used to estimate whole-body concentrations from tissue-specific measurements. However, we recommend that any given whole-body to tissue concentration ratio should not be used if the value falls between 0.75 and 1.5. Instead, a value of one should be assumed.

[Diagnostic reference levels in interventional radiology].

PubMed

Vañó Carruana, E; Fernández Soto, J M; Sánchez Casanueva, R M; Ten Morón, J I

2013-12-01

This article discusses the diagnostic reference levels for radiation exposure proposed by the International Commission on Radiological Protection (ICRP) to facilitate the application of the optimization criteria in diagnostic imaging and interventional procedures. These levels are normally established as the third quartile of the dose distributions to patients in an ample sample of centers and are supposed to be representative of good practice regarding patient exposure. In determining these levels, it is important to evaluate image quality as well to ensure that it is sufficient for diagnostic purposes. When the values for the dose received by patients are systematically higher or much lower than the reference levels, an investigation should determine whether corrective measures need to be applied. The European and Spanish regulations require the use of these reference values in quality assurance programs. For interventional procedures, the dose area product (or kerma area product) values are usually used as reference values together with the time under fluoroscopy and the total number of images acquired. The most modern imaging devices allow the value of the accumulated dose at the entrance to the patient to be calculated to optimize the distribution of the dose on the skin. The ICRP recommends that the complexity of interventional procedures be taken into account when establishing reference levels. In the future, diagnostic imaging departments will have automatic systems to manage patient dosimetric data; these systems will enable continuous dosage auditing and alerts about individual procedures that might involve doses several times above the reference values. This article also discusses aspects that need to be clarified to take better advantage of the reference levels in interventional procedures. Copyright © 2013 SERAM. Published by Elsevier Espana. All rights reserved.

Spatial variation of dosimetric leaf gap and its impact on dose delivery

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumaraswamy, Lalith K., E-mail: Lalith.Kumaraswamy@roswellpark.org; Schmitt, Jonathan D.; Bailey, Daniel W.

Purpose: During dose calculation, the Eclipse treatment planning system (TPS) retracts the multileaf collimator (MLC) leaf positions by half of the dosimetric leaf gap (DLG) value (measured at central axis) for all leaf positions in a dynamic MLC plan to accurately model the rounded leaf ends. The aim of this study is to map the variation of DLG along the travel path of each MLC leaf pair and quantify how this variation impacts delivered dose. Methods: 6 MV DLG values were measured for all MLC leaf pairs in increments of 1.0 cm (from the line intersecting the CAX and perpendicularmore » to MLC motion) to 13.0 cm off axis distance at dmax. The measurements were performed on two Varian linear accelerators, both employing the Millennium 120-leaf MLCs. The measurements were performed at several locations in the beam with both a Sun Nuclear MapCHECK device and a PTW pinpoint ion chamber. Results: The measured DLGs for the middle 40 MLC leaf pairs (each 0.5 cm width) at positions along a line through the CAX and perpendicular to MLC leaf travel direction were very similar, varying maximally by only 0.2 mm. The outer 20 MLC leaf pairs (each 1.0 cm width) have much lower DLG values, about 0.3–0.5 mm lower than the central MLC leaf pair, at their respective central line position. Overall, the mean and the maximum variation between the 0.5 cm width leaves and the 1.0 cm width leaf pairs are 0.32 and 0.65 mm, respectively. Conclusions: The spatial variation in DLG is caused by the variation of intraleaf transmission through MLC leaves. Fluences centered on the CAX would not be affected since DLG does not vary; but any fluences residing significantly off axis with narrow sweeping leaves may exhibit significant dose differences. This is due to the fact that there are differences in DLG between the true DLG exhibited by the 1.0 cm width outer leaves and the constant DLG value utilized by the TPS for dose calculation. Since there are large differences in DLG between the 0.5 cm width leaf pairs and 1.0 cm width leaf pairs, there is a need to correct the TPS plans, especially those with high modulation (narrow dynamic MLC gap), with 2D variation of DLG.« less

SU-F-T-17: A Feasibility Study for the Transit Dosimetry with a Glass Dosimeter in Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moon, S; Yoon, M; Chung, W

Purpose: Confirming the dose delivered to a patient is important to make sure the treatment quality and safety of the radiotherapy. Measuring a transit dose of the patient during the radiotherapy could be an interesting way to confirm the patient dose. In this study, we evaluated the feasibility of the transit dosimetry with a glass dosimeter in brachytherapy. Methods: We made a phantom that inserted the glass dosimeters and placed under patient lying on a couch for cervix cancer brachytherapy. The 18 glass dosimeters were placed in the phantom arranged 6 per row. A point putting 1cm vertically from themore » source was prescribed as 500.00 cGy. Solid phantoms of 0, 2, 4, 6, 8, 10 cm were placed between the source and the glass dosimeter. The transit dose was measured each thickness using the glass dosimeters and compared with a treatment planning system (TPS). Results: When the transit dose was smaller than 10 cGy, the average of the differences between measured values and calculated values by TPS was 0.50 cGy and the standard deviation was 0.69 cGy. If the transit dose was smaller than 100 cGy, the average of the error was 1.67 ± 4.01 cGy. The error to a point near the prescription point was −14.02 cGy per 500.00 cGy of the prescription dose. Conclusion: The distances from the sources to skin of the patient generally are within 10 cm for cervix cancer cases in brachytherapy. The results of this preliminary study showed the probability of the glass dosimeter as the transit dosimeter in brachytherapy.« less

Evaluating health risks from occupational exposure to pesticides and the regulatory response.

PubMed Central

Woodruff, T J; Kyle, A D; Bois, F Y

1994-01-01

In this study, we used measurements of occupational exposures to pesticides in agriculture to evaluate health risks and analyzed how the federal regulatory program is addressing these risks. Dose estimates developed by the State of California from measured occupational exposures to 41 pesticides were compared to standard indices of acute toxicity (LD50) and chronic effects (reference dose). Lifetime cancer risks were estimated using cancer potencies. Estimated absorbed daily doses for mixers, loaders, and applicators of pesticides ranged from less than 0.0001% to 48% of the estimated human LD50 values, and doses for 10 of 40 pesticides exceeded 1% of the estimated human LD50 values. Estimated lifetime absorbed daily doses ranged from 0.1% to 114,000% of the reference doses developed by the U.S. Environmental Protection Agency, and doses for 13 of 25 pesticides were above them. Lifetime cancer risks ranged from 1 per million to 1700 per million, and estimates for 12 of 13 pesticides were above 1 per million. Similar results were obtained for field workers and flaggers. For the pesticides examined, exposures pose greater risks of chronic effects than acute effects. Exposure reduction measures, including use of closed mixing systems and personal protective equipment, significantly reduced exposures. Proposed regulations rely primarily on requirements for personal protective equipment and use restrictions to protect workers. Chronic health risks are not considered in setting these requirements. Reviews of pesticides by the federal pesticide regulatory program have had little effect on occupational risks. Policy strategies that offer immediate protection for workers and that are not dependent on extensive review of individual pesticides should be pursued. Images Figure 1. PMID:7713022

A Low LET Radiation Spectrometer for Measuring Particle Doses in Space and Aircraft

NASA Technical Reports Server (NTRS)

Stassinopoulos, E. G.; Stauffer, C. A.; Brucker, G. J.; Dachev, T. P.; Day, John H. (Technical Monitor)

2002-01-01

This paper presents experimental data that demonstrates the feasibility of fabricating a miniature nuclear particle dosimeter for monitoring doses in aircraft and satellites. The basic instrument is a Low Linear-Energy-Transfer (LET) Radiation Spectrometer (LoLRS) that is designed to measure the energy deposited by particles with low LET values. The heart of the instrument is a Silicon-Lithium Drifted Diode (SLDD). Test results show that the LoLRS can be used to monitor the radiation threat to personnel in flights of space- and aircraft and also to generate a comprehensive data base from aviation and satellite measurements that can contribute to the formulation of more accurate environmental radiation models for dose predictions with reduced uncertainty factors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hartman, E. Frederick; Zarick, Thomas Andrew; Sheridan, Timothy J.

We performed measurements and analyses of the prompt radiation-induced conductivity (RIC) in thin samples of polyurethane foam and glass microballoon foam at the Little Mountain Medusa LINAC facility in Ogden, UT. The RIC coefficient was non-linear with dose rate for polyurethane foam; however, typical values at 1E11 rad(si)/s dose rate was measured as 0.8E-11 mho/m/rad/s for 5 lb./cu ft. foam and 0.3E-11 mho/m/rad/s for 10 lb./cu ft. density polyurethane foam. For encapsulated glass microballoons (GMB) the RIC coefficient was approximately 1E-15 mho/m/rad/s and was not a strong function of dose rate.

First radon measurements and occupational exposure assessments in underground geodynamic laboratory the Polish Academy of Sciences Space Research Centre in Książ Castle (SW Poland).

PubMed

Fijałkowska-Lichwa, Lidia; Przylibski, Tadeusz A

2016-12-01

The article presents the results of the first radon activity concentration measurements conducted continuously between 17 th May 2014 and 16 th May 2015 in the underground geodynamic laboratory of the Polish Academy of Sciences Space Research Centre in Książ. The data were registered with the use of three Polish semiconductor SRDN-3 detectors located the closest (SRDN-3 No. 6) to and the furthest (SRDN-3 No. 3) from the facility entrance, and in the fault zone (SRDN-3 No. 4). The study was conducted to characterize the radon behaviour and check it possibility to use with reference to long- and short-term variations of radon activity concentration observed in sedimentary rocks strongly fractured and intersected by systems of multiple faults, for integrated comparative assessments of changes in local orogen kinetics. The values of radon activity concentration in the underground geodynamic laboratory of the Polish Academy of Sciences (PAN) Space Research Centre in Książ undergo changes of a distinctly seasonal character. The highest values of radon activity concentration are recorded from late spring (May/June) to early autumn (October), and the lowest - from November to April. Radon activity concentrations varied depending on the location of measurement points. Between late spring and autumn they ranged from 800 Bq·m -3 to 1200 Bq·m -3 , and even 3200 Bq·m -3 in the fault zone. Between November and April, values of radon activity concentration are lower, ranging from 500 Bq·m -3 to 1000 Bq·m -3 and 2700 Bq·m -3 in the fault zone. The values of radon activity concentration recorded in the studied facility did not undergo short-term changes in either the whole annual measuring cycle or any of its months. Effective doses received by people staying in the underground laboratory range from 0.001 mSv/h to 0.012 mSv/h. The mean annual effective dose, depending on the measurement site, equals 1 or is slightly higher than 10 mSv/year, while the maximum dose exceeds 20 mSv/year. The estimated annual effective doses are comparable to the standard value of 20 mSv/year defined by Polish law for people employed in the conditions of radiation exposure. They are also in the range of annual effective dose value (8 mSv/year) recommended in workplaces by International Commission on Radiation Protection. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dose-dependent effects of vitamin 1,25(OH)2D3 on oxidative stress and apoptosis.

PubMed

Cakici, Cagri; Yigitbasi, Turkan; Ayla, Sule; Karimkhani, Hadi; Bayramoglu, Feyza; Yigit, Pakize; Kilic, Ertugrul; Emekli, Nesrin

2018-02-08

Background The purpose of this study is to examine the dose-dependent effects of vitamin 1,25(OH)2D3 on apoptosis and oxidative stress. Methods In this study, 50 male Balb/c mice were used as control and experiment groups. The mice were divided into 5 groups each consisting of 10 mice. Calcitriol was intraperitoneally administered as low dose, medium dose, medium-high dose and high dose vitamin D groups (at 0.5, 1, 5 and 10 μg/kg, respectively), for three times a week during 14 days. At the end of the study, annexin V was measured by enzyme-linked immunosorbent assay method, and total antioxidant capacity and total oxidant status values were measured by colorimetric method in serum. Hematoxylin eosin staining was performed in liver tissues and periodic acid schiff staining was performed in kidney tissues. Results While comparing the results of medium-high dose (5 μg/kg) and high dose (10 μg/kg) vitamin D administration to that of the control group, it was observed that serum antioxidant status and annexin V levels decreased and glomerular mesenchial matrix ratio increased in kidney (p<0.05). In addition to these findings, in the group receiving high dose vitamin D (10 μg/kg), it was observed that the damage to the liver increased together with the the oxidative stress index values (p<0.05). Conclusions As a result, this study was the first in the literature to report that use of high-dose vitamin D (10 μg/kg) results in oxidant effect, rather than being an antioxidant, and causes severe histopathological toxicity in the liver and kidney.

Experimental analysis of a novel and low-cost pin photodiode dosimetry system for diagnostic radiology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nazififard, Mohammad, E-mail: nazifi@kashanu.ac.ir; Mahmoudieh, Afshin; Suh, Kune Y.

Silicon PIN photodiode has recently found broad and exciting applications in the ionizing radiation dosimetry. In this study a compact and novel dosimetry system using a commercially available PIN photodiode (BPW34) has been experimentally tested for diagnostic radiology. The system was evaluated with clinical beams routinely used for diagnostic radiology and calibrated using a secondary reference standard. Measured dose with PIN photodiode (Air Kerma) varied from 10 to 430 μGy for tube voltages from 40 to 100 kVp and tube current from 0.4 to 40 mAs. The minimum detectable organ dose was estimated to be 10 μGy with 20% uncertainty.more » Results showed a linear correlation between the PIN photodiode readout and dose measured with standard dosimeters spanning doses received. The present dosimetry system having advantages of suitable sensitivity with immediate readout of dose values, low cost, and portability could be used as an alternative to passive dosimetry system such as thermoluminescent dosimeter for dose measurements in diagnostic radiology.« less

Convolutional auto-encoder for image denoising of ultra-low-dose CT.

PubMed

Nishio, Mizuho; Nagashima, Chihiro; Hirabayashi, Saori; Ohnishi, Akinori; Sasaki, Kaori; Sagawa, Tomoyuki; Hamada, Masayuki; Yamashita, Tatsuo

2017-08-01

The purpose of this study was to validate a patch-based image denoising method for ultra-low-dose CT images. Neural network with convolutional auto-encoder and pairs of standard-dose CT and ultra-low-dose CT image patches were used for image denoising. The performance of the proposed method was measured by using a chest phantom. Standard-dose and ultra-low-dose CT images of the chest phantom were acquired. The tube currents for standard-dose and ultra-low-dose CT were 300 and 10 mA, respectively. Ultra-low-dose CT images were denoised with our proposed method using neural network, large-scale nonlocal mean, and block-matching and 3D filtering. Five radiologists and three technologists assessed the denoised ultra-low-dose CT images visually and recorded their subjective impressions of streak artifacts, noise other than streak artifacts, visualization of pulmonary vessels, and overall image quality. For the streak artifacts, noise other than streak artifacts, and visualization of pulmonary vessels, the results of our proposed method were statistically better than those of block-matching and 3D filtering (p-values < 0.05). On the other hand, the difference in the overall image quality between our proposed method and block-matching and 3D filtering was not statistically significant (p-value = 0.07272). The p-values obtained between our proposed method and large-scale nonlocal mean were all less than 0.05. Neural network with convolutional auto-encoder could be trained using pairs of standard-dose and ultra-low-dose CT image patches. According to the visual assessment by radiologists and technologists, the performance of our proposed method was superior to that of large-scale nonlocal mean and block-matching and 3D filtering.

Experimental depth dose curves of a 67.5 MeV proton beam for benchmarking and validation of Monte Carlo simulation

PubMed Central

Faddegon, Bruce A.; Shin, Jungwook; Castenada, Carlos M.; Ramos-Méndez, José; Daftari, Inder K.

2015-01-01

Purpose: To measure depth dose curves for a 67.5 ± 0.1 MeV proton beam for benchmarking and validation of Monte Carlo simulation. Methods: Depth dose curves were measured in 2 beam lines. Protons in the raw beam line traversed a Ta scattering foil, 0.1016 or 0.381 mm thick, a secondary emission monitor comprised of thin Al foils, and a thin Kapton exit window. The beam energy and peak width and the composition and density of material traversed by the beam were known with sufficient accuracy to permit benchmark quality measurements. Diodes for charged particle dosimetry from two different manufacturers were used to scan the depth dose curves with 0.003 mm depth reproducibility in a water tank placed 300 mm from the exit window. Depth in water was determined with an uncertainty of 0.15 mm, including the uncertainty in the water equivalent depth of the sensitive volume of the detector. Parallel-plate chambers were used to verify the accuracy of the shape of the Bragg peak and the peak-to-plateau ratio measured with the diodes. The uncertainty in the measured peak-to-plateau ratio was 4%. Depth dose curves were also measured with a diode for a Bragg curve and treatment beam spread out Bragg peak (SOBP) on the beam line used for eye treatment. The measurements were compared to Monte Carlo simulation done with geant4 using topas. Results: The 80% dose at the distal side of the Bragg peak for the thinner foil was at 37.47 ± 0.11 mm (average of measurement with diodes from two different manufacturers), compared to the simulated value of 37.20 mm. The 80% dose for the thicker foil was at 35.08 ± 0.15 mm, compared to the simulated value of 34.90 mm. The measured peak-to-plateau ratio was within one standard deviation experimental uncertainty of the simulated result for the thinnest foil and two standard deviations for the thickest foil. It was necessary to include the collimation in the simulation, which had a more pronounced effect on the peak-to-plateau ratio for the thicker foil. The treatment beam, being unfocussed, had a broader Bragg peak than the raw beam. A 1.3 ± 0.1 MeV FWHM peak width in the energy distribution was used in the simulation to match the Bragg peak width. An additional 1.3–2.24 mm of water in the water column was required over the nominal values to match the measured depth penetration. Conclusions: The proton Bragg curve measured for the 0.1016 mm thick Ta foil provided the most accurate benchmark, having a low contribution of proton scatter from upstream of the water tank. The accuracy was 0.15% in measured beam energy and 0.3% in measured depth penetration at the Bragg peak. The depth of the distal edge of the Bragg peak in the simulation fell short of measurement, suggesting that the mean ionization potential of water is 2–5 eV higher than the 78 eV used in the stopping power calculation for the simulation. The eye treatment beam line depth dose curves provide validation of Monte Carlo simulation of a Bragg curve and SOBP with 4%/2 mm accuracy. PMID:26133619

Measurement of computed tomography dose profile with pitch variation using Gafchromic XR-QA2 and thermoluminescence dosimeter (TLD)

NASA Astrophysics Data System (ADS)

Purwaningsih, S.; Lubis, L. E.; Pawiro, S. A.; Soejoko, D. S.

2016-03-01

This research was aimed to check the patterns of dose profile on adult and pediatric head scan. We compared measurement result on dose profile along the z- axis rotation at peripheries and center phantom with a variety of pitch, i.e. 0.75, 1, 1.5 for adult and pediatric head protocol, keeping the rest of the scan parameters constant. Measurements were performed on homogeneous, cylindrical PMMA phantom with diameters of 16 and 10 cm using XR-QA2 Gafchromic film and TLD as dosimeters. The measurement result indicated a decrease in the dose about 50% and 47% for adult and pediatric head scan with the increase of pitch. For 0.75 value of pitch adult head scan, dose range for each position were (2.4 - 5.0) cGy, (3.1 - 5.3) cGy, (2.2 - 4.5) cGy, (2.8 - 5.3) cGy, and (3.3 - 5.6) cGy for position of center, 3, 6, 9 and 12 o'clock peripheral phantom position respectively. Dose profile for adult and pediatric head scan protocols has pattern curve with the maximum dose in the middle and tendency of symmetry near the edges, with different the plateau length along z- axis direction in accordance to the measurement position in the phantom.

Simulation and experimental measurement of radon activity using a multichannel silicon-based radiation detector.

PubMed

Ozdemir, F B; Selcuk, A B; Ozkorucuklu, S; Alpat, A B; Ozdemir, T; Ӧzek, N

2018-05-01

In this study, high-precision radiation detector (HIPRAD), a new-generation semiconductor microstrip detector, was used for detecting radon (Rn-222) activity. The aim of this study was to detect radon (Rn-222) activity experimentally by measuring the energy of particles in this detector. Count-ADC channel, eta-charge, and dose-response values were experimentally obtained using HIPRAD. The radon simulation in the radiation detector was theoretically performed using the Geant4 software package. The obtained radioactive decay, energy generation, energy values, and efficiency values of the simulation were plotted using the root program. The new-generation radiation detector proved to have 95% reliability according to the obtained dose-response graphs. The experimental and simulation results were found to be compatible with each other and with the radon decays and literature studies. Copyright © 2018 Elsevier Ltd. All rights reserved.

Biases in Multicenter Longitudinal PET Standardized Uptake Value Measurements1

PubMed Central

Doot, Robert K; Pierce, Larry A; Byrd, Darrin; Elston, Brian; Allberg, Keith C; Kinahan, Paul E

2014-01-01

This study investigates measurement biases in longitudinal positron-emission tomography/computed tomography (PET/CT) studies that are due to instrumentation variability including human error. Improved estimation of variability between patient scans is of particular importance for assessing response to therapy and multicenter trials. We used National Institute of Standards and Technology-traceable calibration methodology for solid germanium-68/gallium-68 (68Ge/68Ga) sources used as surrogates for fluorine-18 (18F) in radionuclide activity calibrators. One cross-calibration kit was constructed for both dose calibrators and PET scanners using the same 9-month half-life batch of 68Ge/68Ga in epoxy. Repeat measurements occurred in a local network of PET imaging sites to assess standardized uptake value (SUV) errors over time for six dose calibrators from two major manufacturers and for six PET/CT scanners from three major manufacturers. Bias in activity measures by dose calibrators ranged from -50% to 9% and was relatively stable over time except at one site that modified settings between measurements. Bias in activity concentration measures by PET scanners ranged from -27% to 13% with a median of 174 days between the six repeat scans (range, 29 to 226 days). Corresponding errors in SUV measurements ranged from -20% to 47%. SUV biases were not stable over time with longitudinal differences for individual scanners ranging from -11% to 59%. Bias in SUV measurements varied over time and between scanner sites. These results suggest that attention should be paid to PET scanner calibration for longitudinal studies and use of dose calibrator and scanner cross-calibration kits could be helpful for quality assurance and control. PMID:24772207

Fractionation in normal tissues: the (α/β)eff concept can account for dose heterogeneity and volume effects.

PubMed

Hoffmann, Aswin L; Nahum, Alan E

2013-10-07

The simple Linear-Quadratic (LQ)-based Withers iso-effect formula (WIF) is widely used in external-beam radiotherapy to derive a new tumour dose prescription such that there is normal-tissue (NT) iso-effect when changing the fraction size and/or number. However, as conventionally applied, the WIF is invalid unless the normal-tissue response is solely determined by the tumour dose. We propose a generalized WIF (gWIF) which retains the tumour prescription dose, but replaces the intrinsic fractionation sensitivity measure (α/β) by a new concept, the normal-tissue effective fractionation sensitivity, [Formula: see text], which takes into account both the dose heterogeneity in, and the volume effect of, the late-responding normal-tissue in question. Closed-form analytical expressions for [Formula: see text] ensuring exact normal-tissue iso-effect are derived for: (i) uniform dose, and (ii) arbitrary dose distributions with volume-effect parameter n = 1 from the normal-tissue dose-volume histogram. For arbitrary dose distributions and arbitrary n, a numerical solution for [Formula: see text] exhibits a weak dependence on the number of fractions. As n is increased, [Formula: see text] increases from its intrinsic value at n = 0 (100% serial normal-tissue) to values close to or even exceeding the tumour (α/β) at n = 1 (100% parallel normal-tissue), with the highest values of [Formula: see text] corresponding to the most conformal dose distributions. Applications of this new concept to inverse planning and to highly conformal modalities are discussed, as is the effect of possible deviations from LQ behaviour at large fraction sizes.

Experimental verification of the Acuros XB and AAA dose calculation adjacent to heterogeneous media for IMRT and RapidArc of nasopharygeal carcinoma.

PubMed

Kan, Monica W K; Leung, Lucullus H T; So, Ronald W K; Yu, Peter K N

2013-03-01

To compare the doses calculated by the Acuros XB (AXB) algorithm and analytical anisotropic algorithm (AAA) with experimentally measured data adjacent to and within heterogeneous medium using intensity modulated radiation therapy (IMRT) and RapidArc(®) (RA) volumetric arc therapy plans for nasopharygeal carcinoma (NPC). Two-dimensional dose distribution immediately adjacent to both air and bone inserts of a rectangular tissue equivalent phantom irradiated using IMRT and RA plans for NPC cases were measured with GafChromic(®) EBT3 films. Doses near and within the nasopharygeal (NP) region of an anthropomorphic phantom containing heterogeneous medium were also measured with thermoluminescent dosimeters (TLD) and EBT3 films. The measured data were then compared with the data calculated by AAA and AXB. For AXB, dose calculations were performed using both dose-to-medium (AXB_Dm) and dose-to-water (AXB_Dw) options. Furthermore, target dose differences between AAA and AXB were analyzed for the corresponding real patients. The comparison of real patient plans was performed by stratifying the targets into components of different densities, including tissue, bone, and air. For the verification of planar dose distribution adjacent to air and bone using the rectangular phantom, the percentages of pixels that passed the gamma analysis with the ± 3%/3mm criteria were 98.7%, 99.5%, and 97.7% on the axial plane for AAA, AXB_Dm, and AXB_Dw, respectively, averaged over all IMRT and RA plans, while they were 97.6%, 98.2%, and 97.7%, respectively, on the coronal plane. For the verification of planar dose distribution within the NP region of the anthropomorphic phantom, the percentages of pixels that passed the gamma analysis with the ± 3%/3mm criteria were 95.1%, 91.3%, and 99.0% for AAA, AXB_Dm, and AXB_Dw, respectively, averaged over all IMRT and RA plans. Within the NP region where air and bone were present, the film measurements represented the dose close to unit density water in a heterogeneous medium, produced the best agreement with the AXB_Dw. For the verification of point doses within the target using TLD in the anthropomorphic phantom, the absolute percentage deviations between the calculated and measured data when averaged over all IMRT and RA plans were 1.8%, 1.7%, and 1.8% for AAA, AXB_Dm and AXB_Dw, respectively. From all the verification results, no significant difference was found between the IMRT and RA plans. The target dose analysis of the real patient plans showed that the discrepancies in mean doses to the PTV component in tissue among the three dose calculation options were within 2%, but up to about 4% in the bone content, with AXB_Dm giving the lowest values and AXB_Dw giving the highest values. In general, the verification measurements demonstrated that both algorithms produced acceptable accuracy when compared to the measured data. GafChromic(®) film results indicated that AXB produced slightly better accuracy compared to AAA for dose calculation adjacent to and within the heterogeneous media. Users should be aware of the differences in calculated target doses between options AXB_Dm and AXB_Dw, especially in bone, for IMRT and RA in NPC cases.

Preliminary results of an attempt to predict over apron occupational exposure of cardiologists from cardiac fluoroscopy procedures based on DAP (dose area product) values.

PubMed

Toossi, Mohammad Taghi Bahreyni; Mehrpouyan, Mohammad; Nademi, Hossein; Fardid, Reza

2015-03-01

This study is an effort to propose a mathematical relation between the occupational exposure measured by a dosimeter worn on a lead apron in the chest region of a cardiologist and the dose area product (DAP) recorded by a meter attached to the X-ray tube. We aimed to determine factors by which DAP values attributed to patient exposure could be converted to the over-apron entrance surface air kerma incurred by cardiologists during an angiographic procedure. A Rando phantom representing a patient was exposed by an X-ray tube from 77 pre-defined directions. DAP value for each exposure angle was recorded. Cardiologist exposure was measured by a Radcal ionization chamber 10X5-180 positioned on a second phantom representing the physician. The exposure conversion factor was determined as the quotient of over apron exposure by DAP value. To verify the validity of this method, the over-apron exposure of a cardiologist was measured using the ionization chamber while performing coronary angiography procedures on 45 patients weighing on average 75 ± 5 kg. DAP values for the corresponding procedures were also obtained. Conversion factors obtained from phantom exposure were applied to the patient DAP values to calculate physician exposure. Mathematical analysis of our results leads us to conclude that a linear relationship exists between two sets of data: (a) cardiologist exposure measured directly by Radcal & DAP values recorded by the X-ray machine system (R (2) = 0.88), (b) specialist measured and estimated exposure derived from DAP values (R (2) = 0.91). The results demonstrate that cardiologist occupational exposure can be derived from patient data accurately.

Fiber-optic detector for real time dosimetry of a micro-planar x-ray beam

PubMed Central

Belley, Matthew D.; Stanton, Ian N.; Hadsell, Mike; Ger, Rachel; Langloss, Brian W.; Lu, Jianping; Zhou, Otto; Chang, Sha X.; Therien, Michael J.; Yoshizumi, Terry T.

2015-01-01

Purpose: Here, the authors describe a dosimetry measurement technique for microbeam radiation therapy using a nanoparticle-terminated fiber-optic dosimeter (nano-FOD). Methods: The nano-FOD was placed in the center of a 2 cm diameter mouse phantom to measure the deep tissue dose and lateral beam profile of a planar x-ray microbeam. Results: The continuous dose rate at the x-ray microbeam peak measured with the nano-FOD was 1.91 ± 0.06 cGy s−1, a value 2.7% higher than that determined via radiochromic film measurements (1.86 ± 0.15 cGy s−1). The nano-FOD-determined lateral beam full-width half max value of 420 μm exceeded that measured using radiochromic film (320 μm). Due to the 8° angle of the collimated microbeam and resulting volumetric effects within the scintillator, the profile measurements reported here are estimated to achieve a resolution of ∼0.1 mm; however, for a beam angle of 0°, the theoretical resolution would approach the thickness of the scintillator (∼0.01 mm). Conclusions: This work provides proof-of-concept data and demonstrates that the novel nano-FOD device can be used to perform real-time dosimetry in microbeam radiation therapy to measure the continuous dose rate at the x-ray microbeam peak as well as the lateral beam shape. PMID:25832087

Skin Dosimetry in Breast Teletherapy on a Phantom Anthropomorphic and Anthropometric Phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Batista Nogueira, Luciana; Lemos Silva, Hugo Leonardo; Donato da Silva, Sabrina

This paper addresses the breast teletherapy dosimetry. The goal is to evaluate and compare absorbed doses in equivalent skin tissue, TE-skin, of an anthropomorphic and anthropometric breast phantom submitted to breast radiotherapy. The methodology involved the reproduction of a set of tomographic images of the phantom; the elaboration of conformational radiotherapy planning in the SOMAVISION and CadPlan (TPS) software; and the synthetic breast irradiation by parallel opposed fields in 3D conformal teletherapy at 6 MV linear accelerator Clinac-2100 C from VARIAN with prescribed dose (PD) of 180 cGy to the target volume (PTV), referent to the glandular tissue. Radiochromic filmsmore » EBT2 were selected as dosimeters. Two independent calibration processes of films with solid water Gammex 457 plates and water filled box were produced. Curves of optical density (OD) versus absorbed dose were produced. Dosimeters were positioned in the external region of the breast phantom in contact with TE-skin, area of 4.0 cm{sup 2} each. The irradiation process was prepared in duplicate to check the reproducibility of the technique. The radiochromic films were scanned and their response in RGB (Red, Green, Blue) analyzed by the ImageJ software. The optical density was obtained and converted to dose based on the calibration curves. Thus, the spatial dose distribution in the skin was reproduced. The absorbed doses measured on the radiochromic films in TE-skin showed values between upper and lower quadrants at 9 o'clock in the range of 54% of PD, between the upper and lower quadrants 3 o'clock in the range of 72% and 6 o'clock at the lower quadrant in the range of 68 % of PD. The values are ±64% (p <0.05) according to the TPS. It is concluded that the depth dose measured in solid water plates or water box reproduce equivalent dose values for both calibration processes of the radiochromic films. It was observed that the skin received doses ranging from 50% to 78% of the prescribed dose after two parallel opposed irradiation fields. (authors)« less

Evaluation of polymer gels and MRI as a 3-D dosimeter for intensity-modulated radiation therapy.

PubMed

Low, D A; Dempsey, J F; Venkatesan, R; Mutic, S; Markman, J; Mark Haacke, E; Purdy, J A

1999-08-01

BANG gel (MGS Research, Inc., Guilford, CT) has been evaluated for measuring intensity-modulated radiation therapy (IMRT) dose distributions. Treatment plans with target doses of 1500 cGy were generated by the Peacock IMRT system (NOMOS Corp., Sewickley, PA) using test target volumes. The gels were enclosed in 13 cm outer diameter cylindrical glass vessels. Dose calibration was conducted using seven smaller (4 cm diameter) cylindrical glass vessels irradiated to 0-1800 cGy in 300 cGy increments. Three-dimensional maps of the proton relaxation rate R2 were obtained using a 1.5 T magnetic resonance imaging (MRI) system (Siemens Medical Systems, Erlangen, Germany) and correlated with dose. A Hahn spin echo sequence was used with TR = 3 s, TE = 20 and 100 ms, NEX = 1, using 1 x 1 x 3 mm3 voxels. The MRI measurements were repeated weekly to identify the gel-aging characteristics. Ionization chamber, thermoluminescent dosimetry (TLD), and film dosimetry measurements of the IMRT dose distributions were obtained to compare against the gel results. The other dosimeters were used in a phantom with the same external cross-section as the gel phantom. The irradiated R2 values of the large vessels did not precisely track the smaller vessels, so the ionization chamber measurements were used to normalize the gel dose distributions. The point-to-point standard deviation of the gel dose measurements was 7.0 cGy. When compared with the ionization chamber measurements averaged over the chamber volume, 1% agreement was obtained. Comparisons against radiographic film dose distribution measurements and the treatment planning dose distribution calculation were used to determine the spatial localization accuracy of the gel and MRI. Spatial localization was better than 2 mm, and the dose was accurately determined by the gel both within and outside the target. The TLD chips were placed throughout the phantom to determine gel measurement precision in high- and low-dose regions. A multidimensional dose comparison tool that simultaneously examines the dose-difference and distance-to-agreement was used to evaluate the gel in both low-and high-dose gradient regions. When 3% and 3 mm criteria were used for the comparisons, more than 90% of the TLD measurements agreed with the gel, with the worst of 309 TLD chip measurements disagreeing by 40% of the criteria. All four MRI measurement session gel-measured dose distributions were compared to evaluate the time behavior of the gel. The low-dose regions were evaluated by comparison with TLD measurements at selected points, while high-dose regions were evaluated by directly comparing measured dose distributions. Tests using the multidimensional comparison tool showed detectable degradation beyond one week postirradiation, but all low-dose measurements passed relative to the test criteria and the dose distributions showed few regions that failed.

SU-E-T-67: A Quality Assurance Procedure for VMAT Delivery Technique with Multiple Verification Metric Using TG-119 Protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Katsuta, Y; Kadoya, N; Shimizu, E

2015-06-15

Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi-leaf collimator shapes. The purpose of this research is to construct routine QA protocol which focuses on VMAT delivery technique and to obtain a baseline including dose error, fluence distribution and mechanical accuracy during VMAT. Methods: The mock prostate, head and neck (HN) cases supplied from AAPM were used in this study. A VMAT plans were generated in Monaco TPS according to TG-119 protocol. Plans were created using 6 MV and 10 MV photon beams for each case. The phantom based measurement, fluence measurement andmore » log files analysis were performed. The dose measurement was performed using 0.6 cc ion chamber, which located at isocenter. The fluence distribution were acquired using the MapCHECK2 mounted in the MapPHAN. The trajectory log files recorded inner 20 leaf pairs and gantry angle positions at every 0.25 sec interval were exported to in-house software developed by MATLAB and determined those RMS values. Results: The dose difference is expressed as a ratio of the difference between measured and planned doses. The dose difference for 6 MV was 0.91%, for 10 MV was 0.67%. In turn, the fluence distribution using gamma criteria of 2%/2 mm with a 50% minimum dose threshold for 6 MV was 98.8%, for 10 MV was 97.5%, respectively. The RMS values of MLC for 6 MV and 10 MV were 0.32 mm and 0.37 mm, of gantry were 0.33 degree and 0.31 degree. Conclusion: In this study, QA protocol to assess VMAT delivery accuracy is constructed and results acquired in this study are used as a baseline of VMAT delivery performance verification.« less

Entrance surface dose measurements using a small OSL dosimeter with a computed tomography scanner having 320 rows of detectors.

PubMed

Takegami, Kazuki; Hayashi, Hiroaki; Yamada, Kenji; Mihara, Yoshiki; Kimoto, Natsumi; Kanazawa, Yuki; Higashino, Kousaku; Yamashita, Kazuta; Hayashi, Fumio; Okazaki, Tohru; Hashizume, Takuya; Kobayashi, Ikuo

2017-03-01

Entrance surface dose (ESD) measurements are important in X-ray computed tomography (CT) for examination, but in clinical settings it is difficult to measure ESDs because of a lack of suitable dosimeters. We focus on the capability of a small optically stimulated luminescence (OSL) dosimeter. The aim of this study is to propose a practical method for using an OSL dosimeter to measure the ESD when performing a CT examination. The small OSL dosimeter has an outer width of 10 mm; it is assumed that a partial dose may be measured because the slice thickness and helical pitch can be set to various values. To verify our method, we used a CT scanner having 320 rows of detectors and checked the consistencies of the ESDs measured using OSL dosimeters by comparing them with those measured using Gafchromic™ films. The films were calibrated using an ionization chamber on the basis of half-value layer estimation. On the other hand, the OSL dosimeter was appropriately calibrated using a practical calibration curve previously proposed by our group. The ESDs measured using the OSL dosimeters were in good agreement with the reference ESDs from the Gafchromic™ films. Using these data, we also estimated the uncertainty of ESDs measured with small OSL dosimeters. We concluded that a small OSL dosimeter can be considered suitable for measuring the ESD with an uncertainty of 30 % during CT examinations in which pitch factors below 1.000 are applied.

Abdominal Pediatric Cancer Surveillance using Serial CT: Evaluation of Organ Absorbed Dose and Effective Dose

PubMed Central

Lam, Diana; Wootton-Gorges, Sandra L.; McGahan, John P.; Stern, Robin; Boone, John M.

2012-01-01

Computed tomography (CT) is used extensively in cancer diagnosis, staging, evaluation of response to treatment, and in active surveillance for cancer reoccurrence. A review of CT technology is provided, at a level of detail appropriate for a busy clinician to review. The basis of x-ray CT dosimetry is also discussed, and concepts of absorbed dose and effective dose are distinguished. Absorbed dose is a physical quantity (measured in milliGray) equal to the x-ray energy deposited in a mass of tissue, whereas effective dose utilizes an organ-specific weighting method which converts organ doses to effective dose measured in milliSieverts. The organ weighting values carry with them a measure of radiation risk, and so effective dose (in mSv) is not a physical dose metric but rather is one that conveys radiation risk. The use of CT in a cancer surveillance protocol was used as an example of a pediatric patient who had kidney cancer, with surgery and radiation therapy. The active use of CT for cancer surveillance along with diagnostic CT scans led to a total of 50 CT scans performed on this child in a 7 year period. It was estimated that the patient received an average organ dose of 431 mGy from these CT scans. By comparison, the radiation therapy was performed and delivered 50.4 Gy to the patient’s abdomen. Thus, the total dose from CT represented only 0.8% of the patients radiation dose. PMID:21362521

EFFECTIVE DOSE IN TWO DIFFERENT DENTAL CBCT SYSTEMS: NEWTOM VGi AND PLANMECA 3D MID.

PubMed

Ghaedizirgar, Mohammad; Faghihi, Reza; Paydar, Reza; Sina, Sedigheh

2017-11-01

Cone beam computed tomography, CBCT, is a kind of CT scanner producing conical diverging X-rays, in which a large area of a two-dimensional detector is irradiated in each rotation. Different investigations have been performed on dosimetry of dental CBCT. As there is no special protocol for dental CBCT, CT scan protocols are used for dosimetry. The purpose of this study is measurement of dose to head and neck organs in two CBCT systems, i.e. Planmeca 3D Mid (PM) and NewTom VGi (NT), using thermoluminescence dosimetry and Rando phantom. The thermoluminescent dosimetry (TLD)-100 chips were put at the position of different organs of the head and neck. Two TLD-100 chips were inserted at each position, the dose values were measured for several different field sizes, i.e. 8 × 8, 12 × 8 and 15 × 15 cm2 for NewTom, and 10 × 10 and 20 × 17 cm2 for Planmeca systems. According to the results, the average effective dose in PM is much more than the NT system in the same field size, because of the greater mAs values. For routine imaging protocols used for NT, the effective dose values are 70, 73 and 121 µSv for 8 × 8, 12 × 8 and 15 × 15 cm2 field sizes, respectively. In PM, the effective dose in 10 × 10 cm2 and 17 × 20 cm2 is 259 and 341 µSv, respectively. © The Author 2017. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Summary of LET spectra and dose measurements on ten STS missions

NASA Technical Reports Server (NTRS)

1995-01-01

A comparison of linear energy transfer (LET) spectra measurements made with plastic nuclear track detectors (PNTD's) from area passive dosimeters (APD's), was made for ten different STS missions under similar shielding. The results show that integral flux, dose rate and equivalent dose rate values follow a general increase with respect to increasing orbital inclination and altitude but that there are large variations from a simple relationship. This is to be expected since it has been shown that Shuttle attitude variations, combined with the anisotropic particle flux at the South Atlantic Anomaly (SAA), can result in differences of a factor of 2 in dose rate inside the Shuttle (Badhwar et al., 1995). Solar cycle and shielding differences also result in variations in radiation dose between STS missions. Spaceflight dosimeters from the STS missions are also being used in the development of a method for increasing LET spectra measurement accuracy by extending LET measurements to particle tracks of ranges 10-80 microns. Refinements in processing and measurement techniques for the flight PNTD's have yielded increased detection efficiencies for the short tracks when LET spectra determined by using the standard and refined methods were intercompared.

Small field depth dose profile of 6 MV photon beam in a simple air-water heterogeneity combination: A comparison between anisotropic analytical algorithm dose estimation with thermoluminescent dosimeter dose measurement.

PubMed

Mandal, Abhijit; Ram, Chhape; Mourya, Ankur; Singh, Navin

2017-01-01

To establish trends of estimation error of dose calculation by anisotropic analytical algorithm (AAA) with respect to dose measured by thermoluminescent dosimeters (TLDs) in air-water heterogeneity for small field size photon. TLDs were irradiated along the central axis of the photon beam in four different solid water phantom geometries using three small field size single beams. The depth dose profiles were estimated using AAA calculation model for each field sizes. The estimated and measured depth dose profiles were compared. The over estimation (OE) within air cavity were dependent on field size (f) and distance (x) from solid water-air interface and formulated as OE = - (0.63 f + 9.40) x2+ (-2.73 f + 58.11) x + (0.06 f2 - 1.42 f + 15.67). In postcavity adjacent point and distal points from the interface have dependence on field size (f) and equations are OE = 0.42 f2 - 8.17 f + 71.63, OE = 0.84 f2 - 1.56 f + 17.57, respectively. The trend of estimation error of AAA dose calculation algorithm with respect to measured value have been formulated throughout the radiation path length along the central axis of 6 MV photon beam in air-water heterogeneity combination for small field size photon beam generated from a 6 MV linear accelerator.

Evaluation of nonrigid registration models for interfraction dose accumulation in radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janssens, Guillaume; Orban de Xivry, Jonathan; Fekkes, Stein

2009-09-15

Purpose: Interfraction dose accumulation is necessary to evaluate the dose distribution of an entire course of treatment by adding up multiple dose distributions of different treatment fractions. This accumulation of dose distributions is not straightforward as changes in the patient anatomy may occur during treatment. For this purpose, the accuracy of nonrigid registration methods is assessed for dose accumulation based on the calculated deformations fields. Methods: A phantom study using a deformable cubic silicon phantom with implanted markers and a cylindrical silicon phantom with MOSFET detectors has been performed. The phantoms were deformed and images were acquired using a cone-beammore » CT imager. Dose calculations were performed on these CT scans using the treatment planning system. Nonrigid CT-based registration was performed using two different methods, the Morphons and Demons. The resulting deformation field was applied on the dose distribution. For both phantoms, accuracy of the registered dose distribution was assessed. For the cylindrical phantom, also measured dose values in the deformed conditions were compared with the dose values of the registered dose distributions. Finally, interfraction dose accumulation for two treatment fractions of a patient with primary rectal cancer has been performed and evaluated using isodose lines and the dose volume histograms of the target volume and normal tissue. Results: A significant decrease in the difference in marker or MOSFET position was observed after nonrigid registration methods (p<0.001) for both phantoms and with both methods, as well as a significant decrease in the dose estimation error (p<0.01 for the cubic phantom and p<0.001 for the cylindrical) with both methods. Considering the whole data set at once, the difference between estimated and measured doses was also significantly decreased using registration (p<0.001 for both methods). The patient case showed a slightly underdosed planning target volume and an overdosed bladder volume due to anatomical deformations. Conclusions: Dose accumulation using nonrigid registration methods is possible using repeated CT imaging. This opens possibilities for interfraction dose accumulation and adaptive radiotherapy to incorporate possible differences in dose delivered to the target volume and organs at risk due to anatomical deformations.« less

A method for depth-dose distribution measurements in tissue irradiated by a proton beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gambarini, G.; Birattari, C.; Bartolo, D. de

1994-12-31

The use of protons and heavy ions for the treatment of malignant and non-malignant disease has aroused a growing interest in the last decade. The notable advantage of heavy charged particles over photons in external beam radiotherapy lies in the possibility of irradiating a small localized region within the body, keeping a low value for the entrance dose. Owing to this high disuniformity of energy deposition, an essential requirement for treatment planning is a precise evaluation of the spatial distribution of absorbed dose. The proposed method for depth-dose distribution measurements utilizes a chemical dosimeter (ferrous sulphate solution plus sulfuric acidmore » and eventually xylenol orange) incorporated in a gelatine, whose role is the maintenance of spatial information. Ionizing radiation causes a variation in some parameters of the system such as the proton relaxation rates in the solution (measurable by NMR analysis) or the optical absorption of the gel in the visible spectrum (measurable by spectrophotometry).« less

Radiation exposure to the eye lens of orthopaedic surgeons during various orthopaedic procedures.

PubMed

Romanova, K; Vassileva, J; Alyakov, M

2015-07-01

The aim of the present study was to assess the radiation dose to the eye lens of orthopaedic surgeons during various orthopaedic procedures and to make efforts to ensure that radiation protection is optimised. The study was performed for Fractura femoris and Fractura cruris procedures performed in orthopaedic operating theatres, as well as for fractures of wrist, ankle and hand/shoulder performed in the emergency trauma room. The highest mean value of the eye lens dose of 47.2 μSv and higher mean fluoroscopy time of 3 min, as well as the corresponding highest maximum values of 77.1 μSv and 5.0 min were observed for the Fractura femoris procedure performed with the Biplanar 500e fluoroscopy systems. At a normal workload, the estimated mean annual dose values do not exceed the annual occupational dose limit for the lens of eye, but at a heavy workload in the department, this dose limit could be achieved or exceeded. The use of protective lead glasses is recommended as they could reduce the radiation exposure of the lens of the eye. The phantom measurements demonstrated that the use of half-dose mode could additionally reduce dose to the operator's eye lens. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Methamphetamine blood concentrations in human abusers: application to pharmacokinetic modeling.

PubMed

Melega, William P; Cho, Arthur K; Harvey, Dennis; Laćan, Goran

2007-04-01

Characterization of methamphetamine's (METH) dose-dependent effects on brain neurochemistry may represent a critical component for better understanding the range of resultant behavioral pathologies. Most human studies, however, have assessed only the effects of long term, high dose METH abuse (e.g., greater than 1000 mg/day) in individuals meeting DSM-IV criteria for METH dependence. Yet, for the majority of METH abusers, their patterns of METH exposure that consist of lower doses remain less well-characterized. In this study, blood samples were obtained from 105 individuals detained by police for possible criminal activity and testing positive for stimulants by EMIT assay. METH blood concentrations were subsequently quantified by GC-MS and were predominantly in the low micromolar range (0.1-11.1 microM), with median and mean values of 1.3 microM (0.19 mg/l) and 2 microM (0.3 mg/l), respectively. Pharmacokinetic calculations based on these measured values were used to estimate initial METH body burdens, the median value being 52 mg. Modeling a 52 mg dose for a 4 day-METH maintenance exposure pattern of 4 doses/day at 4 h intervals showed that blood concentrations remained between 1 and 4 microM during this period. Collectively, these data present evidence for a METH exposure pattern distinct from high dose-METH abuse and provide the rationale for assessing potential brain pathology associated with such lower dose-METH exposure.

Measurements to predict the time of target replacement of a helical tomotherapy.

PubMed

Kampfer, Severin; Schell, Stefan; Duma, Marciana N; Wilkens, Jan J; Kneschaurek, Peter

2011-11-15

Intensity-modulated radiation therapy (IMRT) requires more beam-on time than normal open field treatment. Consequently, the machines wear out and need more spare parts. A helical tomotherapy treatment unit needs a periodical tungsten target replacement, which is a time consuming event. To be able to predict the next replacement would be quite valuable. We observed unexpected variations towards the end of the target lifetime in the performed pretreatment measurements for patient plan verification. Thus, we retrospectively analyze the measurements of our quality assurance program. The time dependence of the quotient of two simultaneous dose measurements at different depths within a phantom for a fixed open field irradiation is evaluated. We also assess the time-dependent changes of an IMRT plan measurement and of a relative depth dose curve measurement. Additionally, we performed a Monte Carlo simulation with Geant4 to understand the physical reasons for the measured values. Our measurements show that the dose at a specified depth compared to the dose in shallower regions of the phantom declines towards the end of the target lifetime. This reproducible effect can be due to the lowering of the mean energy of the X-ray spectrum. These results are supported by the measurements of the IMRT plan, as well as the study of the relative depth dose curve. Furthermore, the simulation is consistent with these findings since it provides a possible explanation for the reduction of the mean energy for thinner targets. It could be due to the lowering of low energy photon self-absorption in a worn out and therefore thinner target. We state a threshold value for our measurement at which a target replacement should be initiated. Measurements to observe a change in the energy are good predictors of the need for a target replacement. However, since all results support the softening of the spectrum hypothesis, all depth-dependent setups are viable for analyzing the deterioration of the tungsten target. The suggested measurements and criteria to replace the target can be very helpful for every user of a TomoTherapy machine.

ESTIMATING SYSTEMIC EXPOSURE TO ETHINYL ESTRADIOL FROM AN ORAL CONTRACEPTIVE

PubMed Central

WESTHOFF, Carolyn L.; PIKE, Malcolm C.; TANG, Rosalind; DINAPOLI, Marianne N.; SULL, Monica; CREMERS, Serge

2015-01-01

Objectives This study was conducted to compare single-dose pharmacokinetics of ethinyl estradiol in an oral contraceptive to steady-state values, and to assess whether any simpler measures could provide an adequate proxy of the ‘gold standard’ 24-hour steady-state area-under-the-curve. Identifying a simple, less expensive, measure of systemic ethinyl estradiol exposure would be useful for larger studies designed to assess the relationship between an individual’s ethinyl estradiol exposure and her side effects. Study Design We conducted a 13 samples over 24 hours pharmacokinetic analysis on day 1 and day 21 of the first cycle of a monophasic oral contraceptive containing 30 mcg ethinyl estradiol and 150 mcg levonorgestrel in 17 non-obese healthy white women. We also conducted an abbreviated single dose 9-sample pharmacokinetic analysis after a month washout. Ethinyl estradiol was measured by liquid chromatography-tandem mass spectrometry. We compared results of full 13-sample steady-state pharmacokinetic analysis with results calculated using fewer samples (9 or 5) and following the single doses. We calculated Pearson correlation coefficients to evaluate the relationships between these estimates of systemic ethinyl estradiol exposure. Results The area-under-the-curve, maximum (Cmax), and 24-hour (C24) values were similar following the two single oral contraceptive doses (area-under-the-curve, r = 0.92). The steady-state 13-sample 24-hour area-under-the-curve was highly correlated with the average 9-sample area-under-the-curve after the two single doses (r = 0.81, p = 0.0002). This correlation remained the same if the number of samples was reduced to 4, taken at time 1, 2.5, 4 and 24 hours. The C24 at steady-state was highly correlated with the 24-hour steady-state area-under-the-curve (r = 0.92, p < 0.0001). The average of the C24 values following the two single doses was also quite highly correlated with the steady-state area-under-the-curve (r = 0.72, p = 0.0026). Conclusions Limited blood sampling, including results from two single doses, gave highly correlated estimates of an oral contraceptive user’s steady-state ethinyl estradiol exposure. PMID:25511238

Accuracy and calibration of integrated radiation output indicators in diagnostic radiology: A report of the AAPM Imaging Physics Committee Task Group 190

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Pei-Jan P., E-mail: Pei-Jan.Lin@vcuhealth.org; Schueler, Beth A.; Balter, Stephen

2015-12-15

Due to the proliferation of disciplines employing fluoroscopy as their primary imaging tool and the prolonged extensive use of fluoroscopy in interventional and cardiovascular angiography procedures, “dose-area-product” (DAP) meters were installed to monitor and record the radiation dose delivered to patients. In some cases, the radiation dose or the output value is calculated, rather than measured, using the pertinent radiological parameters and geometrical information. The AAPM Task Group 190 (TG-190) was established to evaluate the accuracy of the DAP meter in 2008. Since then, the term “DAP-meter” has been revised to air kerma-area product (KAP) meter. The charge of TGmore » 190 (Accuracy and Calibration of Integrated Radiation Output Indicators in Diagnostic Radiology) has also been realigned to investigate the “Accuracy and Calibration of Integrated Radiation Output Indicators” which is reflected in the title of the task group, to include situations where the KAP may be acquired with or without the presence of a physical “meter.” To accomplish this goal, validation test protocols were developed to compare the displayed radiation output value to an external measurement. These test protocols were applied to a number of clinical systems to collect information on the accuracy of dose display values in the field.« less

In vivo dosimetry using Gafchromic films during pelvic intraoperative electron radiation therapy (IOERT)

PubMed Central

Costa, Filipa; Gomes, Dora; Magalhães, Helena; Arrais, Rosário; Moreira, Graciete; Cruz, Maria Fátima; Silva, José Pedro; Santos, Lúcio; Sousa, Olga

2016-01-01

Objective: To characterize in vivo dose distributions during pelvic intraoperative electron radiation therapy (IOERT) for rectal cancer and to assess the alterations introduced by irregular irradiation surfaces in the presence of bevelled applicators. Methods: In vivo measurements were performed with Gafchromic films during 32 IOERT procedures. 1 film per procedure was used for the first 20 procedures. The methodology was then optimized for the remaining 12 procedures by using a set of 3 films. Both the average dose and two-dimensional dose distributions for each film were determined. Phantom measurements were performed for comparison. Results: For flat and concave surfaces, the doses measured in vivo agree with expected values. For concave surfaces with step-like irregularities, measured doses tend to be higher than expected doses. Results obtained with three films per procedure show a large variability along the irradiated surface, with important differences from expected profiles. These results are consistent with the presence of surface hotspots, such as those observed in phantoms in the presence of step-like irregularities, as well as fluid build-up. Conclusion: Clinical dose distributions in the IOERT of rectal cancer are often different from the references used for prescription. Further studies are necessary to assess the impact of these differences on treatment outcomes. In vivo measurements are important, but need to be accompanied by accurate imaging of positioning and irradiated surfaces. Advances in knowledge: These results confirm that surface irregularities occur frequently in rectal cancer IOERT and have a measurable effect on the dose distribution. PMID:27188847

The feasibility of a scanner-independent technique to estimate organ dose from MDCT scans: Using CTDI{sub vol} to account for differences between scanners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Turner, Adam C.; Zankl, Maria; DeMarco, John J.

2010-04-15

Purpose: Monte Carlo radiation transport techniques have made it possible to accurately estimate the radiation dose to radiosensitive organs in patient models from scans performed with modern multidetector row computed tomography (MDCT) scanners. However, there is considerable variation in organ doses across scanners, even when similar acquisition conditions are used. The purpose of this study was to investigate the feasibility of a technique to estimate organ doses that would be scanner independent. This was accomplished by assessing the ability of CTDI{sub vol} measurements to account for differences in MDCT scanners that lead to organ dose differences. Methods: Monte Carlo simulationsmore » of 64-slice MDCT scanners from each of the four major manufacturers were performed. An adult female patient model from the GSF family of voxelized phantoms was used in which all ICRP Publication 103 radiosensitive organs were identified. A 120 kVp, full-body helical scan with a pitch of 1 was simulated for each scanner using similar scan protocols across scanners. From each simulated scan, the radiation dose to each organ was obtained on a per mA s basis (mGy/mA s). In addition, CTDI{sub vol} values were obtained from each scanner for the selected scan parameters. Then, to demonstrate the feasibility of generating organ dose estimates from scanner-independent coefficients, the simulated organ dose values resulting from each scanner were normalized by the CTDI{sub vol} value for those acquisition conditions. Results: CTDI{sub vol} values across scanners showed considerable variation as the coefficient of variation (CoV) across scanners was 34.1%. The simulated patient scans also demonstrated considerable differences in organ dose values, which varied by up to a factor of approximately 2 between some of the scanners. The CoV across scanners for the simulated organ doses ranged from 26.7% (for the adrenals) to 37.7% (for the thyroid), with a mean CoV of 31.5% across all organs. However, when organ doses are normalized by CTDI{sub vol} values, the differences across scanners become very small. For the CTDI{sub vol}, normalized dose values the CoVs across scanners for different organs ranged from a minimum of 2.4% (for skin tissue) to a maximum of 8.5% (for the adrenals) with a mean of 5.2%. Conclusions: This work has revealed that there is considerable variation among modern MDCT scanners in both CTDI{sub vol} and organ dose values. Because these variations are similar, CTDI{sub vol} can be used as a normalization factor with excellent results. This demonstrates the feasibility of establishing scanner-independent organ dose estimates by using CTDI{sub vol} to account for the differences between scanners.« less

Diagnostic value of different adherence measures using electronic monitoring and virologic failure as reference standards.

PubMed

Deschamps, Ann E; De Geest, Sabina; Vandamme, Anne-Mieke; Bobbaers, Herman; Peetermans, Willy E; Van Wijngaerden, Eric

2008-09-01

Nonadherence to antiretroviral therapy is a substantial problem in HIV and jeopardizes the success of treatment. Accurate measurement of nonadherence is therefore imperative for good clinical management but no gold standard has been agreed on yet. In a single-center prospective study nonadherence was assessed by electronic monitoring: percentage of doses missed and drug holidays and by three self reports: (1) a visual analogue scale (VAS): percentage of overall doses taken; (2) the Swiss HIV Cohort Study Adherence Questionnaire (SHCS-AQ): percentage of overall doses missed and drug holidays and (3) the European HIV Treatment Questionnaire (EHTQ): percentage of doses missed and drug holidays for each antiretroviral drug separately. Virologic failure prospectively assessed during 1 year, and electronic monitoring were used as reference standards. Using virologic failure as reference standard, the best results were for (1) the SHCS-AQ after electronic monitoring (sensitivity, 87.5%; specificity, 78.6%); (2) electronic monitoring (sensitivity, 75%; specificity, 85.6%), and (3) the VAS combined with the SHCS-AQ before electronic monitoring (sensitivity, 87.5%; specificity, 58.6%). The sensitivity of the complex EHTQ was less than 50%. Asking simple questions about doses taken or missed is more sensitive than complex questioning about each drug separately. Combining the VAS with the SHCS-AQ seems a feasible nonadherence measure for daily clinical practice. Self-reports perform better after electronic monitoring: their diagnostic value could be lower when given independently.

Comparison of calculations and measurements of the off-axis radiation dose (SI) in liquid nitrogen as a function of radiation length

NASA Astrophysics Data System (ADS)

Cromar, P. F.

1984-12-01

In this thesis results are presented from a study of the off-axis X and Gamma radiation field caused by a highly relativistic electron beam in liquid Nitrogen at various path lengths out to 2 radiation lengths. The off-axis dose in Silicon was calculated using electron/photon transport code CYLTRAN and measured using thermal luminescent dosimeters (TLD's). Calculations were performed on a CDC-7600 computer ar Los Alamos National Laboratory and measurements were made using the Naval Postgraduate School 100 Mev Linac. Comparison of the results is made and CYLTRAN is found to be in agreement with experimentally measured values. The CYLTRAN results are extended to the off-axis dose caused by a 100 Mev electron beam in air at Standard Temperature and Pressure (STP).

Vocal Dose Measures: Quantifying Accumulated Vibration Exposure in Vocal Fold Tissues

PubMed Central

Titze, Ingo R.; Švec, Jan G.; Popolo, Peter S.

2011-01-01

To measure the exposure to self-induced tissue vibration in speech, three vocal doses were defined and described: distance dose, which accumulates the distance that tissue particles of the vocal folds travel in an oscillatory trajectory; energy dissipation dose, which accumulates the total amount of heat dissipated over a unit volume of vocal fold tissues; and time dose, which accumulates the total phonation time. These doses were compared to a previously used vocal dose measure, the vocal loading index, which accumulates the number of vibration cycles of the vocal folds. Empirical rules for viscosity and vocal fold deformation were used to calculate all the doses from the fundamental frequency (F0) and sound pressure level (SPL) values of speech. Six participants were asked to read in normal, monotone, and exaggerated speech and the doses associated with these vocalizations were calculated. The results showed that large F0 and SPL variations in speech affected the dose measures, suggesting that accumulation of phonation time alone is insufficient. The vibration exposure of the vocal folds in normal speech was related to the industrial limits for hand-transmitted vibration, in which the safe distance dose was derived to be about 500 m. This limit was found rather low for vocalization; it was related to a comparable time dose of about 17 min of continuous vocalization, or about 35 min of continuous reading with normal breathing and unvoiced segments. The voicing pauses in normal speech and dialogue effectively prolong the safe time dose. The derived safety limits for vocalization will likely require refinement based on a more detailed knowledge of the differences in hand and vocal fold tissue morphology and their response to vibrational stress, and on the effect of recovery of the vocal fold tissue during voicing pauses. PMID:12959470

Vocal dose measures: quantifying accumulated vibration exposure in vocal fold tissues.

PubMed

Titze, Ingo R; Svec, Jan G; Popolo, Peter S

2003-08-01

To measure the exposure to self-induced tissue vibration in speech, three vocal doses were defined and described: distance dose, which accumulates the distance that tissue particles of the vocal folds travel in an oscillatory trajectory; energy dissipation dose, which accumulates the total amount of heat dissipated over a unit volume of vocal fold tissues; and time dose, which accumulates the total phonation time. These doses were compared to a previously used vocal dose measure, the vocal loading index, which accumulates the number of vibration cycles of the vocal folds. Empirical rules for viscosity and vocal fold deformation were used to calculate all the doses from the fundamental frequency (F0) and sound pressure level (SPL) values of speech. Six participants were asked to read in normal, monotone, and exaggerated speech and the doses associated with these vocalizations were calculated. The results showed that large F0 and SPL variations in speech affected the dose measures, suggesting that accumulation of phonation time alone is insufficient. The vibration exposure of the vocal folds in normal speech was related to the industrial limits for hand-transmitted vibration, in which the safe distance dose was derived to be about 500 m. This limit was found rather low for vocalization; it was related to a comparable time dose of about 17 min of continuous vocalization, or about 35 min of continuous reading with normal breathing and unvoiced segments. The voicing pauses in normal speech and dialogue effectively prolong the safe time dose. The derived safety limits for vocalization will likely require refinement based on a more detailed knowledge of the differences in hand and vocal fold tissue morphology and their response to vibrational stress, and on the effect of recovery of the vocal fold tissue during voicing pauses.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Heng; Sahoo, Narayan; Poenisch, Falk

Purpose: The purpose of this work was to assess the monitor unit (MU) values and position accuracy of spot scanning proton beams as recorded by the daily treatment logs of the treatment control system, and furthermore establish the feasibility of using the delivered spot positions and MU values to calculate and evaluate delivered doses to patients. Methods: To validate the accuracy of the recorded spot positions, the authors generated and executed a test treatment plan containing nine spot positions, to which the authors delivered ten MU each. The spot positions were measured with radiographic films and Matrixx 2D ion-chambers arraymore » placed at the isocenter plane and compared for displacements from the planned and recorded positions. Treatment logs for 14 patients were then used to determine the spot MU values and position accuracy of the scanning proton beam delivery system. Univariate analysis was used to detect any systematic error or large variation between patients, treatment dates, proton energies, gantry angles, and planned spot positions. The recorded patient spot positions and MU values were then used to replace the spot positions and MU values in the plan, and the treatment planning system was used to calculate the delivered doses to patients. The results were compared with the treatment plan. Results: Within a treatment session, spot positions were reproducible within {+-}0.2 mm. The spot positions measured by film agreed with the planned positions within {+-}1 mm and with the recorded positions within {+-}0.5 mm. The maximum day-to-day variation for any given spot position was within {+-}1 mm. For all 14 patients, with {approx}1 500 000 spots recorded, the total MU accuracy was within 0.1% of the planned MU values, the mean (x, y) spot displacement from the planned value was (-0.03 mm, -0.01 mm), the maximum (x, y) displacement was (1.68 mm, 2.27 mm), and the (x, y) standard deviation was (0.26 mm, 0.42 mm). The maximum dose difference between calculated dose to the patient based on the plan and recorded data was within 2%. Conclusions: The authors have shown that the treatment log file in a spot scanning proton beam delivery system is precise enough to serve as a quality assurance tool to monitor variation in spot position and MU value, as well as the delivered dose uncertainty from the treatment delivery system. The analysis tool developed here could be useful for assessing spot position uncertainty and thus dose uncertainty for any patient receiving spot scanning proton beam therapy.« less

SU-E-T-367: Optimization of DLG Using TG-119 Test Cases and a Weighted Mean Approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sintay, B; Vanderstraeten, C; Terrell, J

2014-06-01

Purpose: Optimization of the dosimetric leaf gap (DLG) is an important step in commissioning the Eclipse treatment planning system for sliding window intensity-modulated radiation therapy (SW-IMRT) and RapidArc. Often the values needed for optimal dose delivery differ markedly from those measured at commissioning. We present a method to optimize this value using the AAPM TG-119 test cases. Methods: For SW-IMRT and RapidArc, TG-119 based test plans were created using a water-equivalent phantom. Dose distributions measured on film and ion chamber (IC) readings taken in low-gradient regions within the targets were analyzed separately. Since DLG is a single value per energy,more » SW-IMRT and RapidArc must be considered simultaneously. Plans were recalculated using a linear sweep from 0.02cm (the minimum DLG) to 0.3 cm. The calculated point doses were compared to the measured doses for each plan, and based on these comparisons an optimal DLG value was computed for each plan. TG-119 cases are designed to push the system in various ways, thus, a weighted mean of the DLG was computed where the relative importance of each type of plan was given a score from 0.0 to 1.0. Finally, SW-IMRT and RapidArc are assigned an overall weight based on clinical utilization. Our routine patient-QA (PQA) process was performed as independent validation. Results: For a Varian TrueBeam, the optimized DLG varied with σ = 0.044cm for SW-IMRT and σ = 0.035cm for RapidArc. The difference between the weighted mean SW-IMRT and RapidArc value was 0.038cm. We predicted utilization of 25% SW-IMRT and 75% RapidArc. The resulting DLG was ~1mm different than that found by commissioning and produced an average error of <1% for SW-IMRT and RapidArc PQA test cases separately. Conclusion: The weighted mean method presented is a useful tool for determining an optimal DLG value for commissioning Eclipse.« less

Medical dosimetry in Hungary

NASA Astrophysics Data System (ADS)

Turák, O.; Osvay, M.; Ballay, L.

2012-09-01

Radiation exposure of medical staff during cardiological and radiological procedures was investigated. The exposure of medical staff is directly connected to patient exposure. The aim of this study was to determine the distribution of doses on uncovered part of body of medical staff using LiF thermoluminescent (TL) dosimeters in seven locations. Individual Kodak film dosimeters (as authorized dosimetry system) were used for the assessment of medical staff's effective dose. Results achieved on dose distribution measurements confirm that wearing only one film badge under the lead apron does not provide enough information on the personal dose. The value of estimated annual doses on eye lens and extremities (fingers) were in good correlation with international publications.

In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans

PubMed Central

Zhang, Da; Padole, Atul; Li, Xinhua; Singh, Sarabjeet; Khawaja, Ranish Deedar Ali; Lira, Diego; Liu, Tianyu; Shi, Jim Q.; Otrakji, Alexi; Kalra, Mannudeep K.; Xu, X. George; Liu, Bob

2014-01-01

Purpose: To present a study of radiation dose measurements with a human cadaver scanned on a clinical CT scanner. Methods: Multiple point dose measurements were obtained with high-accuracy Thimble ionization chambers placed inside the stomach, liver, paravertebral gutter, ascending colon, left kidney, and urinary bladder of a human cadaver (183 cm in height and 67.5 kg in weight) whose abdomen/pelvis region was scanned repeatedly with a multidetector row CT. The flat energy response and precision of the dosimeters were verified, and the slight differences in each dosimeter's response were evaluated and corrected to attain high accuracy. In addition, skin doses were measured for radiosensitive organs outside the scanned region with OSL dosimeters: the right eye, thyroid, both nipples, and the right testicle. Three scan protocols were used, which shared most scan parameters but had different kVp and mA settings: 120-kVp automA, 120-kVp 300 mA, and 100-kVp 300 mA. For each protocol three repeated scans were performed. Results: The tube starting angle (TSA) was found to randomly vary around two major conditions, which caused large fluctuations in the repeated point dose measurements: for the 120-kVp 300 mA protocol this angle changed from approximately 110° to 290°, and caused 8% − 25% difference in the point dose measured at the stomach, liver, colon, and urinary bladder. When the fluctuations of the TSA were small (within 5°), the maximum coefficient of variance was approximately 3.3%. The soft tissue absorbed doses averaged from four locations near the center of the scanned region were 27.2 ± 3.3 and 16.5 ± 2.7 mGy for the 120 and 100-kVp fixed-mA scans, respectively. These values were consistent with the corresponding size specific dose estimates within 4%. The comparison of the per-100-mAs tissue doses from the three protocols revealed that: (1) dose levels at nonsuperficial locations in the TCM scans could not be accurately deduced by simply scaling the fix-mA doses with local mA values; (2) the general power law relationship between dose and kVp varied from location to location, with the power index ranged between 2.7 and 3.5. The averaged dose measurements at both nipples, which were about 0.6 cm outside the prescribed scan region, ranged from 23 to 27 mGy at the left nipple, and varied from 3 to 20 mGy at the right nipple over the three scan protocols. Large fluctuations over repeated scans were also observed, as a combined result of helical scans of large pitch (1.375) and small active areas of the skin dosimeters. In addition, the averaged skin dose fell off drastically with the distance to the nearest boundary of the scanned region. Conclusions: This study revealed the complexity of CT dose fluctuation and variation with a human cadaver. PMID:25186398

Absorbed dose measurements on external surface of Kosmos-satellites with glass thermoluminescent detectors.

PubMed

Akatov YuA; Arkhangelsky, V V; Kovalev, E E; Spurny, F; Votochkova, I

1989-01-01

In this paper we present absorbed dose measurements with glass thermoluminescent detectors on external surface of satellites of Kosmos-serie flying in 1983-87. Experiments were performed with thermoluminescent aluminophosphate glasses of thicknesses 0.1, 0.3, 0.4, 0.5, and 1 mm. They were exposed in sets of total thickness between 5 and 20 mm, which were protected against sunlight with thin aluminized foils. In all missions, extremely high absorbed dose values were observed in the first layers of detectors, up to the thickness of 0.2 to 0.5 gcm-2. These experimental results confirm that, during flights at 250 to 400 km, doses on the surface of the satellites are very high, due to the low energy component of the proton and electron radiation.

Quality factor and dose equivalent investigations aboard the Soviet Space Station Mir

NASA Astrophysics Data System (ADS)

Bouisset, P.; Nguyen, V. D.; Parmentier, N.; Akatov, Ia. A.; Arkhangel'Skii, V. V.; Vorozhtsov, A. S.; Petrov, V. M.; Kovalev, E. E.; Siegrist, M.

1992-07-01

Since Dec 1988, date of the French-Soviet joint space mission 'ARAGATZ', the CIRCE device, had recorded dose equivalent and quality factor values inside the Mir station (380-410 km, 51.5 deg). After the initial gas filling two years ago, the low pressure tissue equivalent proportional counter is still in good working conditions. Some results of three periods are presented. The average dose equivalent rates measured are respectively 0.6, 0.8 and 0.6 mSv/day with a quality factor equal to 1.9. Some detailed measurements show the increasing of the dose equivalent rates through the SAA and near polar horns. The real time determination of the quality factors allows to point out high linear energy transfer events with quality factors in the range 10-20.

LET spectra measurements from the STS-35 CPDs

NASA Technical Reports Server (NTRS)

1995-01-01

Linear energy transfer (LET) spectra derived form automated track analysis system (ATAS) track parameter measurements for crew passive dosimeters (CPD's) flown with the astronauts on STS-35 are plotted. The spread between the seven individual spectra is typical of past manual measurements of sets of CPD's. This difference is probably due to the cumulative net shielding variations experienced by the CPD's as the astronauts carrying them went about their activities on the Space Shuttle. The STS-35 mission was launched on Dec. 2, 1990, at 28.5 degrees inclination and 352-km altitude. This is somewhat higher than the nominal 300-km flights and the orbit intersects more of the high intensity trapped proton region in the South Atlantic Anomaly (SAA). However, in comparison with APD spectra measured on earlier lower altitude missions (STS-26, -29, -30, -32), the flux spectra are all roughly comparable. This may be due to the fact that the STS-35 mission took place close to solar maximum (Feb. 1990), or perhaps to shielding differences. The corresponding dose and dose equivalent spectra for this mission are shown. The effect of statistical fluctuations at the higher LET values, where track densities are small, is very noticeable. This results in an increased spread within the dose rate and dose equivalent rate spectra, as compared to the flux spectra. The contribution to dose and dose equivalent per measured track is much greater in the high LET region and the differences, though numerically small, are heavily weighted in the integral spectra. The optimum measurement and characterization of the high LET tails of the spectra represent an important part of the research into plastic nuclear track detector (PNTD) response. The integral flux, dose rate, dose equivalent rate and mission dose equivalent for the seven astronauts are also given.

SU-E-I-42: Measurement of X-Ray Beam Width and Geometric Efficiency in MDCT Using Radiochromic Films.

PubMed

Liillau, T; Liebmann, M; von Boetticher, H; Poppe, B

2012-06-01

The purpose of this work was to measure the x-ray beam width and geometric efficiency (GE) of a multi detector computed tomography scanner (MDCT) for different beam collimations using radiochromic films. In MDCT, the primary beam width extends the nominal beam collimation to irradiate the active detector elements uniformly (called 'over-beaming') which contributes to increased radiation dose to the patient compared to single detector CT. Therefore, the precise determination of the primary beam width and GE is of value for any CT dose calculation using Monte Carlo or analytical methods. Single axial dose profiles free in air were measured for 6 different beam collimations nT for a Siemens SOMATOM Sensation 64 Scanner with Gafchromic XR-QA2 films. The films were calibrated relative to the measured charge of a PTW semiflex ionization chamber (type: 31010) for a single rotation in the CT scanner at the largest available beam collimation of 28.8 mm. The beam energy for all measurements in this work was set to 120 kVp. For every measured dose profile and beam collimation the GEin-air and the full-width-at-half- maximum value (FWHM) as a value for the x-ray beam width was determined. Over-beaming factors FWHM / nT were calculated accordingly. For MDCT beam collimations from 7.2 (12×0.6 mm) to 28.8 (24×1.2 mm) the geometric efficiency was between 58 and 85 %. The over- beaming factor ranged from 1.43 to 1.11. For beam collimations of 1×5 mm and 1×10 mm the GE was 77 % and 84 % respectively. The over-beaming factors were close to 1, as expected. This work has shown that radiochromic films can be used for accurate x-ray beam width and geometric efficiency measurements due to their high spatial resolution. The measured free-in-air geometric efficiency and the over-beaming factor depend strongly on beam collimation. © 2012 American Association of Physicists in Medicine.

Attenuation properties and percentage depth dose of tannin-based Rhizophora spp. particleboard phantoms using computed tomography (CT) and treatment planning system (TPS) at high energy x-ray beams

NASA Astrophysics Data System (ADS)

Yusof, M. F. Mohd; Abdullah, R.; Tajuddin, A. A.; Hashim, R.; Bauk, S.

2016-01-01

A set of tannin-based Rhizophora spp. particleboard phantoms with dimension of 30 cm x 30 cm was fabricated at target density of 1.0 g/cm3. The mass attenuation coefficient of the phantom was measured using 60Co gamma source. The phantoms were scanned using Computed Tomography (CT) scanner and the percentage depth dose (PDD) of the phantom was calculated using treatment planning system (TPS) at 6 MV and 10 MV x-ray and compared to that in solid water phantoms. The result showed that the mass attenuation coefficient of tannin-based Rhizohora spp. phantoms was near to the value of water with χ2 value of 1.2. The measured PDD also showed good agreement with solid water phantom at both 6 MV and 10 MV x-ray with percentage deviation below 8% at depth beyond the maximum dose, Zmax.

Pharmacokinetics of low-dose nedaplatin and validation of AUC prediction in patients with non-small-cell lung carcinoma.

PubMed

Niioka, Takenori; Uno, Tsukasa; Yasui-Furukori, Norio; Takahata, Takenori; Shimizu, Mikiko; Sugawara, Kazunobu; Tateishi, Tomonori

2007-04-01

The aim of this study was to determine the pharmacokinetics of low-dose nedaplatin combined with paclitaxel and radiation therapy in patients having non-small-cell lung carcinoma and establish the optimal dosage regimen for low-dose nedaplatin. We also evaluated predictive accuracy of reported formulas to estimate the area under the plasma concentration-time curve (AUC) of low-dose nedaplatin. A total of 19 patients were administered a constant intravenous infusion of 20 mg/m(2) body surface area (BSA) nedaplatin for an hour, and blood samples were collected at 1, 2, 3, 4, 6, 8, and 19 h after the administration. Plasma concentrations of unbound platinum were measured, and the actual value of platinum AUC (actual AUC) was calculated based on these data. The predicted value of platinum AUC (predicted AUC) was determined by three predictive methods reported in previous studies, consisting of Bayesian method, limited sampling strategies with plasma concentration at a single time point, and simple formula method (SFM) without measured plasma concentration. Three error indices, mean prediction error (ME, measure of bias), mean absolute error (MAE, measure of accuracy), and root mean squared prediction error (RMSE, measure of precision), were obtained from the difference between the actual and the predicted AUC, to compare the accuracy between the three predictive methods. The AUC showed more than threefold inter-patient variation, and there was a favorable correlation between nedaplatin clearance and creatinine clearance (Ccr) (r = 0.832, P < 0.01). In three error indices, MAE and RMSE showed significant difference between the three AUC predictive methods, and the method of SFM had the most favorable results, in which %ME, %MAE, and %RMSE were 5.5, 10.7, and 15.4, respectively. The dosage regimen of low-dose nedaplatin should be established based on Ccr rather than on BSA. Since prediction accuracy of SFM, which did not require measured plasma concentration, was most favorable among the three methods evaluated in this study, SFM could be the most practical method to predict AUC of low-dose nedaplatin in a clinical situation judging from its high accuracy in predicting AUC without measured plasma concentration.

Measurement of the stochastic radial dose distribution for a 30-MeV proton beam using a wall-less tissue-equivalent proportional counter.

PubMed

Tsuda, S; Sato, T; Ogawa, T

2016-02-01

The frequency distribution of the lineal energy, y, of a 30-MeV proton beam was measured as a function of the radial distance from the beam path, and the dosed mean of y, y¯(D), was obtained to investigate the radial dependence of y¯(D). A wall-less tissue-equivalent proportional counter, in a cylindrical volume with simulated diameters of 0.36, 0.72 and 1.44 µm was used for the measurement of y distributions, yf(y). The measured values of yf(y) summed in the radial direction agreed fairly well with the corresponding data taken from the microdosimetric calculations using the PHITS code. The y¯(D) value of the 30-MeV proton beam presented its smallest value at r = 0.0 and gradually increased with radial distance, and the y¯(D) values of heavy ions such as iron showed rapid decrease with radial distance. This experimental result demonstrated that the stochastic deposited energy distribution of high-energy protons in the microscopic region is rather constant in the core as well as in the penumbra region of the track structure. © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Staff Radiation Doses in a Real-Time Display Inside the Angiography Room

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sanchez, Roberto, E-mail: rmsanchez.hcsc@salud.madrid.org; Vano, E.; Fernandez, J. M.

MethodsThe evaluation of a new occupational Dose Aware System (DAS) showing staff radiation doses in real time has been carried out in several angiography rooms in our hospital. The system uses electronic solid-state detectors with high-capacity memory storage. Every second, it archives the dose and dose rate measured and is wirelessly linked to a base-station screen mounted close to the diagnostic monitors. An easy transfer of the values to a data sheet permits further analysis of the scatter dose profile measured during the procedure, compares it with patient doses, and seeks to find the most effective actions to reduce operatormore » exposure to radiation.ResultsThe cumulative occupational doses measured per procedure (shoulder-over lead apron) ranged from 0.6 to 350 {mu}Sv when the ceiling-suspended screen was used, and DSA (Digital Subtraction Acquisition) runs were acquired while the personnel left the angiography room. When the suspended screen was not used and radiologists remained inside the angiography room during DSA acquisitions, the dose rates registered at the operator's position reached up to 1-5 mSv/h during fluoroscopy and 12-235 mSv/h during DSA acquisitions. In such case, the cumulative scatter dose could be more than 3 mSv per procedure.ConclusionReal-time display of doses to staff members warns interventionists whenever the scatter dose rates are too high or the radiation protection tools are not being properly used, providing an opportunity to improve personal protection accordingly.« less

Sensitivity to change in cognitive performance and mood measures of energy and fatigue in response to differing doses of caffeine or breakfast.

PubMed

Maridakis, Victor; Herring, Matthew P; O'Connor, Patrick J

2009-01-01

This double-blind, placebo-controlled, within-subjects (N = 18) experiment compared the sensitivity to change of cognitive performance and mood measures of mental energy following consumption of either 100 or 200-mg caffeine or a 440-calorie breakfast. Breakfast and 200-mg caffeine improved mood and cognitive performance. The sensitivity to change of the measures did not differ in response to any treatment (all p values > .05). The mood and cognitive measures of mental energy used here have similar sensitivity to detecting change in response to a moderate dose of caffeine and breakfast consumption.

Individual dose monitoring of the nuclear medicine departments staff controlled by Central Laboratory for Radiological Protection.

PubMed

Szewczak, Kamil; Jednoróg, Sławomir; Krajewski, Paweł

2013-01-01

Presented paper describes the results of the individual doses measurements for ionizing radiation, carried out by the Laboratory of Individual and Environmental Doses Monitoring (PDIS) of the Central Laboratory for Radiological Protection in Warsaw (CLOR) for the medical staff employees in several nuclear medicine (NM) departments across Poland. In total there are48 NM departments in operation in Poland [1] (consultation in Nuclear Atomic Agency). Presented results were collected over the period from January 2011 to December 2011 at eight NM departments located in Krakow, Warszawa (two departments), Rzeszow (two departments), Opole, Przemysl and Gorzow Wielkopolski. For radiation monitoring three kinds of thermo luminescence dosimeters (TLD) were used. The first TLD h collected information about whole body (C) effective dose, the second dosimeter was mounted in the ring (P) meanwhile the third on the wrist (N) of the tested person. Reading of TLDs was performed in quarterly periods. As a good approximation of effective and equivalent dose assessment of operational quantities both the individual dose equivalent Hp(10) and the Hp(0.07) were used. The analysis of the data was performed using two methods The first method was based on quarterly estimations of Hp(10)q and Hp(0.07)q while the second measured cumulative annual doses Hp(10)a and Hp(0.07)a. The highest recorded value of the radiation dose for quarterly assessments reached 24.4 mSv and was recorded by the wrist type dosimeter worn by a worker involved in source preparation procedure. The mean values of Hp(10)q(C type dosimeter) and Hp(0.07)q (P and N type dosimeter) for all monitored departments were respectively 0.46 mSv and 3.29 mSv. There was a strong correlation between the performed job and the value of the received dose. The highest doses always were absorbed by those staff members who were involved in sources preparation. The highest annual cumulative dose for a particular worker in the considered time period was 4.22 mSv for Hp(10)a and 67.7 mSv for Hp(0.07)a. In 2011 no case of exceeding the allowed dose limits was noted.

Noise exposure levels for musicians during rehearsal and performance times.

PubMed

McIlvaine, Devon; Stewart, Michael; Anderson, Robert

2012-03-01

The purpose of this study was to determine daily noise doses and 8-hour time weighted averages for rock band musicians, crew members, and spectators during a typical rehearsal and performance using both Occupational Safety and Health Administration (OSHA) and National Institute of Occupational Safety and Health (NIOSH) measurement criteria. Personal noise dosimetry was completed on five members of a rock band during one 2-hr rehearsal and one 4-hr performance. Time-weighted averages (TWA) and daily dose values were calculated using both OSHA and NIOSH criteria and compared to industry guidelines for enrollment in hearing conservation programs and the use of hearing protection devices. TWA values ranged from 84.3 to 90.4 dBA (OSHA) and from 90.0 to 96.4 dBA (NIOSH) during the rehearsal. The same values ranged from 91.0 to 99.7 dBA (OSHA) and 94.0 to 102.8 dBA (NIOSH) for the performance. During the rehearsal, daily noise doses ranged from 45.54% to 106.7% (OSHA) and from 317.74% to 1396.07% (NIOSH). During the performance, doses ranged from 114.66% to 382.49% (OSHA) and from 793.31% to 5970.15% (NIOSH). The musicians in this study were exposed to dangerously high levels of noise and should be enrolled in a hearing conservation programs. Hearing protection devices should be worn, especially during performances. The OSHA measurement criteria yielded values significantly more conservative than those produced by NIOSH criteria. Audiologists should counsel musician-patients about the hazards of excessive noise (music) exposure and how to protect their hearing.

SU-E-J-101: Retroactive Calculation of TLD and Film Dose in Anthropomorphic Phantom as Assessment of Updated TPS Performance

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alkhatib, H; Oves, S

Purpose: To demonstrate a quick and comprehensive method verifying the accuracy of the updated dose model by recalculating dose distribution in an anthropomorphic phantom with a new version of the TPS and comparing the results to measured values. Methods: CT images and IMRT plan of an RPC anthropomorphic head phantom, previously calculated by Pinnacle 9.0, was re-computed using Pinnacle 9.2 and 9.6. The dosimeters within the phantom include four TLD capsules representing a primary PTV, two TLD capsules representing a secondary PTV, and two TLD capsules representing an organ at risk. Also included were three sheets of Gafchromic film. Performancemore » of the updated TPS version was assessed by recalculating point doses and dose profiles corresponding to TLD and film position respectively and then comparing the results to reported values by the RPC. Results: Comparing calculated doses to reported measured doses from the RPC yielded an average disagreement of 1.48%, 2.04% and 2.10% for versions 9.0, 9.2, 9.6 respectively. Computed doses points all meet the RPC's passing criteria with the exception of the point representing the superior organ at risk in version 9.6. However, qualitative analysis of the recalculated dose profiles showed improved agreement with those of the RPC, especially in the penumbra region. Conclusion: This work has demonstrated the calculation results of Pinnacle 9.2 and 9.6 vs 9.0 version. Additionally, this study illustrates a method for the user to gain confidence upgrade to a newer version of the treatment planning system.« less

The velocity of antihypertensive effect of losartan/hydrochlorothiazide and angiotensin II receptor blocker.

PubMed

Metoki, Hirohito; Ohkubo, Takayoshi; Kikuya, Masahiro; Asayama, Kei; Inoue, Ryusuke; Obara, Taku; Hirose, Takuo; Sato, Michihiro; Hashimoto, Takanao; Imai, Yutaka

2012-07-01

The hypotensive effect and the time to attain the maximum antihypertensive effect (stabilization time) of losartan/hydrochlorothiazide (HCTZ) combination therapy and therapy with a maximal dose of angiotensin II receptor blockers (ARBs) in patients who failed to achieve adequate blood pressure (BP) control on a medium-dose of ARBs were compared by analyzing exponential decay functions using daily serial morning home BP measurements. Essential hypertensive patients treated with a medium dose of ARB, in whom a target home SBP (135 mmHg) was not achieved, were randomized into two groups: a combination group (n = 110) and a maximal-dose ARB group (n = 111). The combination therapy provided additional reduction of 5.2 mmHg [95% confidence interval (CI) 1.8 to 8.5 mmHg, P = 0.003] in home SBP over the maximal-dose ARB therapy in 8 weeks after randomization. A greater reduction in the home SBP values was seen in the combination group than in the maximal-dose ARB group from the second day after randomization on the basis of a linear mixed model. The maximum antihypertensive effect and stabilization time for home SBP were 10.9 ± 5.0 mmHg and 7.3 ± 29.7 days, respectively, in the combination group, whereas the corresponding values in the maximal-dose ARB group were 7.9 ± 2.6  mmHg and 122.3 ± 42.7 days, respectively, on the basis of a nonlinear mixed model. Changing from a medium dose of ARB monotherapy to combination therapy was more effective in the reduction of home SBP and achieved goal BP more rapidly than increasing the ARB dose. Home BP measurement is a useful tool for characterizing the antihypertensive effects of drugs.

Cancer risk estimation caused by radiation exposure during endovascular procedure

NASA Astrophysics Data System (ADS)

Kang, Y. H.; Cho, J. H.; Yun, W. S.; Park, K. H.; Kim, H. G.; Kwon, S. M.

2014-05-01

The objective of this study was to identify the radiation exposure dose of patients, as well as staff caused by fluoroscopy for C-arm-assisted vascular surgical operation and to estimate carcinogenic risk due to such exposure dose. The study was conducted in 71 patients (53 men and 18 women) who had undergone vascular surgical intervention at the division of vascular surgery in the University Hospital from November of 2011 to April of 2012. It had used a mobile C-arm device and calculated the radiation exposure dose of patient (dose-area product, DAP). Effective dose was measured by attaching optically stimulated luminescence on the radiation protectors of staff who participates in the surgery to measure the radiation exposure dose of staff during the vascular surgical operation. From the study results, DAP value of patients was 308.7 Gy cm2 in average, and the maximum value was 3085 Gy cm2. When converted to the effective dose, the resulted mean was 6.2 m Gy and the maximum effective dose was 61.7 milliSievert (mSv). The effective dose of staff was 3.85 mSv; while the radiation technician was 1.04 mSv, the nurse was 1.31 mSv. All cancer incidences of operator are corresponding to 2355 persons per 100,000 persons, which deemed 1 of 42 persons is likely to have all cancer incidences. In conclusion, the vascular surgeons should keep the radiation protection for patient, staff, and all participants in the intervention in mind as supervisor of fluoroscopy while trying to understand the effects by radiation by themselves to prevent invisible danger during the intervention and to minimize the harm.

Ambient Dose Equivalent measured at the Instituto Nacional de Cancerologia Department of Nuclear Medicine

DOE Office of Scientific and Technical Information (OSTI.GOV)

Avila, O.; Torres-Ulloa, C. L.; Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, AP 70-542, 04510, DF

2010-12-07

Ambient dose equivalent values were determined in several sites at the Instituto Nacional de Cancerologia, Departmento de Medicina Nuclear, using TLD-100 and TLD-900 thermoluminescent dosemeters. Additionally, ambient dose equivalent was measured at a corridor outside the hospitalization room for patients treated with {sup 137}Cs brachytherapy. Dosemeter calibration was performed at the Instituto Nacional de Investigaciones Nucleares, Laboratorio de Metrologia, to known {sup 137}Cs gamma radiation air kerma. Radionuclides considered for this study are {sup 131}I, {sup 18}F, {sup 67}Ga, {sup 99m}Tc, {sup 111}In, {sup 201}Tl and {sup 137}Cs, with main gamma energies between 93 and 662 keV. Dosemeters were placedmore » during a five month period in the nuclear medicine rooms (containing gamma-cameras), injection corridor, patient waiting areas, PET/CT study room, hot lab, waste storage room and corridors next to the hospitalization rooms for patients treated with {sup 131}I and {sup 137}Cs. High dose values were found at the waste storage room, outside corridor of {sup 137}Cs brachytherapy patients and PET/CT area. Ambient dose equivalent rate obtained for the {sup 137}Cs brachytherapy corridor is equal to (18.51{+-}0.02)x10{sup -3} mSv/h. Sites with minimum doses are the gamma camera rooms, having ambient dose equivalent rates equal to (0.05{+-}0.03)x10{sup -3} mSv/h. Recommendations have been given to the Department authorities so that further actions are taken to reduce doses at high dose sites in order to comply with the ALARA principle (as low as reasonably achievable).« less

Neutron field characterization at the independent spent fuel storage installation of the Trillo nuclear power plant.

PubMed

Campo, Xandra; Méndez, Roberto; Embid, Miguel; Ortego, Alberto; Novo, Manuel; Sanz, Javier

2018-05-01

Neutron fields inside and outside the independent spent fuel storage installation of Trillo Nuclear Power Plant are characterized exhaustively in terms of neutron spectra and ambient dose equivalent, measured by Bonner sphere system and LB6411 monitor. Measurements are consistent with storage casks and building shield characteristics, and also with casks distribution inside the building. Outer values at least five times lower than dose limit for free access area are found. Measurements with LB6411 and spectrometer are consistent with each other. Copyright © 2018 Elsevier Ltd. All rights reserved.

[Neutron Dosimetry System Using CR-39 for High-energy X-ray Radiation Therapy].

PubMed

Yabuta, Kazutoshi; Monzen, Hajime; Tamura, Masaya; Tsuruta, Takao; Itou, Tetsuo; Nohtomi, Akihiro; Nishimura, Yasumasa

2014-01-01

Neutrons are produced during radiation treatment by megavolt X-ray energies. However, it is difficult to measure neutron dose especially just during the irradiation. Therefore, we have developed a system for measuring neutrons with the solid state track detector CR-39, which is free from the influence of the X-ray beams. The energy spectrum of the neutrons was estimated by a Monte Carlo simulation method, and the estimated neutron dose was corrected by the contribution ratio of each energy. Pit formation rates of CR-39 ranged from 2.3 x 10(-3) to 8.2 x 10(-3) for each detector studied. According to the estimated neutron energy spectrum, the energy values for calibration were 144 keV and 515keV, and the contribution ratios were approximately 40:60 for 10 MV photons and 20:70 for photons over 15 MV. Neutron doses measured in the center of a high-energy X-ray field were 0.045 mSv/Gy for a 10 MV linear accelerator and 0.85 mSv/Gy for a 20 MV linear accelerator. We successfully developed the new neutron dose measurement system using the solid track detector, CR-39. This on-time neutron measurement system allows users to measure neutron doses produced in the radiation treatment room more easily.

Validation of GPU-accelerated superposition-convolution dose computations for the Small Animal Radiation Research Platform.

PubMed

Cho, Nathan; Tsiamas, Panagiotis; Velarde, Esteban; Tryggestad, Erik; Jacques, Robert; Berbeco, Ross; McNutt, Todd; Kazanzides, Peter; Wong, John

2018-05-01

The Small Animal Radiation Research Platform (SARRP) has been developed for conformal microirradiation with on-board cone beam CT (CBCT) guidance. The graphics processing unit (GPU)-accelerated Superposition-Convolution (SC) method for dose computation has been integrated into the treatment planning system (TPS) for SARRP. This paper describes the validation of the SC method for the kilovoltage energy by comparing with EBT2 film measurements and Monte Carlo (MC) simulations. MC data were simulated by EGSnrc code with 3 × 10 8 -1.5 × 10 9 histories, while 21 photon energy bins were used to model the 220 kVp x-rays in the SC method. Various types of phantoms including plastic water, cork, graphite, and aluminum were used to encompass the range of densities of mouse organs. For the comparison, percentage depth dose (PDD) of SC, MC, and film measurements were analyzed. Cross beam (x,y) dosimetric profiles of SC and film measurements are also presented. Correction factors (CFz) to convert SC to MC dose-to-medium are derived from the SC and MC simulations in homogeneous phantoms of aluminum and graphite to improve the estimation. The SC method produces dose values that are within 5% of film measurements and MC simulations in the flat regions of the profile. The dose is less accurate at the edges, due to factors such as geometric uncertainties of film placement and difference in dose calculation grids. The GPU-accelerated Superposition-Convolution dose computation method was successfully validated with EBT2 film measurements and MC calculations. The SC method offers much faster computation speed than MC and provides calculations of both dose-to-water in medium and dose-to-medium in medium. © 2018 American Association of Physicists in Medicine.

Comparison of dose response functions for EBT3 model GafChromic™ film dosimetry system.

PubMed

Aldelaijan, Saad; Devic, Slobodan

2018-05-01

Different dose response functions of EBT3 model GafChromic™ film dosimetry system have been compared in terms of sensitivity as well as uncertainty vs. error analysis. We also made an assessment of the necessity of scanning film pieces before and after irradiation. Pieces of EBT3 film model were irradiated to different dose values in Solid Water (SW) phantom. Based on images scanned in both reflection and transmission mode before and after irradiation, twelve different response functions were calculated. For every response function, a reference radiochromic film dosimetry system was established by generating calibration curve and by performing the error vs. uncertainty analysis. Response functions using pixel values from the green channel demonstrated the highest sensitivity in both transmission and reflection mode. All functions were successfully fitted with rational functional form, and provided an overall one-sigma uncertainty of better than 2% for doses above 2 Gy. Use of pre-scanned images to calculate response functions resulted in negligible improvement in dose measurement accuracy. Although reflection scanning mode provides higher sensitivity and could lead to a more widespread use of radiochromic film dosimetry, it has fairly limited dose range and slightly increased uncertainty when compared to transmission scan based response functions. Double-scanning technique, either in transmission or reflection mode, shows negligible improvement in dose accuracy as well as a negligible increase in dose uncertainty. Normalized pixel value of the images scanned in transmission mode shows linear response in a dose range of up to 11 Gy. Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Calculation of out-of-field dose distribution in carbon-ion radiotherapy by Monte Carlo simulation.

PubMed

Yonai, Shunsuke; Matsufuji, Naruhiro; Namba, Masao

2012-08-01

Recent radiotherapy technologies including carbon-ion radiotherapy can improve the dose concentration in the target volume, thereby not only reducing side effects in organs at risk but also the secondary cancer risk within or near the irradiation field. However, secondary cancer risk in the low-dose region is considered to be non-negligible, especially for younger patients. To achieve a dose estimation of the whole body of each patient receiving carbon-ion radiotherapy, which is essential for risk assessment and epidemiological studies, Monte Carlo simulation plays an important role because the treatment planning system can provide dose distribution only in∕near the irradiation field and the measured data are limited. However, validation of Monte Carlo simulations is necessary. The primary purpose of this study was to establish a calculation method using the Monte Carlo code to estimate the dose and quality factor in the body and to validate the proposed method by comparison with experimental data. Furthermore, we show the distributions of dose equivalent in a phantom and identify the partial contribution of each radiation type. We proposed a calculation method based on a Monte Carlo simulation using the PHITS code to estimate absorbed dose, dose equivalent, and dose-averaged quality factor by using the Q(L)-L relationship based on the ICRP 60 recommendation. The values obtained by this method in modeling the passive beam line at the Heavy-Ion Medical Accelerator in Chiba were compared with our previously measured data. It was shown that our calculation model can estimate the measured value within a factor of 2, which included not only the uncertainty of this calculation method but also those regarding the assumptions of the geometrical modeling and the PHITS code. Also, we showed the differences in the doses and the partial contributions of each radiation type between passive and active carbon-ion beams using this calculation method. These results indicated that it is essentially important to include the dose by secondary neutrons in the assessment of the secondary cancer risk of patients receiving carbon-ion radiotherapy with active as well as passive beams. We established a calculation method with a Monte Carlo simulation to estimate the distribution of dose equivalent in the body as a first step toward routine risk assessment and an epidemiological study of carbon-ion radiotherapy at NIRS. This method has the advantage of being verifiable by the measurement.

Propofol dose and incidence of dreaming during sedation.

PubMed

Eer, Audrey Singyi; Padmanabhan, Usha; Leslie, Kate

2009-10-01

Dreaming is commonly reported after propofol-based sedation. We measured the incidence of dreaming and bispectral index (BIS) values in colonoscopy patients sedated with combinations of propofol, midazolam and fentanyl. Two hundred patients presenting for elective outpatient colonoscopy were sedated with combinations of propofol, midazolam and fentanyl. BIS was monitored throughout the procedure. Patients were interviewed immediately after they emerged from sedation. The primary end point was a report of dreaming during sedation. Ninety-seven patients were administered propofol alone, 44 were administered propofol and fentanyl, 16 were administered propofol and midazolam and 43 were administered propofol, midazolam and fentanyl. Dreaming was reported by 19% of patients. Dreamers received higher doses of propofol and had lower BIS values during sedation. Age of 50 years or less, preoperative quality of recovery score of less than 14, higher home dream recall, propofol dose of more than 300 mg and time to Observers' Assessment of Alertness/Sedation score equalling 5 of 8 min or less were independent predictors of dreaming. Dreaming during sedation is associated with higher propofol dose and lower BIS values.

Validation of a Monte Carlo model used for simulating tube current modulation in computed tomography over a wide range of phantom conditions/challenges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bostani, Maryam, E-mail: mbostani@mednet.ucla.edu; McMillan, Kyle; Cagnon, Chris H.

2014-11-01

Purpose: Monte Carlo (MC) simulation methods have been widely used in patient dosimetry in computed tomography (CT), including estimating patient organ doses. However, most simulation methods have undergone a limited set of validations, often using homogeneous phantoms with simple geometries. As clinical scanning has become more complex and the use of tube current modulation (TCM) has become pervasive in the clinic, MC simulations should include these techniques in their methodologies and therefore should also be validated using a variety of phantoms with different shapes and material compositions to result in a variety of differently modulated tube current profiles. The purposemore » of this work is to perform the measurements and simulations to validate a Monte Carlo model under a variety of test conditions where fixed tube current (FTC) and TCM were used. Methods: A previously developed MC model for estimating dose from CT scans that models TCM, built using the platform of MCNPX, was used for CT dose quantification. In order to validate the suitability of this model to accurately simulate patient dose from FTC and TCM CT scan, measurements and simulations were compared over a wide range of conditions. Phantoms used for testing range from simple geometries with homogeneous composition (16 and 32 cm computed tomography dose index phantoms) to more complex phantoms including a rectangular homogeneous water equivalent phantom, an elliptical shaped phantom with three sections (where each section was a homogeneous, but different material), and a heterogeneous, complex geometry anthropomorphic phantom. Each phantom requires varying levels of x-, y- and z-modulation. Each phantom was scanned on a multidetector row CT (Sensation 64) scanner under the conditions of both FTC and TCM. Dose measurements were made at various surface and depth positions within each phantom. Simulations using each phantom were performed for FTC, detailed x–y–z TCM, and z-axis-only TCM to obtain dose estimates. This allowed direct comparisons between measured and simulated dose values under each condition of phantom, location, and scan to be made. Results: For FTC scans, the percent root mean square (RMS) difference between measurements and simulations was within 5% across all phantoms. For TCM scans, the percent RMS of the difference between measured and simulated values when using detailed TCM and z-axis-only TCM simulations was 4.5% and 13.2%, respectively. For the anthropomorphic phantom, the difference between TCM measurements and detailed TCM and z-axis-only TCM simulations was 1.2% and 8.9%, respectively. For FTC measurements and simulations, the percent RMS of the difference was 5.0%. Conclusions: This work demonstrated that the Monte Carlo model developed provided good agreement between measured and simulated values under both simple and complex geometries including an anthropomorphic phantom. This work also showed the increased dose differences for z-axis-only TCM simulations, where considerable modulation in the x–y plane was present due to the shape of the rectangular water phantom. Results from this investigation highlight details that need to be included in Monte Carlo simulations of TCM CT scans in order to yield accurate, clinically viable assessments of patient dosimetry.« less

SU-F-T-274: Modified Dose Calibration Methods for IMRT QA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, W; Westlund, S

2016-06-15

Purpose: To investigate IMRT QA uncertainties caused by dose calibration and modify widely used dose calibration procedures to improve IMRT QA accuracy and passing rate. Methods: IMRT QA dose measurement is calibrated using a calibration factor (CF) that is the ratio between measured value and expected value corresponding to the reference fields delivered on a phantom. Two IMRT QA phantoms were used for this study: a 30×30×30 cm3 solid water cube phantom (Cube), and the PTW Octavius phantom. CF was obtained by delivering 100 MUs to the phantoms with different reference fields ranging from 3×3 cm2 to 20×20 cm{sup 2}.more » For Cube, CFs were obtained using the following beam arrangements: 2-AP Field - chamber at dmax, 2-AP Field - chamber at isocenter, 4-beam box - chamber at isocenter, and 8 equally spaced fields and chamber at isocenter. The same plans were delivered on Octavius and CFs were derived for the dose at the isocenter using the above beam arrangements. The Octavius plans were evaluated with PTW-VeriSoft (Gamma criteria of 3%/3mm). Results: Four head and neck IMRT plans were included in this study. For point dose measurement with Cube, the CFs with 4-Field gave the best agreement between measurement and calculation within 4% for large field plans. All the measurement results agreed within 2% for a small field plan. Compared with calibration field sizes, 5×5 to 15×15 were more accurate than other field sizes. For Octavius, 4-Field calibration increased passing rate by up to 10% compared to AP calibration. Passing rate also increased by up to 4% with the increase of field size from 3×3 to 20×20. Conclusion: IMRT QA results are correlated with calibration methods used. The dose calibration using 4-beam box with field sizes from 5×5 to 20×20 can improve IMRT QA accuracy and passing rate.« less

Analysis of measurement deviations for the patient-specific quality assurance using intensity-modulated spot-scanning particle beams

NASA Astrophysics Data System (ADS)

Li, Yongqiang; Hsi, Wen C.

2017-04-01

To analyze measurement deviations of patient-specific quality assurance (QA) using intensity-modulated spot-scanning particle beams, a commercial radiation dosimeter using 24 pinpoint ionization chambers was utilized. Before the clinical trial, validations of the radiation dosimeter and treatment planning system were conducted. During the clinical trial 165 measurements were performed on 36 enrolled patients. Two or three fields of particle beam were used for each patient. Measurements were typically performed with the dosimeter placed at special regions of dose distribution along depth and lateral profiles. In order to investigate the dosimeter accuracy, repeated measurements with uniform dose irradiations were also carried out. A two-step approach was proposed to analyze 24 sampling points over a 3D treatment volume. The mean value and the standard deviation of each measurement did not exceed 5% for all measurements performed on patients with various diseases. According to the defined intervention thresholds of mean deviation and the distance-to-agreement concept with a Gamma index analysis using criteria of 3.0% and 2 mm, a decision could be made regarding whether the dose distribution was acceptable for the patient. Based measurement results, deviation analysis was carried out. In this study, the dosimeter was used for dose verification and provided a safety guard to assure precise dose delivery of highly modulated particle therapy. Patient-specific QA will be investigated in future clinical operations.

ANALYSIS OF THE MOMENTS METHOD EXPERIMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kloster, R.L.

1959-09-01

Monte Cario calculations show the effects of a plane water-air boundary on both fast neutron and gamma dose rates. Multigroup diffusion theory calculation for a reactor source shows the effects of a plane water-air boundary on thermal neutron dose rate. The results of Monte Cario and multigroup calculations are compared with experimental values. The predicted boundary effect for fast neutrons of 7.3% agrees within 16% with the measured effect of 6.3%. The gamma detector did not measure a boundary effect because it lacked sensitivity at low energies. However, the effect predicted for gamma rays of 5 to 10% is asmore » large as that for neutrons. An estimate of the boundary effect for thermal neutrons from a PoBe source is obtained from the results of muitigroup diffusion theory calcuiations for a reactor source. The calculated boundary effect agrees within 13% with the measured values. (auth)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lau, A; Ahmad, S; Chen, Y

Purpose: To quantify the simulated mean absorbed dose per technique (cGy/mAs) from a commercially available microCT scanner using various filtration techniques. Methods: Monte Carlo simulations using the Geant4 toolkit (version 10) was used utilizing the standard electromagnetic physics model. The Quantum FX microCT scanner (PerkinElmer, Waltham, MA) was modeled incorporating measured energy spectra and spatial dimensions of nominal source-to-object (SOD) distances. The energy distribution was measured using a spectrometer (X-123CdTe, Amptek Inc., Bedford, USA) for the 90 kVp X-ray beams with various filters (including no filter, 1 mm, 2 mm, 3 mm, 4 mm Al and 0.2 mm Cu +more » 2.5 mm Al). The SOD was set to 154 mm, 104 mm, and 52 mm. A total of 10 million incident particles were processed per simulation. Cutout value was set to 0.1 mm for both photon and electron. The mean dose absorbed (cGy/per incident particle) in a PMMA phantom (length of 2 cm and radius of 3 cm) were recorded. Exposure measurements were taken using a Radcal 9095 system with a protocol of 90 kVp, 200 µA, and ∼12 s beam-On time for the various filters. Results: The mean absorbed dose per mAs for various filtrations and different SOD setups indicated that the dose decreased as the SOD increased and as the amount of filtration increased. For a given SOD, the dose was reduced by as much as ∼13.7% by varying the filter (from 0.2 mm Cu + 2.5 mm Al to no filter). The maximum dose was found to be 0.39 cGy/mAs (SOD of 5.196 cm, no filter) while the minimum dose value was 0.077 cGy/mAs (SOD of 15.4 cm, .2mm Cu + 2mm Al filter). Conclusion: This study estimates easily the mean dose for objects scanned with a microCT scanner with different filtration.« less

Ten years of measured UV Index from the Spanish UVB Radiometric Network.

PubMed

Utrillas, M P; Marín, M J; Esteve, A R; Estellés, V; Gandía, S; Núnez, J A; Martínez-Lozano, J A

2013-08-05

An analysis is made of the UV Index (UVI) obtained from the ultraviolet erythemal solar radiation (UVER) data measured by the Spanish UVB Radiometric Network between the years 2000 and 2009. Previously, the daily UVI has been evaluated using two different criteria: (a) the value corresponding to solar noon; and (b) the daily maximum value. The mean percentage of agreement is 92% if we consider the cases for which the difference is zero or one UVI unit. These results are similar to those obtained in a previous work where only 2 years were analyzed. In all the stations the UVI reaches very high values (8-10) in spring-summer, and the very high and extreme (≥ 11) UVI values are more dependent on the continental effect than on the latitude effect. From the UVI values it is possible to classify the stations into four groups: Coastal stations, Continental stations (more than 200 km from the coast), Southern stations (Coastal stations but with similar values of UVI as the Continental ones due to their low latitude) and Canary Islands stations (1400 km southwest from the Iberian Peninsula thus lower latitude). The monthly mean maximum of UVI is reached in July due to the annual evolution of the total ozone column. This value corresponds, for a skin phototype II, to three times the minimal erythemal dose (MED) in an hour in a Coastal station, 3.5 MEDs in an hour measured in a Continental or Southern station and up five MEDs in an hour in the Izaña station (Canary Islands). The cumulative dose on a horizontal plane over an average year has been calculated for each station. More than 40% of the annual dose is received in summer, about 35% in spring, more than 11% in autumn and less than 10% in winter except for the stations in the Canary Islands where the difference between seasons is less significant. Copyright © 2013 Elsevier B.V. All rights reserved.

Measurements of air dose rates in and around houses in the Fukushima Prefecture in Japan after the Fukushima accident.

PubMed

Matsuda, Norihiro; Mikami, Satoshi; Sato, Tetsuro; Saito, Kimiaki

2017-01-01

Measurements of air dose rates for 192 houses in a less contaminated area (<0.5 μSv h -1 ) of the Fukushima Prefecture in Japan were conducted in both living rooms and/or bedrooms using optically stimulated luminescence (OSL) dosimeters and around the houses via a man-borne survey at intervals of several meters. The relation of the two air dose rates (inside and outside) for each house, including the background from natural radionuclides, was divided into several categories, determined by construction materials (light and heavy) and floor number, with the dose reduction factors being expressed as the ratio of the dose inside to that outside the house. For wooden and lightweight steel houses (classed as light), the dose rates inside and outside the houses showed a positive correlation and linear regression with a slope-intercept form due to the natural background, although the degree of correlation was not very high. The regression coefficient, i.e., the average dose reduction factor, was 0.38 on the first floor and 0.49 on the second floor. It was found that the contribution of natural radiation cannot be neglected when we consider dose reduction factors in less contaminated areas. The reductions in indoor dose rates are observed because a patch of ground under each house is not contaminated (this is the so-called uncontaminated effect) since the shielding capability of light construction materials is typically low. For reinforced steel-framed concrete houses (classed as heavy), the dose rates inside the houses did not show a correlation with those outside the houses due to the substantial shielding capability of these materials. The average indoor dose rates were slightly higher than the arithmetic mean value of the outdoor dose rates from the natural background because concrete acts as a source of natural radionuclides. The characteristics of the uncontaminated effect were clarified through Monte Carlo simulations. It was found that there is a great variation in air dose rates even within one house, depending on the height of the area and its closeness to the outside boundary. Measurements of outdoor dose rates required consideration of local variations depending on the environment surrounding each house. The representative value was obtained from detailed distributions of air dose rates around the house, as measured by a man-borne survey. Therefore, it is imperative to recognize that dose reduction factors fluctuate in response to various factors such as the size and shape of a house, construction materials acting as a shield and as sources, position (including height) within a room, floor number, total number of floors, and surrounding environment. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

Dose calibrator linearity test: 99mTc versus 18F radioisotopes*

PubMed Central

Willegaignon, José; Sapienza, Marcelo Tatit; Coura-Filho, George Barberio; Garcez, Alexandre Teles; Alves, Carlos Eduardo Gonzalez Ribeiro; Cardona, Marissa Anabel Rivera; Gutterres, Ricardo Fraga; Buchpiguel, Carlos Alberto

2015-01-01

Objective The present study was aimed at evaluating the viability of replacing 18F with 99mTc in dose calibrator linearity testing. Materials and Methods The test was performed with sources of 99mTc (62 GBq) and 18F (12 GBq) whose activities were measured up to values lower than 1 MBq. Ratios and deviations between experimental and theoretical 99mTc and 18F sources activities were calculated and subsequently compared. Results Mean deviations between experimental and theoretical 99mTc and 18F sources activities were 0.56 (± 1.79)% and 0.92 (± 1.19)%, respectively. The mean ratio between activities indicated by the device for the 99mTc source as measured with the equipment pre-calibrated to measure 99mTc and 18F was 3.42 (± 0.06), and for the 18F source this ratio was 3.39 (± 0.05), values considered constant over the measurement time. Conclusion The results of the linearity test using 99mTc were compatible with those obtained with the 18F source, indicating the viability of utilizing both radioisotopes in dose calibrator linearity testing. Such information in association with the high potential of radiation exposure and costs involved in 18F acquisition suggest 99mTc as the element of choice to perform dose calibrator linearity tests in centers that use 18F, without any detriment to the procedure as well as to the quality of the nuclear medicine service. PMID:25798005

Use of a control film piece in radiochromic film dosimetry.

PubMed

Aldelaijan, Saad; Alzorkany, Faisal; Moftah, Belal; Buzurovic, Ivan; Seuntjens, Jan; Tomic, Nada; Devic, Slobodan

2016-01-01

Radiochromic films change their color upon irradiation due to polymerization of the sensitive component embedded within the sensitive layer. However, agents, other than monitored radiation, can lead to a change in the color of the sensitive layer (temperature, humidity, UV light) that can be considered as a background signal and can be removed from the actual measurement by using a control film piece. In this work, we investigate the impact of the use of control film pieces on both accuracy and uncertainty of dose measured using radiochromic film based reference dosimetry protocol. We irradiated "control" film pieces (EBT3 GafChromic(TM) film model) to known doses in a range of 0.05-1 Gy, and five film pieces of the same size to 2, 5, 10, 15 and 20 Gy, considered to be "unknown" doses. Depending on a dose range, two approaches to incorporating control film piece were investigated: signal and dose corrected method. For dose values greater than 10 Gy, the increase in accuracy of 3% led to uncertainty loss of 5% by using dose corrected approach. At lower doses and signals of the order of 5%, we observed an increase in accuracy of 10% with a loss of uncertainty lower than 1% by using the corrected signal approach. Incorporation of the signal registered by the control film piece into dose measurement analysis should be a judgment call of the user based on a tradeoff between deemed accuracy and acceptable uncertainty for a given dose measurement. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Assessing the dose values received by patients during conventional radiography X-ray examinations and the technical condition of the equipment used for this purpose.

PubMed

Bekas, Marcin; Pachocki, Krzysztof A; Waśniewska, Elżbieta; Bogucka, Dagmara; Magiera, Andrzej

2014-01-01

X-ray examination is associated with patient exposure to ionizing radiation. Dose values depend on the type of medical procedure used, the X-ray unit technical condition and exposure conditions selected. The aim of this study was to determine the dose value received by patients during certain conventional radiography X-ray examinations and to assess the technical condition of medical equipment used for this purpose. The study covered the total number of 118 conventional diagnostic X-ray units located in the Masovian Voivodeship. The methodology used to assess the conventional diagnostic X-ray unit technical condition and the measurement of the radiation dose rate received by patients are based on test procedures developed by the Department of Radiation Protection and Radiobiology of the National Institute of Public Health - National Institute of Hygiene (Warszawa, Poland) accredited for compliance with PN-EN 17025 standard by the Polish Centre for Accreditation. It was found that 84.7% of X-ray units fully meet the criteria set out in the Polish legislation regarding the safe use of ionizing radiation in medicine, while 15.3% of the units do not meet some of them. The broadest dose value range was recorded for adult patients. Particularly, during lateral (LATl) lumbar spine radiography the recorded entrance surface dose (ESD) values ranged from 283.5 to 7827 µGy (mean: 2183.3 µGy). It is absolutely necessary to constantly monitor the technical condition of all X-ray units, because it affects population exposure to ionizing radiation. Furthermore, it is essential to raise radiographers' awareness of the effects that ionizing radiation exposure can have on the human body.

In vitro dose measurements in a human cadaver with abdomen/pelvis CT scans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Da; Padole, Atul; Li, Xinhua

2014-09-15

Purpose: To present a study of radiation dose measurements with a human cadaver scanned on a clinical CT scanner. Methods: Multiple point dose measurements were obtained with high-accuracy Thimble ionization chambers placed inside the stomach, liver, paravertebral gutter, ascending colon, left kidney, and urinary bladder of a human cadaver (183 cm in height and 67.5 kg in weight) whose abdomen/pelvis region was scanned repeatedly with a multidetector row CT. The flat energy response and precision of the dosimeters were verified, and the slight differences in each dosimeter's response were evaluated and corrected to attain high accuracy. In addition, skin dosesmore » were measured for radiosensitive organs outside the scanned region with OSL dosimeters: the right eye, thyroid, both nipples, and the right testicle. Three scan protocols were used, which shared most scan parameters but had different kVp and mA settings: 120-kVp automA, 120-kVp 300 mA, and 100-kVp 300 mA. For each protocol three repeated scans were performed. Results: The tube starting angle (TSA) was found to randomly vary around two major conditions, which caused large fluctuations in the repeated point dose measurements: for the 120-kVp 300 mA protocol this angle changed from approximately 110° to 290°, and caused 8% − 25% difference in the point dose measured at the stomach, liver, colon, and urinary bladder. When the fluctuations of the TSA were small (within 5°), the maximum coefficient of variance was approximately 3.3%. The soft tissue absorbed doses averaged from four locations near the center of the scanned region were 27.2 ± 3.3 and 16.5 ± 2.7 mGy for the 120 and 100-kVp fixed-mA scans, respectively. These values were consistent with the corresponding size specific dose estimates within 4%. The comparison of the per-100-mAs tissue doses from the three protocols revealed that: (1) dose levels at nonsuperficial locations in the TCM scans could not be accurately deduced by simply scaling the fix-mA doses with local mA values; (2) the general power law relationship between dose and kVp varied from location to location, with the power index ranged between 2.7 and 3.5. The averaged dose measurements at both nipples, which were about 0.6 cm outside the prescribed scan region, ranged from 23 to 27 mGy at the left nipple, and varied from 3 to 20 mGy at the right nipple over the three scan protocols. Large fluctuations over repeated scans were also observed, as a combined result of helical scans of large pitch (1.375) and small active areas of the skin dosimeters. In addition, the averaged skin dose fell off drastically with the distance to the nearest boundary of the scanned region. Conclusions: This study revealed the complexity of CT dose fluctuation and variation with a human cadaver.« less

Dose profile variation with voltage in head CT scans using radiochromic films

NASA Astrophysics Data System (ADS)

Mourão, A. P.; Alonso, T. C.; DaSilva, T. A.

2014-02-01

The voltage source used in an X-ray tube is an important part of defining the generated beam spectrum energy profile. The X-ray spectrum energy defines the X-ray beam absorption as well as the characteristics of the energy deposition in an irradiated object. Although CT scanners allow one to choose between four different voltage values, most of them employ a voltage of 120 kV in their scanning protocols, regardless of the patient characteristics. Based on this fact, this work investigated the deposited dose in a polymethyl methacrylate (PMMA) cylindrical head phantom. The entire volume was irradiated twice. Two CT scanning protocols were used with two different voltage values: 100 and 120 kV. The phantom volume was irradiated, and radiochromic films were employed to record dose profiles. Measurements were conducted with a calibrated pencil ionization chamber, which was positioned in the center and in four peripheral bores of the head PMMA phantom, to calibrate the radiochromic films. The central slice was then irradiated. This procedure allowed us to find the conversion factors necessary to obtain dose values recorded in the films. The data obtained allowed us to observe the dose variation profile inside the phantom head as well as in the peripheral and central regions. The peripheral region showed higher dose values than those of the central region for scans using both voltage values: approximately 31% higher for scanning with 120 kV and 25% higher with 100 kV. Doses recorded with the highest voltage are significantly higher, approximately 50% higher in the peripheral region and 40% higher in the central region. A longitudinal variation could be observed, and the maximum dose was recorded at the peripheral region, at the midpoint of the longitudinal axis. The obtained results will most likely contribute to the dissemination of proper procedure as well as to optimize dosimetry and tests of quality control in CT because the choice of protocols with different voltage values can be a way to optimize the CT scans.

[Absorbed dose and the effective dose of panoramic temporo mandibular joint radiography].

PubMed

Matsuo, Ayae; Okano, Tsuneichi; Gotoh, Kenichi; Yokoi, Midori; Hirukawa, Akiko; Okumura, Shinji; Koyama, Syuji

2011-01-01

This study measured the radiation doses absorbed by the patient during Panoramic temporo mandibular joint radiography (Panoramic TMJ), Schüllers method and Orbitoramus projection. The dose of the frontal view in Panoramic TMJ was compared to that with Orbitoramus projection and the lateral view in Panoramic TMJ was compared to that with Schüllers method. We measured the doses received by various organs and calculated the effective doses using the guidelines of the International Commission on Radiological Protection in Publication 103. Organ absorbed doses were measured using an anthropomorphic phantom, loaded with thermoluminescent dosimeters (TLD), located at 160 sensitive sites. The dose shows the sum value of irradiation on both the right and left sides. In addition, we set a few different exposure field sizes. The effective dose for a frontal view in Panoramic TMJ was 11 µSv, and that for the lateral view was 14 µSv. The lens of the Orbitoramus projection was 40 times higher than the frontal view in Panoramic TMJ. Although the effective dose of the lateral view in Panoramic TMJ was 3 times higher than that of the small exposure field (10×10 cm on film) in Schüller's method, it was the same as that of a mid-sized exposure field. When the exposure field in the inferior 1/3 was reduced during panoramic TMJ, the effective doses could be decreased. Therefore we recommend that the size of the exposure field in Panoramic TMJ be decreased.

Validity of linear measurements of the jaws using ultralow-dose MDCT and the iterative techniques of ASIR and MBIR.

PubMed

Al-Ekrish, Asma'a A; Al-Shawaf, Reema; Schullian, Peter; Al-Sadhan, Ra'ed; Hörmann, Romed; Widmann, Gerlig

2016-10-01

To assess the comparability of linear measurements of dental implant sites recorded from multidetector computed tomography (MDCT) images obtained using standard-dose filtered backprojection (FBP) technique with those from various ultralow doses combined with FBP, adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR) techniques. The results of the study may contribute to MDCT dose optimization for dental implant site imaging. MDCT scans of two cadavers were acquired using a standard reference protocol and four ultralow-dose test protocols (TP). The volume CT dose index of the different dose protocols ranged from a maximum of 30.48-36.71 mGy to a minimum of 0.44-0.53 mGy. All scans were reconstructed using FBP, ASIR-50, ASIR-100, and MBIR, and either a bone or standard reconstruction kernel. Linear measurements were recorded from standardized images of the jaws by two examiners. Intra- and inter-examiner reliability of the measurements were analyzed using Cronbach's alpha and inter-item correlation. Agreement between the measurements obtained with the reference-dose/FBP protocol and each of the test protocols was determined with Bland-Altman plots and linear regression. Statistical significance was set at a P-value of 0.05. No systematic variation was found between the linear measurements obtained with the reference protocol and the other imaging protocols. The only exceptions were TP3/ASIR-50 (bone kernel) and TP4/ASIR-100 (bone and standard kernels). The mean measurement differences between these three protocols and the reference protocol were within ±0.1 mm, with the 95 % confidence interval limits being within the range of ±1.15 mm. A nearly 97.5 % reduction in dose did not significantly affect the height and width measurements of edentulous jaws regardless of the reconstruction algorithm used.

[Nephrotoxicity of Aristolochia manshuriensis and aristolochic acids in mice].

PubMed

Ding, Xiao-shuang; Liang, Ai-hua; Wang, Jin-hua; Xiao, Yong-qing; Wu, Zi-lun; Li, Chun-ying; Li, Li; He, Rong; Hui, Lian-qiang; Liu, Bao-yan

2005-07-01

The acute toxic effects of Aristolochia manshuriensis (GMT) and the total aristolochic acids (TA) were compared in mice with aristolochic acid A (AA) as the dose standard. The dose relationship of the renal toxicity induced by Aristolochia manshuriensis was determined. A single dose of GMT extract or TA was given intragastrically to mice at different doses. LD50 values, the blood levels of BUN, Cr and ALT were measured. A histomorphological study was also performed in livers and kidneys of mice. LD50 value of GMT extract was 4.4 g x kg(-1) which was equivalent to 40 mg x kg(-1) as calculated by the content of AA in GMT extract, and this value was comparable with LD50 obtained from TA given intragastrically in mice (equivalent to 33 mg x kg(-1) of AA for male and 37 mg x kg(-1) for female). GMT extract caused a significant increase in blood BUN and Cr and an obvious morphological change in kidney in a dose-dependent manner at doses of AA 4.5 mg x kg(-1) and above. Liver damage, characterized by both an increase in blood level of AST and histomorphological change, was observed at doses of AA 25 mg x kg(-1) and above. All changes were in proportion to the doses of AA. GMT causes both renal and liver toxicity. The dose leading to nephrotoxicity is much lower than that inducing hepatatoxicity. Aristolochic acids existed in GMT are the main toxic components to cause renal toxicity which is a crucial cause to result in death. The lethality and nephrotoxicity of GMT is in proportion to the doses of AA.

Measurements of radioactivity and dose assessments in some building materials in Bitlis, Turkey.

PubMed

Kayakökü, Halime; Karatepe, Şule; Doğru, Mahmut

2016-09-01

In this study, samples of perlite, pumice and Ahlat stones (Ignimbrite) extracted from mines in Bitlis and samples of other building materials produced in facilities in Bitlis were collected and analyzed. Activity concentrations of (226)Ra, (232)Th and (40)K in samples of building materials were measured using NaI detector (NaI(Tl)) with an efficiency of 24%. The radon measurements of building material samples were determined using CR-39 nuclear track detectors. (226)Ra, (232)Th and (40)K radioactivity concentrations ranged from (29.6±5.9 to 228.2±38.1Bq/kg), (10.8±5.4 to 95.5±26.1Bq/kg) and (249.3±124.7 to 2580.1±266.9Bq/kg), respectively. Radon concentration, radium equivalent activities, absorbed dose rate, excess lifetime cancer risk and the values of hazard indices were calculated for the measured samples to assess the radiation hazards arising from using those materials in the construction of dwellings. Radon concentration ranged between 89.2±12.0Bq/m(3) and 1141.0±225.0Bq/m(3). It was determined that Raeq values of samples conformed to world standards except for perlite and single samples of brick and Ahlat stone. Calculated values of absorbed dose rate ranged from 81.3±20.5 to 420.6±42.8nGy/h. ELCR values ranged from (1.8±0.3)×10(-3) to (9.0±1.0)×10(-3). All samples had ELCR values higher than the world average. The values of Hin and Hex varied from 0.35±0.11 to 1.78±0.18 and from 0.37±0.09 to 1.17±0.13, respectively. The results were compared with standard radioactivity values determined by international organizations and with similar studies. There would be a radiation risk for people living in buildings made of perlite, Ahlat-1 and Brick-3. Copyright © 2016 Elsevier Ltd. All rights reserved.

Research on radiation exposure from CT part of hybrid camera and diagnostic CT

NASA Astrophysics Data System (ADS)

Solný, Pavel; Zimák, Jaroslav

2014-11-01

Research on radiation exposure from CT part of hybrid camera in seven different Departments of Nuclear Medicine (DNM) was conducted. Processed data and effective dose (E) estimations led to the idea of phantom verification and comparison of absorbed doses and software estimation. Anonymous data from about 100 examinations from each DNM was gathered. Acquired data was processed and utilized by dose estimation programs (ExPACT, ImPACT, ImpactDose) with respect to the type of examination and examination procedures. Individual effective doses were calculated using enlisted programs. Preserving the same procedure in dose estimation process allows us to compare the resulting E. Some differences and disproportions during dose estimation led to the idea of estimated E verification. Consequently, two different sets of about 100 of TLD 100H detectors were calibrated for measurement inside the Aldersnon RANDO Anthropomorphic Phantom. Standard examination protocols were examined using a 2 Slice CT- part of hybrid SPECT/CT. Moreover, phantom exposure from body examining protocol for 32 Slice and 64 Slice diagnostic CT scanner was also verified. Absorbed dose (DT,R) measured using TLD detectors was compared with software estimation of equivalent dose HT values, computed by E estimation software. Though, only limited number of cavities for detectors enabled measurement within the regions of lung, liver, thyroid and spleen-pancreas region, some basic comparison is possible.

Correlation between prescribed daily dose, seizure freedom and defined daily dose in antiepileptic drug treatment.

PubMed

Horváth, László; Fekete, Klára; Márton, Sándor; Fekete, István

2017-04-01

Background Although defined daily doses (DDD) for antiepileptic drugs (AED) have been assigned only in combination therapy, based on the literature, most patients take them in monotherapy. Furthermore, discrepancies between DDD and prescribed daily dose (PDD) were observed. Objective First, to determine PDDs of AEDs and to reveal PDD/DDD ratio among seizure free versus not seizure free patients in everyday clinical practice. Second, to test the applicability of 75% cut-off of DDD to achieve seizure freedom. Furthermore, to find out what factors might influence PDD. Setting Outpatient data files at a Hungarian university hospital were studied. Methods A retrospective, 20-year cross-sectional database was compiled from 1282 epileptic outpatients' files. Main outcome measure Seizure freedom and PDD were used as outcome measures. Results The mean DDD% of all prescribed AEDs increased steadily from monotherapy, through bitherapy towards polytherapy (p < 0.0001). Most seizure free patients took AEDs in doses in the range of ≤75% of DDDs in monotherapy and bitherapy. Older AEDs (carbamazepine and valproate) were given in a significantly higher mean dose in bitherapy in the seizure free group. Among the newer types, only levetiracetam and lamotrigine had a significantly higher DDD% in mono-, bi-, and polytherapy. Confirmed by logistic regression analysis, gender, age, type of epilepsy, and number of AEDs had a significant impact on the value of 75% DDD. Conclusion No significant unfavourable impact of the lower ratio of PDD/DDD on the outcome of achieving seizure freedom has been confirmed. As a measure of seizure freedom, 75% of DDD may be used, although individual therapy must be emphasised. Precisely quantified DDD would provide a more accurate calculation of other derived values.

Out-of-Field Dose Equivalents Delivered by Passively Scattered Therapeutic Proton Beams for Clinically Relevant Field Configurations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wroe, Andrew; Centre for Medical Radiation Physics, University of Wollongong, Wollongong; Clasie, Ben

2009-01-01

Purpose: Microdosimetric measurements were performed at Massachusetts General Hospital, Boston, MA, to assess the dose equivalent external to passively delivered proton fields for various clinical treatment scenarios. Methods and Materials: Treatment fields evaluated included a prostate cancer field, cranial and spinal medulloblastoma fields, ocular melanoma field, and a field for an intracranial stereotactic treatment. Measurements were completed with patient-specific configurations of clinically relevant treatment settings using a silicon-on-insulator microdosimeter placed on the surface of and at various depths within a homogeneous Lucite phantom. The dose equivalent and average quality factor were assessed as a function of both lateral displacement frommore » the treatment field edge and distance downstream of the beam's distal edge. Results: Dose-equivalent value range was 8.3-0.3 mSv/Gy (2.5-60-cm lateral displacement) for a typical prostate cancer field, 10.8-0.58 mSv/Gy (2.5-40-cm lateral displacement) for the cranial medulloblastoma field, 2.5-0.58 mSv/Gy (5-20-cm lateral displacement) for the spinal medulloblastoma field, and 0.5-0.08 mSv/Gy (2.5-10-cm lateral displacement) for the ocular melanoma field. Measurements of external field dose equivalent for the stereotactic field case showed differences as high as 50% depending on the modality of beam collimation. Average quality factors derived from this work ranged from 2-7, with the value dependent on the position within the phantom in relation to the primary beam. Conclusions: This work provides a valuable and clinically relevant comparison of the external field dose equivalents for various passively scattered proton treatment fields.« less

Patient exposure dose for chest and skull radiographies in Mazandaran hospitals.

PubMed

Etemadinezhad, Siavash; Rahimi, Seyed Ali

2010-01-01

Radiographic techniques are essential methods of diagnosis, and their use has been increased, especially with the development of the new technologies. Inappropriate administration of these techniques may put both the patients and personnel at unnecessary risks. The objective of this research was to measure the skin dose of chest and skull radiographies used in Mazandaran hospitals and to compare these doses with national and international standards. In this cross-sectional study, six X-ray generators at six hospitals affiliated to Mazandaran University of Medical Sciences were included. One hundred and twenty patients referred to the radiology wards for radiographic examinations of chest and skull with normal body mass index (BMI) were selected (20 patients for each radiography unit). The generators were matched for mAs, kvp, type of amplifier sheets, and technical conditions as much as possible. Calibrated thermo luminescence dosimeters (TLD-USA, Lif-100) were used to measure the skin dose by placing them on the patients' back and the absorbed doses by TLDs were read by a TLD reader (model: Harshuu, TLD3500, Japan). The mean values of the skin dose were 0.51 mGray for posteroanterior (PA), chest X-ray (CXR), 3.36 mGray for lateral CXR, 7.25 mGray for anterroposterior (AP) or PA skull X-rays, and 7.59 mGray for lateral skull X-rays. The measured values were higher than the national and international standards. The results of this research revealed that the conditions of the X-ray generators should be monitored and modified periodically. Modifying the X-ray generators plus improving technicians' skills would, to some extent, reduce the radiation exposure of the patients.

Quantitative measurement of natural radioactivity in some roofing tile materials used in upper Egypt.

PubMed

Uosif, M A M

2013-09-01

The quantitative measurement of radionuclides ((226)Ra, (232)Th and (40)K) in some roofing tile materials (granite, alabaster, marble, traditional and advanced ceramic) used in Upper Egypt is presented in this paper. Measurements were done by using gamma spectrometry (NaI (Tl) 3" × 3"). The values of concentration of natural radionuclides were in the following ranges: 12-78.9 Bq kg(-1) for (226)Ra, 8.4-113.1 Bq kg(-1) for (232)Th and 94.9-509 Bq kg(-1)for (40)K. The activity concentration index (I), the specific dose rates indoors ( ) and the annual effective dose (DE) due to gamma radiation were calculated for each investigated sample. The lowest value of I is 0.19 for alabaster, while the highest one is 0.88 for traditional and advanced ceramic. The ranges of DE are between 0.03 and 0.13 mSv, it is below the maximal permitted values, so that the examined materials could be used as roofing tiles in the construction of new buildings.

Assessment of natural radioactivity and gamma-ray dose in monazite rich black Sand Beach of Penang Island, Malaysia.

PubMed

Shuaibu, Hauwau Kulu; Khandaker, Mayeen Uddin; Alrefae, Tareq; Bradley, D A

2017-06-15

Activity concentrations of primordial radionuclides in sand samples collected from the coastal beaches surrounding Penang Island have been measured using conventional γ-ray spectrometry, while in-situ γ-ray doses have been measured through use of a portable radiation survey meter. The mean activity concentrations for 226 Ra, 232 Th and 40 K at different locations were found to be less than the world average values, while the Miami Bay values for 226 Ra and 232 Th were found to be greater, at 1023±47 and 2086±96Bqkg ̶ 1 respectively. The main contributor to radionuclide enrichment in Miami Bay is the presence of monazite-rich black sands. The measured data were compared against literature values and also recommended limits set by the relevant international bodies. With the exception of Miami Bay, considered an elevated background radiation area that would benefit from regular monitoring, Penang island beach sands typically pose no significant radiological risk to the local populace and tourists visiting the leisure beaches. Copyright © 2017 Elsevier Ltd. All rights reserved.

A comparison of mean parotid gland dose with measures of parotid gland function after radiotherapy for head-and-neck cancer: Implications for future trials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roesink, Judith M.; Schipper, Maria; Busschers, Wim

2005-11-15

Purpose: To determine the most adequate parameter to measure the consequences of reducing the parotid gland dose. Methods and Materials: One hundred eight patients treated with radiotherapy for various malignancies of the head and neck were prospectively evaluated using three methods. Parotid gland function was objectively determined by measuring stimulated parotid flow using Lashley cups and scintigraphy. To assess xerostomia-related quality of life, the head-and-neck cancer module European Organization for Research and Treatment of Cancer QLQ (Quality of Life Questionnaire) H and N35 was used. Measurements took place before radiotherapy and 6 weeks and 12 months after the completion ofmore » radiotherapy. Complication was defined for each method using cutoff values. The correlation between these complications and the mean parotid gland dose was investigated to find the best measure for parotid gland function. Results: For both flow and scintigraphy data, the best definition for objective parotid gland toxicity seemed to be reduction of stimulated parotid flow to {<=}25% of the preradiotherapy flow. Of all the subjective variables, only the single item dry mouth 6 weeks after radiotherapy was found to be significant. The best correlation with the mean parotid gland dose was found for the stimulated flow measurements. The predictive ability was the highest for the time point 1 year after radiotherapy. Subjective findings did not correlate with the mean parotid dose. Conclusions: Stimulated flow measurements using Lashley cups, with a complication defined as flow {<=}25% of the preradiotherapy output, correlated best with the mean parotid gland dose. When reduction of the mean dose to the parotid gland is intended, the stimulated flow measurement is the best method for evaluating parotid gland function.« less

4D dose simulation in volumetric arc therapy: Accuracy and affecting parameters

PubMed Central

Werner, René

2017-01-01

Radiotherapy of lung and liver lesions has changed from normofractioned 3D-CRT to stereotactic treatment in a single or few fractions, often employing volumetric arc therapy (VMAT)-based techniques. Potential unintended interference of respiratory target motion and dynamically changing beam parameters during VMAT dose delivery motivates establishing 4D quality assurance (4D QA) procedures to assess appropriateness of generated VMAT treatment plans when taking into account patient-specific motion characteristics. Current approaches are motion phantom-based 4D QA and image-based 4D VMAT dose simulation. Whereas phantom-based 4D QA is usually restricted to a small number of measurements, the computational approaches allow simulating many motion scenarios. However, 4D VMAT dose simulation depends on various input parameters, influencing estimated doses along with mitigating simulation reliability. Thus, aiming at routine use of simulation-based 4D VMAT QA, the impact of such parameters as well as the overall accuracy of the 4D VMAT dose simulation has to be studied in detail–which is the topic of the present work. In detail, we introduce the principles of 4D VMAT dose simulation, identify influencing parameters and assess their impact on 4D dose simulation accuracy by comparison of simulated motion-affected dose distributions to corresponding dosimetric motion phantom measurements. Exploiting an ITV-based treatment planning approach, VMAT treatment plans were generated for a motion phantom and different motion scenarios (sinusoidal motion of different period/direction; regular/irregular motion). 4D VMAT dose simulation results and dose measurements were compared by local 3% / 3 mm γ-evaluation, with the measured dose distributions serving as ground truth. Overall γ-passing rates of simulations and dynamic measurements ranged from 97% to 100% (mean across all motion scenarios: 98% ± 1%); corresponding values for comparison of different day repeat measurements were between 98% and 100%. Parameters of major influence on 4D VMAT dose simulation accuracy were the degree of temporal discretization of the dose delivery process (the higher, the better) and correct alignment of the assumed breathing phases at the beginning of the dose measurements and simulations. Given the high γ-passing rates between simulated motion-affected doses and dynamic measurements, we consider the simulations to provide a reliable basis for assessment of VMAT motion effects that–in the sense of 4D QA of VMAT treatment plans–allows to verify target coverage in hypofractioned VMAT-based radiotherapy of moving targets. Remaining differences between measurements and simulations motivate, however, further detailed studies. PMID:28231337

4D dose simulation in volumetric arc therapy: Accuracy and affecting parameters.

PubMed

Sothmann, Thilo; Gauer, Tobias; Werner, René

2017-01-01

Radiotherapy of lung and liver lesions has changed from normofractioned 3D-CRT to stereotactic treatment in a single or few fractions, often employing volumetric arc therapy (VMAT)-based techniques. Potential unintended interference of respiratory target motion and dynamically changing beam parameters during VMAT dose delivery motivates establishing 4D quality assurance (4D QA) procedures to assess appropriateness of generated VMAT treatment plans when taking into account patient-specific motion characteristics. Current approaches are motion phantom-based 4D QA and image-based 4D VMAT dose simulation. Whereas phantom-based 4D QA is usually restricted to a small number of measurements, the computational approaches allow simulating many motion scenarios. However, 4D VMAT dose simulation depends on various input parameters, influencing estimated doses along with mitigating simulation reliability. Thus, aiming at routine use of simulation-based 4D VMAT QA, the impact of such parameters as well as the overall accuracy of the 4D VMAT dose simulation has to be studied in detail-which is the topic of the present work. In detail, we introduce the principles of 4D VMAT dose simulation, identify influencing parameters and assess their impact on 4D dose simulation accuracy by comparison of simulated motion-affected dose distributions to corresponding dosimetric motion phantom measurements. Exploiting an ITV-based treatment planning approach, VMAT treatment plans were generated for a motion phantom and different motion scenarios (sinusoidal motion of different period/direction; regular/irregular motion). 4D VMAT dose simulation results and dose measurements were compared by local 3% / 3 mm γ-evaluation, with the measured dose distributions serving as ground truth. Overall γ-passing rates of simulations and dynamic measurements ranged from 97% to 100% (mean across all motion scenarios: 98% ± 1%); corresponding values for comparison of different day repeat measurements were between 98% and 100%. Parameters of major influence on 4D VMAT dose simulation accuracy were the degree of temporal discretization of the dose delivery process (the higher, the better) and correct alignment of the assumed breathing phases at the beginning of the dose measurements and simulations. Given the high γ-passing rates between simulated motion-affected doses and dynamic measurements, we consider the simulations to provide a reliable basis for assessment of VMAT motion effects that-in the sense of 4D QA of VMAT treatment plans-allows to verify target coverage in hypofractioned VMAT-based radiotherapy of moving targets. Remaining differences between measurements and simulations motivate, however, further detailed studies.

Comparison of evening and morning dosing of travoprost 0.004%/timolol 0.5% fixed combination in 6 month period.

PubMed

Suić, Smiljka Popović; Laus, Katia Novak; Dosen, Vukosava Maricic; Ekert, Miroslav; Mandić, Zdravko; Bojić, Lovro

2010-09-01

An open label, multi-center, 6 months observational study of new fixed combination (travoprost 0.004%/timolol 0.5%), in order to evaluate both efficacy (intraocular pressure lowering) and tolerability (patient and investigator satisfaction) of two dosing regimens--evening (PM) and morning (AM). After screening for enrollment, to 40 patients (79 eyes with primary open angle glaucoma or ocular hypertension), new fixed combination travoprost 0.004%/timolol 0.5% was prescribed once a day in the evening (PM). Patients were enrolled according to each investigator decision on indication for travoprost 0.004%/timolol 0.5% fixed combination once a day, without washout period after previous medication. Intraocular pressure was measured at 9 AM at all time control points: at baseline, after 1 month, after 3 months and after 6 month. After 1 month, screening for nonresponders (criteria: 20% intraocular pressure lowering) and subjects with major side effects was performed. At second control visit, after 3 months PM dosing, intraocular pressure was measured and patients were instructed to continue once a day the same medication, but in the morning (AM) for consequent 3 months. After 1 month, reduction in mean intraocular pressure value was 21.66%. At the visit after 3 month, the mean intraocular pressure was 15.67 +/- 2.17 mm Hg (reduction 21.14%). 3 month after dosing regimen changed to AM (6 month after beginning of travoprost 0.004%/timolol 0.5% combination therapy), reduction in intraocular pressure value was 19.86%. The differences (mean +/- standard deviation) in intraocular pressure values after 1, 3 and 6 month were all highly statistically significant compared to baseline values. The tolerability was evaluated in five steps (Likert scale) ranging from unsatisfactory to excellent by both patient and investigator--taken at 3 and 6 month control visit. 95% of patients and 100% of investigators were satisfied with the possibility of choosing dosing regimen for travoprost 0.004%/timolol 0.5% fixed combination. Travoprost 0.004%/timolol 0.5% fixed combination proved sufficient intraocular pressure control dosed either PM or AM with no statistically significant difference between two dosing regimens. Possibility to choose between two dosing regimens gives each practitioner additional reassurance that glaucoma therapy will be individualised to needs of each patient.

Chemiluminescence measurements on irradiated garlic powder by the single photon counting technique

NASA Astrophysics Data System (ADS)

Narvaiz, P.

1995-02-01

The feasibility of identifying irradiated garlic powder measuring chemiluminescence by liquid scintillation spectrometry was studied. Samples packed in 100 μm thick polyethylene bags were irradiated in a 60Co semi-industrial facility, with doses of 10 and 30 kGy. Control and irradiated samples were stored at 20 ± 4°C and 70 ± 10% RH in darkness for 2 years. Assays were performed to establish the best sample concentration and pH of the buffer solution in which garlic powder was to be suspended for its measurement. The water content of garlic samples was also analyzed throughout storage time, as it related to the stability of the species causing luminescence. Chemiluminescence values diminished in every sample over storage time following an exponential pattern. Irradiated samples showed values significantly higher than those of the control samples, according to the radiation dose, throughout the storage period. This does not necessarily imply that the identification of the irradiated samples would be certain, since values of control samples coming from different origins have been found to fluctuate within a rather wide range. Nonetheless, in principle, the method looks promising for the measurement of chemiluminescence in irradiated samples

Radon Dose Determination for Cave Guides in Czech Republic

NASA Astrophysics Data System (ADS)

Thinova, Lenka; Rovenska, Katerina

2008-08-01

According to recommended approach there are six (from total of twelve) open-to-public caves in Czech Republic, reaching near to an effective lung-dose of 6mSv/year. A conservative approach for estimating the potential effective lung-dose in caves (or underground) is based on two season's measurements, using solid state alpha track detector (Kodak in plastic diffusion chamber). The obtained dataset is converted into an annual effective dose, in agreement with the ICRP65 recommendation, using the "cave factor" 1.5. The value of "cave factor" which depends on the spectrum of aerosol particles, or on the proportional representation of the unattached/attached ratio (6.5 : 93.5 for residential places, 13.6 : 86.4 for caves due to lower concentration of free aerosols) and on the equilibrium factor. Thus conversion factor is 1.5 times higher in comparison with ICRP 65. Is this correct? Because a more precisely determined dose value would have a significant impact on radon remedies, or on restricting the time workers stay underground, a series of measurement was initiated in 2003 with the aim to specify input data, computation and errors in effective dose assessment in each one of the evaluated caves separately. The enhancement of personal dosimetry for underground work places includes a study of the given questions, from the following points of view in each cave: continual radon measurement; regular measurements of radon and its daughters to estimate the equilibrium factor and the presence of free 218Po; regular indoor air flow measurements to study the location of the radon supply and its transfer among individual areas of the cave; natural radioactive element content evaluation in subsoil and in water inside/outside, a study of the radon sources in the cave; determination of the free fraction from continual unattached and attached fraction measurement (grid and filter); thoron measurement. Air flow measurements provide very interesting information about the origin of "radon pockets" with very high radon concentration, and enable study of the location of the radon supply and its transfer among individual areas of the cave. Most of the results show the equilibrium factor around F = 0.2-0.7 and the unattached fraction around 2%-30%. One of the most important question remains: how accurately was the unattached fraction measured? Part of this project was to verify the influence of etched track detector position in the cave.

Characterisation of an anthropomorphic chest phantom for dose measurements in radiology beams

NASA Astrophysics Data System (ADS)

Henriques, L. M. S.; Cerqueira, R. A. D.; Santos, W. S.; Pereira, A. J. S.; Rodrigues, T. M. A.; Carvalho Júnior, A. B.; Maia, A. F.

2014-02-01

The objective of this study was to characterise an anthropomorphic chest phantom for dosimetric measurements of conventional radiology beams. This phantom was developed by a previous research project at the Federal University of Sergipe for image quality control tests. As the phantom consists of tissue-equivalent material, it is possible to characterise it for dosimetric studies. For comparison, a geometric chest phantom, consisting of PMMA (polymethylmethacrylate) with dimensions of 30×30×15 cm³ was used. Measurements of incident air kerma (Ki) and entrance surface dose (ESD) were performed using ionisation chambers. From the results, backscatter factors (BSFs) of the two phantoms were determined and compared with values estimated by CALDose_X software, based on a Monte Carlo simulation. For the technical parameters evaluated in this study, the ESD and BSF values obtained experimentally showed a good similarity between the two phantoms, with minimum and maximum difference of 0.2% and 7.0%, respectively, and showed good agreement with the results published in the literature. Organ doses and effective doses for the anthropomorphic phantom were also estimated by the determination of conversion coefficients (CCs) using the visual Monte Carlo (VMC) code. Therefore, the results of this study prove that the anthropomorphic thorax phantom proposed is a good tool to use in dosimetry and can be used for risk evaluation of X-ray diagnostic procedures.

Internal Dose from Food and Drink Ingestion in the Early Phase after the Accident

NASA Astrophysics Data System (ADS)

Kawai, Masaki; Yoshizawa, Nobuaki; Hirakawa, Sachiko; Murakami, Kana; Takizawa, Mari; Sato, Osamu; Takagi, Shunji; Miyatake, Hirokazu; Takahashi, Tomoyuki; Suzuki, Gen

2017-09-01

Activity concentrations in food and drink, represented by water and vegetables, have been monitored continuously since the Fukushima Daiichi Nuclear Power Plant accident, with a focus on radioactive cesium. On the other hand, iodine-131 was not measured systematically in the early phase after the accident. The activity concentrations of iodine-131 in food and drink are important to estimate internal exposure due to ingestion pathway. When the internal dose from ingestion in the evacuation areas is estimated, water is considered as the main ingestion pathway. In this study, we estimated the values of activity concentrations in water in the early phase after the accident, using a compartment model as an estimation method. The model uses measurement values of activity concentration and deposition rate of iodine-131 onto the ground, which is calculated from an atmospheric dispersion simulation. The model considers how drinking water would be affected by radionuclides deposited into water. We estimated the activity concentrations of water on Kawamata town and Minamisouma city during March of 2011 and the committed effective doses were 0.08 mSv and 0.06 mSv. We calculated the transfer parameters in the model for estimating the activity concentrations in the areas with a small amount of measurement data. In addition, we estimated the committed effective doses from vegetables using atmospheric dispersion simulation and FARMLAND model in case of eating certain vegetables as option information.

The feasibility of a regional CTDI{sub vol} to estimate organ dose from tube current modulated CT exams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khatonabadi, Maryam; Kim, Hyun J.; Lu, Peiyun

Purpose: In AAPM Task Group 204, the size-specific dose estimate (SSDE) was developed by providing size adjustment factors which are applied to the Computed Tomography (CT) standardized dose metric, CTDI{sub vol}. However, that work focused on fixed tube current scans and did not specifically address tube current modulation (TCM) scans, which are currently the majority of clinical scans performed. The purpose of this study was to extend the SSDE concept to account for TCM by investigating the feasibility of using anatomic and organ specific regions of scanner output to improve accuracy of dose estimates. Methods: Thirty-nine adult abdomen/pelvis and 32more » chest scans from clinically indicated CT exams acquired on a multidetector CT using TCM were obtained with Institutional Review Board approval for generating voxelized models. Along with image data, raw projection data were obtained to extract TCM functions for use in Monte Carlo simulations. Patient size was calculated using the effective diameter described in TG 204. In addition, the scanner-reported CTDI{sub vol} (CTDI{sub vol,global}) was obtained for each patient, which is based on the average tube current across the entire scan. For the abdomen/pelvis scans, liver, spleen, and kidneys were manually segmented from the patient datasets; for the chest scans, lungs and for female models only, glandular breast tissue were segmented. For each patient organ doses were estimated using Monte Carlo Methods. To investigate the utility of regional measures of scanner output, regional and organ anatomic boundaries were identified from image data and used to calculate regional and organ-specific average tube current values. From these regional and organ-specific averages, CTDI{sub vol} values, referred to as regional and organ-specific CTDI{sub vol}, were calculated for each patient. Using an approach similar to TG 204, all CTDI{sub vol} values were used to normalize simulated organ doses; and the ability of each normalized dose to correlate with patient size was investigated. Results: For all five organs, the correlations with patient size increased when organ doses were normalized by regional and organ-specific CTDI{sub vol} values. For example, when estimating dose to the liver, CTDI{sub vol,global} yielded a R{sup 2} value of 0.26, which improved to 0.77 and 0.86, when using the regional and organ-specific CTDI{sub vol} for abdomen and liver, respectively. For breast dose, the global CTDI{sub vol} yielded a R{sup 2} value of 0.08, which improved to 0.58 and 0.83, when using the regional and organ-specific CTDI{sub vol} for chest and breasts, respectively. The R{sup 2} values also increased once the thoracic models were separated for the analysis into females and males, indicating differences between genders in this region not explained by a simple measure of effective diameter. Conclusions: This work demonstrated the utility of regional and organ-specific CTDI{sub vol} as normalization factors when using TCM. It was demonstrated that CTDI{sub vol,global} is not an effective normalization factor in TCM exams where attenuation (and therefore tube current) varies considerably throughout the scan, such as abdomen/pelvis and even thorax. These exams can be more accurately assessed for dose using regional CTDI{sub vol} descriptors that account for local variations in scanner output present when TCM is employed.« less

Exposure to radon in the Gadime Cave, Kosovo.

PubMed

Bahtijari, M; Vaupotic, J; Gregoric, A; Stegnar, P; Kobal, I

2008-02-01

Air radon concentration was measured in summer and winter at 11 points along the tourist guided route in the Gadime Cave in Kosovo using alpha scintillation cells and etched track detectors. At two points in summer, values higher than 1700Bqm(-3) were observed; they otherwise were in the range 400-1000Bqm(-3). Values were lower in winter. The effective dose received by a person during a 90min visit is 3.7microSv in summer and 2.5microSv in winter. For a tourist guide the annual effective dose is less than 3.5mSv.

Complexity metric based on fraction of penumbra dose - initial study

NASA Astrophysics Data System (ADS)

Bäck, A.; Nordström, F.; Gustafsson, M.; Götstedt, J.; Karlsson Hauer, A.

2017-05-01

Volumetric modulated arc therapy improve radiotherapy outcome for many patients compared to conventional three dimensional conformal radiotherapy but require a more extensive, most often measurement based, quality assurance. Multi leaf collimator (MLC) aperture-based complexity metrics have been suggested to be used to distinguish complex treatment plans unsuitable for treatment without time consuming measurements. This study introduce a spatially resolved complexity score that correlate to the fraction of penumbra dose and will give information on the spatial distribution and the clinical relevance of the calculated complexity. The complexity metric is described and an initial study on the correlation between the complexity score and the difference between measured and calculated dose for 30 MLC openings is presented. The result of an analysis of the complexity scores were found to correlate to differences between measurements and calculations with a Pearson’s r-value of 0.97.

Dosimetric comparison of Acuros XB, AAA, and XVMC in stereotactic body radiotherapy for lung cancer.

PubMed

Tsuruta, Yusuke; Nakata, Manabu; Nakamura, Mitsuhiro; Matsuo, Yukinori; Higashimura, Kyoji; Monzen, Hajime; Mizowaki, Takashi; Hiraoka, Masahiro

2014-08-01

To compare the dosimetric performance of Acuros XB (AXB), anisotropic analytical algorithm (AAA), and x-ray voxel Monte Carlo (XVMC) in heterogeneous phantoms and lung stereotactic body radiotherapy (SBRT) plans. Water- and lung-equivalent phantoms were combined to evaluate the percentage depth dose and dose profile. The radiation treatment machine Novalis (BrainLab AG, Feldkirchen, Germany) with an x-ray beam energy of 6 MV was used to calculate the doses in the composite phantom at a source-to-surface distance of 100 cm with a gantry angle of 0°. Subsequently, the clinical lung SBRT plans for the 26 consecutive patients were transferred from the iPlan (ver. 4.1; BrainLab AG) to the Eclipse treatment planning systems (ver. 11.0.3; Varian Medical Systems, Palo Alto, CA). The doses were then recalculated with AXB and AAA while maintaining the XVMC-calculated monitor units and beam arrangement. Then the dose-volumetric data obtained using the three different radiation dose calculation algorithms were compared. The results from AXB and XVMC agreed with measurements within ± 3.0% for the lung-equivalent phantom with a 6 × 6 cm(2) field size, whereas AAA values were higher than measurements in the heterogeneous zone and near the boundary, with the greatest difference being 4.1%. AXB and XVMC agreed well with measurements in terms of the profile shape at the boundary of the heterogeneous zone. For the lung SBRT plans, AXB yielded lower values than XVMC in terms of the maximum doses of ITV and PTV; however, the differences were within ± 3.0%. In addition to the dose-volumetric data, the dose distribution analysis showed that AXB yielded dose distribution calculations that were closer to those with XVMC than did AAA. Means ± standard deviation of the computation time was 221.6 ± 53.1 s (range, 124-358 s), 66.1 ± 16.0 s (range, 42-94 s), and 6.7 ± 1.1 s (range, 5-9 s) for XVMC, AXB, and AAA, respectively. In the phantom evaluations, AXB and XVMC agreed better with measurements than did AAA. Calculations differed in the density-changing zones (substance boundaries) between AXB/XVMC and AAA. In the lung SBRT cases, a comparative analysis of dose-volumetric data and dose distributions with XVMC demonstrated that the AXB provided better agreement with XVMC than AAA. The computation time of AXB was faster than that of XVMC; therefore, AXB has better balance in terms of the dosimetric performance and computation speed for clinical use than XVMC.

Current status of radiological protection at nuclear power stations in Japan.

PubMed

Suzuki, Akira; Hori, Shunsuke

2011-07-01

The radiation dose to workers at nuclear power stations (NPSs) in Japan was drastically reduced between the late-1970s and the early-1990s by continuous dose-reduction programmes. The total collective dose of radiation workers in FY 2008 was 84.04 person Sv, while the average collective dose was 1.5 person Sv per reactor. The average annual individual dose was 1.1 mSv and the maximum annual individual dose was 19.5 mSv. These values are sufficiently lower than the regulatory dose limits. Radioactive effluent released from NPSs is already so trivial that additional protective measures will not be necessary. Experience in radiation protection at NPSs has been accumulated over 40 y and will be very useful in establishing a rational radiation control system in the future.

The advantages of absorbed-dose calibration factors.

PubMed

Rogers, D W

1992-01-01

A formalism for clinical external beam dosimetry based on use of ion chamber absorbed-dose calibration factors is outlined in the context and notation of the AAPM TG-21 protocol. It is shown that basing clinical dosimetry on absorbed-dose calibration factors ND leads to considerable simplification and reduced uncertainty in dose measurement. In keeping with a protocol which is used in Germany, a quantity kQ is defined which relates an absorbed-dose calibration factor in a beam of quality Q0 to that in a beam of quality Q. For 38 cylindrical ion chambers, two sets of values are presented for ND/NX and Ngas/ND and for kQ for photon beams with beam quality specified by the TPR20(10) ratio. One set is based on TG-21's protocol to allow the new formalism to be used while maintaining equivalence to the TG-21 protocol. To demonstrate the magnitude of the overall error in the TG-21 protocol, the other set uses corrected versions of the TG-21 equations and the more consistent physical data of the IAEA Code of Practice. Comparisons are made to procedures based on air-kerma or exposure calibration factors and it is shown that accuracy and simplicity are gained by avoiding the determination of Ngas from NX. It is also shown that the kQ approach simplifies the use of plastic phantoms in photon beams since kQ values change by less than 0.6% compared to those in water although an overall correction factor of 0.973 is needed to go from absorbed dose in water calibration factors to those in PMMA or polystyrene. Values of kQ calculated using the IAEA Code of Practice are presented but are shown to be anomalous because of the way the effective point of measurement changes for 60Co beams. In photon beams the major difference between the IAEA Code of Practice and the corrected AAPM TG-21 protocol is shown to be the Prepl correction factor. Calculated kQ curves and three parameter equations for them are presented for each wall material and are shown to represent accurately the kQ curve for all ion chambers in this study with a wall of that specified material and a thickness less than 0.25 g/cm2. Values of kQ can be measured using the primary standards for absorbed dose in photon beams.

Experimental determination of the response functions of a Bonner sphere spectrometer to monoenergetic neutrons

NASA Astrophysics Data System (ADS)

Hu, Z.; Chen, Z.; Peng, X.; Du, T.; Cui, Z.; Ge, L.; Zhu, W.; Wang, Z.; Zhu, X.; Chen, J.; Zhang, G.; Li, X.; Chen, J.; Zhang, H.; Zhong, G.; Hu, L.; Wan, B.; Gorini, G.; Fan, T.

2017-06-01

A Bonner sphere spectrometer (BSS) plays an important role in characterizing neutron spectra and determining their neutron dose in a neutron-gamma mixed field. A BSS consisting of a set of nine polyethylene spheres with a 3He proportional counter was developed at Peking University to perform neutron spectrum and dosimetry measurements. Response functions (RFs) of the BSS were calculated with the general Monte Carlo code MCNP5 for the neutron energy range from thermal up to 20 MeV, and were experimentally calibrated with monoenergetic neutron beams from 144 keV to 14 MeV on a 4.5 MV Van de Graaff accelerator. The calculated RFs were corrected with the experimental values, and the whole response matrix was completely established. The spectrum of a 241Am-Be source was obtained after unfolding the measurement data of the BSS to the source and in fair agreement with the expected one. The integral ambient dose equivalent corresponding to the spectrum was 0.95 of the expected value. Results of the unfolded spectrum and the integral dose equivalent measured by the BSS verified that the RFs of the BSS were well established.

The validation of tomotherapy dose calculations in low-density lung media

NASA Astrophysics Data System (ADS)

Chaudhari, Summer R.; Pechenaya, Olga L.; Goddu, S. Murty; Mutic, Sasa; Rangaraj, Dharanipathy; Bradley, Jeffrey D.; Low, Daniel

2009-04-01

The dose-calculation accuracy of the tomotherapy Hi-Art II® (Tomotherapy, Inc., Madison, WI) treatment planning system (TPS) in the presence of low-density lung media was investigated. In this evaluation, a custom-designed heterogeneous phantom mimicking the mediastinum geometry was used. Gammex LN300 and balsa wood were selected as two lung-equivalent materials with different densities. Film analysis and ionization chamber measurements were performed. Treatment plans for esophageal cancers were used in the evaluation. The agreement between the dose calculated by the TPS and the dose measured via ionization chambers was, in most cases, within 0.8%. Gamma analysis using 3% and 3 mm criteria for radiochromic film dosimetry showed that 98% and 95% of the measured dose distribution had passing gamma values <=1 for LN300 and balsa wood, respectively. For a homogeneous water-equivalent phantom, 95% of the points passed the gamma test. It was found that for the interface between the low-density medium and water-equivalent medium, the TPS calculated the dose distribution within acceptable limits. The phantom developed for this work enabled detailed quality-assurance testing under realistic conditions with heterogeneous media.

The validation of tomotherapy dose calculations in low-density lung media.

PubMed

Chaudhari, Summer R; Pechenaya, Olga L; Goddu, S Murty; Mutic, Sasa; Rangaraj, Dharanipathy; Bradley, Jeffrey D; Low, Daniel

2009-04-21

The dose-calculation accuracy of the tomotherapy Hi-Art II(R) (Tomotherapy, Inc., Madison, WI) treatment planning system (TPS) in the presence of low-density lung media was investigated. In this evaluation, a custom-designed heterogeneous phantom mimicking the mediastinum geometry was used. Gammex LN300 and balsa wood were selected as two lung-equivalent materials with different densities. Film analysis and ionization chamber measurements were performed. Treatment plans for esophageal cancers were used in the evaluation. The agreement between the dose calculated by the TPS and the dose measured via ionization chambers was, in most cases, within 0.8%. Gamma analysis using 3% and 3 mm criteria for radiochromic film dosimetry showed that 98% and 95% of the measured dose distribution had passing gamma values < or =1 for LN300 and balsa wood, respectively. For a homogeneous water-equivalent phantom, 95% of the points passed the gamma test. It was found that for the interface between the low-density medium and water-equivalent medium, the TPS calculated the dose distribution within acceptable limits. The phantom developed for this work enabled detailed quality-assurance testing under realistic conditions with heterogeneous media.

SU-E-I-57: Evaluation and Optimization of Effective-Dose Using Different Beam-Hardening Filters in Clinical Pediatric Shunt CT Protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gill, K; Aldoohan, S; Collier, J

Purpose: Study image optimization and radiation dose reduction in pediatric shunt CT scanning protocol through the use of different beam-hardening filters Methods: A 64-slice CT scanner at OU Childrens Hospital has been used to evaluate CT image contrast-to-noise ratio (CNR) and measure effective-doses based on the concept of CT dose index (CTDIvol) using the pediatric head shunt scanning protocol. The routine axial pediatric head shunt scanning protocol that has been optimized for the intrinsic x-ray tube filter has been used to evaluate CNR by acquiring images using the ACR approved CT-phantom and radiation dose CTphantom, which was used to measuremore » CTDIvol. These results were set as reference points to study and evaluate the effects of adding different filtering materials (i.e. Tungsten, Tantalum, Titanium, Nickel and Copper filters) to the existing filter on image quality and radiation dose. To ensure optimal image quality, the scanner routine air calibration was run for each added filter. The image CNR was evaluated for different kVps and wide range of mAs values using above mentioned beam-hardening filters. These scanning protocols were run under axial as well as under helical techniques. The CTDIvol and the effective-dose were measured and calculated for all scanning protocols and added filtration, including the intrinsic x-ray tube filter. Results: Beam-hardening filter shapes energy spectrum, which reduces the dose by 27%. No noticeable changes in image low contrast detectability Conclusion: Effective-dose is very much dependent on the CTDIVol, which is further very much dependent on beam-hardening filters. Substantial reduction in effective-dose is realized using beam-hardening filters as compare to the intrinsic filter. This phantom study showed that significant radiation dose reduction could be achieved in CT pediatric shunt scanning protocols without compromising in diagnostic value of image quality.« less

Radiation protection for an intra-operative X-ray device

PubMed Central

Eaton, D J; Gonzalez, R; Duck, S; Keshtgar, M

2011-01-01

Objectives Therapeutic partial breast irradiation can be delivered intra-operatively using the Intrabeam 50 kVp compact X-ray device. Spherical applicators are added to the source to give an isotropic radiation dose. The low energy of this unit leads to rapid attenuation with distance, but dose rates are much greater than for diagnostic procedures. Methods To investigate the shielding requirements for this unit, attenuation measurements were carried out with manufacturer-provided tungsten–rubber sheets, lead, plasterboard and bricks. A prospective environmental dose rate survey was also conducted in the designated theatre. Results As a result of isotropic geometry, the scattered dose around shielding can be 1% of primary and thus often dominates measured dose rates compared with transmission. The absorbed dose rate of the unshielded source at 1 m was 11.6 mGy h−1 but this was reduced by 95% with the shielding sheets. Measured values for the common shielding materials were similar to reference data for the attenuation of a 50 kVp diagnostic X-ray beam. Two lead screens were constructed to shield operators remaining in the theatre and an air vent into a service corridor. A lead apron would also provide suitable attenuation, although a screen allows greater flexibility for treatment operators. With these measures, staff doses were reduced to negligible quantities. Survey measurements taken during patient treatments confirmed no additional measures were required, but the theatre should be a controlled area and access restricted. Conclusion Results from this study and reference data can be used for planning other facilities. PMID:21304003

Doses from radon 222 irradiation for workers of the granite mining industry.

PubMed

Сrygorieva, L; Tomilin, Yu

2017-12-01

determining the integral value of annual effective dose from 222Rn for workers of the granite mining industry and assessment for the expected life effective dose from 222Rn. Materials were the results of measurements of external exposure dose of radiation measurements equiv alent equilibrium volume activity of 222Rn in workrooms and workplaces of major groups of granite quarry workers Mykolaiv region, studies EROA 222Rn air premises of these workers, research content 222Rn in drinking water. Granite quarry workers receive double radiation exposure of 222Rn due to exposure in the workplace and at home. The load in the workplace due to inhalation of 222Rn the air was (2.1 ± 0.2) mSv / year (vari ation 0.9-5.9) in a residential area - (4,1 ± 0,2) mSv/year (variation 1.8-5.9). The total annual effective dose from internal exposure from air flow and working premises and drinking water was on average (6,5 ± 0,2) mSv/year, equal to a maximum value of 20 mSv/year. The expected life for the chronic exposure dose of technological naturally occurring radioactive sources for people who work in the granite quarries and, while living in high risk from radon is in the range of 0.16-1.12 Sv. The research results indicate that in assessing the effects associated with exposure due to radon 222 contingents persons such surveys must take into account all sources of this radionuclide dose. L. Сrygorieva, Yu. Tomilin.

Validation of ELDO approaches for retrospective assessment of cumulative eye lens doses of interventional cardiologists-results from DoReMi project.

PubMed

Domienik, J; Farah, J; Struelens, L

2016-12-01

The first validation results of the two approaches developed in the ELDO project for retrospective assessment of eye lens doses for interventional cardiologists (ICs) are presented in this paper. The first approach (a) is based on both the readings from the routine whole body dosimeter worn above the lead apron and procedure-dependent conversion coefficients, while the second approach (b) is based on detailed information related to the occupational exposure history of the ICs declared in a questionnaire and eye lens dose records obtained from the relevant literature. The latter approach makes use of various published eye lens doses per procedure as well as the appropriate correction factors which account for the use of radiation protective tools designed to protect the eye lens. To validate both methodologies, comprehensive measurements were performed in several Polish clinics among recruited physicians. Two dosimeters measuring whole body and eye lens doses were worn by every physician for at least two months. The estimated cumulative eye lens doses, calculated from both approaches, were then compared against the measured eye lens dose value for every physician separately. Both approaches results in comparable estimates of eye lens doses and tend to overestimate rather than underestimate the eye lens doses. The measured and estimated doses do not differ, on average, by a factor higher than 2.0 in 85% and 62% of the cases used to validate approach (a) and (b), respectively. In specific cases, however, the estimated doses differ from the measured ones by as much as a factor of 2.7 and 5.1 for method (a) and (b), respectively. As such, the two approaches can be considered accurate when retrospectively estimating the eye lens doses for ICs and will be of great benefit for ongoing epidemiological studies.

Agreement Between Institutional Measurements and Treatment Planning System Calculations for Basic Dosimetric Parameters as Measured by the Imaging and Radiation Oncology Core-Houston

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerns, James R.; Followill, David S.; Imaging and Radiation Oncology Core-Houston, The University of Texas Health Science Center-Houston, Houston, Texas

Purpose: To compare radiation machine measurement data collected by the Imaging and Radiation Oncology Core at Houston (IROC-H) with institutional treatment planning system (TPS) values, to identify parameters with large differences in agreement; the findings will help institutions focus their efforts to improve the accuracy of their TPS models. Methods and Materials: Between 2000 and 2014, IROC-H visited more than 250 institutions and conducted independent measurements of machine dosimetric data points, including percentage depth dose, output factors, off-axis factors, multileaf collimator small fields, and wedge data. We compared these data with the institutional TPS values for the same points bymore » energy, class, and parameter to identify differences and similarities using criteria involving both the medians and standard deviations for Varian linear accelerators. Distributions of differences between machine measurements and institutional TPS values were generated for basic dosimetric parameters. Results: On average, intensity modulated radiation therapy–style and stereotactic body radiation therapy–style output factors and upper physical wedge output factors were the most problematic. Percentage depth dose, jaw output factors, and enhanced dynamic wedge output factors agreed best between the IROC-H measurements and the TPS values. Although small differences were shown between 2 common TPS systems, neither was superior to the other. Parameter agreement was constant over time from 2000 to 2014. Conclusions: Differences in basic dosimetric parameters between machine measurements and TPS values vary widely depending on the parameter, although agreement does not seem to vary by TPS and has not changed over time. Intensity modulated radiation therapy–style output factors, stereotactic body radiation therapy–style output factors, and upper physical wedge output factors had the largest disagreement and should be carefully modeled to ensure accuracy.« less

An evaluation of in-plane shields during thoracic CT.

PubMed

Foley, S J; McEntee, M F; Rainford, L A

2013-08-01

The object of this study was to compare organ dose and image quality effects of using bismuth and barium vinyl in-plane shields with standard and low tube current thoracic CT protocols. A RANDO phantom was scanned using a 64-slice CT scanner and three different thoracic protocols. Thermoluminescent dosemeters were positioned in six locations to record surface and absorbed breast and lung doses. Image quality was assessed quantitatively using region of interest measurements. Scanning was repeated using bismuth and barium vinyl in-plane shields to cover the breasts and the results were compared with standard and reduced dose protocols. Dose reductions were most evident in the breast, skin and anterior lung when shielding was used, with mean reductions of 34, 33 and 10 % for bismuth and 23, 18 and 11 % for barium, respectively. Bismuth was associated with significant increases in both noise and CT attenuation values for all the three protocols, especially anteriorly and centrally. Barium shielding had a reduced impact on image quality. Reducing the overall tube current reduced doses in all the locations by 20-27 % with similar increases in noise as shielding, without impacting on attenuation values. Reducing the overall tube current best optimises dose with minimal image quality impact. In-plane shields increase noise and attenuation values, while reducing anterior organ doses primarily. Shielding remains a useful optimisation tool in CT and barium is an effective alternative to bismuth especially when image quality is of concern.

Poster - Thur Eve - 45: Commissioning of the Varian ECLIPSE eMC algorithm for clinical electron treatment planning.

PubMed

Serban, M; Ruo, R; Sarfehnia, A; Parker, W; Evans, M

2012-07-01

Fast electron Monte Carlo systems have been developed commercially, and implemented for clinical practice in radiation therapy clinics. In this work the Varian eMC (electron Monte Carlo) algorithm was commissioned for clinical electron beams of energies between 6 MeV and 20 MeV. Beam outputs, PDDs and profiles were measured for 29 regular and irregular cutouts using the IC-10 (Wellhöfer) ionization chamber. Detailed percentage depth dose comparisons showed that the agreement between measurement and eMC for different characteristic points on the PDD are generally less than 1 mm and always less than 2 mm, with the eMC calculated values being lower than the measured values. Of the 145 measured output factors, 19 cases fail a ±2% agreement but only 8 cases fail a ±3% agreement between calculation and measurement. Comparison of central axis dose distributions for two electron energies (9, and 20 MeV) for a 10 × 10 cm 2 field, centrally shielded with Pb of width 0 cm (open), 1, 2 and 3 cm, shows agreement to within 3% except near the surface. Comparison of central axis dose distributions for 9 MeV in heterogeneous phantoms including bone and lung inserts showed agreement of 1 mm and 3 mm respectively with measured TLD data. The overall agreement between measurement and eMC calculation has enabled us to begin implementing this calculation model for clinical use. © 2012 American Association of Physicists in Medicine.

Fiber-optic detector for real time dosimetry of a micro-planar x-ray beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Belley, Matthew D.; Stanton, Ian N.; Langloss, Brian W.

2015-04-15

Purpose: Here, the authors describe a dosimetry measurement technique for microbeam radiation therapy using a nanoparticle-terminated fiber-optic dosimeter (nano-FOD). Methods: The nano-FOD was placed in the center of a 2 cm diameter mouse phantom to measure the deep tissue dose and lateral beam profile of a planar x-ray microbeam. Results: The continuous dose rate at the x-ray microbeam peak measured with the nano-FOD was 1.91 ± 0.06 cGy s{sup −1}, a value 2.7% higher than that determined via radiochromic film measurements (1.86 ± 0.15 cGy s{sup −1}). The nano-FOD-determined lateral beam full-width half max value of 420 μm exceeded thatmore » measured using radiochromic film (320 μm). Due to the 8° angle of the collimated microbeam and resulting volumetric effects within the scintillator, the profile measurements reported here are estimated to achieve a resolution of ∼0.1 mm; however, for a beam angle of 0°, the theoretical resolution would approach the thickness of the scintillator (∼0.01 mm). Conclusions: This work provides proof-of-concept data and demonstrates that the novel nano-FOD device can be used to perform real-time dosimetry in microbeam radiation therapy to measure the continuous dose rate at the x-ray microbeam peak as well as the lateral beam shape.« less

Dose-volume metrics and their relation to memory performance in pediatric brain tumor patients: A preliminary study.

PubMed

Raghubar, Kimberly P; Lamba, Michael; Cecil, Kim M; Yeates, Keith Owen; Mahone, E Mark; Limke, Christina; Grosshans, David; Beckwith, Travis J; Ris, M Douglas

2018-06-01

Advances in radiation treatment (RT), specifically volumetric planning with detailed dose and volumetric data for specific brain structures, have provided new opportunities to study neurobehavioral outcomes of RT in children treated for brain tumor. The present study examined the relationship between biophysical and physical dose metrics and neurocognitive ability, namely learning and memory, 2 years post-RT in pediatric brain tumor patients. The sample consisted of 26 pediatric patients with brain tumor, 14 of whom completed neuropsychological evaluations on average 24 months post-RT. Prescribed dose and dose-volume metrics for specific brain regions were calculated including physical metrics (i.e., mean dose and maximum dose) and biophysical metrics (i.e., integral biological effective dose and generalized equivalent uniform dose). We examined the associations between dose-volume metrics (whole brain, right and left hippocampus), and performance on measures of learning and memory (Children's Memory Scale). Biophysical dose metrics were highly correlated with the physical metric of mean dose but not with prescribed dose. Biophysical metrics and mean dose, but not prescribed dose, correlated with measures of learning and memory. These preliminary findings call into question the value of prescribed dose for characterizing treatment intensity; they also suggest that biophysical dose has only a limited advantage compared to physical dose when calculated for specific regions of the brain. We discuss the implications of the findings for evaluating and understanding the relation between RT and neurocognitive functioning. © 2018 Wiley Periodicals, Inc.

Concepts for dose determination in flat-detector CT

NASA Astrophysics Data System (ADS)

Kyriakou, Yiannis; Deak, Paul; Langner, Oliver; Kalender, Willi A.

2008-07-01

Flat-detector computed tomography (FD-CT) scanners provide large irradiation fields of typically 200 mm in the cranio-caudal direction. In consequence, dose assessment according to the current definition of the computed tomography dose index CTDIL=100 mm, where L is the integration length, would demand larger ionization chambers and phantoms which do not appear practical. We investigated the usefulness of the CTDI concept and practical dosimetry approaches for FD-CT by measurements and Monte Carlo (MC) simulations. An MC simulation tool (ImpactMC, VAMP GmbH, Erlangen, Germany) was used to assess the dose characteristics and was calibrated with measurements of air kerma. For validation purposes measurements were performed on an Axiom Artis C-arm system (Siemens Medical Solutions, Forchheim, Germany) equipped with a flat detector of 40 cm × 30 cm. The dose was assessed for 70 kV and 125 kV in cylindrical PMMA phantoms of 160 mm and 320 mm diameter with a varying phantom length from 150 to 900 mm. MC simulation results were compared to the values obtained with a calibrated ionization chambers of 100 mm and 250 mm length and to thermoluminesence (TLD) dose profiles. The MCs simulations were used to calculate the efficiency of the CTDIL determination with respect to the desired CTDI∞. Both the MC simulation results and the dose distributions obtained by MC simulation were in very good agreement with the CTDI measurements and with the reference TLD profiles, respectively, to within 5%. Standard CTDI phantoms which have a z-extent of 150 mm underestimate the dose at the center by up to 55%, whereas a z-extent of >=600 mm appears to be sufficient for FD-CT; the baseline value of the respective profile was within 1% to the reference baseline. As expected, the measurements with ionization chambers of 100 mm and 250 mm offer a limited accuracy, whereas an increased integration length of >=600 mm appeared to be necessary to approximate CTDI∞ in within 1%. MC simulations appear to offer a practical and accurate way of assessing conversion factors for arbitrary dosimetry setups using a standard pencil chamber to provide estimates of CTDI∞. This would eliminate the need for extra-long phantoms and ionization chambers or excessive amounts of TLDs.

Feasibility study of a photoconductor based dosimeter for quality assurance in radiotherapy

NASA Astrophysics Data System (ADS)

Lee, Y. K.; Kim, S. W.; Kim, J. N.; Kang, Y. N.; Kim, J. Y.; Lee, D. S.; Kim, K. T.; Han, M. J.; Ahn, K. J.; Park, S. K.

2017-09-01

With the recent market entries of new types of linear accelerators (LINACs) with a multi leaf collimator (MLC) mounted on them, high-precision radiosurgery applying a LINAC to measure high-dose radiation on the target region has been gaining popularity. Systematic and accurate quality assurance (QA) is of vital important for high-precision radiosurgery because of its increased risk of side effects including life-threatening ones such as overexposure of healthy tissues to high-dose radiation beams concentrated on small areas. Therefore, accurate dose and dose-distribution measurements are crucial in the treatment procedure. The accurate measurement of the properties of beams concentrated on small areas requires high-precision dosimeters capable of high-resolution output and dose mapping as well as accurate dosimetry in penumbra regions. In general, the properties of beams concentrated on small areas are measured using thermos luminescent dosimeters (TLD), diode detectors, ion chambers, diamond detectors, or films, and many papers have presented the advantages and disadvantages of each of these detectors for dosimetry. In this study, a solid-state photoconductor dosimeter was developed, and its clinical usability was tested by comparing its relative dosimetric performance with that of a conventional ion chamber. As materials best-suited for radiation dosimeters, four candidates namely lead (II) iodide (PbI2), lead (II) oxide (PbO), mercury (II) iodide (HgI2), and HgI2/ titanium dioxide (TiO2) composite, the performances of which were proved in previous studies, were used. The electrical properties of each candidate material were examined using the sedimentation method, one of the particle-in-binder (PIB) methods, and unit-cell-type prototypes were fabricated. The unit-cell samples thus prepared were cut into specimens of area 1 × 1 cm2 with 400-μ m thickness. The electrical properties of each sample, such as sensitivity, dark current, output current, rising time, falling time, and response delay, were then measured, in addition to the consistency, reproducibility and linearity of each unit-cell. According to the measurement results, HgI2/TiO2 composite outperformed the other candidate materials. A radiation dosimeter with a chamber-type structure was fabricated in this study using a LINAC under accelerating voltages of 6, and 15 MV and compared with a commercial ion chamber. Percent depth dose (PDD) and beam profile were measured on a water phantom at a fixed area of 10 × 10 cm2 by using the fabricated chamber-type dosimeter, and the values were compared with those measured by a commercial ion chamber. Additionally, a homogeneous phantom was fabricated, and the exposure doses of the center points were measured according to a real treatment plan, followed by a comparison of the measured values as relative values. In this paper, we report that the manufactured dosimeter shows similar characteristics in terms of PDD and beam profile and results for the conventional ion chamber. Based on these results, it is demonstrated that the HgI2/TiO2-based dosimeter complies with radiotherapy QA requirements, namely Superior detection characteristics, consistency, dose linearity, reproducibility. Thus, we expect the HgI2/TiO2-based dosimeter to be used commercially in the future.

Patient doses from fluoroscopically guided cardiac procedures in pediatrics

NASA Astrophysics Data System (ADS)

Martinez, L. C.; Vano, E.; Gutierrez, F.; Rodriguez, C.; Gilarranz, R.; Manzanas, M. J.

2007-08-01

Infants and children are a higher risk population for radiation cancer induction compared to adults. Although some values on pediatric patient doses for cardiac procedures have been reported, data to determine reference levels are scarce, especially when compared to those available for adults in diagnostic and therapeutic procedures. The aim of this study is to make a new contribution to the scarce published data in pediatric cardiac procedures and help in the determination of future dose reference levels. This paper presents a set of patient dose values, in terms of air kerma area product (KAP) and entrance surface air kerma (ESAK), measured in a pediatric cardiac catheterization laboratory equipped with a biplane x-ray system with dynamic flat panel detectors. Cardiologists were properly trained in radiation protection. The study includes 137 patients aged between 10 days and 16 years who underwent diagnostic catheterizations or therapeutic procedures. Demographic data and technical details of the procedures were also gathered. The x-ray system was submitted to a quality control programme, including the calibration of the transmission ionization chamber. The age distribution of the patients was 47 for <1 year; 52 for 1-<5 years; 25 for 5-<10 years and 13 for 10-<16 years. Median values of KAP were 1.9, 2.9, 4.5 and 15.4 Gy cm2 respectively for the four age bands. These KAP values increase by a factor of 8 when moving through the four age bands. The probability of a fatal cancer per fluoroscopically guided cardiac procedure is about 0.07%. Median values of ESAK for the four age bands were 46, 50, 56 and 163 mGy, which lie far below the threshold for deterministic effects on the skin. These dose values are lower than those published in previous papers.

The effects of a 5-HT2 receptor antagonist (ICI 169,369) on changes in waking EEG, pupillary responses and state of arousal in human volunteers.

PubMed Central

Millson, D S; Haworth, S J; Rushton, A; Wilkinson, D; Hobson, S; Harry, J

1991-01-01

1. ICI 169,369 (2-(2-dimethylamino ethylthio)-3-phenyl quinoline) is a potent selective competitive antagonist of the 5-HT2 receptor in animal models. Effects of ICI 169,369 as single oral doses (80 and 120 mg) separated by 1 week, on the power spectrum of waking EEG, dark adapted pupil responses and sedation score, were studied in a double-blind, placebo controlled, randomised cross over within subject comparison, in six healthy male volunteers. 2. Pupillary responses were measured using a portable infrared pupillometer following 15 min dark adaptation, assessing resting vertical pupil diameter (RPD), light constricted diameter (MPD) and recovered final diameter (FPD) at the end of a 3 s measurement cycle. 3. Both doses of ICI 169,369 produced a mean 36% (range 10-54%) decrease in log 10 power of the waking EEG alpha activity with eyes closed (P less than 0.02), and mean 38% (range 2-86%) increase in theta activity at 2 h compared with placebo. 4. Both 80 and 120 mg doses of ICI 169,369 reduced RPD by approximately 30% from a predose value of 6.25 mm (+/- 0.87; 95% CI) and from placebo values 6.41 mm (+/- 1.06) and 7.48 mm (+/- 1.49) at 3 and 5 h after dosing. MPD was reduced by 50% with the 120 mg dose at 5 h after dosing (placebo 5.2 mm; ICI 169,369 2.7 mm; P less than 0.05). FPD was significantly reduced (P less than 0.01) by both doses at 3 h after dosing.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:1958438

[Combined internal-external radiotherapy (CIERT) in a cell model].

PubMed

Oehme, Liane; Bartzsch, Thomas; Maucksch, Ute; Freudenberg, Robert; Wunderlich, Gerd; Kotzerke, Jörg

2018-06-01

Combined internal-external radiotherapy (CIERT) requires a unified assessment of biologic radiation effects in addition to the total dose. The concept of biological effective dose (BED) was evaluated in a cell model. The thyroid NIS-positive cell line FRTL-5 was irradiated with X-ray and the radiotracer Tc-99m pertechnetate either alone or in combination. The cellular uptake of the radionuclide during the incubation time of 24 h was controlled by the presence or absence of perchlorate. Dose calculation was performed based on measured uptake values. Cell specific radiobiologic parameters were derived from dose effect curves using the colony forming assay as biological endpoint. For the combination of the radiation qualities the sequence and time difference were varied. Cell survival was compared with the prediction of the BED model. The radiobiologic parameters from X-ray dose response were α = (0.22 ± 0.02) Gy -1 and β = (0.021 ± 0.001) Gy -2 . The half life for repair was (1.51 ± 0.21) h. These values could also explain the dose response curves for Tc-99m-irradiation with exponential decreasing dose rate. CIERT experiments showed no significant differences in cell survival regarding sequence and irradiation break. When the radionuclide uptake was not prevented the cell survival for the combination of X-ray and Tc-99m was lower than the prediction by BED calculations. The validity of the BED formalism for different dose rates and radiation qualities was verified. Supraaddive effects measured in the combination of X-ray and intracellular Tc-99m might be caused by Auger and conversion electrons, however further experiments are necessary. Schattauer GmbH.

High dose microCT does not contribute towards improved microPET/CT image quantitative accuracy and can limit longitudinal scanning of small animals

NASA Astrophysics Data System (ADS)

McDougald, Wendy A.; Collins, Richard; Green, Mark; Tavares, Adriana A. S.

2017-10-01

Obtaining accurate quantitative measurements in preclinical Positron Emission Tomography/Computed Tomography (PET/CT) imaging is of paramount importance in biomedical research and helps supporting efficient translation of preclinical results to the clinic. The purpose of this study was two-fold: (1) to investigate the effects of different CT acquisition protocols on PET/CT image quality and data quantification; and (2) to evaluate the absorbed dose associated with varying CT parameters. Methods: An air/water quality control CT phantom, tissue equivalent material phantom, an in-house 3D printed phantom and an image quality PET/CT phantom were imaged using a Mediso nanoPET/CT scanner. Collected data was analyzed using PMOD software, VivoQuant software and National Electric Manufactures Association (NEMA) software implemented by Mediso. Measured Hounsfield Unit (HU) in collected CT images were compared to the known HU values and image noise was quantified. PET recovery coefficients (RC), uniformity and quantitative bias were also measured. Results: Only less than 2% and 1% of CT acquisition protocols yielded water HU values < -80 and air HU values < -840, respectively. Four out of eleven CT protocols resulted in more than 100 mGy absorbed dose. Different CT protocols did not impact PET uniformity and RC, and resulted in <4% overall bias relative to expected radioactive concentration. Conclusion: Preclinical CT protocols with increased exposure times can result in high absorbed doses to the small animals. These should be avoided, as they do not contributed towards improved microPET/CT image quantitative accuracy and could limit longitudinal scanning of small animals.

Treatment and therapeutic monitoring of canine hypothyroidism.

PubMed

Dixon, R M; Reid, S W J; Mooney, C T

2002-08-01

Thirty-one dogs with spontaneous hypothyroidism were treated with thyroid hormone replacement therapy (THRT) and monitored for approximately three months. Good clinical and laboratory control was ultimately achieved in all cases with a mean L-thyroxine (T4) dose of 0.026 mg/kg administered once daily. There was a significant increase and decrease in circulating total T4 and canine thyroid stimulating hormone (cTSH) concentrations, respectively, after starting THRT. After commencing treatment, 11 cases subsequently required an increase and three cases required a decrease in dose to achieve optimal clinical control. Median (semi interquartile range [SIR]) circulating six-hour post-pill total T4 (53.6 [27.91 nmol/litre) and cTSH (0.03 [0] microg/litre) concentrations were significantly increased and decreased, respectively, in treated dogs that did not require a dose change; corresponding values in treated dogs in which an increase in dose was required were 29.3 (12.7) nmol/litre and 0.15 (0.62) microg/litre, respectively. However, circulating cTSH measurement was of limited value in assessing therapeutic control because, although increased values were associated with inadequate therapy, reference range cTSH values were common in inadequately treated dogs. Lethargy and mental demeanour were typically the first clinical signs to improve, with significant bodyweight reduction occurring within two weeks of commencing THRT. Routine clinicopathological monitoring was of value in confirming a general metabolic response to THRT, but was of limited value in accurately monitoring cases or tailoring therapy in individual cases.

Impact on dose and image quality of a software-based scatter correction in mammography.

PubMed

Monserrat, Teresa; Prieto, Elena; Barbés, Benigno; Pina, Luis; Elizalde, Arlette; Fernández, Belén

2018-06-01

Background In 2014, Siemens developed a new software-based scatter correction (Progressive Reconstruction Intelligently Minimizing Exposure [PRIME]), enabling grid-less digital mammography. Purpose To compare doses and image quality between PRIME (grid-less) and standard (with anti-scatter grid) modes. Material and Methods Contrast-to-noise ratio (CNR) was measured for various polymethylmethacrylate (PMMA) thicknesses and dose values provided by the mammograph were recorded. CDMAM phantom images were acquired for various PMMA thicknesses and inverse Image Quality Figure (IQF inv ) was calculated. Values of incident entrance surface air kerma (ESAK) and average glandular dose (AGD) were obtained from the DICOM header for a total of 1088 pairs of clinical cases. Two experienced radiologists compared subjectively the image quality of a total of 149 pairs of clinical cases. Results CNR values were higher and doses were lower in PRIME mode for all thicknesses. IQF inv values in PRIME mode were lower for all thicknesses except for 40 mm of PMMA equivalent, in which IQF inv was slightly greater in PRIME mode. A mean reduction of 10% in ESAK and 12% in AGD in PRIME mode with respect to standard mode was obtained. The clinical image quality in PRIME and standard acquisitions resulted to be similar in most of the cases (84% for the first radiologist and 67% for the second one). Conclusion The use of PRIME software reduces, in average, the dose of radiation to the breast without affecting image quality. This reduction is greater for thinner and denser breasts.

SU-E-T-272: Direct Verification of a Treatment Planning System Megavoltage Linac Beam Photon Spectra Models, and Analysis of the Effects On Patient Plans

DOE Office of Scientific and Technical Information (OSTI.GOV)

Leheta, D; Shvydka, D; Parsai, E

2015-06-15

Purpose: For the photon dose calculation Philips Pinnacle Treatment Planning System (TPS) uses collapsed cone convolution algorithm, which relies on energy spectrum of the beam in computing the scatter component. The spectrum is modeled based on Linac’s standard commissioning data and typically is not independently verified. We explored a methodology of using transmission measurements in combination with regularization data processing to unfold Linac spectra. The measured spectra were compared to those modeled by the TPS, and the effect on patient plans was evaluated. Methods: Transmission measurements were conducted in narrow-beam geometry using a standard Farmer ionization chamber. Two attenuating materialsmore » and two build -up caps, having different atomic numbers, served to enhance discrimination between absorption of low and high-energy portions of the spectra, thus improving the accuracy of the results. The data was analyzed using a regularization technique implemented through spreadsheet-based calculations. Results: The unfolded spectra were found to deviate from the TPS beam models. The effect of such deviations on treatment planning was evaluated for patient plans through dose distribution calculations with either TPS modeled or measured energy spectra. The differences were reviewed through comparison of isodose distributions, and quantified based on maximum dose values for critical structures. While in most cases no drastic differences in the calculated doses were observed, plans with deviations of 4 to 8% in the maximum dose values for critical structures were discovered. The anatomical sites with large scatter contributions are the most vulnerable to inaccuracies in the modeled spectrum. Conclusion: An independent check of the TPS model spectrum is highly desirable and should be included as part of commissioning of a new Linac. The effect is particularly important for dose calculations in high heterogeneity regions. The developed approach makes acquisition of megavoltage Linac beam spectra achievable in a typical radiation oncology clinic.« less

Physical analysis of breast cancer using dual-source computed tomography

NASA Astrophysics Data System (ADS)

Kim, H. J.; Lee, H. K.; Cho, J. H.

2014-12-01

This study was aimed to analyze various physical characteristics of breast cancer using dual-source computed tomography (CT). A phantom study and a clinical trial were performed in order and a 64-multidetector CT device was used for the examinations. In the phantom study, single-source (SS) CT was set up with a conventional scanning condition that is usually applied for breast CT examination and implementation was done at tube voltage of 120 kVp. Dual-source CT acquired images by irradiating X-ray sources with fast switching between two kilovoltage settings (80 and 140 kVp). After scanning, Hounsfield Unit (HU) values and radiation doses in a region of interest were measured and analyzed. In the clinical trial, the HU values were measured and analyzed after single-source computed tomography (SSCT) and dual-source CT in patients diagnosed with breast cancer. Also, the tumor size measured by dual-source CT was compared with the actual tumor size. The phantom study determined that the tumor region was especially measured by dual-source CT, while nylon fiber and specks region were especially measured by SSCT. The radiation dose was high with dual-source CT. The clinical trial showed a higher HU value of cancerous regions when scanned by dual-source CT compared with SSCT.

Estimation of low-level neutron dose-equivalent rate by using extrapolation method for a curie level Am-Be neutron source.

PubMed

Li, Gang; Xu, Jiayun; Zhang, Jie

2015-01-01

Neutron radiation protection is an important research area because of the strong radiation biological effect of neutron field. The radiation dose of neutron is closely related to the neutron energy, and the connected relationship is a complex function of energy. For the low-level neutron radiation field (e.g. the Am-Be source), the commonly used commercial neutron dosimeter cannot always reflect the low-level dose rate, which is restricted by its own sensitivity limit and measuring range. In this paper, the intensity distribution of neutron field caused by a curie level Am-Be neutron source was investigated by measuring the count rates obtained through a 3 He proportional counter at different locations around the source. The results indicate that the count rates outside of the source room are negligible compared with the count rates measured in the source room. In the source room, 3 He proportional counter and neutron dosimeter were used to measure the count rates and dose rates respectively at different distances to the source. The results indicate that both the count rates and dose rates decrease exponentially with the increasing distance, and the dose rates measured by a commercial dosimeter are in good agreement with the results calculated by the Geant4 simulation within the inherent errors recommended by ICRP and IEC. Further studies presented in this paper indicate that the low-level neutron dose equivalent rates in the source room increase exponentially with the increasing low-energy neutron count rates when the source is lifted from the shield with different radiation intensities. Based on this relationship as well as the count rates measured at larger distance to the source, the dose rates can be calculated approximately by the extrapolation method. This principle can be used to estimate the low level neutron dose values in the source room which cannot be measured directly by a commercial dosimeter. Copyright © 2014 Elsevier Ltd. All rights reserved.

SU-G-201-10: Experimental Determination of Modified TG-43 Dosimetry Parameters for the Xoft Axxent® Electronic Brachytherapy Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Simiele, S; Palmer, B; DeWerd, L

Purpose: The establishment of an air kerma rate standard at NIST for the Xoft Axxent{sup ®} electronic brachytherapy source (Axxent{sup ®} source) motivated the establishment of a modified TG-43 dosimetry formalism. This work measures the modified dosimetry parameters for the Axxent{sup ®} source in the absence of a treatment applicator for implementation in Xoft’s treatment planning system. Methods: The dose-rate conversion coefficient (DRCC), radial dose function (RDF) values, and polar anisotropy (PA) were measured using TLD-100 microcubes with NIST-calibrated sources. The DRCC and RDF measurements were performed in liquid water using an annulus of Virtual Water™ designed to align themore » TLDs at the height of the anode at fixed radii from the source. The PA was measured at several distances from the source in a PMMA phantom. MCNP-determined absorbed dose energy dependence correction factors were used to convert from dose to TLD to dose to liquid water for the DRCC, RDF, and PA measurements. The intrinsic energy dependence correction factor from the work of Pike was used. The AKR was determined using a NIST-calibrated HDR1000 Plus well-type ionization chamber. Results: The DRCC was determined to be 8.6 (cGy/hr)/(µGy/min). The radial dose values were determined to be 1.00 (1cm), 0.60 (2cm), 0.42 (3cm), and 0.32 (4cm), with agreement ranging from (5.7% to 10.9%) from the work of Hiatt et al. 2015 and agreement from (2.8% to 6.8%) with internal MCNP simulations. Conclusion: This work presents a complete dataset of modified TG-43 dosimetry parameters for the Axxent{sup ®} source in the absence of an applicator. Prior to this study a DRCC had not been measured for the Axxent{sup ®} source. This data will be used for calculating dose distributions for patients receiving treatment with the Axxent{sup ®} source in Xoft’s breast balloon and vaginal applicators, and for intraoperative radiotherapy. Sources and partial funding for this work were provided by Xoft Inc. (a subsidiary of iCAD). This work was also supported by the Radiological Sciences T32 Training Grant through the University of Wisconsin-Madison Medical Physics department (5T32CA009206-37).« less

Compensating measured intra-wafer ring oscillator stage delay with intra-wafer exposure dose corrections

NASA Astrophysics Data System (ADS)

Verhaegen, Staf; Nackaerts, Axel; Dusa, Mircea; Carpaij, Rene; Vandenberghe, Geert; Finders, Jo

2006-03-01

The purpose of this paper is to use measurements on real working devices to derive more information than typically measured by the classic line-width measurement techniques. The first part of the paper will discuss the principle of the measurements with a ring oscillator, a circuit used to measure the speed of elementary logic gates. These measurements contribute to the understanding of the exact timing dependencies in circuits, which is of utmost importance for the design and simulation of these circuits. When connecting an odd number of digital inverting stages in a ring, the circuit has no stable digital state but acts as an analog oscillator with the oscillation frequency dependent on the analog propagation delay of the signals through the stages. By varying some conditions during a litho step, the delay change caused by the process condition change can be measured very accurately. The response of the ring oscillator delay to exposure dose is measured and presented in this paper together with a comparison of measured line-width values of the poly gate lines. The second part of the paper will focus on improving the intra-wafer variation of the stage delay. A number of ring oscillators are put in a design at different slit and scan locations. 200mm wafers are processed with 48 full dies present. From the intra-wafer delay fingerprint and the dose sensitivity of the delay an intra-wafer dose correction, also called a dose recipe, is calculated. This dose recipe is used on the scanner to compensate for effects that are the root cause for the delay profile; including reticle and processing such as track, etch and annealing.

[Investigation of radiation dose for lower tube voltage CT using automatic exposure control].

PubMed

Takata, Mitsuo; Matsubara, Kousuke; Koshida, Kichirou; Tarohda, Tohru

2015-04-01

The purpose of our study was to investigate radiation dose for lower tube voltage CT using automatic exposure control (AEC). An acrylic body phantom was used, and volume CT dose indices (CTDIvol) for tube voltages of 80, 100, 120, and 135 kV were investigated with combination of AEC. Average absorbed dose in the abdomen for 100 and 120 kV were also measured using thermoluminescence dosimeters. In addition, we examined noise characteristics under the same absorbed doses. As a result, the exposure dose was not decreased even when the tube voltage was lowered, and the organ absorbed dose value became approximately 30% high. And the noise was increased under the radiographic condition to be an equal absorbed dose. Therefore, radiation dose increases when AEC is used for lower tube voltage CT under the same standard deviation (SD) setting with 120 kV, and the optimization of SD setting is crucial.

Simulation of beta radiator handling procedures in nuclear medicine by means of a movable hand phantom.

PubMed

Blunck, Ch; Becker, F; Urban, M

2011-03-01

In nuclear medicine therapies, people working with beta radiators such as (90)Y may be exposed to non-negligible partial body doses. For radiation protection, it is important to know the characteristics of the radiation field and possible dose exposures at relevant positions in the working area. Besides extensive measurements, simulations can provide these data. For this purpose, a movable hand phantom for Monte Carlo simulations was developed. Specific beta radiator handling scenarios can be modelled interactively with forward kinematics or automatically with an inverse kinematics procedure. As a first investigation, the dose distribution on a medical doctor's hand injecting a (90)Y solution was measured and simulated with the phantom. Modelling was done with the interactive method based on five consecutive frames from a video recorded during the injection. Owing to the use of only one camera, not each detail of the radiation scenario is visible in the video. In spite of systematic uncertainties, the measured and simulated dose values are in good agreement.

Estimating systemic exposure to levonorgestrel from an oral contraceptive.

PubMed

Basaraba, Cale N; Westhoff, Carolyn L; Pike, Malcolm C; Nandakumar, Renu; Cremers, Serge

2017-04-01

The gold standard for measuring oral contraceptive (OC) pharmacokinetics is the 24-h steady-state area under the curve (AUC). We conducted this study to assess whether limited sampling at steady state or measurements following use of one or two OCs could provide an adequate proxy in epidemiological studies for the progestin 24-h steady-state AUC of a particular OC. We conducted a 13-sample, 24-h pharmacokinetic study on both day 1 and day 21 of the first cycle of a monophasic OC containing 30-mcg ethinyl estradiol and 150-mcg levonorgestrel (LNG) in 17 normal-weight healthy White women and a single-dose 9-sample study of the same OC after a 1-month washout. We compared the 13-sample steady-state results with several steady-state and single-dose results calculated using parsimonious sampling schemes. The 13-sample steady-state 24-h LNG AUC was highly correlated with the steady-state 24-h trough value [r=0.95; 95% confidence interval (0.85, 0.98)] and with the steady-state 6-, 8-, 12- and 16-h values (0.92≤r≤0.95). The trough values after one or two doses were moderately correlated with the steady-state 24-h AUC value [r=0.70; 95% CI (0.27, 0.90) and 0.77; 95% CI (0.40, 0.92), respectively]. Single time-point concentrations at steady state and after administration of one or two OCs gave highly to moderately correlated estimates of steady-state LNG AUC. Using such measures could facilitate prospective pharmaco-epidemiologic studies of the OC and its side effects. A single time-point LNG concentration at steady state is an excellent proxy for complete and resource-intensive steady-state AUC measurement. The trough level after two single doses is a fair proxy for steady-state AUC. These results provide practical tools to facilitate large studies to investigate the relationship between systemic LNG exposure and side effects in a real-life setting. Copyright © 2017 Elsevier Inc. All rights reserved.

Phantom-derived estimation of effective dose equivalent from X rays with and without a lead apron.

PubMed

Mateya, C F; Claycamp, H G

1997-06-01

Organ dose equivalents were measured in a humanoid phantom in order to estimate effective dose equivalent (H(E)) and effective dose (E) from low-energy x rays and in the presence or absence of a protective lead apron. Plane-parallel irradiation conditions were approximated using direct x-ray beams of 76 and 104 kVp and resulting dosimetry data was adjusted to model exposures conditions in fluoroscopy settings. Values of H(E) and E estimated under-shielded conditions were compared to the results of several recent studies that used combinations of measured and calculated dosimetry to model exposures to radiologists. While the estimates of H(E) and E without the lead apron were within 0.2 to 20% of expected values, estimates based on personal monitors worn at the (phantom) waist (underneath the apron) underestimated either H(E) or E while monitors placed at the neck (above the apron) significantly overestimated both quantities. Also, the experimentally determined H(E) and E were 1.4 to 3.3 times greater than might be estimated using recently reported "two-monitor" algorithms for the estimation of effective dose quantities. The results suggest that accurate estimation of either H(E) or E from personal monitors under conditions of partial body exposures remains problematic and is likely to require the use of multiple monitors.

SU-E-I-09: Application of LiF:Mg,Cu (TLD-100H) Dosimeters for in Diagnostic Radiology

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sina, S; Zeinali, B; Karimipourfard, M

Purpose: Accurate dosimetery is very essential in diagnostic radiology. The goal of this study is to verify the application of LiF:Mg,Cu,P (TLD100H) in obtaining the Entrance skin dose (ESD) of patients undergoing diagnostic radiology. The results of dosimetry performed by TLD-100H, were compared with those obtained by TLD100, which is a common dosimeter in diagnostic radiology. Methods: In this study the ESD values were measured using two types of Thermoluminescence dosimeters (TLD-100, and TLD-100H) for 16 patients undergoing diagnostic radiology (lumbar spine imaging). The ESD values were also obtained by putting the two types of TLDs at the surface ofmore » Rando phantom for different imaging techniques and different views (AP, and lateral). The TLD chips were annealed with a standard procedure, and the ECC values for each TLD was obtained by exposing the chips to equal amount of radiation. Each time three TLD chips were covered by thin dark plastic covers, and were put at the surface of the phantom or the patient. The average reading of the three chips was used for obtaining the dose. Results: The results show a close agreement between the dose measuered by the two dosimeters.According to the results of this study, the TLD-100H dosimeters have higher sensitivities (i.e.signal(nc)/dose) than TLD-100.The ESD values varied between 2.71 mGy and 26.29 mGy with the average of 11.89 mGy for TLD-100, and between 2.55 mGy and 27.41 mGy with the average of 12.32 mGy for measurements. Conclusion: The TLD-100H dosimeters are suggested as effective dosimeters for dosimetry in low dose fields because of their higher sensitivities.« less

An assessment of the accuracy of a novel weight estimation device for children.

PubMed

Jung, Jae Yun; Kwak, Young Ho; Kim, Do Kyun; Suh, Dongbum; Chang, Ikwan; Yoon, Chiyul; Lee, Jung Chan; Kim, Hee Chan; Choi, Jae Yeon; Ahn, HeeJeong

2017-03-01

We sought to validate the accuracy and assess the efficacy of a newly developed electronic weight estimation device (ie, the rolling tape) for paediatric weight estimation. We enrolled a convenience sample of children aged <17 years presenting to our emergency department who volunteered to participate in the study. The children's heights and weights were measured, and three researchers estimated these values using the rolling tape and Broselow tape at 5 min intervals. The weight estimates of researcher 1, researcher 2 and the Broselow tape were compared with measured values, and mean percentage error (MPE), root mean square error (RMSE) and percentage of estimates within 10% of the actual measured values were calculated. For 30 randomly selected subjects, we compared the time interval from the start of the measurement to the time that orders for epinephrine, defibrillation dose and instrument size could be given in a simulated arrest scenario. We enrolled 906 children (median age 4.0 years). For researcher 1, researcher 2 and the Broselow tape, MPE values were 0.11% (RMSE 2.61 kg), 1.41% (RMSE, 2.61 kg) and 1.72% (RMSE 5.41 kg), respectively, and the percentages of children with predictions within 10% of their actual weight were 75.1%, 75.7% and 60.6%, respectively. In the 30 simulated cases, the mean time for measurement to ordering was significantly shorter (25.8 s vs 35.5 s, p<0.001) for the rolling tape compared with the Broselow tape method. The rolling tape is a good weight estimation tool for children compared with other methods. The rolling tape method significantly decreased the time from weight estimation to orders for essential drug dose, instrument size and defibrillation dose for resuscitation. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Impact of Multileaf Collimator Configuration Parameters on the Dosimetric Accuracy of 6-MV Intensity-Modulated Radiation Therapy Treatment Plans.

PubMed

Petersen, Nick; Perrin, David; Newhauser, Wayne; Zhang, Rui

2017-01-01

The purpose of this study was to evaluate the impact of selected configuration parameters that govern multileaf collimator (MLC) transmission and rounded leaf offset in a commercial treatment planning system (TPS) (Pinnacle 3 , Philips Medical Systems, Andover, MA, USA) on the accuracy of intensity-modulated radiation therapy (IMRT) dose calculation. The MLC leaf transmission factor was modified based on measurements made with ionization chambers. The table of parameters containing rounded-leaf-end offset values was modified by measuring the radiation field edge as a function of leaf bank position with an ionization chamber in a scanning water-tank dosimetry system and comparing the locations to those predicted by the TPS. The modified parameter values were validated by performing IMRT quality assurance (QA) measurements on 19 gantry-static IMRT plans. Planar dose measurements were performed with radiographic film and a diode array (MapCHECK2) and compared to TPS calculated dose distributions using default and modified configuration parameters. Based on measurements, the leaf transmission factor was changed from a default value of 0.001 to 0.005. Surprisingly, this modification resulted in a small but statistically significant worsening of IMRT QA gamma-index passing rate, which revealed that the overall dosimetric accuracy of the TPS depends on multiple configuration parameters in a manner that is coupled and not intuitive because of the commissioning protocol used in our clinic. The rounded leaf offset table had little room for improvement, with the average difference between the default and modified offset values being -0.2 ± 0.7 mm. While our results depend on the current clinical protocols, treatment unit and TPS used, the methodology used in this study is generally applicable. Different clinics could potentially obtain different results and improve their dosimetric accuracy using our approach.

Experimental determination of the effective point of measurement of cylindrical ionization chambers for high-energy photon and electron beams.

PubMed

Huang, Yanxiao; Willomitzer, Christian; Zakaria, Golam Abu; Hartmann, Guenther H

2010-01-01

Measurements of depth-dose curves in water phantom using a cylindrical ionization chamber require that its effective point of measurement is located at the measuring depth. Recommendations for the position of the effective point of measurement with respect to the central axis valid for high-energy electron and photon beams are given in dosimetry protocols. According to these protocols, the use of a constant shift P(eff) is currently recommended. However, this is still based on a very limited set of experimental results. It is therefore expected that an improved knowledge of the exact position of the effective point of measurement will further improve the accuracy of dosimetry. Recent publications have revealed that the position of the effective point of measurement is indeed varying with beam energy, field size and also with chamber geometry. The aim of this study is to investigate whether the shift of P(eff) can be taken to be constant and independent from the beam energy. An experimental determination of the effective point of measurement is presented based on a comparison between cylindrical chambers and a plane-parallel chamber using conventional dosimetry equipment. For electron beams, the determination is based on the comparison of halfvalue depth R(50) between the cylindrical chamber of interest and a well guarded plane-parallel Roos chamber. For photon beams, the depth of dose maximum, d(max), the depth of 80% dose, d(80), and the dose parameter PDD(10) were used. It was again found that the effective point of measurement for both, electron and photon beams Dosimetry, depends on the beam energy. The deviation from a constant value remains very small for photons, whereas significant deviations were found for electrons. It is therefore concluded that use of a single upstream shift value from the centre of the cylindrical chamber as recommended in current dosimetry protocols is adequate for photons, however inadequate for accurate electron beam dosimetry.

Martian Radiation Environment: Model Calculations and Recent Measurements with "MARIE"

NASA Technical Reports Server (NTRS)

Saganti, P. B.; Cucinotta, F. A.; zeitlin, C. J.; Cleghorn, T. F.

2004-01-01

The Galactic Cosmic Ray spectra in Mars orbit were generated with the recently expanded HZETRN (High Z and Energy Transport) and QMSFRG (Quantum Multiple-Scattering theory of nuclear Fragmentation) model calculations. These model calculations are compared with the first eighteen months of measured data from the MARIE (Martian Radiation Environment Experiment) instrument onboard the 2001 Mars Odyssey spacecraft that is currently in Martian orbit. The dose rates observed by the MARIE instrument are within 10% of the model calculated predictions. Model calculations are compared with the MARIE measurements of dose, dose-equivalent values, along with the available particle flux distribution. Model calculated particle flux includes GCR elemental composition of atomic number, Z = 1-28 and mass number, A = 1-58. Particle flux calculations specific for the current MARIE mapping period are reviewed and presented.

Organ doses for reference adult male and female undergoing computed tomography estimated by Monte Carlo simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Choonsik; Kim, Kwang Pyo; Long, Daniel

2011-03-15

Purpose: To develop a computed tomography (CT) organ dose estimation method designed to readily provide organ doses in a reference adult male and female for different scan ranges to investigate the degree to which existing commercial programs can reasonably match organ doses defined in these more anatomically realistic adult hybrid phantomsMethods: The x-ray fan beam in the SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code MCNPX2.6. The simulated CT scanner model was validated through comparison with experimentally measured lateral free-in-air dose profiles and computed tomography dose index (CTDI) values. The reference adult malemore » and female hybrid phantoms were coupled with the established CT scanner model following arm removal to simulate clinical head and other body region scans. A set of organ dose matrices were calculated for a series of consecutive axial scans ranging from the top of the head to the bottom of the phantoms with a beam thickness of 10 mm and the tube potentials of 80, 100, and 120 kVp. The organ doses for head, chest, and abdomen/pelvis examinations were calculated based on the organ dose matrices and compared to those obtained from two commercial programs, CT-EXPO and CTDOSIMETRY. Organ dose calculations were repeated for an adult stylized phantom by using the same simulation method used for the adult hybrid phantom. Results: Comparisons of both lateral free-in-air dose profiles and CTDI values through experimental measurement with the Monte Carlo simulations showed good agreement to within 9%. Organ doses for head, chest, and abdomen/pelvis scans reported in the commercial programs exceeded those from the Monte Carlo calculations in both the hybrid and stylized phantoms in this study, sometimes by orders of magnitude. Conclusions: The organ dose estimation method and dose matrices established in this study readily provides organ doses for a reference adult male and female for different CT scan ranges and technical parameters. Organ doses from existing commercial programs do not reasonably match organ doses calculated for the hybrid phantoms due to differences in phantom anatomy, as well as differences in organ dose scaling parameters. The organ dose matrices developed in this study will be extended to cover different technical parameters, CT scanner models, and various age groups.« less

Investigation of the chamber correction factor (k(ch)) for the UK secondary standard ionization chamber (NE2561/NE2611) using medium-energy x-rays.

PubMed

Rosser, K E

1998-11-01

This paper evaluates the characteristics of ionization chambers for the measurement of absorbed dose to water for medium-energy x-rays. The values of the chamber correction factor, k(ch), used in the IPEMB code of practice for the UK secondary standard (NE2561/NE2611) ionization chamber are derived and their constituent factors examined. The comparison of the chambers' responses in air revealed that of the chambers tested only the NE2561, NE2571 and NE2505 exhibit a flat (within 5%) energy response in air. Under no circumstances should the NACP, Sanders electron chamber, or any chamber that has a wall made of high atomic number material, be used for medium-energy x-ray dosimetry. The measurements in water reveal that a chamber that has a substantial housing, such as the PTW Grenz chamber, should not be used to measure absorbed dose to water in this energy range. The value of k(ch) for an NE2561 chamber was determined by measuring the absorbed dose to water and comparing it with that for an NE2571 chamber, for which k(ch) data have been published. The chamber correction factor varies from 1.023 +/- 0.03 to 1.018 +/- 0.001 for x-ray beams with HVL between 0.15 and 4 mm Cu. The values agree with that for an NE2571 chamber within the experimental uncertainty. The corrections due to the stem, waterproof sleeve and replacement of the phantom material by the chamber for an NE2561 chamber are described.

Validation of an improved helical diode array and dose reconstruction software using TG-244 datasets and stringent dose comparison criteria.

PubMed

Ahmed, Saeed; Nelms, Benjamin; Kozelka, Jakub; Zhang, Geoffrey; Moros, Eduardo; Feygelman, Vladimir

2016-11-08

The original helical ArcCHECK (AC) diode array and associated software for 3D measurement-guided dose reconstruction were characterized and validated; however, recent design changes to the AC required that the subject be revisited. The most important AC change starting in 2014 was a significant reduction in the overresponse of diodes to scattered radiation outside of the direct beam, accom-plished by reducing the amount of high-Z materials adjacent to the diodes. This change improved the diode measurement accuracy, but in the process invalidated the dose reconstruction models that were assembled based on measured data acquired with the older version of the AC. A correction mechanism was intro-duced in the reconstruction software (3DVH) to accommodate this and potential future design changes without requiring updating model parameters. For each permutation of AC serial number and beam model, the user can define in 3DVH a single correction factor which will be used to compensate for the difference in the out-of-field response between the new and original AC designs. The exact value can be determined by minimizing the dose-difference with an ionization chamber or another independent dosimeter. A single value of 1.17, corresponding to the maximum measured out-of-field response difference between the new and old AC, provided satisfactory results for all studied energies (6X, 15X, and flatten-ing filter-free 10XFFF). A library of standard cases recommended by the AAPM TG-244 Report was used for reconstructed dose verification. The overall difference between reconstructed dose and an ion chamber in a water-equivalent phantom in the targets was 0.0% ± 1.4% (1 SD). The reconstructed dose on a homogeneous phantom was also compared to a biplanar diode dosimeter (Delta4) using gamma analysis with 2% (local dose-error normalization) / 2 mm / 10% cutoff criteria. The mean agreement rate was 96.7% ± 3.7%. For the plans common with the previous comparison, the mean agreement rate was 98.3% ± 0.8%, essentially unchanged. We conclude that the proposed software modification adequately addresses the change in the dosimeter response. © 2016 The Authors.

Radon measurements and effective dose from radon inhalation estimation in the Neapolitan catacombs.

PubMed

Quarto, M; Pugliese, M; Loffredo, F; Zambella, C; Roca, V

2014-03-01

In this study, the indoor radon activity concentrations have been measured in the Neapolitan catacombs using LR115 detectors. The detectors were exposed for two quarters, one in the warm season and the other in the cold. This has allowed one to evaluate the seasonal variations of concentrations, while the diurnal variations were evaluated performing continuous measurements by a Radim 5 monitor. The authors found that radon concentrations were lower in winter than in summer. Based on their values, taking into consideration the working hours in the catacombs and the equilibrium factor of 0.4, the effective dose to workers was estimated.

The Biological Effectiveness of Different Radiation Qualities for the Induction of Chromosome Damage in Human Lymphocytes

NASA Technical Reports Server (NTRS)

Hada, M.; George, K.; Cucinotta, F. A.

2010-01-01

Chromosome aberrations were measured in human peripheral blood lymphocytes after in vitro exposure to 28Si- ions with energies ranging from 90 to 600 MeV/u, or to 56Fe-ions with energies ranging from 200 to 5,000 MeV/u. The LET of the various Fe beams in this study ranged from 145 to 440 keV/micron and the LET of the Si ions ranged from 48 to 158 keV/ m. Doses delivered were in the 10- to 200-cGy range. Dose-response curves for chromosome exchanges in cells at first division after exposure, measured using fluorescence in situ hybridization (FISH) with whole-chromosome probes, were fitted with linear or linear-quadratic functions. The relative biological effectiveness (RBE) was estimated from the initial slope of the dose-response curve for chromosome damage with respect to -rays. The estimates of RBE(sub max) values for total chromosome exchanges ranged from 4.4+/-0.4 to 31.5+/-2.6 for Fe ions, and 11.8+/-1.0 to 42.2+/-3.3 for Si ions. The highest RBE(sub max) value for Fe ions was obtained with the 600-Mev/u beam, and the highest RBE(sub max) value for Si ions was obtained with the 170 MeV/u beam. For both ions the RBEmax values increased with LET, reaching a maximum at about 180 keV/micron for Fe and about 100 keV/ m for Si, and decreasing with further increase in LET. Additional studies for low doses 28Si-ions down to 0.02 Gy will be discussed.

Assessment of indoor radon, thoron concentrations, and their relationship with seasonal variation and geology of Udhampur district, Jammu & Kashmir, India.

PubMed

Kumar, Ajay; Sharma, Sumit; Mehra, Rohit; Narang, Saurabh; Mishra, Rosaline

2017-07-01

Background The inhalation doses resulting from the exposure to radon, thoron, and their progeny are important quantities in estimating the radiation risk for epidemiological studies as the average global annual effective dose due to radon and its progeny is 1.3 mSv as compared to that of 2.4 mSv due to all other natural sources of ionizing radiation. Objectives The annual inhalation dose has been assessed with an aim of investigating the health risk to the inhabitants of the studied region. Methods Time integrated deposition based 222 Rn/ 220 Rn sensors have been used to measure concentrations in 146 dwellings of Udhampur district, Jammu and Kashmir. An active smart RnDuo monitor has also been used for comparison purposes. Results The range of indoor radon/thoron concentrations is found to vary from 11 to 58 Bqm -3 with an average value of 29 ± 9 Bqm -3 and from 25 to 185 Bqm -3 with an average value of 83 ± 32 Bqm -3 , respectively. About 10.7% dwellings have higher values than world average of 40 Bqm -3 prescribed by UNSCEAR. The relationship of indoor radon and thoron levels with different seasons, ventilation conditions, and different geological formations have been discussed. Conclusions The observed values of concentrations and average annual effective dose due to radon, thoron, and its progeny in the study area have been found to be below the recommended level of ICRP. The observed concentrations of 222 Rn and 220 Rn measured with active and passive techniques are found to be in good agreement.

Continuing education: online monitoring of haemodialysis dose.

PubMed

Vartia, Aarne

2018-01-25

Kt/V urea reflects the efficacy of haemodialysis scaled to patient size (urea distribution volume). The guidelines recommend monthly Kt/V measurements based on blood samples. Modern haemodialysis machines are equipped with accessories monitoring the dose online at every session without extra costs, blood samples and computers. To describe the principles, devices, benefits and shortcomings of online monitoring of haemodialysis dose. A critical literature overview and discussion. UV absorbance methods measure Kt/V, ionic dialysance Kt (product of clearance and treatment time; cleared volume without scaling). Both are easy and useful methods, but comparison is difficult due to problems in scaling of the dialysis dose to the patient's size. The best dose estimation method is the one which predicts the quality of life and survival most accurately. There is some evidence on the predictive value of ionic dialysance Kt, but more documentation is required on the UV method. Online monitoring is a useful tool in everyday quality assurance, but blood samples are still required for more accurate kinetic modelling. After reading this article the reader should be able to: Understand the elements of the Kt/V equation for dialysis dose. Compare and contrast different methods of measurement of dialysis dose. Reflect on the importance of adequate dialysis dose for patient survival and life quality. © 2018 European Dialysis and Transplant Nurses Association/European Renal Care Association.

Outcomes Across the Value Chain for a Comprehensive Employee Health and Wellness Intervention: A Cohort Study by Degrees of Health Engagement.

PubMed

Long, D Adam; Reed, Roger W; Duncan, Ian

2016-07-01

Evaluate a large employer's wellness intervention by studying outcomes across the value chain, and testing Health Engagement's (HE) dose-response relationship to outcomes. Evaluation included 37 measures across eight outcomes domains (OD) using repeated measures, analysis of variance and logistic regression. Participants with higher HE had better pre-post percent changes than control: 1.7% higher for Motivation (OD1), 3.4% for Behavior (OD2), 1.0% for Emotion (OD3), 5.8% for Biometrics (OD4), 6.3% for Compliance (OD5), and 5.2% for Claims (OD6). They also had 0.5% less Productivity loss (OD7), and odds of Turnover (OD8) one-quarter to one-half that of control. A dose-response relationship with degrees of HE was also shown. Three outcomes domains (OD6 to OD8) can be monetized for cost-benefit analysis. Authors recommend, however, staying focused on driving HE and using metrics from all OD to assess value.

Distribution of Absorbed Dose in Cone-Beam Breast Computed Tomography: A Phantom Study With Radiochromic Films

NASA Astrophysics Data System (ADS)

Russo, Paolo; Coppola, Teresa; Mettivier, Giovanni

2010-08-01

Cone-Beam Breast Computed Tomography (CBBCT) of the pendant breast with dedicated scanners is an experimental 3D X-ray imaging technique for breast cancer diagnosis under evaluation in comparison to conventional two-view 2-D mammography of the compressed breast. In CBBCT it is generally assumed that a more uniform distribution of the radiation dose to the breast volume can be obtained, with respect to mammography, at equal Mean Glandular Dose (MGD) levels. In fact, in CBBCT the X-ray beam rotates for 360 deg around the breast, while in each mammography view the breast is irradiated from one side only. Using a CBBCT laboratory scanner developed by our group, we have measured the distribution of the radiation dose in a hemi-ellipsoidal PMMA breast phantom of 14 cm diameter simulating the average uncompressed breast, using radiochromic films type XR-SP inserted at mid-plane in the phantom. The technique factors were 80 kVp (5.6 mm Al Half Value Layer), tube load in the range 23-100 mAs, for an air kerma at isocenter in the range 4.7-20 mGy, for a calculated MGD in the range 3.5-15 mGy for a 14 cm diameter breast of 50% glandularity. Results indicate that the dose decreases from the periphery to the center of the phantom, and that along a transverse profile, the relative dose variation Δ = ((edge-center)/center) is up to (25 ±4)% at a distance of 80 mm from the nipple. As for the relative dose variation along the phantom longitudinal axis, the maximum value at middle of the phantom measured is δ = ((nipple-chest wall)/chest wall) = -(15 ±4)%, indicating that the dose decreases from the chest wall toward the nipple. The values of the parameters Δ and δ depend also on the height of the X-ray tube focal spot with respect to the phantom vertex (nipple). Results are in rough agreement with similar previous determinations using thermoluminescence dosimeters.

Dosimetric accuracy of Kodak EDR2 film for IMRT verifications.

PubMed

Childress, Nathan L; Salehpour, Mohammad; Dong, Lei; Bloch, Charles; White, R Allen; Rosen, Isaac I

2005-02-01

Patient-specific intensity-modulated radiotherapy (IMRT) verifications require an accurate two-dimensional dosimeter that is not labor-intensive. We assessed the precision and reproducibility of film calibrations over time, measured the elemental composition of the film, measured the intermittency effect, and measured the dosimetric accuracy and reproducibility of calibrated Kodak EDR2 film for single-beam verifications in a solid water phantom and for full-plan verifications in a Rexolite phantom. Repeated measurements of the film sensitometric curve in a single experiment yielded overall uncertainties in dose of 2.1% local and 0.8% relative to 300 cGy. 547 film calibrations over an 18-month period, exposed to a range of doses from 0 to a maximum of 240 MU or 360 MU and using 6 MV or 18 MV energies, had optical density (OD) standard deviations that were 7%-15% of their average values. This indicates that daily film calibrations are essential when EDR2 film is used to obtain absolute dose results. An elemental analysis of EDR2 film revealed that it contains 60% as much silver and 20% as much bromine as Kodak XV2 film. EDR2 film also has an unusual 1.69:1 silver:halide molar ratio, compared with the XV2 film's 1.02:1 ratio, which may affect its chemical reactions. To test EDR2's intermittency effect, the OD generated by a single 300 MU exposure was compared to the ODs generated by exposing the film 1 MU, 2 MU, and 4 MU at a time to a total of 300 MU. An ion chamber recorded the relative dose of all intermittency measurements to account for machine output variations. Using small MU bursts to expose the film resulted in delivery times of 4 to 14 minutes and lowered the film's OD by approximately 2% for both 6 and 18 MV beams. This effect may result in EDR2 film underestimating absolute doses for patient verifications that require long delivery times. After using a calibration to convert EDR2 film's OD to dose values, film measurements agreed within 2% relative difference and 2 mm criteria to ion chamber measurements for both sliding window and step-and-shoot fluence map verifications. Calibrated film results agreed with ion chamber measurements to within 5 % /2 mm criteria for transverse-plane full-plan verifications, but were consistently low. When properly calibrated, EDR2 film can be an adequate two-dimensional dosimeter for IMRT verifications, although it may underestimate doses in regions with long exposure times.

Digital mammography--DQE versus optimized image quality in clinical environment: an on site study

NASA Astrophysics Data System (ADS)

Oberhofer, Nadia; Fracchetti, Alessandro; Springeth, Margareth; Moroder, Ehrenfried

2010-04-01

The intrinsic quality of the detection system of 7 different digital mammography units (5 direct radiography DR; 2 computed radiography CR), expressed by DQE, has been compared with their image quality/dose performances in clinical use. DQE measurements followed IEC 62220-1-2 using a tungsten test object for MTF determination. For image quality assessment two different methods have been applied: 1) measurement of contrast to noise ratio (CNR) according to the European guidelines and 2) contrast-detail (CD) evaluation. The latter was carried out with the phantom CDMAM ver. 3.4 and the commercial software CDMAM Analyser ver. 1.1 (both Artinis) for automated image analysis. The overall image quality index IQFinv proposed by the software has been validated. Correspondence between the two methods has been shown figuring out a linear correlation between CNR and IQFinv. All systems were optimized with respect to image quality and average glandular dose (AGD) within the constraints of automatic exposure control (AEC). For each equipment, a good image quality level was defined by means of CD analysis, and the corresponding CNR value considered as target value. The goal was to achieve for different PMMA-phantom thicknesses constant image quality, that means the CNR target value, at minimum dose. All DR systems exhibited higher DQE and significantly better image quality compared to CR systems. Generally switching, where available, to a target/filter combination with an x-ray spectrum of higher mean energy permitted dose savings at equal image quality. However, several systems did not allow to modify the AEC in order to apply optimal radiographic technique in clinical use. The best ratio image quality/dose was achieved by a unit with a-Se detector and W anode only recently available on the market.

Irradiation of members of the general public from radioactive caesium following the Chernobyl reactor accident: Field studies in a highly contaminated area in the Bryansk region, Russia

NASA Astrophysics Data System (ADS)

Thornberg, Charlotte

From 1990 to 1998, estimations of the effective dose due to irradiation from 137Cs and 134Cs were carried out for inhabitants in rural villages in the Bryansk region, Russia. The villages, situated about 180 km from the Chernobyl power plant received deposition of 137Cs in the range 0.9-2.7 MBq m-2 due to the accident in 1986. The body burden of 137,134Cs was estimated from measurements of the urinary concentration of caesium radionuclides, together with in vivo measurements using a portable detector. The external effective dose was estimated from measurements with thermoluminescent (TL)-dosemeters worn by the participants during one month each year. In a case study, the changes in biokinetics of 137Cs during pregnancy was investigated in a woman with an unintended intake of 137Cs via mushrooms grown in the area. During pregnancy the biological half-time of caesium was 54% of that before pregnancy. The ratio of the 137Cs concentration in breast milk (Bq L-1) to that in the mother's body (Bq kg-1) was 15% one month after the child was born. The body burden of 137Cs in the Russian individuals calculated from urine samples showed a good agreement with the body burden estimated from in vivo measurements in the same individuals. Normalisation of the caesium concentration in the urine samples by the use of potassium or creatinine excretion introduced systematic differences and a larger spread in the calculated values of the 137Cs body burden as compared with calculations without normalisation. The yearly effective dose to inhabitants in the Russian villages varied between 1.2 and 2.5 mSv as a mean for all villages between 1991 and 1998 and the internal effective dose was 30-50% of the total effective dose. The external effective dose decreased on average 15% per year, while the internal effective dose varied, depending to a great extent on the availability of mushrooms. The cumulated effective dose for a 70-year period after the accident was calculated to be 100 mSv assuming that the effective dose will decrease by only the physical decay of 137Cs (2% per year) after 1998. Individuals may receive considerably higher effective doses, up to 0.5 Sv during a life-time considering the large spread in dose values among individuals.

Singular-value decomposition of a tomosynthesis system

PubMed Central

Burvall, Anna; Barrett, Harrison H.; Myers, Kyle J.; Dainty, Christopher

2010-01-01

Tomosynthesis is an emerging technique with potential to replace mammography, since it gives 3D information at a relatively small increase in dose and cost. We present an analytical singular-value decomposition of a tomosynthesis system, which provides the measurement component of any given object. The method is demonstrated on an example object. The measurement component can be used as a reconstruction of the object, and can also be utilized in future observer studies of tomosynthesis image quality. PMID:20940966

SU-E-T-482: In Vivo Dosimetry of An Anthropomorphic Phantom by Using the RADPOS System for Proton Beam Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohno, R; Motegi, K; Hotta, K

Purpose: Delivered doses in an anthropomorphic phantom were evaluated by using the RADPOS system for proton beam therapy. Methods: The RADPOS in vivo dosimetry system combines an electromagnetic positioning sensor with MOSFET dosimetry, allowing simultaneous online measurements of dose and spatial position. Through the RADPOS system, dose evaluation points can be determined. In vivo proton dosimetry was evaluated by using the RADPOS system and anthropomorphic head and neck phantom. MOSFET doses measured at 3D positions obtained with the RADPOS were compared to the treatment plan values that were calculated by a simplified Monte Carlo (SMC) method. Although the MOSFET responsemore » depends strongly on the linear energy transfer (LET) of proton beam, the MOSFET responses to proton beams were corrected with the SMC. Here, the SMC calculated only dose deposition determined by the experimental depth–dose distribution and lateral displacement of protons due to both multiple scattering effect in materials and incident angle. As a Result, the SMC could quickly calculate accurate doses in even heterogeneities. Results: In vivo dosimetry by using the RADPOS, as well as the MOSFET doses agreed in comparison with calculations by the SMC in the range of −3.0% to 8.3%. Most measurement errors occurred because of the uncertainties of dose calculations due to the position error of 1 mm. Conclusion: We evaluated the delivered doses in the anthropomorphic phantom by using the RADPOS system for proton beam therapy. The MOSFET doses agreed in comparison with calculations by the SMC within the measurement error. Therefore, we could successfully control the uncertainties of the measurement positions by using the RADPOS system within 1 mm in in vivo proton dosimetry. We aim for the clinical application of in vivo proton dosimetry with this RADPOS system.« less

Optimal mapping of terrestrial gamma dose rates using geological parent material and aerogeophysical survey data.

PubMed

Rawlins, B G; Scheib, C; Tyler, A N; Beamish, D

2012-12-01

Regulatory authorities need ways to estimate natural terrestrial gamma radiation dose rates (nGy h⁻¹) across the landscape accurately, to assess its potential deleterious health effects. The primary method for estimating outdoor dose rate is to use an in situ detector supported 1 m above the ground, but such measurements are costly and cannot capture the landscape-scale variation in dose rates which are associated with changes in soil and parent material mineralogy. We investigate the potential for improving estimates of terrestrial gamma dose rates across Northern Ireland (13,542 km²) using measurements from 168 sites and two sources of ancillary data: (i) a map based on a simplified classification of soil parent material, and (ii) dose estimates from a national-scale, airborne radiometric survey. We used the linear mixed modelling framework in which the two ancillary variables were included in separate models as fixed effects, plus a correlation structure which captures the spatially correlated variance component. We used a cross-validation procedure to determine the magnitude of the prediction errors for the different models. We removed a random subset of 10 terrestrial measurements and formed the model from the remainder (n = 158), and then used the model to predict values at the other 10 sites. We repeated this procedure 50 times. The measurements of terrestrial dose vary between 1 and 103 (nGy h⁻¹). The median absolute model prediction errors (nGy h⁻¹) for the three models declined in the following order: no ancillary data (10.8) > simple geological classification (8.3) > airborne radiometric dose (5.4) as a single fixed effect. Estimates of airborne radiometric gamma dose rate can significantly improve the spatial prediction of terrestrial dose rate.

Accurate dosimetry with GafChromic EBT film of a 6 MV photon beam in water: what level is achievable?

PubMed

van Battum, L J; Hoffmans, D; Piersma, H; Heukelom, S

2008-02-01

This paper focuses on the accuracy, in absolute dose measurements, with GafChromicTM EBT film achievable in water for a 6 MV photon beam up to a dose of 2.3 Gy. Motivation is to get an absolute dose detection system to measure up dose distributions in a (water) phantom, to check dose calculations. An Epson 1680 color (red green blue) transmission flatbed scanner has been used as film scanning system, where the response in the red color channel has been extracted and used for the analyses. The influence of the flatbed film scanner on the film based dose detection process was investigated. The scan procedure has been optimized; i.e. for instance a lateral correction curve was derived to correct the scan value, up to 10%, as a function of optical density and lateral position. Sensitometric curves of different film batches were evaluated in portrait and landscape scan mode. Between various batches important variations in sensitometric curve were observed. Energy dependence of the film is negligible, while a slight variation in dose response is observed for very large angles between film surface and incident photon beam. Improved accuracy in absolute dose detection can be obtained by repetition of a film measurement to tackle at least the inherent presence of film inhomogeneous construction. We state that the overall uncertainty is random in absolute EBT film dose detection and of the order of 1.3% (1 SD) under the condition that the film is scanned in a limited centered area on the scanner and at least two films have been applied. At last we advise to check a new film batch on its characteristics compared to available information, before using that batch for absolute dose measurements.

Digital holographic interferometry: a novel optical calorimetry technique for radiation dosimetry.

PubMed

Cavan, Alicia; Meyer, Juergen

2014-02-01

To develop and demonstrate the proof-of-principle of a novel optical calorimetry method to determine radiation absorbed dose in a transparent medium. The calorimetric property of water is measured during irradiation by means of an interferometer, which detects temperature-induced changes in the refractive index that can be mathematically related to absorbed dose. The proposed method uses a technique called digital holographic interferometry (DHI), which comprises an optical laser interferometer setup and consecutive physical reconstruction of the recorded wave fronts by means of the Fresnel transform. This paper describes the conceptual framework and provides the mathematical basis for DHI dosimetry. Dose distributions from a high dose rate Brachytherapy source were measured by a prototype optical setup to demonstrate the feasibility of the approach. The developed DHI dosimeter successfully determined absorbed dose distributions in water in the region adjacent to a high dose rate Brachytherapy source. A temperature change of 0.0381 K across a distance of 6.8 mm near the source was measured, corresponding to a dose of 159.3 Gy. The standard deviation in a typical measurement set was ± 3.45 Gy (corresponding to an uncertainty in the temperature value of ± 8.3 × 10(-4) K). The relative dose fall off was in agreement with treatment planning system modeled data. First results with a prototype optical setup and a Brachytherapy source demonstrate the proof-of-principle of the approach. The prototype achieves high spatial resolution of approximately 3 × 10(-4) m. The general approach is fundamentally independent of the radiation type and energy. The sensitivity range determined indicates that the method is predominantly suitable for high dose rate applications. Further work is required to determine absolute dose in all three dimensions.

Design, development of water tank-type lung phantom and dosimetric verification in institutions participating in a phase I study of stereotactic body radiation therapy in patients with T2N0M0 non-small cell lung cancer: Japan Clinical Oncology Group trial (JCOG0702).

PubMed

Nishio, Teiji; Shirato, Hiroki; Ishikawa, Masayori; Miyabe, Yuki; Kito, Satoshi; Narita, Yuichirou; Onimaru, Rikiya; Ishikura, Satoshi; Ito, Yoshinori; Hiraoka, Masahiro

2014-05-01

A domestic multicenter phase I study of stereotactic body radiotherapy (SBRT) for T2N0M0 non-small cell lung cancer in inoperable patients or elderly patients who refused surgery was initiated as the Japan Clinical Oncology Group trial (JCOG0702) in Japan. Prior to the clinical study, the accuracy of dose calculation in radiation treatment-planning systems was surveyed in participating institutions, and differences in the irradiating dose between the institutions were investigated. We developed a water tank-type lung phantom appropriate for verification of the exposure dose in lung SBRT. Using this water tank-type lung phantom, the dose calculated in the radiation treatment-planning system and the measured dose using a free air ionization chamber and dosimetric film were compared in a visiting survey of the seven institutions participating in the clinical study. In all participating institutions, differences between the calculated and the measured dose in the irradiation plan were as follows: the accuracy of the absolute dose in the center of the simulated tumor measured using a free air ionization chamber was within 2%, the mean gamma value was ≤ 0.47 on gamma analysis following the local dose criteria, and the pass rate was >87% for 3%/3 mm from measurement of dose distribution with dosimetric film. These findings confirmed the accuracy of delivery doses in the institutions participating in the clinical study, so that a study with integration of the institutions could be initiated.

Measurement of soil contamination by radionuclides due to the Fukushima Dai-ichi Nuclear Power Plant accident and associated estimated cumulative external dose estimation.

PubMed

Endo, S; Kimura, S; Takatsuji, T; Nanasawa, K; Imanaka, T; Shizuma, K

2012-09-01

Soil sampling was carried out at an early stage of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Samples were taken from areas around FDNPP, at four locations northwest of FDNPP, at four schools and in four cities, including Fukushima City. Radioactive contaminants in soil samples were identified and measured by using a Ge detector and included (129 m)Te, (129)Te, (131)I, (132)Te, (132)I, (134)Cs, (136)Cs, (137)Cs, (140)Ba and (140)La. The highest soil depositions were measured to the northwest of FDNPP. From this soil deposition data, variations in dose rates over time and the cumulative external doses at the locations for 3 months and 1y after deposition were estimated. At locations northwest of FDNPP, the external dose rate at 3 months after deposition was 4.8-98 μSv/h and the cumulative dose for 1 y was 51 to 1.0 × 10(3)mSv; the highest values were at Futaba Yamada. At the four schools, which were used as evacuation shelters, and in the four urban cities, the external dose rate at 3 months after deposition ranged from 0.03 to 3.8μSv/h and the cumulative doses for 1 y ranged from 3 to 40 mSv. The cumulative dose at Fukushima Niihama Park was estimated as the highest in the four cities. The estimated external dose rates and cumulative doses show that careful countermeasures and remediation will be needed as a result of the accident, and detailed measurements of radionuclide deposition densities in soil will be important input data to conduct these activities. Copyright © 2011 Elsevier Ltd. All rights reserved.

In-Plane Shielding for CT: Effect of Off-Centering, Automatic Exposure Control and Shield-to-Surface Distance

PubMed Central

Dang, Pragya; Singh, Sarabjeet; Saini, Sanjay; Shepard, Jo-Anne O.

2009-01-01

Objective To assess effects of off-centering, automatic exposure control, and padding on attenuation values, noise, and radiation dose when using in-plane bismuth-based shields for CT scanning. Materials and Methods A 30 cm anthropomorphic chest phantom was scanned on a 64-multidetector CT, with the center of the phantom aligned to the gantry isocenter. Scanning was repeated after placing a bismuth breast shield on the anterior surface with no gap and with 1, 2, and 6 cm of padding between the shield and the phantom surface. The "shielded" phantom was also scanned with combined modulation and off-centering of the phantom at 2 cm, 4 cm and 6 cm below the gantry isocenter. CT numbers, noise, and surface radiation dose were measured. The data were analyzed using an analysis of variance. Results The in-plane shield was not associated with any significant increment for the surface dose or CT dose index volume, which was achieved by comparing the radiation dose measured by combined modulation technique to the fixed mAs (p > 0.05). Irrespective of the gap or the surface CT numbers, surface noise increased to a larger extent compared to Hounsfield unit (HU) (0-6 cm, 26-55%) and noise (0-6 cm, 30-40%) in the center. With off-centering, in-plane shielding devices are associated with less dose savings, although dose reduction was still higher than in the absence of shielding (0 cm off-center, 90% dose reduction; 2 cm, 61%) (p < 0.0001). Streak artifacts were noted at 0 cm and 1 cm gaps but not at 2 cm and 6 cm gaps of shielding to the surface distances. Conclusion In-plane shields are associated with greater image noise, artifactually increased attenuation values, and streak artifacts. However, shields reduce radiation dose regardless of the extent of off-centering. Automatic exposure control did not increase radiation dose when using a shield. PMID:19270862

Technical Note: Scanning of parallel-plate ionization chamber and diamond detector for measurements of water-dose profiles in the vicinity of a narrow x-ray microbeam.

PubMed

Nariyama, Nobuteru

2017-12-01

Scanning of dosimeters facilitates dose distribution measurements with fine spatial resolutions. This paper presents a method of conversion of the scanning results to water-dose profiles and provides an experimental verification. An Advanced Markus chamber and a diamond detector were scanned at a resolution of 6 μm near the beam edges during irradiation with a 25-μm-wide white narrow x-ray beam from a synchrotron radiation source. For comparison, GafChromic films HD-810 and HD-V2 were also irradiated. The conversion procedure for the water dose values was simulated with Monte Carlo photon-electron transport code as a function of the x-ray incidence position. This method was deduced from nonstandard beam reference-dosimetry protocols used for high-energy x-rays. Among the calculated nonstandard beam correction factors, P wall , which is the ratio of the absorbed dose in the sensitive volume of the chamber with water wall to that with a polymethyl methacrylate wall, was found to be the most influential correction factor in most conditions. The total correction factor ranged from 1.7 to 2.7 for the Advanced Markus chamber and from 1.15 to 1.86 for the diamond detector as a function of the x-ray incidence position. The water dose values obtained with the Advanced Markus chamber and the HD-810 film were in agreement in the vicinity of the beam, within 35% and 18% for the upper and lower sides of the beam respectively. The beam width obtained from the diamond detector was greater, and the doses out of the beam were smaller than the doses of the others. The comparison between the Advanced Markus chamber and HD-810 revealed that the dose obtained with the scanned chamber could be converted to the water dose around the beam by applying nonstandard beam reference-dosimetry protocols. © 2017 American Association of Physicists in Medicine.

A distributed lag approach to fitting non-linear dose-response models in particulate matter air pollution time series investigations.

PubMed

Roberts, Steven; Martin, Michael A

2007-06-01

The majority of studies that have investigated the relationship between particulate matter (PM) air pollution and mortality have assumed a linear dose-response relationship and have used either a single-day's PM or a 2- or 3-day moving average of PM as the measure of PM exposure. Both of these modeling choices have come under scrutiny in the literature, the linear assumption because it does not allow for non-linearities in the dose-response relationship, and the use of the single- or multi-day moving average PM measure because it does not allow for differential PM-mortality effects spread over time. These two problems have been dealt with on a piecemeal basis with non-linear dose-response models used in some studies and distributed lag models (DLMs) used in others. In this paper, we propose a method for investigating the shape of the PM-mortality dose-response relationship that combines a non-linear dose-response model with a DLM. This combined model will be shown to produce satisfactory estimates of the PM-mortality dose-response relationship in situations where non-linear dose response models and DLMs alone do not; that is, the combined model did not systemically underestimate or overestimate the effect of PM on mortality. The combined model is applied to ten cities in the US and a pooled dose-response model formed. When fitted with a change-point value of 60 microg/m(3), the pooled model provides evidence for a positive association between PM and mortality. The combined model produced larger estimates for the effect of PM on mortality than when using a non-linear dose-response model or a DLM in isolation. For the combined model, the estimated percentage increase in mortality for PM concentrations of 25 and 75 microg/m(3) were 3.3% and 5.4%, respectively. In contrast, the corresponding values from a DLM used in isolation were 1.2% and 3.5%, respectively.

[Body build and radiation exposure in static roentgen studies (I): A contribution for determining a national reference dose value. Promoted by the Federal Office for Radiation Protection (St.Sch 4163)].

PubMed

Golder, W; Weiner, G

2001-06-01

To contribute data on radiation exposure in static x-ray procedures and to compare them with anthropometric parameters. 121 chest x-rays and 100 lumbar spine examinations were carried out and the dose-area product (DAP) measured for each of the projections. Additionally, body height, body weight and the sagittal and transversal diameters of the examined regions were recorded. Dose measurements were statistically evaluated and the following data determined: Frequency distribution, median, 25%- and 75%-percentiles as well as correlations with sex, body weight and diameters. Median DAP was 13 (men: 16; women: 11) resp. 50 (62; 37) cGycm2 with pa resp lateral chest x-ray. Values were closely correlated with body weight (r = 0.704/0.659) and diameter of the chest (r = 0.657/0.579). Median DAP was 175 (239; 126) resp 531 (670; 361) cGycm2 with ap resp lateral lumbar spine examinations. Values were closely correlated with body weight (r = 0.678/0.666) and diameter of the abdomen (r = 0.664/0.658). DAP of chest x-rays and lumbar spine examinations is strongly influenced by the constitution of the patients. Men are nearly twice as largely exposed to radiation as women.

On the need for quality assurance in superficial kilovoltage radiotherapy.

PubMed

Austerlitz, C; Mota, H; Gay, H; Campos, D; Allison, R; Sibata, C

2008-01-01

External auditing of beam output and energy qualities of four therapeutic X-ray machines were performed in three radiation oncology centres in northeastern Brazil. The output and half-value layers (HVLs) were determined using a parallel-plate ionisation chamber and high-purity aluminium foils, respectively. The obtained values of absorbed dose to water and energy qualities were compared with those obtained by the respective institutions. The impact on the prescribed dose was analysed by determining the half-value depth (D(1/2)). The beam outputs presented percent differences ranging from -13 to +25%. The ratio between the HVL in use by the institution and the measurements obtained in this study ranged from 0.75 to 2.33. Such deviations in HVL result in percent differences in dose at D(1/2) ranging from -52 to +8%. It was concluded that dosimetric quality audit programmes in radiation therapy should be expanded to include dermatological radiation therapy and such audits should include HVL verification.

Personal radiofrequency electromagnetic field exposure measurements in Swiss adolescents.

PubMed

Roser, Katharina; Schoeni, Anna; Struchen, Benjamin; Zahner, Marco; Eeftens, Marloes; Fröhlich, Jürg; Röösli, Martin

2017-02-01

Adolescents belong to the heaviest users of wireless communication devices, but little is known about their personal exposure to radiofrequency electromagnetic fields (RF-EMF). The aim of this paper is to describe personal RF-EMF exposure of Swiss adolescents and evaluate exposure relevant factors. Furthermore, personal measurements were used to estimate average contributions of various sources to the total absorbed RF-EMF dose of the brain and the whole body. Personal exposure was measured using a portable RF-EMF measurement device (ExpoM-RF) measuring 13 frequency bands ranging from 470 to 3600MHz. The participants carried the device for three consecutive days and kept a time-activity diary. In total, 90 adolescents aged 13 to 17years participated in the study conducted between May 2013 and April 2014. In addition, personal measurement values were combined with dose calculations for the use of wireless communication devices to quantify the contribution of various RF-EMF sources to the daily RF-EMF dose of adolescents. Main contributors to the total personal RF-EMF measurements of 63.2μW/m 2 (0.15V/m) were exposures from mobile phones (67.2%) and from mobile phone base stations (19.8%). WLAN at school and at home had little impact on the personal measurements (WLAN accounted for 3.5% of total personal measurements). According to the dose calculations, exposure from environmental sources (broadcast transmitters, mobile phone base stations, cordless phone base stations, WLAN access points, and mobile phones in the surroundings) contributed on average 6.0% to the brain dose and 9.0% to the whole-body dose. RF-EMF exposure of adolescents is dominated by their own mobile phone use. Environmental sources such as mobile phone base stations play a minor role. Copyright © 2016 Elsevier Ltd. All rights reserved.

Prediction and Measurement of X-Ray Spectral and Intensity Distributions from Low Energy Electron Impact Sources

NASA Technical Reports Server (NTRS)

Edwards, David L.

1999-01-01

In-vacuum electron beam welding is a technology that NASA considered as a joining technique for manufacture of space structures. The interaction of energetic electrons with metal produces x-rays. The radiation exposure to astronauts performing the in-vacuum electron beam welding must be characterized and minimized to insure safe operating conditions. This investigation characterized the x-ray environment due to operation of an in-vacuum electron beam welding tool. NASA, in a joint venture with the Russian Space Agency, was scheduled to perform a series of welding in space experiments on board the United States Space Shuttle. This series of experiments was named the International Space Welding Experiment (ISWE). The hardware associated with the ISWE was leased to NASA, by the Paton Welding Institute (PWI) in Ukraine, for ground based welding experiments in preparation for flight. Two tests were scheduled, using the ISWE electron beam welding tool, to characterize the radiation exposure to an astronaut during the operation of the ISWE. These radiation exposure tests consisted of Thermoluminescence Dosimeters (TLD's) shielded with material currently used by astronauts during Extra Vehicular Activities (EVA) and exposed to x-ray radiation generated by operation of an in-vacuum electron beam welding tool. This investigation was the first known application of TLD's to measure absorbed dose from x-rays of energy less than 10 KeV. The ISWE hardware was returned to Ukraine before the issue of adequate shielding for the astronauts was verified. Therefore, alternate experimental and analytical methods were developed to measure and predict the x-ray spectral and intensity distribution generated by electron impact with metal. These x-ray spectra were used to calculate the absorbed radiation dose to astronauts. These absorbed dose values were compared to TLD measurements obtained during actual operation of the in-vacuum electron beam welding tool. The calculated absorbed dose values were found to be in good agreement with the TLD values.

Use of treatment log files in spot scanning proton therapy as part of patient-specific quality assurance

PubMed Central

Li, Heng; Sahoo, Narayan; Poenisch, Falk; Suzuki, Kazumichi; Li, Yupeng; Li, Xiaoqiang; Zhang, Xiaodong; Lee, Andrew K.; Gillin, Michael T.; Zhu, X. Ronald

2013-01-01

Purpose: The purpose of this work was to assess the monitor unit (MU) values and position accuracy of spot scanning proton beams as recorded by the daily treatment logs of the treatment control system, and furthermore establish the feasibility of using the delivered spot positions and MU values to calculate and evaluate delivered doses to patients. Methods: To validate the accuracy of the recorded spot positions, the authors generated and executed a test treatment plan containing nine spot positions, to which the authors delivered ten MU each. The spot positions were measured with radiographic films and Matrixx 2D ion-chambers array placed at the isocenter plane and compared for displacements from the planned and recorded positions. Treatment logs for 14 patients were then used to determine the spot MU values and position accuracy of the scanning proton beam delivery system. Univariate analysis was used to detect any systematic error or large variation between patients, treatment dates, proton energies, gantry angles, and planned spot positions. The recorded patient spot positions and MU values were then used to replace the spot positions and MU values in the plan, and the treatment planning system was used to calculate the delivered doses to patients. The results were compared with the treatment plan. Results: Within a treatment session, spot positions were reproducible within ±0.2 mm. The spot positions measured by film agreed with the planned positions within ±1 mm and with the recorded positions within ±0.5 mm. The maximum day-to-day variation for any given spot position was within ±1 mm. For all 14 patients, with ∼1 500 000 spots recorded, the total MU accuracy was within 0.1% of the planned MU values, the mean (x, y) spot displacement from the planned value was (−0.03 mm, −0.01 mm), the maximum (x, y) displacement was (1.68 mm, 2.27 mm), and the (x, y) standard deviation was (0.26 mm, 0.42 mm). The maximum dose difference between calculated dose to the patient based on the plan and recorded data was within 2%. Conclusions: The authors have shown that the treatment log file in a spot scanning proton beam delivery system is precise enough to serve as a quality assurance tool to monitor variation in spot position and MU value, as well as the delivered dose uncertainty from the treatment delivery system. The analysis tool developed here could be useful for assessing spot position uncertainty and thus dose uncertainty for any patient receiving spot scanning proton beam therapy. PMID:23387726

Dose mapping using MCNP code and experiment for SVST-Co-60/B irradiator in Vietnam.

PubMed

Tran, Van Hung; Tran, Khac An

2010-06-01

By using MCNP code and ethanol-chlorobenzene (ECB) dosimeters the simulations and measurements of absorbed dose distribution in a tote-box of the Cobalt-60 irradiator, SVST-Co60/B at VINAGAMMA have been done. Based on the results Dose Uniformity Ratios (DUR), positions and values of minimum and maximum dose extremes in a tote-box, and efficiency of the irradiator for the different dummy densities have been gained. There is a good agreement between simulation and experimental results in comparison and they have valuable meanings for operation of the irradiator. Copyright 2010 Elsevier Ltd. All rights reserved.

Effect of ultra-low doses, ASIR and MBIR on density and noise levels of MDCT images of dental implant sites.

PubMed

Widmann, Gerlig; Al-Shawaf, Reema; Schullian, Peter; Al-Sadhan, Ra'ed; Hörmann, Romed; Al-Ekrish, Asma'a A

2017-05-01

Differences in noise and density values in MDCT images obtained using ultra-low doses with FBP, ASIR, and MBIR may possibly affect implant site density analysis. The aim of this study was to compare density and noise measurements recorded from dental implant sites using ultra-low doses combined with FBP, ASIR, and MBIR. Cadavers were scanned using a standard protocol and four low-dose protocols. Scans were reconstructed using FBP, ASIR-50, ASIR-100, and MBIR, and either a bone or standard reconstruction kernel. Density (mean Hounsfield units [HUs]) of alveolar bone and noise levels (mean standard deviation of HUs) was recorded from all datasets and measurements were compared by paired t tests and two-way ANOVA with repeated measures. Significant differences in density and noise were found between the reference dose/FBP protocol and almost all test combinations. Maximum mean differences in HU were 178.35 (bone kernel) and 273.74 (standard kernel), and in noise, were 243.73 (bone kernel) and 153.88 (standard kernel). Decreasing radiation dose increased density and noise regardless of reconstruction technique and kernel. The effect of reconstruction technique on density and noise depends on the reconstruction kernel used. • Ultra-low-dose MDCT protocols allowed more than 90 % reductions in dose. • Decreasing the dose generally increased density and noise. • Effect of IRT on density and noise varies with reconstruction kernel. • Accuracy of low-dose protocols for interpretation of bony anatomy not known. • Effect of low doses on accuracy of computer-aided design models unknown.

A Dosimetric Evaluation of The Eclipse and Pinnacle Treatment Planning Systems in Treatment of Vertebral Bodies Using IMRT and VMAT with Modeled and Commissioned Flattening Filter Free (FFF) Fields

NASA Astrophysics Data System (ADS)

Ajo, Ramzi, Jr.

Modern treatment planning systems (TPS's) utilize different algorithms in computing dose within the patient medium. The algorithms rely on properly modeled clinical setups in order to perform optimally. Aside from various parameters of the beam, modifiers, such as multileaf collimators (MLC's), must also be modeled properly. That could not be more true today, where dynamic delivery such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) are being increasingly utilized due to their ability to deliver higher dose precisely to the target while sparing more surrounding normal tissue. Two of the most popular TPS's, Pinnacle (Philips) and Eclipse (Varian), were compared, with special emphasis placed on parameterization of the dosimetric leaf gap (DLG) in Eclipse. The DLG is a parameter that accounts for Varian's rounded MLC leaf ends. While Pinnacle accounts for the rounded leaf end by modeling the MLC's, Eclipse uses a measured parameter. This study investigated whether a single value measured DLG is sufficient for dynamic delivery. Using five planning volumes for vertebral body SBRT treatments, each prescribed for 3000 cGy in 5 fractions, an array of 20 treatment plans was generated using varying energies of 6MV-FFF and 10MV-FFF. Treatment techniques consisted of 9-field Step-and-shoot IMRT, and dual-arc VMAT using patient specific optimization criteria in the Pinnacle TPS v9.8. Each plan was normalized to ensure coverage of 3000cGy to 95% of the target volume. The dose was computed in Pinnacle v9.8, with the Collapsed Cone Convolution Superposition algorithm and Eclipse v11, with the Acuros XB algorithm, using a dose grid resolution of 2 mm in both systems. Dose volume histograms (DVH's) were generated for a comparison of max and mean dose to the targets and spinal cord, as well as 95% coverage of the targets and the volume of the spinal cord receiving 14.5 Gy (V14.5). Patient specific quality assurance (PSQA) fields were generated and then delivered, using a Varian Edge linear accelerator, to a 4D QA phantom for a gamma analysis and distance to agreement (DTA) comparison. All Eclipse calculations were made for both measured and optimized DLG parameters. Calculated vs. measured point dose for the Pinnacle TPS had an average difference of 2.79 +/- 2.00%. Gamma analysis using a 3% and 3 mm DTA had 99/100 fields passing at > 95%. Using measured values of the DLG in Eclipse, calculated vs. measured point dose was -4.44 +/- 1.97%, and DTA had 33/110 fields passing at > 95%. After an optimization of the DLG in Eclipse, calculated vs. measured point dose had an average difference of 2.20 +/- 2.23%, and DTA with 95/110 fields passing at > 95%. This study looked at the performance of the Pinnacle and Eclipse TPS's, with special consideration given to the DLG parameterization used by Eclipse. The results support the idea that a single valued DLG is not sufficient for dynamic delivery. An optimization of the parameter is necessary to account for the high modulation of IMRT and VMAT techniques.

Comparison of measurement methods for benzene and toluene

NASA Astrophysics Data System (ADS)

Wideqvist, U.; Vesely, V.; Johansson, C.; Potter, A.; Brorström-Lundén, E.; Sjöberg, K.; Jonsson, T.

Diffusive sampling and active (pumped) sampling (tubes filled with Tenax TA or Carbopack B) were compared with an automatic BTX instrument (Chrompack, GC/FID) for measurements of benzene and toluene. The measurements were made during differing pollution levels and different weather conditions at a roof-top site and in a densely trafficked street canyon in Stockholm, Sweden. The BTX instrument was used as the reference method for comparison with the other methods. Considering all data the Perkin-Elmer diffusive samplers, containing Tenax TA and assuming a constant uptake rate of 0.406 cm3 min-1, showed about 30% higher benzene values compared to the BTX instrument. This discrepancy may be explained by a dose-dependent uptake rate with higher uptake rates at lower dose as suggested by laboratory experiments presented in the literature. After correction by applying the relationship between uptake rate and dose as suggested by Roche et al. (Atmos. Environ. 33 (1999) 1905), the two methods agreed almost perfectly. For toluene there was much better agreement between the two methods. No sign of a dose-dependent uptake could be seen. The mean concentrations and 95% confidence intervals of all toluene measurements (67 values) were (10.80±1.6) μg m -3 for diffusive sampling and (11.3±1.6) μg m -3 for the BTX instrument, respectively. The overall ratio between the concentrations obtained using diffusive sampling and the BTX instrument was 0.91±0.07 (95% confidence interval). Tenax TA was found to be equal to Carbopack B for measuring benzene and toluene in this concentration range, although it has been proposed not to be optimal for benzene. There was also good agreement between the active samplers and the BTX instrument.

Luminescence isochron dating: a new approach using different grain sizes.

PubMed

Zhao, H; Li, S H

2002-01-01

A new approach to isochron dating is described using different sizes of quartz and K-feldspar grains. The technique can be applied to sites with time-dependent external dose rates. It is assumed that any underestimation of the equivalent dose (De) using K-feldspar is by a factor F, which is independent of grain size (90-350 microm) for a given sample. Calibration of the beta source for different grain sizes is discussed, and then the sample ages are calculated using the differences between quartz and K-feldspar De from grains of similar size. Two aeolian sediment samples from north-eastern China are used to illustrate the application of the new method. It is confirmed that the observed values of De derived using K-feldspar underestimate the expected doses (based on the quartz De) but, nevertheless, these K-feldspar De values correlate linearly with the calculated internal dose rate contribution, supporting the assumption that the underestimation factor F is independent of grain size. The isochron ages are also compared with the results obtained using quartz De and the measured external dose rates.

Radioactivity concentrations in soils in the Qingdao area, China.

PubMed

Qu, Limei; Yao, De; Cong, Pifu; Xia, Ning

2008-10-01

The specific activity concentrations of radionuclides (238)U, (232)Th, and (40)K of 2300 sampling points in the Qingdao area were measured by an FD-3022 gamma-ray spectrometer. The radioactivity concentrations of (238)U, (232)Th, and (40)K ranged from 3.3 to 185.3, from 6.9 to 157.2, and from 115.8 to 7834.4 Bq kg(-1), respectively. The air-absorbed dose at 1 meter above ground, effective annual dose, external hazard index, and radium equivalent activity were also calculated to systematically evaluate the radiological hazards of the natural radioactivity in Qingdao. The air-absorbed dose, effective annual dose, external hazard index, and radium equivalent activity in the study area were 98.6 nGy h(-1), 0.12 mSv, 0.56, 197 Bq kg(-1), respectively. Compared with the worldwide value, the air-absorbed dose is slightly high, but the other factors are all lower than the recommended value. The natural external exposure will not pose significant radiological threat to the population. In conclusion, the Qingdao area is safe with regard to the radiological level and suitable for living.

SU-F-P-19: Fetal Dose Estimate for a High-Dose Fluoroscopy Guided Intervention Using Modern Data Tools

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moirano, J

Purpose: An accurate dose estimate is necessary for effective patient management after a fetal exposure. In the case of a high-dose exposure, it is critical to use all resources available in order to make the most accurate assessment of the fetal dose. This work will demonstrate a methodology for accurate fetal dose estimation using tools that have recently become available in many clinics, and show examples of best practices for collecting data and performing the fetal dose calculation. Methods: A fetal dose estimate calculation was performed using modern data collection tools to determine parameters for the calculation. The reference pointmore » air kerma as displayed by the fluoroscopic system was checked for accuracy. A cumulative dose incidence map and DICOM header mining were used to determine the displayed reference point air kerma. Corrections for attenuation caused by the patient table and pad were measured and applied in order to determine the peak skin dose. The position and depth of the fetus was determined by ultrasound imaging and consultation with a radiologist. The data collected was used to determine a normalized uterus dose from Monte Carlo simulation data. Fetal dose values from this process were compared to other accepted calculation methods. Results: An accurate high-dose fetal dose estimate was made. Comparison to accepted legacy methods were were within 35% of estimated values. Conclusion: Modern data collection and reporting methods ease the process for estimation of fetal dose from interventional fluoroscopy exposures. Many aspects of the calculation can now be quantified rather than estimated, which should allow for a more accurate estimation of fetal dose.« less

Radon survey and soil gamma doses in primary schools of Batman, Turkey.

PubMed

Damla, Nevzat; Aldemir, Kamuran

2014-06-01

A survey was conducted to evaluate levels of indoor radon and gamma doses in 42 primary schools located in Batman, southeastern Anatolia, Turkey. Indoor radon measurements were carried out using CR-39 solid-state nuclear track detector-based radon dosimeters. The overall mean annual (222)Rn activity in the surveyed area was found to be 49 Bq m(-3) (equivalent to an annual effective dose of 0.25 mSv). However, in one of the districts (Besiri) the maximum radon value turned out to be 307 Bq m(-3). The estimated annual effective doses are less than the recommended action level (3-10 mSv). It is found that the radon concentration decreases with increasing floor number. The concentrations of natural and artificial radioisotopes were determined using gamma-ray spectroscopy for soil samples collected in close vicinity of the studied schools. The mean gamma activity concentrations in the soil samples were 31, 25, 329 and 12 Bq kg(-1) for (226)Ra, (232)Th, (40)K and (137)Cs, respectively. The radiological parameters such as the absorbed dose rate in air and the annual effective dose equivalent were calculated. These radiological parameters were evaluated and compared with the internationally recommended values.

Effect of sodium ascorbate dose on the shelf life stability of reduced nitrite liver pâtés.

PubMed

Vossen, Els; Doolaege, Evelyne H A; Moges, Haile Demewez; De Meulenaer, Bruno; Szczepaniak, Slawomir; Raes, Katleen; De Smet, Stefaan

2012-05-01

The effect of sodium ascorbate (SA; 500, 750, 1000 mg/kg) and sodium nitrite (SN; 40, 80, 120 mg/kg) doses on the shelf-life stability of liver pâtés was investigated in a full factorial design. Clear dose-dependent responses of the added SN or SA were found for the concentrations of nitrite, ascorbic acid and dehydroascorbic acid in the raw batters and in the cooked pâtés before and after 48 h of chilled display. Decreasing the SN dose to 80 mg/kg had no negative impact on the colour stability (a* value) and lipid oxidation (TBARS), and no additional antioxidant effect of SA was noticed. Lowering SN to 40 mg/kg resulted in proper colour formation, but the colour stability was inferior and lipid oxidation increased. Yet, increasing the amount of SA, at this low SN dose, resulted in lower TBARS values. Decreasing the SN dose to 80 or 40 mg/kg had no distinct effect on protein oxidation, which was however only measured by carbonyl content. Copyright © 2011 Elsevier Ltd. All rights reserved.

SU-D-12A-06: A Comprehensive Parameter Analysis for Low Dose Cone-Beam CT Reconstruction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, W; Southern Medical University, Guangzhou; Yan, H

Purpose: There is always a parameter in compressive sensing based iterative reconstruction (IR) methods low dose cone-beam CT (CBCT), which controls the weight of regularization relative to data fidelity. A clear understanding of the relationship between image quality and parameter values is important. The purpose of this study is to investigate this subject based on experimental data and a representative advanced IR algorithm using Tight-frame (TF) regularization. Methods: Three data sets of a Catphan phantom acquired at low, regular and high dose levels are used. For each tests, 90 projections covering a 200-degree scan range are used for reconstruction. Threemore » different regions-of-interest (ROIs) of different contrasts are used to calculate contrast-to-noise ratios (CNR) for contrast evaluation. A single point structure is used to measure modulation transfer function (MTF) for spatial-resolution evaluation. Finally, we analyze CNRs and MTFs to study the relationship between image quality and parameter selections. Results: It was found that: 1) there is no universal optimal parameter. The optimal parameter value depends on specific task and dose level. 2) There is a clear trade-off between CNR and resolution. The parameter for the best CNR is always smaller than that for the best resolution. 3) Optimal parameters are also dose-specific. Data acquired under a high dose protocol require less regularization, yielding smaller optimal parameter values. 4) Comparing with conventional FDK images, TF-based CBCT images are better under a certain optimally selected parameters. The advantages are more obvious for low dose data. Conclusion: We have investigated the relationship between image quality and parameter values in the TF-based IR algorithm. Preliminary results indicate optimal parameters are specific to both the task types and dose levels, providing guidance for selecting parameters in advanced IR algorithms. This work is supported in part by NIH (1R01CA154747-01)« less

Estimation of the influence of radical effect in the proton beams using a combined approach with physical data and gel data

NASA Astrophysics Data System (ADS)

Haneda, K.

2016-04-01

The purpose of this study was to estimate an impact on radical effect in the proton beams using a combined approach with physical data and gel data. The study used two dosimeters: ionization chambers and polymer gel dosimeters. Polymer gel dosimeters have specific advantages when compared to other dosimeters. They can measure chemical reaction and they are at the same time a phantom that can map in three dimensions continuously and easily. First, a depth-dose curve for a 210 MeV proton beam measured using an ionization chamber and a gel dosimeter. Second, the spatial distribution of the physical dose was calculated by Monte Carlo code system PHITS: To verify of the accuracy of Monte Carlo calculation, and the calculation results were compared with experimental data of the ionization chamber. Last, to evaluate of the rate of the radical effect against the physical dose. The simulation results were compared with the measured depth-dose distribution and showed good agreement. The spatial distribution of a gel dose with threshold LET value of proton beam was calculated by the same simulation code. Then, the relative distribution of the radical effect was calculated from the physical dose and gel dose. The relative distribution of the radical effect was calculated at each depth as the quotient of relative dose obtained using physical and gel dose. The agreement between the relative distributions of the gel dosimeter and Radical effect was good at the proton beams.

Phenytoin kinetics during pregnancy and the puerperium.

PubMed

Knott, C; Williams, C P; Reynolds, F

1986-10-01

During pregnancy changes in maternal physiology and plasma composition may alter drug binding and dose requirements. We have measured plasma unbound and total phenytoin, and saliva concentrations at intervals in 11 pregnant epileptics. Plasma albumin concentrations were also measured in pregnant and non-pregnant women. Saliva phenytoin correlated closely with the plasma unbound concentrations (r = 0.98). The saliva:plasma (S:P) ratio, reflecting the free fraction, was variable during pregnancy but tended to increase to maximal values at delivery and return to non-pregnant values within 2-8 weeks thereafter. Plasma albumin concentrations correlated poorly with phenytoin binding. Binding in umbilical cord plasma appeared higher than that in maternal plasma and total fetal concentrations correlated closely with maternal plasma concentrations at delivery. No ill effects of phenytoin were detected in the newborn infant. During the third trimester phenytoin dose increments were necessary to maintain therapeutic concentrations. After delivery maternal saliva phenytoin concentrations rose, and dose reductions were necessary to avoid clinical symptoms of toxicity. It is therefore appropriate to monitor saliva phenytoin concentrations regularly both during pregnancy and the puerperium.

SU-F-T-09: In Phantom Full-Implant Validation of Plastic Scintillation Detectors for in Vivo Dosimetry During Low Dose Rate Brachytherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Therriault-Proulx, F; Bruno, T; Beddar, S

Purpose: To validate in a water phantom the use of plastic scintillation detectors to measure dose to the urethra and the rectal wall during a clinically realistic low dose rate (LDR) brachytherapy implant. Methods: A template was designed to replicate a clinically realistic LDR brachytherapy prostate implant inside a water phantom. Twenty-two catheters were inserted, including one mimicking the urethra and another the rectal wall. The needles inserted in the remaining 20 catheters were composed of thin-walled nylon tubes in which I-125 radioactive seeds (Air Kerma Strengths of (0.328±0.020)U) were abutted together with plastic spacers to replicate a typical loading.more » A plastic scintillation detector (PSD) with a 5-mm long × 1-mm diameter sensitive element was first placed inside the urethra and 1-second measurements were performed for 60s after each needle implant. Measurements were also performed at multiple positions along the urethra once all the needles were inserted. The procedure was then repeated with the PSD placed at the rectal wall. Results: Individual dose-rates ranging from 0.07µGy/s to 1.5µGy/s were measured after each needle implant. The average absolute relative differences were (6.2±3.6)% and (6.9±6.5)% to the values calculated with the TG-43 formalism, for the urethra and rectal wall respectively. These results are within expectations from the error uncertainty budget once accounting for uncertainties in seeds’ strength and positioning. Interestingly, the PSD allowed for unplanned error detection as the study was performed. Finally, the measured dose after the full implant at different positions along the mimicked organs at risk were in agreement with TG-43 values for all of the positions tested. Conclusion: Plastic scintillation detectors could be used as in vivo detectors for LDR brachytherapy as they would provide accurate dose information after each needle implant as well as along the organs at risk at the end of the implant.« less

Applicability of Glass Dosimeters for In-vivo Dosimetry in Brachytherapy

NASA Astrophysics Data System (ADS)

Moon, Sun Young; Son, Jaeman; Yoon, Myonggeun; Jeang, EunHee; Lim, Young Kyung; Chung, Weon Kyu; Kim, Dong Wook

2018-06-01

During brachytherapy, confirming the dose delivered is very important in order to prevent radiation-associated side effects. Therefore, we aimed to confirm the accuracy of dose delivery near the source by inserting glass dosimeters within the applicator. We created an alternative pelvic phantom with the same shape and internal structures as the usual patient. In addition, we created a tandem for insertion of the glass dosimeters and measured the dose near the source by inserting the glass dosimeters into the tandem and evaluating the accuracy of the dwell position and time through the dose near the source. Errors between the values obtained from the five glass dosimeters and the values from the treatment planning system were -6.27, -2.1, -4.18, 6.31, and -0.39%, respectively. The mean error was 3.85%. This value was acceptable considering that the error of the glass dosimeter itself is approximately 3%. Even though a complement of the applicator and the error calibration is required in order to apply this technique clinically, we believe that radiation accidents and overdoses can be prevented through in-vivo dosimetry using a glass dosimeter for brachytherapy.

Assessment of Annual Effective Dose for Natural Radioactivity of Gamma Emitters in Biscuit Samples in Iraq.

PubMed

Abojassim, Ali Abid; Al-Alasadi, Lubna A; Shitake, Ahmed R; Al-Tememie, Faeq A; Husain, Afnan A

2015-09-01

Biscuits are an important type of food, widely consumed by babies in Iraq and other countries. This work uses gamma spectroscopy to measure the natural radioactivity due to long-lived gamma emitters in children's biscuits; it also estimates radiation hazard indices, that is, the radium equivalent activity, the representative of gamma level index, the internal hazard index, and the annual effective dose in children. Ten samples were collected from the Iraqi market from different countries of origin. The average specific activities for (226)Ra, (232)Th, and (40)K were 9.390, 3.1213, and 214.969 Bq/kg, respectively, but the average of the radium equivalent activity and the internal hazard index were 33.101 Bq/kg and 0.107, respectively. The total average annual effective dose from consumption by adults, children, and infants is estimated to be 0.655, 1.009, and 0.875 mSv, respectively. The values found for specific activity, radiation hazard indices, and annual effective dose in all samples in this study were lower than worldwide median values for all groups; therefore, these values are found to be safe.

MPC and ALI: their basis and their comparison

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kennedy, W.E. Jr.; Watson, E.C.

Radiation protection regulations in the United States have evolved from the recommendations of the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP). In 1959, the ICRP issued Publication 2 which contained specific recommendations on dose rate limits, permissible body burdens, metabolic data for radionuclides, and maximum permissible concentrations (MPC) in air or water. Over the next 20 years, new information became available concerning the effects of radiation, the uptake and retention of radionuclides, and the radioactive decay schemes of parent radionuclides. To include this newer information, the ICRP issued Publication 30 inmore » 1978 to supersede Publication 2. One of the secondary limits defined in Publication 30 is the annual limit of intake (ALI). Radionuclide specific ALI values are intended to replace MPC values in determining whether or not ambient air and water concentrations are sufficiently low to maintain the dose to workers within accepted dose rate limits. In this paper, we discuss the derivation of MPC and ALI values, compare inhalation committed dose equivalent factors derived from ICRP Publications 2 and 30, and discuss the practical implications of using either MPC or ALI in determining compliance with occupational exposure limits. 6 references.« less

Kilovoltage cone-beam CT: Comparative dose and image quality evaluations in partial and full-angle scan protocols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Sangroh; Yoo, Sua; Yin Fangfang

2010-07-15

Purpose: To assess imaging dose of partial and full-angle kilovoltage CBCT scan protocols and to evaluate image quality for each protocol. Methods: The authors obtained the CT dose index (CTDI) of the kilovoltage CBCT protocols in an on-board imager by ion chamber (IC) measurements and Monte Carlo (MC) simulations. A total of six new CBCT scan protocols were evaluated: Standard-dose head (100 kVp, 151 mA s, partial-angle), low-dose head (100 kVp, 75 mA s, partial-angle), high-quality head (100 kVp, 754 mA s, partial-angle), pelvis (125 kVp, 706 mA s, full-angle), pelvis spotlight (125 kVp, 752 mA s, partial-angle), and low-dosemore » thorax (110 kVp, 271 mA s, full-angle). Using the point dose method, various CTDI values were calculated by (1) the conventional weighted CTDI (CTDI{sub w}) calculation and (2) Bakalyar's method (CTDI{sub wb}). The MC simulations were performed to obtain the CTDI{sub w} and CTDI{sub wb}, as well as from (3) central slice averaging (CTDI{sub 2D}) and (4) volume averaging (CTDI{sub 3D}) techniques. The CTDI values of the new protocols were compared to those of the old protocols (full-angle CBCT protocols). Image quality of the new protocols was evaluated following the CBCT image quality assurance (QA) protocol [S. Yoo et al., ''A quality assurance program for the on-board imager registered ,'' Med. Phys. 33(11), 4431-4447 (2006)] testing Hounsfield unit (HU) linearity, spatial linearity/resolution, contrast resolution, and HU uniformity. Results: The CTDI{sub w} were found as 6.0, 3.2, 29.0, 25.4, 23.8, and 7.7 mGy for the new protocols, respectively. The CTDI{sub w} and CTDI{sub wb} differed within +3% between IC measurements and MC simulations. Method (2) results were within {+-}12% of method (1). In MC simulations, the CTDI{sub w} and CTDI{sub wb} were comparable to the CTDI{sub 2D} and CTDI{sub 3D} with the differences ranging from -4.3% to 20.6%. The CTDI{sub 3D} were smallest among all the CTDI values. CTDI{sub w} of the new protocols were found as {approx}14 times lower for standard head scan and 1.8 times lower for standard body scan than the old protocols, respectively. In the image quality QA tests, all the protocols except low-dose head and low-dose thorax protocols were within the tolerance in the HU verification test. The HU value for the two protocols was always higher than the nominal value. All the protocols passed the spatial linearity/resolution and HU uniformity tests. In the contrast resolution test, only high-quality head and pelvis scan protocols were within the tolerance. In addition, crescent effect was found in the partial-angle scan protocols. Conclusions: The authors found that CTDI{sub w} of the new CBCT protocols has been significantly reduced compared to the old protocols with acceptable image quality. The CTDI{sub w} values in the point dose method were close to the volume averaging method within 9%-21% for all the CBCT scan protocols. The Bakalyar's method produced more accurate dose estimation within 14%. The HU inaccuracy from low-dose head and low-dose thorax protocols can render incorrect dose results in the treatment planning system. When high soft-tissue contrast data are desired, high-quality head or pelvis scan protocol is recommended depending on the imaging area. The point dose method can be applicable to estimate CBCT dose with reasonable accuracy in the clinical environment.« less

Dosimetric Consistency of Co-60 Teletherapy Unit- a ten years Study.

PubMed

Baba, Misba H; Mohib-Ul-Haq, M; Khan, Aijaz A

2013-01-01

The goal of the Radiation standards and Dosimetry is to ensure that the output of the Teletherapy Unit is within ±2% of the stated one and the output of the treatment dose calculation methods are within ±5%. In the present paper, we studied the dosimetry of Cobalt-60 (Co-60) Teletherapy unit at Sher-I-Kashmir Institute of Medical Sciences (SKIMS) for last 10 years. Radioactivity is the phenomenon of disintegration of unstable nuclides called radionuclides. Among these radionuclides, Cobalt-60, incorporated in Telecobalt Unit, is commonly used in therapeutic treatment of cancer. Cobalt-60 being unstable decays continuously into Ni-60 with half life of 5.27 years thereby resulting in the decrease in its activity, hence dose rate (output). It is, therefore, mandatory to measure the dose rate of the Cobalt-60 source regularly so that the patient receives the same dose every time as prescribed by the radiation oncologist. The under dosage may lead to unsatisfactory treatment of cancer and over dosage may cause radiation hazards. Our study emphasizes the consistency between actual output and output obtained using decay method. The methodology involved in the present study is the calculations of actual dose rate of Co-60 Teletherapy Unit by two techniques i.e. Source to Surface Distance (SSD) and Source to Axis Distance (SAD), used for the External Beam Radiotherapy, of various cancers, using the standard methods. Thereby, a year wise comparison has been made between average actual dosimetric output (dose rate) and the average expected output values (obtained by using decay method for Co-60.). The present study shows that there is a consistency in the average output (dose rate) obtained by the actual dosimetry values and the expected output values obtained using decay method. The values obtained by actual dosimetry are within ±2% of the expected values. The results thus obtained in a year wise comparison of average output by actual dosimetry done regularly as a part of Quality Assurance of the Telecobalt Radiotherapy Unit and its deviation from the expected output data is within the permissible limits. Thus our study shows a trend towards uniformity and a better dose delivery.

Comparison of the dose distribution obtained from dosimetric systems with intensity modulated radiotherapy planning system in the treatment of prostate cancer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gökçe, M., E-mail: mgokce@adu.edu.tr; Uslu, D. Koçyiğit; Ertunç, C.

The aim of this study is to compare Intensity Modulated Radiation Therapy (IMRT) plan of prostate cancer patients with different dose verification systems in dosimetric aspects and to compare these systems with each other in terms of reliability, applicability and application time. Dosimetric control processes of IMRT plan of three prostate cancer patients were carried out using thermoluminescent dosimeter (TLD), ion chamber (IC) and 2D Array detector systems. The difference between the dose values obtained from the dosimetric systems and treatment planning system (TPS) were found to be about % 5. For the measured (TLD) and calculated (TPS) doses %3more » percentage differences were obtained for the points close to center while percentage differences increased at the field edges. It was found that TLD and IC measurements will increase the precision and reliability of the results of 2D Array.« less

Epid cine acquisition mode for in vivo dosimetry in dynamic arc radiation therapy

NASA Astrophysics Data System (ADS)

Fidanzio, Andrea; Mameli, Alessandra; Placidi, Elisa; Greco, Francesca; Stimato, Gerardina; Gaudino, Diego; Ramella, Sara; D'Angelillo, Rolando; Cellini, Francesco; Trodella, Lucio; Cilla, Savino; Grimaldi, Luca; D'Onofrio, Guido; Azario, Luigi; Piermattei, Angelo

2008-02-01

In this paper the cine acquisition mode of an electronic portal imaging device (EPID) has been calibrated and tested to determine the in vivo dose for dynamic conformal arc radiation therapy (DCAT). The EPID cine acquisition mode, that allows a frame acquisition rate of one image every 1.66 s, was studied with a monitor unit rate equal to 100 UM/min. In these conditions good signal stability, ±1% (2SD) evaluated during three months, signal reproducibility within ±0.8% (2SD) and linearity with dose and dose rate within ±1% (2SD) were obtained. The transit signal, St, (due to the transmitted beam below the phantom) measured by the EPID cine acquisition mode was used to determine, (i) a set of correlation functions, F(w,L), defined as the ratio between St and the dose at half thickness, Dm, measured in solid water phantoms of different thicknesses, w and with square fields of side L, (ii) a set of factors, f(d,L), that take into account the different X-ray scatter contribution from the phantom to the St signal as a function of the variation, d, of the air gap between the phantom and the EPID. The reconstruction of the isocenter dose, Diso, for DCAT was obtained convolving the transit signal values, obtained at different gantry angles, with the respective reconstruction factors determined by a house-made software. The method was tested with cylindrical and anthropomorphic phantoms and the results show that the reconstructed Diso values can be obtained with an accuracy within ±2.5% in cylindrical phantom and within ±3.4% for anthropomorphic phantom. In conclusion, the transit dosimetry by EPID was assessed to be adequate to perform DCAT in vivo dosimetry, that is not realizable with the other traditional techniques. Moreover, the method proposed here could be implemented to supply in vivo dose values in real time.

Absorbed dose measurements for kV-cone beam computed tomography in image-guided radiation therapy

NASA Astrophysics Data System (ADS)

Hioki, Kazunari; Araki, Fujio; Ohno, Takeshi; Nakaguchi, Yuji; Tomiyama, Yuuki

2014-12-01

In this study, we develope a novel method to directly evaluate an absorbed dose-to-water for kilovoltage-cone beam computed tomography (kV-CBCT) in image-guided radiation therapy (IGRT). Absorbed doses for the kV-CBCT systems of the Varian On-Board Imager (OBI) and the Elekta X-ray Volumetric Imager (XVI) were measured by a Farmer ionization chamber with a 60Co calibration factor. The chamber measurements were performed at the center and four peripheral points in body-type (30 cm diameter and 51 cm length) and head-type (16 cm diameter and 33 cm length) cylindrical water phantoms. The measured ionization was converted to the absorbed dose-to-water by using a 60Co calibration factor and a Monte Carlo (MC)-calculated beam quality conversion factor, kQ, for 60Co to kV-CBCT. The irradiation for OBI and XVI was performed with pelvis and head modes for the body- and the head-type phantoms, respectively. In addition, the dose distributions in the phantom for both kV-CBCT systems were calculated with MC method and were compared with measured values. The MC-calculated doses were calibrated at the center in the water phantom and compared with measured doses at four peripheral points. The measured absorbed doses at the center in the body-type phantom were 1.96 cGy for OBI and 0.83 cGy for XVI. The peripheral doses were 2.36-2.90 cGy for OBI and 0.83-1.06 cGy for XVI. The doses for XVI were lower up to approximately one-third of those for OBI. Similarly, the measured doses at the center in the head-type phantom were 0.48 cGy for OBI and 0.21 cGy for XVI. The peripheral doses were 0.26-0.66 cGy for OBI and 0.16-0.30 cGy for XVI. The calculated peripheral doses agreed within 3% in the pelvis mode and within 4% in the head mode with measured doses for both kV-CBCT systems. In addition, the absorbed dose determined in this study was approximately 4% lower than that in TG-61 but the absorbed dose by both methods was in agreement within their combined uncertainty. This method is more robust and accurate compared to the dosimetry based on a conventional air-kerma calibration factor. Therefore, it is possible to be used as a standard dosimetry protocol for kV-CBCT in IGRT.

Dose conversion coefficients for electron exposure of the human eye lens

NASA Astrophysics Data System (ADS)

Behrens, R.; Dietze, G.; Zankl, M.

2009-07-01

Recent epidemiological studies suggest a rather low dose threshold (below 0.5 Gy) for the induction of a cataract of the eye lens. Some other studies even assume that there is no threshold at all. Therefore, protection measures have to be optimized and current dose limits for the eye lens may be reduced in the future. Two questions arise from this situation: first, which dose quantity is related to the risk of developing a cataract, and second, which personal dose equivalent quantity is appropriate for monitoring this dose quantity. While the dose equivalent quantity Hp(0.07) has often been seen as being sufficiently accurate for monitoring the dose to the lens of the eye, this would be questionable in the case when the dose limits were reduced and, thus, it may be necessary to generally use the dose equivalent quantity Hp(3) for this purpose. The basis for a decision, however, must be the knowledge of accurate conversion coefficients from fluence to equivalent dose to the lens. This is especially important for low-penetrating radiation, for example, electrons. Formerly published values of conversion coefficients are based on quite simple models of the eye. In this paper, quite a sophisticated model of the eye including the inner structure of the lens was used for the calculations and precise conversion coefficients for electrons with energies between 0.2 MeV and 12 MeV, and for angles of radiation incidence between 0° and 45° are presented. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are up to 1000 times smaller for electron energies below 1 MeV, nearly equal at 1 MeV and above 4 MeV, and by a factor of 1.5 larger at about 1.5 MeV electron energy.

Dose conversion coefficients for electron exposure of the human eye lens.

PubMed

Behrens, R; Dietze, G; Zankl, M

2009-07-07

Recent epidemiological studies suggest a rather low dose threshold (below 0.5 Gy) for the induction of a cataract of the eye lens. Some other studies even assume that there is no threshold at all. Therefore, protection measures have to be optimized and current dose limits for the eye lens may be reduced in the future. Two questions arise from this situation: first, which dose quantity is related to the risk of developing a cataract, and second, which personal dose equivalent quantity is appropriate for monitoring this dose quantity. While the dose equivalent quantity H(p)(0.07) has often been seen as being sufficiently accurate for monitoring the dose to the lens of the eye, this would be questionable in the case when the dose limits were reduced and, thus, it may be necessary to generally use the dose equivalent quantity H(p)(3) for this purpose. The basis for a decision, however, must be the knowledge of accurate conversion coefficients from fluence to equivalent dose to the lens. This is especially important for low-penetrating radiation, for example, electrons. Formerly published values of conversion coefficients are based on quite simple models of the eye. In this paper, quite a sophisticated model of the eye including the inner structure of the lens was used for the calculations and precise conversion coefficients for electrons with energies between 0.2 MeV and 12 MeV, and for angles of radiation incidence between 0 degrees and 45 degrees are presented. Compared to the values adopted in 1996 by the International Commission on Radiological Protection (ICRP), the new values are up to 1000 times smaller for electron energies below 1 MeV, nearly equal at 1 MeV and above 4 MeV, and by a factor of 1.5 larger at about 1.5 MeV electron energy.

Amorphous and crystalline optical materials used as instruments for high gamma radiation doses estimations

NASA Astrophysics Data System (ADS)

Ioan, M.-R.

2016-06-01

Nuclear radiation induce some changes to the structure of exposed materials. The main effect of ionizing radiation when interacting with optical materials is the occurrence of color centers, which are quantitatively proportional to the up-taken doses. In this paper, a relation between browning effect magnitude and dose values was found. Using this relation, the estimation of a gamma radiation dose can be done. By using two types of laser wavelengths (532 nm and 633 nm), the optical powers transmitted thru glass samples irradiated to different doses between 0 and 59.1 kGy, were measured and the associated optical browning densities were determined. The use of laser light gives the opportunity of using its particularities: monochromaticity, directionality and coherence. Polarized light was also used for enhancing measurements quality. These preliminary results bring the opportunity of using glasses as detectors for the estimation of the dose in a certain point in space and for certain energy, especially in particles accelerators experiments, where the occurred nuclear reactions are involving the presence of high gamma rays fields.

Local noise reduction for emphysema scoring in low-dose CT images

NASA Astrophysics Data System (ADS)

Schilham, Arnold; Prokop, Mathias; Gietema, Hester; van Ginneken, Bram

2005-04-01

Computed Tomography (CT) has become the new reference standard for quantification of emphysema. The most popular measure for emphysema derived from CT is the Pixel Index (PI), which expresses the fraction of the lung volume with abnormally low intensity values. As PI is calculated from a single, fixed threshold on intensity, this measure is strongly influenced by noise. This effect shows up clearly when comparing the PI score for a high-dose scan to the PI score for a low-dose (i.e. noisy) scan of the same subject. This paper presents a class of noise filters that make use of a local noise estimate to specify the filtering strength: Local Noise Variance Weighted Averaging (LNVWA). The performance of the filter is assessed by comparing high-dose and low-dose PI scores for 11 subjects. LNVWA improves the reproducibility of high-dose PI scores: For an emphysema threshold of -910 HU, the root-mean-square difference in PI score drops from 10% of the lung volume to 3.3% of the lung volume if LNVWA is used.

The Biological Effectiveness of Different Radiation Qualities for the Induction of Chromosome Damage in Human Lymphocytes

NASA Technical Reports Server (NTRS)

Hada, M.; George, Kerry; Cucinotta, F. A.

2011-01-01

Chromosome aberrations were measured in human peripheral blood lymphocytes after in vitro exposure to Si-28-ions with energies ranging from 90 to 600 MeV/u, Ti-48-ions with energies ranging from 240 to 1000 MeV/u, or to Fe-56-ions with energies ranging from 200 to 5,000 MeV/u. The LET of the various Si beams in this study ranged from 48 to 158 keV/ m, the LET of the Ti ions ranged from 107 to 240 keV/micron, and the LET of the Fe-ions ranged from 145 to 440 keV/ m. Doses delivered were in the 10- to 200-cGy range. Dose-response curves for chromosome exchanges in cells at first division after exposure, measured using fluorescence in situ hybridization (FISH) with whole-chromosome probes, were fitted with linear or linear-quadratic functions. The relative biological effectiveness (RBE) was estimated from the initial slope of the dose-response curve for chromosome damage with respect to gamma-rays. The estimates of RBEmax values for total chromosome exchanges ranged from 4.4+/-0.4 to 31.5+/-2.6 for Fe ions, 21.4+/-1.7 to 28.3+/-2.4 for Ti ions, and 11.8+/-1.0 to 42.2+/-3.3 for Si ions. The highest RBEmax value for Fe ions was obtained with the 600 MeV/u beam, the highest RBEmax value for Ti ions was obtained 1000 MeV/u beam, and the highest RBEmax value for Si ions was obtained with the 170 MeV/u beam. For Si and Fe ions the RBEmax values increased with LET, reaching a maximum at about 180 keV/micron for Fe and about 100 keV/micron for Si, and decreasing with further increase in LET. Additional studies for low doses Si-28-ions down to 0.02 Gy will be discussed.

Estimating Systemic Exposure to Levonorgestrel from an Oral Contraceptive

PubMed Central

Basaraba, Cale N; Westhoff, Carolyn L; Pike, Malcolm C; Nandakumar, Renu; Cremers, Serge

2017-01-01

Objective The gold standard for measuring oral contraceptive (OC) pharmacokinetics is the 24-hour steady-state area-under-the-curve (AUC). We conducted this study to assess whether limited sampling at steady state or measurements following use of one or two OCs could provide an adequate proxy in epidemiological studies for the progestin 24-hour steady-state AUC of a particular OC. Study Design We conducted a 13-sample, 24-hour pharmacokinetic study on both day 1 and day 21 of the first cycle of a monophasic OC containing 30 μg ethinyl estradiol and 150 μg levonorgestrel (LNG) in 17 normal-weight healthy white women, and a single-dose 9-sample study of the same OC after a one-month washout. We compared the 13-sample steady-state results with several steady-state and single-dose results calculated using parsimonious sampling schemes. Results The 13-sample steady-state 24-hour LNG AUC was highly correlated with the steady-state 24-hour trough value (r = 0.95; 95% CI [0.85, 0.98]) and with the steady-state 6, 8, 12 and 16-hour values (0.92 ≤ r ≤ 0.95). The trough values after one or two doses were moderately correlated with the steady-state 24-hour AUC value (r = 0.70; 95% CI [0.27, 0.90] and 0.77; 95% CI [0.40, 0.92], respectively). Conclusions Single time-point concentrations at steady-state and after administration of one or two OCs gave highly to moderately correlated estimates of steady-state LNG AUC. Using such measures could facilitate prospective pharmaco-epidemiologic studies of the OC and its side effects. PMID:28041990

Evaluation of total-dose iron sucrose infusions in patients with iron deficiency anemia.

PubMed

Wall, Geoffrey C; Pauly, Rebecca A

2008-01-15

The safety and efficacy of a total-dose iron sucrose infusion protocol used in a large, tertiary care teaching hospital were studied. Nondialysis-dependent patients ages 18 years or older who received > or =250 mg of iron sucrose as a single i.v. infusion between January 2005 and January 2007 were eligible for study inclusion. The protocol for total-dose iron sucrose infusion was the same for all patients. The total dose of iron sucrose for each patient was calculated using an equation that included the desired hemoglobin (Hb) value, observed Hb level, ideal body weight, and sex. The calculated dose was divided into portions, rounded to the nearest 250 mg, and administered over four hours every other day. Outcomes measured included Hb, transferrin saturation, and serum ferritin values. A total of 26 patients met the inclusion criteria. The mean +/- S.D. Hb concentration before total-dose iron sucrose infusion was 9.37 +/- 0.9 g/dL, and the mean +/- S.D. corpuscular volume was 75 +/- 7.1 mum(3). The mean +/- S.D. postinfusion Hb concentration for 19 patients for whom follow-up Hb levels were available was 11.4 +/- 1.2 g/dL, significantly higher than the 9.45 +/- 0.8 g/dL measured before the first infusion (p = 0.03). No significant adverse effects were reported in 47 of 49 infusions, with 2 patients experiencing mild nausea. A treatment protocol consisting of alternate-day total-dose iron sucrose infusions was well tolerated and appeared to be effective in improving Hb concentrations in patients with iron deficiency anemia and without chronic kidney disease.

The use of TLD-700H dosemeters in the assessment of external doses at the former Semipalatinsk nuclear test site.

PubMed

Hill, P; Dederichs, H; Pillath, J; Schlecht, W; Hille, R; Artemev, O; Ptitskaya, L; Akhmetov, M

2002-01-01

The joint projects performed since 1995 by the Jülich Research Centre in co-operation with the Kazakh National Nuclear Centre in the area of the former nuclear test site near Semipalatinsk, in eastern Kazakhstan, have assessed the current dose rate of the population at and around the test site, as well as determining retrospectively the dose rate of persons affected by the atmospheric tests. Measurements of the population by personal dosemeters depend on reliably wearing these dosemeters over prolonged periods of time, and of a sufficient dosemeter return. In the past, such measurements have been particularly successful whenever short wearing times were possible. This requires high sensitivity of the dosemeters. The suitability of the highly sensitive TLD material of the BICRON TLD 700H type for such personal dosimetry measurements was investigated. It was tested in practical field application at the Semipalatinsk nuclear test site in September 2000. Initial results are available from individual doses received by a group of geologists and a group of herdsmen at the test site. For the first time, the individual dose was measured directly in these population groups. Detection limits below 1 microSv permit informative measurements for wearing times of less than two weeks. Most individual doses did not arise significantly out of local fluctuations of natural background. A conservative assessment from the aspect of practical health physics yielded a mean personal dose of 0.55 microSv per day for the herdsmen, whereas the geologists received a mean personal dose of 0.45 microSv per day. For an annual exposure period of typically, about three months, the radiation dose received by the persons investigated, in addition to the natural radiation exposure, is thus well below the international limit value of 1 mSv x a(-1) for the population dose.

Very low-dose (0.15 mGy) chest CT protocols using the COPDGene 2 test object and a third-generation dual-source CT scanner with corresponding third-generation iterative reconstruction software.

PubMed

Newell, John D; Fuld, Matthew K; Allmendinger, Thomas; Sieren, Jered P; Chan, Kung-Sik; Guo, Junfeng; Hoffman, Eric A

2015-01-01

The purpose of this study was to evaluate the impact of ultralow radiation dose single-energy computed tomographic (CT) acquisitions with Sn prefiltration and third-generation iterative reconstruction on density-based quantitative measures of growing interest in phenotyping pulmonary disease. The effects of both decreasing dose and different body habitus on the accuracy of the mean CT attenuation measurements and the level of image noise (SD) were evaluated using the COPDGene 2 test object, containing 8 different materials of interest ranging from air to acrylic and including various density foams. A third-generation dual-source multidetector CT scanner (Siemens SOMATOM FORCE; Siemens Healthcare AG, Erlangen, Germany) running advanced modeled iterative reconstruction (ADMIRE) software (Siemens Healthcare AG) was used.We used normal and very large body habitus rings at dose levels varying from 1.5 to 0.15 mGy using a spectral-shaped (0.6-mm Sn) tube output of 100 kV(p). Three CT scans were obtained at each dose level using both rings. Regions of interest for each material in the test object scans were automatically extracted. The Hounsfield unit values of each material using weighted filtered back projection (WFBP) at 1.5 mGy was used as the reference value to evaluate shifts in CT attenuation at lower dose levels using either WFBP or ADMIRE. Statistical analysis included basic statistics, Welch t tests, multivariable covariant model using the F test to assess the significance of the explanatory (independent) variables on the response (dependent) variable, and CT mean attenuation, in the multivariable covariant model including reconstruction method. Multivariable regression analysis of the mean CT attenuation values showed a significant difference with decreasing dose between ADMIRE and WFBP. The ADMIRE has reduced noise and more stable CT attenuation compared with WFBP. There was a strong effect on the mean CT attenuation values of the scanned materials for ring size (P < 0.0001) and dose level (P < 0.0001). The number of voxels in the region of interest for the particular material studied did not demonstrate a significant effect (P > 0.05). The SD was lower with ADMIRE compared with WFBP at all dose levels and ring sizes (P < 0.05). The third-generation dual-source CT scanners using third-generation iterative reconstruction methods can acquire accurate quantitative CT images with acceptable image noise at very low-dose levels (0.15 mGy). This opens up new diagnostic and research opportunities in CT phenotyping of the lung for developing new treatments and increased understanding of pulmonary disease.

Results of the two incidence screenings in the National Lung Screening Trial.

PubMed

Aberle, Denise R; DeMello, Sarah; Berg, Christine D; Black, William C; Brewer, Brenda; Church, Timothy R; Clingan, Kathy L; Duan, Fenghai; Fagerstrom, Richard M; Gareen, Ilana F; Gatsonis, Constantine A; Gierada, David S; Jain, Amanda; Jones, Gordon C; Mahon, Irene; Marcus, Pamela M; Rathmell, Joshua M; Sicks, JoRean

2013-09-05

The National Lung Screening Trial was conducted to determine whether three annual screenings (rounds T0, T1, and T2) with low-dose helical computed tomography (CT), as compared with chest radiography, could reduce mortality from lung cancer. We present detailed findings from the first two incidence screenings (rounds T1 and T2). We evaluated the rate of adherence of the participants to the screening protocol, the results of screening and downstream diagnostic tests, features of the lung-cancer cases, and first-line treatments, and we estimated the performance characteristics of both screening methods. At the T1 and T2 rounds, positive screening results were observed in 27.9% and 16.8% of participants in the low-dose CT group and in 6.2% and 5.0% of participants in the radiography group, respectively. In the low-dose CT group, the sensitivity was 94.4%, the specificity was 72.6%, the positive predictive value was 2.4%, and the negative predictive value was 99.9% at T1; at T2, the positive predictive value increased to 5.2%. In the radiography group, the sensitivity was 59.6%, the specificity was 94.1%, the positive predictive value was 4.4%, and the negative predictive value was 99.8% at T1; both the sensitivity and the positive predictive value increased at T2. Among lung cancers of known stage, 87 (47.5%) were stage IA and 57 (31.1%) were stage III or IV in the low-dose CT group at T1; in the radiography group, 31 (23.5%) were stage IA and 78 (59.1%) were stage III or IV at T1. These differences in stage distribution between groups persisted at T2. Low-dose CT was more sensitive in detecting early-stage lung cancers, but its measured positive predictive value was lower than that of radiography. As compared with radiography, the two annual incidence screenings with low-dose CT resulted in a decrease in the number of advanced-stage cancers diagnosed and an increase in the number of early-stage lung cancers diagnosed. (Funded by the National Cancer Institute; NLST ClinicalTrials.gov number, NCT00047385.).

Calibrating page sized Gafchromic EBT3 films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crijns, W.; Maes, F.; Heide, U. A. van der

2013-01-15

Purpose: The purpose is the development of a novel calibration method for dosimetry with Gafchromic EBT3 films. The method should be applicable for pretreatment verification of volumetric modulated arc, and intensity modulated radiotherapy. Because the exposed area on film can be large for such treatments, lateral scan errors must be taken into account. The correction for the lateral scan effect is obtained from the calibration data itself. Methods: In this work, the film measurements were modeled using their relative scan values (Transmittance, T). Inside the transmittance domain a linear combination and a parabolic lateral scan correction described the observed transmittancemore » values. The linear combination model, combined a monomer transmittance state (T{sub 0}) and a polymer transmittance state (T{sub {infinity}}) of the film. The dose domain was associated with the observed effects in the transmittance domain through a rational calibration function. On the calibration film only simple static fields were applied and page sized films were used for calibration and measurements (treatment verification). Four different calibration setups were considered and compared with respect to dose estimation accuracy. The first (I) used a calibration table from 32 regions of interest (ROIs) spread on 4 calibration films, the second (II) used 16 ROIs spread on 2 calibration films, the third (III), and fourth (IV) used 8 ROIs spread on a single calibration film. The calibration tables of the setups I, II, and IV contained eight dose levels delivered to different positions on the films, while for setup III only four dose levels were applied. Validation was performed by irradiating film strips with known doses at two different time points over the course of a week. Accuracy of the dose response and the lateral effect correction was estimated using the dose difference and the root mean squared error (RMSE), respectively. Results: A calibration based on two films was the optimal balance between cost effectiveness and dosimetric accuracy. The validation resulted in dose errors of 1%-2% for the two different time points, with a maximal absolute dose error around 0.05 Gy. The lateral correction reduced the RMSE values on the sides of the film to the RMSE values at the center of the film. Conclusions: EBT3 Gafchromic films were calibrated for large field dosimetry with a limited number of page sized films and simple static calibration fields. The transmittance was modeled as a linear combination of two transmittance states, and associated with dose using a rational calibration function. Additionally, the lateral scan effect was resolved in the calibration function itself. This allows the use of page sized films. Only two calibration films were required to estimate both the dose and the lateral response. The calibration films were used over the course of a week, with residual dose errors Less-Than-Or-Slanted-Equal-To 2% or Less-Than-Or-Slanted-Equal-To 0.05 Gy.« less

The development and validation of a Monte Carlo model for calculating the out-of-field dose from radiotherapy treatments

NASA Astrophysics Data System (ADS)

Kry, Stephen

Introduction. External beam photon radiotherapy is a common treatment for many malignancies, but results in the exposure of the patient to radiation away from the treatment site. This out-of-field radiation irradiates healthy tissue and may lead to the induction of secondary malignancies. Out-of-field radiation is composed of photons and, at high treatment energies, neutrons. Measurement of this out-of-field dose is time consuming, often difficult, and is specific to the conditions of the measurements. Monte Carlo simulations may be a viable approach to determining the out-of-field dose quickly, accurately, and for arbitrary irradiation conditions. Methods. An accelerator head, gantry, and treatment vault were modeled with MCNPX and 6 MV and 18 MV beams were simulated. Photon doses were calculated in-field and compared to measurements made with an ion chamber in a water tank. Photon doses were also calculated out-of-field from static fields and compared to measurements made with thermoluminescent dosimeters in acrylic. Neutron fluences were calculated and compared to measurements made with gold foils. Finally, photon and neutron dose equivalents were calculated in an anthropomorphic phantom following intensity-modulated radiation therapy and compared to previously published dose equivalents. Results. The Monte Carlo model was able to accurately calculate the in-field dose. From static treatment fields, the model was also able to calculate the out-of-field photon dose within 16% at 6 MV and 17% at 18 MV and the neutron fluence within 19% on average. From the simulated IMRT treatments, the calculated out-of-field photon dose was within 14% of measurement at 6 MV and 13% at 18 MV on average. The calculated neutron dose equivalent was much lower than the measured value but is likely accurate because the measured neutron dose equivalent was based on an overestimated neutron energy. Based on the calculated out-of-field doses generated by the Monte Carlo model, it was possible to estimate the risk of fatal secondary malignancy, which was consistent with previous estimates except for the neutron discrepancy. Conclusions. The Monte Carlo model developed here is well suited to studying the out-of-field dose equivalent from photons and neutrons under a variety of irradiation configurations, including complex treatments on complex phantoms. Based on the calculated dose equivalents, it is possible to estimate the risk of secondary malignancy associated with out-of-field doses. The Monte Carlo model should be used to study, quantify, and minimize the out-of-field dose equivalent and associated risks received by patients undergoing radiation therapy.

1983 international intercomparison of nuclear accident dosimetry systems at Oak Ridge National Laboratory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swaja, R.E.; Greene, R.T.; Sims, C.S.

1985-04-01

An international intercomparison of nuclear accident dosimetry systems was conducted during September 12-16, 1983, at Oak Ridge National Laboratory (ORNL) using the Health Physics Research Reactor operated in the pulse mode to simulate criticality accidents. This study marked the twentieth in a series of annual accident dosimetry intercomparisons conducted at ORNL. Participants from ten organizations attended this intercomparison and measured neutron and gamma doses at area monitoring stations and on phantoms for three different shield conditions. Results of this study indicate that foil activation techniques are the most popular and accurate method of determining accident-level neutron doses at area monitoringmore » stations. For personnel monitoring, foil activation, blood sodium activation, and thermoluminescent (TL) methods are all capable of providing accurate dose estimates in a variety of radiation fields. All participants in this study used TLD's to determine gamma doses with very good results on the average. Chemical dosemeters were also shown to be capable of yielding accurate estimates of total neutron plus gamma doses in a variety of radiation fields. While 83% of all neutron measurements satisfied regulatory standards relative to reference values, only 39% of all gamma results satisfied corresponding guidelines for gamma measurements. These results indicate that continued improvement in accident dosimetry evaluation and measurement techniques is needed.« less

Measurement of energy deposited by charged particle beams in composite targets. [0. 5 to 28. 5 GeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crase, K.; Farley, W.E.; Kruger, H.

1977-11-03

The energies deposited in composite targets by proton beams from 0.8 to 28.5 GeV energy and by an electron beam at 0.5 GeV energy were measured. The targets consisted of various thicknesses of /sup 238/U shower plates backed by a composite detector plate consisting of a 5-cm-thick CH/sub 2/ moderator and a 0.635-cm /sup 238/U plate. The spacing between the shower and detector plates was varied to allow different spreading of the shower between plates. Passive detectors (thermoluminescence dosimeters, Lexan fission track recorders, photographic emulsions, and removable /sup 238/U pieces) were used to measure the fission-fragment dose and the nonfissionmore » dose at various depths and radial positions in the targets. Plots and numerical values of the measured doses are presented for comparison with computer code calculations. To provide a basis for comparison of the effects of different particle beam energies, data along the beam axes are presented as specific dose (cal/g per incident integrated kJ/cm/sup 2/). In general, the higher the incident proton energy, the larger is the dose in the back of the target relative to that in the front.« less

Environmental dose rate distribution along the Romanian Black Sea shore

NASA Astrophysics Data System (ADS)

Duliu, Octavian G.; Margineanu, Romul M.; Blebea-Apostu, Ana-Maria; Gomoiu, Claudia; Bercea, Sorin

2013-04-01

The radiometric investigation of the natural radioactivity dose rate distribution along the most important Romanian Black Sea tourist resorts showed values between 34 and 54 nSv/h, lower than the 59 nSv/h, the average background reported for the entire Romanian territory. At the same time we have noticed that the experimental dose rates monotonously increase northward, reaching a maximum in the vicinity of Vadu and Corbu beaches, both on the southern part of the Chituc sandbank. Concurrent gamma ray spectrometric measurements, performed at the Slanic-Prahova Low-Background Radiation Laboratory for sand samples collected from the same location, have shown that the natural radionuclides have a major contribution to background radiation while anthropogenic Cs-137 plays, 26 years after Chernobyl catastrophe, a negligible role. The experimental values of activity concentrations of all radionuclides present in sand samples were used to calculate the corresponding values of dose rates to which, by adding the contribution of cosmic rays, we have obtained values coincident, within experimental uncertainties, with the experimental ones. At the same time, on Chituc sandbank, a transverse profile of dose rate distribution revealed the presence of some local maxima, two to thee times higher then the average ones. Subsequent gamma ray spectrometry showed an increased content of natural radionuclides, most probably due to a local accumulation of heavy minerals, a common occurrence in the vicinity of river deltas, in our case the Danube Delta. In such a way, the monitoring of local dose rate distribution could be very useful not only in attesting the environmental quality of various resorts and beaches, but also, in signaling the presence of heavy minerals, with beneficent economic consequences.

Impact of the NTCP modeling on medical decision to select eligible patient for proton therapy: the usefulness of EUD as an indicator to rank modern photon vs proton treatment plans.

PubMed

Chaikh, Abdulhamid; Calugaru, Valentin; Bondiau, Pierre-Yves; Thariat, Juliette; Balosso, Jacques

2018-06-07

The aim of this study is to evaluate the impact of normal tissue complication probability (NTCP)-based radiobiological models on the estimated risk for late radiation lung damages. The second goal is to propose a medical decision-making approach to select the eligible patient for particle therapy. 14 pediatric patients undergoing cranio-spinal irradiation were evaluated. For each patient, two treatment plans were generated using photon and proton therapy with the same dose prescriptions. Late radiation damage to lung was estimated using three NTCP concepts: the Lyman-Kutcher-Burman, the equivalent uniform dose (EUD) and the mean lung dose according to the quantitative analysis of normal tissue effects in the clinic QUANTEC review. Wilcoxon paired test was used to calculate p-value. Proton therapy achieved lower lung EUD (Gy). The average NTCP values were significantly lower with proton plans, p < 0.05, using the three NTCP concepts. However, applying the same TD 50/5 using radiobiological models to compare NTCP from proton and photon therapy, the ΔNTCP was not a convincing method to measure the potential benefit of proton therapy. Late radiation pneumonitis estimated from the mean lung dose model correlated with QUANTEC data better. treatment effectiveness assessed on NTCP reduction depends on radiobiological predictions and parameters used as inputs for in silico evaluation. Since estimates of absolute NTCP values from LKB and GN models are imprecise due to EUD ≪ TD 50/5 , a reduction of the EUD value with proton plans would better predict a reduction of dose/toxicity. The EUD concept appears as a robust radiobiological surrogate of the dose distribution to select the optimal patient's plan.

Dosimetric verification for intensity-modulated arc therapy plans by use of 2D diode array, radiochromic film and radiosensitive polymer gel.

PubMed

Hayashi, Naoki; Malmin, Ryan L; Watanabe, Yoichi

2014-05-01

Several tools are used for the dosimetric verification of intensity-modulated arc therapy (IMAT) treatment delivery. However, limited information is available for composite on-line evaluation of these tools. The purpose of this study was to evaluate the dosimetric verification of IMAT treatment plans using a 2D diode array detector (2D array), radiochromic film (RCF) and radiosensitive polymer gel dosimeter (RPGD). The specific verification plans were created for IMAT for two prostate cancer patients by use of the clinical treatment plans. Accordingly, the IMAT deliveries were performed with the 2D array on a gantry-mounting device, RCF in a cylindrical acrylic phantom, and the RPGD in two cylindrical phantoms. After the irradiation, the planar dose distributions from the 2D array and the RCFs, and the 3D dose distributions from the RPGD measurements were compared with the calculated dose distributions using the gamma analysis method (3% dose difference and 3-mm distance-to-agreement criterion), dose-dependent dose difference diagrams, dose difference histograms, and isodose distributions. The gamma passing rates of 2D array, RCFs and RPGD for one patient were 99.5%, 96.5% and 93.7%, respectively; the corresponding values for the second patient were 97.5%, 92.6% and 92.9%. Mean percentage differences between the RPGD measured and calculated doses in 3D volumes containing PTVs were -0.29 ± 7.1% and 0.97 ± 7.6% for the two patients, respectively. In conclusion, IMAT prostate plans can be delivered with high accuracy, although the 3D measurements indicated less satisfactory agreement with the treatment plans, mainly due to the dosimetric inaccuracy in low-dose regions of the RPGD measurements.

[Characterization of a diode system for in vivo dosimetry with electron beams].

PubMed

Ragona, R; Rossetti, V; Lucio, F; Anglesio, S; Giglioli, F R

2001-10-01

Current quality assurance regulation stresses the basic role of in vivo dosimetry. Our study evaluates the usefulness and reliability of semiconductor diodes in determining the electron absorbed dose. P-type EDE semiconductor detectors were irradiated with electron beams of different energies produced by a CGR Saturn Therac 20. The diode and ionization chamber response were compared, and effect of energy value, collimator opening, source skin distance and gantry angle on diode response was studied. Measurements show a maximum increment of about 20% in diode response increasing the beam energy (6-20 MeV). The response also increases with: collimator opening, reaching 5% with field sizes larger than 10x10 cm2 (with the exception of 20 MeV energy); SSD increase (with a maximum of 8% for 20 MeV); transversal gantry incidence, compared with the diode longitudinal axis; it does not affect the response in the interval of +/- 45 degrees. Absorbed dose attenuation at dmax, due to the presence of diode on the axis of the beam as a function of electron energy was also determined : the maximum attenuation value is 15% in 6 MeV electron beams. A dose calculation algorithm, taking into account diode response dependence was outlined. In vivo dosimetry was performed in 92 fields for 80 patients, with an agreement of +/-4 % (1 SD) between prescribed and measured dose. It is possible to use the EDE semiconductor detectors on a quality control program of dose delivery for electron beam therapy, but particular attention should be paid to the beam incidence angle and diode dose attenuation.

Automatic exposure control systems designed to maintain constant image noise: effects on computed tomography dose and noise relative to clinically accepted technique charts.

PubMed

Favazza, Christopher P; Yu, Lifeng; Leng, Shuai; Kofler, James M; McCollough, Cynthia H

2015-01-01

To compare computed tomography dose and noise arising from use of an automatic exposure control (AEC) system designed to maintain constant image noise as patient size varies with clinically accepted technique charts and AEC systems designed to vary image noise. A model was developed to describe tube current modulation as a function of patient thickness. Relative dose and noise values were calculated as patient width varied for AEC settings designed to yield constant or variable noise levels and were compared to empirically derived values used by our clinical practice. Phantom experiments were performed in which tube current was measured as a function of thickness using a constant-noise-based AEC system and the results were compared with clinical technique charts. For 12-, 20-, 28-, 44-, and 50-cm patient widths, the requirement of constant noise across patient size yielded relative doses of 5%, 14%, 38%, 260%, and 549% and relative noises of 435%, 267%, 163%, 61%, and 42%, respectively, as compared with our clinically used technique chart settings at each respective width. Experimental measurements showed that a constant noise-based AEC system yielded 175% relative noise for a 30-cm phantom and 206% relative dose for a 40-cm phantom compared with our clinical technique chart. Automatic exposure control systems that prescribe constant noise as patient size varies can yield excessive noise in small patients and excessive dose in obese patients compared with clinically accepted technique charts. Use of noise-level technique charts and tube current limits can mitigate these effects.

Scattered dose to radiosensitive organs and associated risk for cancer development from head and neck radiotherapy in pediatric patients.

PubMed

Kourinou, Kalliopi M; Mazonakis, Michalis; Lyraraki, Efrosini; Stratakis, John; Damilakis, John

2013-11-01

The purpose of this study was to measure the scattered dose to out-of-field organs from head and neck radiotherapy in pediatric patients and to estimate the risk for second cancer induction to individual organs. Radiotherapy for thalamic tumor, brain tumor, acute leukemia and Hodgkin's disease in the neck region was simulated on 5 and 10-year-old pediatric phantoms with a 6 MV photon beam. The radiation dose to thyroid, breast, lung, stomach, ovaries, bladder, liver, uterus, prostate and colon was measured using thermoluminescent dosimeters. The methodology, provided by the BEIR VII report was used for the second cancer risk estimations. Peripheral dose range for a simulated 5-year-old patient was 0.019%-1.572% of the given tumor dose. The corresponding range at the advanced patient age was reduced to 0.018%-1.468%. The second cancer risk per fraction for male patients varied from 3 to 215 per 1,000,000 patients depending upon the age at the time of exposure, primary cancer site and organ scattered dose. The corresponding risk for females was 1-1186 per 1,000,000 patients. The higher risk values were found for breast, thyroid and lung cancer development. The current data concerning the risk magnitude for developing subsequent neoplasms to various out-of-field organs may be of value for health care professionals in the follow-up studies of childhood cancer survivors. Copyright © 2012 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Evaluation of annual effective dose from indoor radon concentration in Eastern Province, Dammam, Saudi Arabia

NASA Astrophysics Data System (ADS)

Abuelhia, E.

2017-11-01

The aim of this study is to determine the indoor radon concentration and to evaluate the annual effective dose received by the inhabitants in Dammam, Al-Khobar, and compare it with new premises built at university of dammam. The research has been carried out by using active detection method; Electronic Radon Detector (RAD-7) a solid state α-detector with its special accessories. The indoor radon concentration measured varies from 10.2 Bqm-3 to 25.8 Bqm-3 with an average value of 18.8 Bqm-3 and 19.7 Bqm-3 to 23.5 Bqm-3 with an average value of 21.7 Bqm-3, in Dammam and Al-khobar dwellings, respectively. In university of dammam the radon concentration varies from 7.4 Bqm-3 to 15.8 Bqm-3 with an average value of 9.02 Bqm-3. The values of annual effective doses were found to be 0.47mSv/y, 0.55mSv/y, and 0.23mSv/y, in Dammam, Al-khobar and university new premises, respectively. The average radon concentration in the old dwellings was two times compared to that in the new premises and it was 25.4 Bqm-3 lower than the world average value of 40 Bqm-3 reported by the UNSCEAR. The annual effective doses in the old dwellings was found to be (0.55mSv/y) two times the doses received at the new premises, and below the world wide average of 1.15mSv/y reported by ICRP (2010). The indoor radon concentration in the study region is safe as far as health hazard is concerned.

Diagnostic x-ray dosimetry using Monte Carlo simulation.

PubMed

Ioppolo, J L; Price, R I; Tuchyna, T; Buckley, C E

2002-05-21

An Electron Gamma Shower version 4 (EGS4) based user code was developed to simulate the absorbed dose in humans during routine diagnostic radiological procedures. Measurements of absorbed dose using thermoluminescent dosimeters (TLDs) were compared directly with EGS4 simulations of absorbed dose in homogeneous, heterogeneous and anthropomorphic phantoms. Realistic voxel-based models characterizing the geometry of the phantoms were used as input to the EGS4 code. The voxel geometry of the anthropomorphic Rando phantom was derived from a CT scan of Rando. The 100 kVp diagnostic energy x-ray spectra of the apparatus used to irradiate the phantoms were measured, and provided as input to the EGS4 code. The TLDs were placed at evenly spaced points symmetrically about the central beam axis, which was perpendicular to the cathode-anode x-ray axis at a number of depths. The TLD measurements in the homogeneous and heterogenous phantoms were on average within 7% of the values calculated by EGS4. Estimates of effective dose with errors less than 10% required fewer numbers of photon histories (1 x 10(7)) than required for the calculation of dose profiles (1 x 10(9)). The EGS4 code was able to satisfactorily predict and thereby provide an instrument for reducing patient and staff effective dose imparted during radiological investigations.

Diagnostic x-ray dosimetry using Monte Carlo simulation

NASA Astrophysics Data System (ADS)

Ioppolo, J. L.; Price, R. I.; Tuchyna, T.; Buckley, C. E.

2002-05-01

An Electron Gamma Shower version 4 (EGS4) based user code was developed to simulate the absorbed dose in humans during routine diagnostic radiological procedures. Measurements of absorbed dose using thermoluminescent dosimeters (TLDs) were compared directly with EGS4 simulations of absorbed dose in homogeneous, heterogeneous and anthropomorphic phantoms. Realistic voxel-based models characterizing the geometry of the phantoms were used as input to the EGS4 code. The voxel geometry of the anthropomorphic Rando phantom was derived from a CT scan of Rando. The 100 kVp diagnostic energy x-ray spectra of the apparatus used to irradiate the phantoms were measured, and provided as input to the EGS4 code. The TLDs were placed at evenly spaced points symmetrically about the central beam axis, which was perpendicular to the cathode-anode x-ray axis at a number of depths. The TLD measurements in the homogeneous and heterogenous phantoms were on average within 7% of the values calculated by EGS4. Estimates of effective dose with errors less than 10% required fewer numbers of photon histories (1 × 107) than required for the calculation of dose profiles (1 × 109). The EGS4 code was able to satisfactorily predict and thereby provide an instrument for reducing patient and staff effective dose imparted during radiological investigations.

Internal thyroid doses to Fukushima residents—estimation and issues remaining

PubMed Central

Kim, Eunjoo; Kurihara, Osamu; Kunishima, Naoaki; Momose, Takumaro; Ishikawa, Tetsuo; Akashi, Makoto

2016-01-01

Enormous quantities of radionuclides were released into the environment following the disastrous accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011. It is of great importance to determine the exposure doses received by the populations living in the radiologically affected areas; however, there has been significant difficulty in estimating the internal thyroid dose received through the intake of short-lived radionuclides (mainly, 131I), because of the lack of early measurements on people. An estimation by the National Institute of Radiological Sciences for 1 April 2012 to 31 March 2013 was thus performed using a combination of the following three sources: thyroid measurement data (131I) for 1080 children examined in the screening campaign, whole-body counter measurement data (134Cs, 137Cs) for 3000 adults, and atmospheric transport dispersion model simulations. In this study, the residents of Futaba town, Iitate village and Iwaki city were shown to have the highest thyroid equivalent dose, and their doses were estimated to be mostly below 30 mSv. However, this result involved a lot of uncertainties and provided only representative values for the residents. The present paper outlines a more recent dose estimation and preliminary analyses of personal behavior data used in the new method. PMID:27538842

Spectrophotometric Measurement of Minimal Erythema Dose Sites after Narrowband Ultraviolet B Phototesting: Clinical Implication of Spetrophotometric Values in Phototherapy

PubMed Central

Jeon, Su-Young; Lee, Chae-Young; Song, Ki-Hoon

2014-01-01

Background The spectrophotometer is well known to be a useful tool for estimating the objective minimal erythema dose (MED) during planning of phototherapy protocol. However, only a few spectrophotometric values are used to evaluate the erythema and pigmentation of the MED site during phototesting. Objective To determinea new meaning of the relationships among spectrophotometric values during phototesting. Methods Twenty-five patients with psoriasis and 23 patients with vitiligo were selected before undergoing narrowband ultraviolet B phototherapy. We interpreted the gross findings of erythema and measured the L*a*b* values using a spectrophotometer at each phototest spot. We compared MEDs, basic spectrophotometric values (L*a*b*), and b*/L* values separately according to skin type, and determined the correlation of each spectrophotometric value and the correlation between a* and b*/L* values. Results Among L*a*b* values, only b* values showed a statistically significant difference between the type III and IV groups (p=0.003). There was a positive correlation only between MEDs and b* values (p<0.05). The average b*/L*value in the type IV group was significantly higher than the type III group (p<0.05). Conclusion The higher b* values in type IV skin indicates that skin tanning develops more prominently than type III. The correlation between MEDs and b* values may signify that the skin pigmentation status is deepened with the higher MEDs. The difference in b*/L*values between type III and IV skin reflects that the b*/L*value is thought to be an index of tanning. The a* value, known as an index of erythema, does not influence the degree of tanning. PMID:24648682

Analysis and recent advances in gamma heating measurements in MINERVE facility by using TLD and OSLD techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amharrak, H.; Di Salvo, J.; Lyoussi, A.

2011-07-01

The objective of this study is to develop nuclear heating measurement methods in Zero Power experimental reactors. This paper presents the analysis of Thermo-Luminescent Detector (TLD) and Optically Stimulated Luminescent Detectors (OSLD) experiments in the UO{sub 2} core of the MINERVE research reactor at the CEA Cadarache. The experimental sources of uncertainties on the gamma dose have been reduced by improving the conditions, as well as the repeatability, of the calibration step for each individual TLD. The interpretation of these measurements needs to take into account calculation of cavity correction factors, related to calibration and irradiation configurations, as well asmore » neutron corrections calculations. These calculations are based on Monte Carlo simulations of neutron-gamma and gamma-electron transport coupled particles. TLD and OSLD are positioned inside aluminum pillboxes. The comparison between calculated and measured integral gamma-ray absorbed doses using TLD, shows that calculation slightly overestimates the measurement with a C/E value equal to 1.05 {+-} 5.3 % (k = 2). By using OSLD, the calculation slightly underestimates the measurement with a C/E value equal to 0.96 {+-} 7.0% (k = 2. (authors)« less