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Sample records for 18mv photon beam

  1. Peripheral dose measurements for 6 and 18 MV photon beams on a linear accelerator with multileaf collimator

    SciTech Connect

    Mazonakis, Michalis; Zacharopoulou, Fotini; Varveris, Haralambos; Damilakis, John

    2008-10-15

    Peripheral dose (PD) to critical structures outside treatment volume is of clinical importance. The aim of the current study was to estimate PD on a linear accelerator equipped with multileaf collimator (MLC). Dose measurements were carried out using an ionization chamber embedded in a water phantom for 6 and 18 MV photon beams. PD values were acquired for field sizes from 5x5 to 20x20 cm{sup 2} in increments of 5 cm at distances up to 24 cm from the field edge. Dose data were obtained at two collimator orientations where the measurement points are shielded by MLC and jaws. The variation of PD with the source to skin distance (SSD), depth, and lateral displacement of the measurement point was evaluated. To examine the dependence of PD upon the tissue thickness at the entrance point of the beam, scattered dose was measured using thermoluminescent dosemeters placed on three anthropomorphic phantoms simulating 5- and 10-year-old children and an average adult patient. PD from 6 MV photons varied from 0.13% to 6.75% of the central-axis maximum dose depending upon the collimator orientation, extent of irradiated area, and distance from the treatment field. The corresponding dose range from 18 MV x rays was 0.09% to 5.61%. The variation of PD with depth and with lateral displacements up to 80% of the field dimension was very small. The scattered dose from both photon beams increased with the increase of SSD or tissue thickness along beam axis. The presented dosimetric data set allows the estimation of scattered dose outside the primary beam.

  2. Calculation of effective dose from measurements of secondary neutron spectra and scattered photon dose from dynamic MLC IMRT for 6 MV, 15 MV, and 18 MV beam energies.

    PubMed

    Howell, Rebecca M; Hertel, Nolan E; Wang, Zhonglu; Hutchinson, Jesson; Fullerton, Gary D

    2006-02-01

    Effective doses were calculated from the delivery of 6 MV, 15 MV, and 18 MV conventional and intensity-modulated radiation therapy (IMRT) prostate treatment plans. ICRP-60 tissue weighting factors were used for the calculations. Photon doses were measured in phantom for all beam energies. Neutron spectra were measured for 15 MV and 18 MV and ICRP-74 quality conversion factors used to calculate ambient dose equivalents. The ambient dose equivalents were corrected for each tissue using neutron depth dose data from the literature. The depth corrected neutron doses were then used as a measure of the neutron component of the ICRP protection quantity, organ equivalent dose. IMRT resulted in an increased photon dose to many organs. However, the IMRT treatments resulted in an overall decrease in effective dose compared to conventional radiotherapy. This decrease correlates to the ability of an intensity-modulated field to minimize dose to critical normal structures in close proximity to the treatment volume. In a comparison of the three beam energies used for the IMRT treatments, 6 MV resulted in the lowest effective dose, while 18 MV resulted in the highest effective dose. This is attributed to the large neutron contribution for 18 MV compared to no neutron contribution for 6 MV. PMID:16532941

  3. Comparison of the Effects of High-Energy Photon Beam Irradiation (10 and 18 MV) on 2 Types of Implantable Cardioverter-Defibrillators

    SciTech Connect

    Hashii, Haruko; Hashimoto, Takayuki; Okawa, Ayako; Shida, Koichi; Isobe, Tomonori; Hanmura, Masahiro; Nishimura, Tetsuo; Aonuma, Kazutaka; Sakae, Takeji; Sakurai, Hideyuki

    2013-03-01

    Purpose: Radiation therapy for cancer may be required for patients with implantable cardiac devices. However, the influence of secondary neutrons or scattered irradiation from high-energy photons (≥10 MV) on implantable cardioverter-defibrillators (ICDs) is unclear. This study was performed to examine this issue in 2 ICD models. Methods and Materials: ICDs were positioned around a water phantom under conditions simulating clinical radiation therapy. The ICDs were not irradiated directly. A control ICD was positioned 140 cm from the irradiation isocenter. Fractional irradiation was performed with 18-MV and 10-MV photon beams to give cumulative in-field doses of 600 Gy and 1600 Gy, respectively. Errors were checked after each fraction. Soft errors were defined as severe (change to safety back-up mode), moderate (memory interference, no changes in device parameters), and minor (slight memory change, undetectable by computer). Results: Hard errors were not observed. For the older ICD model, the incidences of severe, moderate, and minor soft errors at 18 MV were 0.75, 0.5, and 0.83/50 Gy at the isocenter. The corresponding data for 10 MV were 0.094, 0.063, and 0 /50 Gy. For the newer ICD model at 18 MV, these data were 0.083, 2.3, and 5.8 /50 Gy. Moderate and minor errors occurred at 18 MV in control ICDs placed 140 cm from the isocenter. The error incidences were 0, 1, and 0 /600 Gy at the isocenter for the newer model, and 0, 1, and 6 /600Gy for the older model. At 10 MV, no errors occurred in control ICDs. Conclusions: ICD errors occurred more frequently at 18 MV irradiation, which suggests that the errors were mainly caused by secondary neutrons. Soft errors of ICDs were observed with high energy photon beams, but most were not critical in the newer model. These errors may occur even when the device is far from the irradiation field.

  4. Energy spectra, angular spread, fluence profiles and dose distributions of 6 and 18 MV photon beams: results of Monte Carlo simulations for a Varian 2100EX accelerator

    NASA Astrophysics Data System (ADS)

    Ding, George X.

    2002-04-01

    The purpose of this study is to provide detailed characteristics of incident photon beams for different field sizes and beam energies. This information is critical to the future development of accurate treatment planning systems. It also enhances our knowledge of radiotherapy photon beams. The EGS4 Monte Carlo code, BEAM, has been used to simulate 6 and 18 MV photon beams from a Varian Clinac-2100EX accelerator. A simulated realistic beam is stored in a phase space data file, which contains details of each particle's complete history including where it has been and where it has interacted. The phase space files are analysed to obtain energy spectra, angular distribution, fluence profile and mean energy profiles at the phantom surface for particles separated according to their charge and history. The accuracy of a simulated beam is validated by the excellent agreement between the Monte Carlo calculated and measured dose distributions. Measured depth-dose curves are obtained from depth-ionization curves by accounting for newly introduced chamber fluence corrections and the stopping-power ratios for realistic beams. The study presents calculated depth-dose components from different particles as well as calculated surface dose and contribution from different particles to surface dose across the field. It is shown that the increase of surface dose with the increase of the field size is mainly due to the increase of incident contaminant charged particles. At 6 MV, the incident charged particles contribute 7% to 21% of maximum dose at the surface when the field size increases from 10 × 10 to 40 × 40 cm2. At 18 MV, their contributions are up to 11% and 29% of maximum dose at the surface for 10 × 10 cm2 and 40 × 40 cm2 fields respectively. However, the fluence of these incident charged particles is less than 1% of incident photon fluence in all cases.

  5. Varian 2100C/D Clinac 18 MV photon phase space file characterization and modeling by using MCNP Code

    NASA Astrophysics Data System (ADS)

    Ezzati, Ahad Ollah

    2015-07-01

    Multiple points and a spatial mesh based surface source model (MPSMBSS) was generated for 18MV Varian 2100 C/D Clinac phase space file (PSF) and implemented in MCNP code. The generated source model (SM) was benchmarked against PSF and measurements. PDDs and profiles were calculated using the SM and original PSF for different field sizes from 5 × 5 to 20 × 20 cm2. Agreement was within 2% of the maximum dose at 100cm SSD for beam profiles at the depths of 4cm and 15cm with respect to the original PSF. Differences between measured and calculated points were less than 2% of the maximum dose or 2mm distance to agreement (DTA) at 100 cm SSD. Thus it can be concluded that the modified MCNP code can be used for radiotherapy calculations including multiple source model (MSM) and using the source biasing capability of MPSMBSS can increase the simulation speed up to 3600 for field sizes smaller than 5 × 5 cm2.

  6. Tenth value layers for 60Co gamma rays and for 4, 6, 10, 15, and 18 MV x rays in concrete for beams of cone angles between 0 degrees and 14 degrees calculated by Monte Carlo simulation.

    PubMed

    Jaradat, Adnan K; Biggs, Peter J

    2007-05-01

    The calculation of shielding barrier thicknesses for radiation therapy facilities according to the NCRP formalism is based on the use of broad beams (that is, the maximum possible field sizes). However, in practice, treatment fields used in radiation therapy are, on average, less than half the maximum size. Indeed, many contemporary treatment techniques call for reduced field sizes to reduce co-morbidity and the risk of second cancers. Therefore, published tenth value layers (TVLs) for shielding materials do not apply to these very small fields. There is, hence, a need to determine the TVLs for various beam modalities as a function of field size. The attenuation of (60)Co gamma rays and photons of 4, 6, 10, 15, and 18 MV bremsstrahlung x ray beams by concrete has been studied using the Monte Carlo technique (MCNP version 4C2) for beams of half-opening angles of 0 degrees , 3 degrees , 6 degrees , 9 degrees , 12 degrees , and 14 degrees . The distance between the x-ray source and the distal surface of the shielding wall was fixed at 600 cm, a distance that is typical for modern radiation therapy rooms. The maximum concrete thickness varied between 76.5 cm and 151.5 cm for (60)Co and 18 MV x rays, respectively. Detectors were placed at 630 cm, 700 cm, and 800 cm from the source. TVLs have been determined down to the third TVL. Energy spectra for 4, 6, 10, 15, and 18 MV x rays for 10 x 10 cm(2) and 40 x 40 cm(2) field sizes were used to generate depth dose curves in water that were compared with experimentally measured values. PMID:17429304

  7. Constituent Components of Out-of-Field Scatter Dose for 18-MV Intensity Modulated Radiation Therapy Versus 3-Dimensional Conformal Radiation Therapy: A Comparison With 6-MV and Implications for Carcinogenesis

    SciTech Connect

    Ruben, Jeremy D.; Smith, Ryan; Lancaster, Craig M.; Haynes, Matthew; Jones, Phillip; Panettieri, Vanessa

    2014-11-01

    Purpose: To characterize and compare the components of out-of-field dose for 18-MV intensity modulated radiation therapy (IMRT) versus 3-dimensional conformal radiation therapy (3D-CRT) and their 6-MV counterparts and consider implications for second cancer induction. Methods and Materials: Comparable plans for each technique/energy were delivered to a water phantom with a sloping wall; under full scatter conditions; with field edge abutting but outside the bath to prevent internal/phantom scatter; and with shielding below the linear accelerator head to attenuate head leakage. Neutron measurements were obtained from published studies. Results: Eighteen-megavolt IMRT produces 1.7 times more out-of-field scatter than 18-MV 3D-CRT. In absolute terms, however, differences are just approximately 0.1% of central axis dose. Eighteen-megavolt IMRT reduces internal/patient scatter by 13%, but collimator scatter (C) is 2.6 times greater than 18-MV 3D-CRT. Head leakage (L) is minimal. Increased out-of-field photon scatter from 18-MV IMRT carries out-of-field second cancer risks of approximately 0.2% over and above the 0.4% from 18-MV 3D-CRT. Greater photoneutron dose from 18-MV IMRT may result in further maximal, absolute increased risk to peripheral tissue of approximately 1.2% over 18-MV 3D-CRT. Out-of-field photon scatter remains comparable for the same modality irrespective of beam energy. Machine scatter (C+L) from 18 versus 6 MV is 1.2 times higher for IMRT and 1.8 times for 3D-CRT. It is 4 times higher for 6-MV IMRT versus 3D-CRT. Reduction in internal scatter with 18 MV versus 6 MV is 27% for 3D-CRT and 29% for IMRT. Compared with 6-MV 3D-CRT, 18-MV IMRT increases out-of-field second cancer risk by 0.2% from photons and adds 0.28-2.2% from neutrons. Conclusions: Out-of-field photon dose seems to be independent of beam energy for both techniques. Eighteen-megavolt IMRT increases out-of-field scatter 1.7-fold over 3D-CRT because of greater collimator scatter despite

  8. Prostatic thermoluminescent dosimeter analysis in a patient treated with 18 MV X rays through a prosthetic hip

    SciTech Connect

    Hazuka, M.B.; Stroud, D.N.; Adams, J.; Ibbott, G.S.; Kinzie, J.J. )

    1993-01-15

    External beam radiation therapy with high energy photon beams through hip protheses has been shown to cause dose inhomogeneities for target volumes in the pelvis. In this work, measurements of dose using thermoluminescent dosimetry were compared with dose calculations from a computerized treatment planning system in a patient with prostatic carcinoma and a cobalt-chromium-molybdenum hip prosthesis. A 39% decrement in dose at isocenter was demonstrated for an 18 MV photon beam passing through the prosthesis. A discrepancy of only 3.1% was shown between measured and calculated dose when the tissue-maximum ratio (TMR) method of heterogeneity correction was used. However, it is recognized that several sources of error are possible when heterogeneity corrections are performed for high density prostheses and these are discussed below. The results of this work stress the importance of accurate data for use with the ratio of TMR's' algorithm in order that accurate treatment planning can be performed.

  9. Volumetric Arc Therapy and Intensity-Modulated Radiotherapy for Primary Prostate Radiotherapy With Simultaneous Integrated Boost to Intraprostatic Lesion With 6 and 18 MV: A Planning Comparison Study

    SciTech Connect

    Ost, Piet; Speleers, Bruno; De Meerleer, Gert; De Neve, Wilfried; Fonteyne, Valerie; Villeirs, Geert; De Gersem, Werner

    2011-03-01

    Purpose: The aim of the present study was to compare intensity-modulated radiotherapy (IMRT) with volumetric arc therapy (VMAT), in the treatment of prostate cancer with maximal dose escalation to the intraprostatic lesion (IPL), without violating the organ-at-risk constraints. Additionally, the use of 6-MV photons was compared with 18-MV photons for all techniques. Methods and Materials: A total of 12 consecutive prostate cancer patients with an IPL on magnetic resonance imaging were selected for the present study. Plans were made for three IMRT field setups (three, five, and seven fields) and one VMAT field setup (single arc). First, optimal plans were created for every technique using biologic and physical planning aims. Next, an additional escalation to the IPL was planned as high as possible without violating the planning aims of the first step. Results: No interaction between the technique and photon energy (p = .928) occurred. No differences were found between the 6- and 18-MV photon beams, except for a reduction in the number of monitor units needed for 18 MV (p < .05). All techniques, except for three-field IMRT, allowed for dose escalation to a median dose of {>=}93 {+-} 6 Gy (mean {+-} standard deviation) to the IPL. VMAT was superior to IMRT for rectal volumes receiving 20-50 Gy (p < .05). Conclusion: VMAT allowed for dose escalation to the IPL with better sparing of the rectum than static three-, five-, and seven-field IMRT setups. High-energy photons had no advantage over low-energy photons.

  10. Photon beam position monitor

    DOEpatents

    Kuzay, Tuncer M.; Shu, Deming

    1995-01-01

    A photon beam position monitor for use in the front end of a beamline of a high heat flux and high energy photon source such as a synchrotron radiation storage ring detects and measures the position and, when a pair of such monitors are used in tandem, the slope of a photon beam emanating from an insertion device such as a wiggler or an undulator inserted in the straight sections of the ring. The photon beam position monitor includes a plurality of spaced blades for precisely locating the photon beam, with each blade comprised of chemical vapor deposition (CVD) diamond with an outer metal coating of a photon sensitive metal such as tungsten, molybdenum, etc., which combination emits electrons when a high energy photon beam is incident upon the blade. Two such monitors are contemplated for use in the front end of the beamline, with the two monitors having vertically and horizontally offset detector blades to avoid blade "shadowing". Provision is made for aligning the detector blades with the photon beam and limiting detector blade temperature during operation.

  11. Photon beam position monitor

    DOEpatents

    Kuzay, T.M.; Shu, D.

    1995-02-07

    A photon beam position monitor is disclosed for use in the front end of a beamline of a high heat flux and high energy photon source such as a synchrotron radiation storage ring detects and measures the position and, when a pair of such monitors are used in tandem, the slope of a photon beam emanating from an insertion device such as a wiggler or an undulator inserted in the straight sections of the ring. The photon beam position monitor includes a plurality of spaced blades for precisely locating the photon beam, with each blade comprised of chemical vapor deposition (CVD) diamond with an outer metal coating of a photon sensitive metal such as tungsten, molybdenum, etc., which combination emits electrons when a high energy photon beam is incident upon the blade. Two such monitors are contemplated for use in the front end of the beamline, with the two monitors having vertically and horizontally offset detector blades to avoid blade ''shadowing''. Provision is made for aligning the detector blades with the photon beam and limiting detector blade temperature during operation. 18 figs.

  12. Second step of the upgrading of the Strasbourg MP (16 18 MV)

    NASA Astrophysics Data System (ADS)

    Letournel, M.; Oberlin, J. C.; Heng, G.; Heugel, J.; Wagner, P.

    1984-02-01

    Following a first upgrade, the Strasbourg MP Tandem operated 16 MV. A second stage was recently completed and in July 1982 the MP ran at 18 MV with beam for the first time. This second stage consisted of two main parts, first the installation of a new number 1 accelerator tube of 96″ length and second the installation of a Vivitron portico which modifiers radially the distribution of the stored energy and the radial field.

  13. A model to calculate the induced dose rate around an 18 MV ELEKTA linear accelerator.

    PubMed

    Perrin, Bruce; Walker, Anne; Mackay, Ranald

    2003-03-01

    The dose rate due to activity induced by (gamma, n) reactions around an ELEKTA Precise accelerator running at 18 MV is reported. A model to calculate the induced dose rate for a variety of working practices has been derived and compared to the measured values. From this model, the dose received by the staff using the machine can be estimated. From measured dose rates at the face of the linear accelerator for a 10 x 10 cm2 jaw setting at 18 MV an activation coefficient per MU was derived for each of the major activation products. The relative dose rates at points around the linac head, for different energy and jaw settings, were measured. Dose rates adjacent to the patient support system and portal imager were also measured. A model to calculate the dose rate at these points was derived, and compared to those measured over a typical working week. The model was then used to estimate the maximum dose to therapists for the current working schedule on this machine. Calculated dose rates at the linac face agreed to within +/- 12% of those measured over a week, with a typical dose rate of 4.5 microSv h(-1) 2 min after the beam has stopped. The estimated maximum annual whole body dose for a treatment therapist, with the machine treating at only 18 MV, for 60000 MUs per week was 2.5 mSv. This compares well with value of 2.9 mSv published for a Clinac 21EX. A model has been derived to calculate the dose from the four dominant activation products of an ELEKTA Precise 18 MV linear accelerator. This model is a useful tool to calculate the induced dose rate around the treatment head. The model can be used to estimate the dose to the staff for typical working patterns. PMID:12696804

  14. Photon Collider Physics with Real Photon Beams

    SciTech Connect

    Gronberg, J; Asztalos, S

    2005-11-03

    Photon-photon interactions have been an important probe into fundamental particle physics. Until recently, the only way to produce photon-photon collisions was parasitically in the collision of charged particles. Recent advances in short-pulse laser technology have made it possible to consider producing high intensity, tightly focused beams of real photons through Compton scattering. A linear e{sup +}e{sup -} collider could thus be transformed into a photon-photon collider with the addition of high power lasers. In this paper they show that it is possible to make a competitive photon-photon collider experiment using the currently mothballed Stanford Linear Collider. This would produce photon-photon collisions in the GeV energy range which would allow the discovery and study of exotic heavy mesons with spin states of zero and two.

  15. Dependences of mucosal dose on photon beams in head-and-neck intensity-modulated radiation therapy: a Monte Carlo study

    SciTech Connect

    Chow, James C.L.; Owrangi, Amir M.

    2012-07-01

    Dependences of mucosal dose in the oral or nasal cavity on the beam energy, beam angle, multibeam configuration, and mucosal thickness were studied for small photon fields using Monte Carlo simulations (EGSnrc-based code), which were validated by measurements. Cylindrical mucosa phantoms (mucosal thickness = 1, 2, and 3 mm) with and without the bone and air inhomogeneities were irradiated by the 6- and 18-MV photon beams (field size = 1 Multiplication-Sign 1 cm{sup 2}) with gantry angles equal to 0 Degree-Sign , 90 Degree-Sign , and 180 Degree-Sign , and multibeam configurations using 2, 4, and 8 photon beams in different orientations around the phantom. Doses along the central beam axis in the mucosal tissue were calculated. The mucosal surface doses were found to decrease slightly (1% for the 6-MV photon beam and 3% for the 18-MV beam) with an increase of mucosal thickness from 1-3 mm, when the beam angle is 0 Degree-Sign . The variation of mucosal surface dose with its thickness became insignificant when the beam angle was changed to 180 Degree-Sign , but the dose at the bone-mucosa interface was found to increase (28% for the 6-MV photon beam and 20% for the 18-MV beam) with the mucosal thickness. For different multibeam configurations, the dependence of mucosal dose on its thickness became insignificant when the number of photon beams around the mucosal tissue was increased. The mucosal dose with bone was varied with the beam energy, beam angle, multibeam configuration and mucosal thickness for a small segmental photon field. These dosimetric variations are important to consider improving the treatment strategy, so the mucosal complications in head-and-neck intensity-modulated radiation therapy can be minimized.

  16. Characterization of electron contamination in megavoltage photon beams

    SciTech Connect

    Medina, Antonio Lopez; Teijeiro, Antonio; Garcia, Juan; Esperon, Jorge; Terron, J. Antonio; Ruiz, Diego P.; Carrion, Maria C.

    2005-05-01

    The purpose of the present study is to characterize electron contamination in photon beams in different clinical situations. Variations with field size, beam modifier (tray, shaping block) and source-surface distance (SSD) were studied. Percentage depth dose measurements with and without a purging magnet and replacing the air by helium were performed to identify the two electron sources that are clearly differentiated: air and treatment head. Previous analytical methods were used to fit the measured data, exploring the validity of these models. Electrons generated in the treatment head are more energetic and more important for larger field sizes, shorter SSD, and greater depths. This difference is much more noticeable for the 18 MV beam than for the 6 MV beam. If a tray is used as beam modifier, electron contamination increases, but the energy of these electrons is similar to that of electrons coming from the treatment head. Electron contamination could be fitted to a modified exponential curve. For machine modeling in a treatment planning system, setting SSD at 90 cm for input data could reduce errors for most isocentric treatments, because they will be delivered for SSD ranging from 80 to 100 cm. For very small field sizes, air-generated electrons must be considered independently, because of their different energetic spectrum and dosimetric influence.

  17. Peripheral photon and neutron doses from prostate cancer external beam irradiation.

    PubMed

    Bezak, Eva; Takam, Rundgham; Marcu, Loredana G

    2015-12-01

    Peripheral photon and neutron doses from external beam radiotherapy (EBRT) are associated with increased risk of carcinogenesis in the out-of-field organs; thus, dose estimations of secondary radiation are imperative. Peripheral photon and neutron doses from EBRT of prostate carcinoma were measured in Rando phantom. (6)LiF:Mg,Cu,P and (7)LiF:Mg,Cu,P glass-rod thermoluminescence dosemeters (TLDs) were inserted in slices of a Rando phantom followed by exposure to 80 Gy with 18-MV photon four-field 3D-CRT technique. The TLDs were calibrated using 6- and 18-MV X-ray beam. Neutron dose equivalents measured with CR-39 etch-track detectors were used to derive readout-to-neutron dose conversion factor for (6)LiF:Mg,Cu,P TLDs. Average neutron dose equivalents per 1 Gy of isocentre dose were 3.8±0.9 mSv Gy(-1) for thyroid and 7.0±5.4 mSv Gy(-1) for colon. For photons, the average dose equivalents per 1 Gy of isocentre dose were 0.2±0.1 mSv Gy(-1) for thyroid and 8.1±9.7 mSv Gy(-1) for colon. Paired (6)LiF:Mg,Cu,P and (7)LiF:Mg,Cu,P TLDs can be used to measure photon and neutron doses simultaneously. Organs in close proximity to target received larger doses from photons than those from neutrons whereas distally located organs received higher neutron versus photon dose. PMID:25564673

  18. High flux photon beam monitor

    SciTech Connect

    Mortazavi, P.; Woodle, M.; Rarback, H.; Shu, D.; Howells, M.

    1985-01-01

    We have designed two photon beam position monitors for use on our x-ray storage ring beam lines. In both designs, a pair of tungsten blades, separated by a pre-determined gap, intercepts a small fraction of the incoming beam. Due to photoemission, an electrical signal is generated which is proportional to the amount of beam intercepted. The thermal load deposited in the blade is transferred by a heat pipe to a heat exchanger outside the vacuum chamber. A prototype monitor with gap adjustment capability was fabricated and tested at a uv beam line. The results show that the generated electrical signal is a good measurement of the photon beam position. In the following sections, design features and test results are discussed.

  19. Photoneutron contamination from an 18 MV Saturne medical linear accelerator in the treatment room.

    PubMed

    Khosravi, Mostafa; Shahbazi-Gahrouei, Daryoush; Jabbari, Keyvan; Nasri-Nasrabadi, Mehdi; Baradaran-Ghahfarokhi, Milad; Siavashpour, Zahra; Gheisari, Ruhollah; Amiri, Behnam

    2013-09-01

    Dose escalation with high-energy X rays of medical linear accelerators (linacs) in radiotherapy offers several distinct advantages over the lower energy photons. However, owing to photoneutron reactions, interaction of high-energy photons (>8 MV) with various high-Z nuclei of the materials in the linac head components produces unavoidable neutrons. The aim of this study was to evaluate the photoneutron dose equivalent per unit therapeutic X-ray dose of 18 MV, GE Saturne 20 linac in the treatment room using Monte Carlo (MC) MCNP linac head full simulation as well as thermoluminescence dosemeter measurements. This machine is one of the old linac models manufactured by General Electric Company; however, it is widely used in the developing countries because of low cost and simple maintenance for radiotherapy applications. The results showed a significant photoneutron dose from Saturne 20 linac head components especially at distances near the linac head (<150 cm). Results of this work could be used in several applications, especially designing bunker and entrance door shielding against neutrons produced by photoneutron reactions in GE Saturne 20. However, a detailed cost optimisation for a specific room would require a dedicated calculation. PMID:23538892

  20. Modelling of electron contamination in clinical photon beams for Monte Carlo dose calculation

    NASA Astrophysics Data System (ADS)

    Yang, J.; Li, J. S.; Qin, L.; Xiong, W.; Ma, C.-M.

    2004-06-01

    The purpose of this work is to model electron contamination in clinical photon beams and to commission the source model using measured data for Monte Carlo treatment planning. In this work, a planar source is used to represent the contaminant electrons at a plane above the upper jaws. The source size depends on the dimensions of the field size at the isocentre. The energy spectra of the contaminant electrons are predetermined using Monte Carlo simulations for photon beams from different clinical accelerators. A 'random creep' method is employed to derive the weight of the electron contamination source by matching Monte Carlo calculated monoenergetic photon and electron percent depth-dose (PDD) curves with measured PDD curves. We have integrated this electron contamination source into a previously developed multiple source model and validated the model for photon beams from Siemens PRIMUS accelerators. The EGS4 based Monte Carlo user code BEAM and MCSIM were used for linac head simulation and dose calculation. The Monte Carlo calculated dose distributions were compared with measured data. Our results showed good agreement (less than 2% or 2 mm) for 6, 10 and 18 MV photon beams.

  1. A 3D pencil-beam-based superposition algorithm for photon dose calculation in heterogeneous media

    NASA Astrophysics Data System (ADS)

    Tillikainen, L.; Helminen, H.; Torsti, T.; Siljamäki, S.; Alakuijala, J.; Pyyry, J.; Ulmer, W.

    2008-07-01

    In this work, a novel three-dimensional superposition algorithm for photon dose calculation is presented. The dose calculation is performed as a superposition of pencil beams, which are modified based on tissue electron densities. The pencil beams have been derived from Monte Carlo simulations, and are separated into lateral and depth-directed components. The lateral component is modeled using exponential functions, which allows accurate modeling of lateral scatter in heterogeneous tissues. The depth-directed component represents the total energy deposited on each plane, which is spread out using the lateral scatter functions. Finally, convolution in the depth direction is applied to account for tissue interface effects. The method can be used with the previously introduced multiple-source model for clinical settings. The method was compared against Monte Carlo simulations in several phantoms including lung- and bone-type heterogeneities. Comparisons were made for several field sizes for 6 and 18 MV energies. The deviations were generally within (2%, 2 mm) of the field central axis dmax. Significantly larger deviations (up to 8%) were found only for the smallest field in the lung slab phantom for 18 MV. The presented method was found to be accurate in a wide range of conditions making it suitable for clinical planning purposes.

  2. Photon-beam subsource sensitivity to the initial electron-beam parameters

    SciTech Connect

    Fix, Michael K.; Keall, Paul J.; Siebers, Jeffrey V.

    2005-04-01

    One limitation to the widespread implementation of Monte Carlo (MC) patient dose-calculation algorithms for radiotherapy is the lack of a general and accurate source model of the accelerator radiation source. Our aim in this work is to investigate the sensitivity of the photon-beam subsource distributions in a MC source model (with target, primary collimator, and flattening filter photon subsources and an electron subsource) for 6- and 18-MV photon beams when the energy and radial distributions of initial electrons striking a linac target change. For this purpose, phase-space data (PSD) was calculated for various mean electron energies striking the target, various normally distributed electron energy spread, and various normally distributed electron radial intensity distributions. All PSD was analyzed in terms of energy, fluence, and energy fluence distributions, which were compared between the different parameter sets. The energy spread was found to have a negligible influence on the subsource distributions. The mean energy and radial intensity significantly changed the target subsource distribution shapes and intensities. For the primary collimator and flattening filter subsources, the distribution shapes of the fluence and energy fluence changed little for different mean electron energies striking the target, however, their relative intensity compared with the target subsource change, which can be accounted for by a scaling factor. This study indicates that adjustments to MC source models can likely be limited to adjusting the target subsource in conjunction with scaling the relative intensity and energy spectrum of the primary collimator, flattening filter, and electron subsources when the energy and radial distributions of the initial electron-beam change.

  3. Modeling transmission and scatter for photon beam attenuators.

    PubMed

    Ahnesjö, A; Weber, L; Nilsson, P

    1995-11-01

    The development of treatment planning methods in radiation therapy requires dose calculation methods that are both accurate and general enough to provide a dose per unit monitor setting for a broad variety of fields and beam modifiers. The purpose of this work was to develop models for calculation of scatter and transmission for photon beam attenuators such as compensating filters, wedges, and block trays. The attenuation of the beam is calculated using a spectrum of the beam, and a correction factor based on attenuation measurements. Small angle coherent scatter and electron binding effects on scattering cross sections are considered by use of a correction factor. Quality changes in beam penetrability and energy fluence to dose conversion are modeled by use of the calculated primary beam spectrum after passage through the attenuator. The beam spectra are derived by the depth dose effective method, i.e., by minimizing the difference between measured and calculated depth dose distributions, where the calculated distributions are derived by superposing data from a database for monoenergetic photons. The attenuator scatter is integrated over the area viewed from the calculation point of view using first scatter theory. Calculations are simplified by replacing the energy and angular-dependent cross-section formulas with the forward scatter constant r2(0) and a set of parametrized correction functions. The set of corrections include functions for the Compton energy loss, scatter attenuation, and secondary bremsstrahlung production. The effect of charged particle contamination is bypassed by avoiding use of dmax for absolute dose calibrations. The results of the model are compared with scatter measurements in air for copper and lead filters and with dose to a water phantom for lead filters for 4 and 18 MV. For attenuated beams, downstream of the buildup region, the calculated results agree with measurements on the 1.5% level. The accuracy was slightly less in situations

  4. On Monte Carlo modeling of megavoltage photon beams: A revisited study on the sensitivity of beam parameters

    SciTech Connect

    Chibani, Omar; Moftah, Belal; Ma, C.-M. Charlie

    2011-01-15

    Purpose: To commission Monte Carlo beam models for five Varian megavoltage photon beams (4, 6, 10, 15, and 18 MV). The goal is to closely match measured dose distributions in water for a wide range of field sizes (from 2x2 to 35x35 cm{sup 2}). The second objective is to reinvestigate the sensitivity of the calculated dose distributions to variations in the primary electron beam parameters. Methods: The GEPTS Monte Carlo code is used for photon beam simulations and dose calculations. The linear accelerator geometric models are based on (i) manufacturer specifications, (ii) corrections made by Chibani and Ma [''On the discrepancies between Monte Carlo dose calculations and measurements for the 18 MV Varian photon beam,'' Med. Phys. 34, 1206-1216 (2007)], and (iii) more recent drawings. Measurements were performed using pinpoint and Farmer ionization chambers, depending on the field size. Phase space calculations for small fields were performed with and without angle-based photon splitting. In addition to the three commonly used primary electron beam parameters (E{sub AV} is the mean energy, FWHM is the energy spectrum broadening, and R is the beam radius), the angular divergence ({theta}) of primary electrons is also considered. Results: The calculated and measured dose distributions agreed to within 1% local difference at any depth beyond 1 cm for different energies and for field sizes varying from 2x2 to 35x35 cm{sup 2}. In the penumbra regions, the distance to agreement is better than 0.5 mm, except for 15 MV (0.4-1 mm). The measured and calculated output factors agreed to within 1.2%. The 6, 10, and 18 MV beam models use {theta}=0 deg., while the 4 and 15 MV beam models require {theta}=0.5 deg. and 0.6 deg., respectively. The parameter sensitivity study shows that varying the beam parameters around the solution can lead to 5% differences with measurements for small (e.g., 2x2 cm{sup 2}) and large (e.g., 35x35 cm{sup 2}) fields, while a perfect agreement is

  5. Geant4 simulations on medical Linac operation at 18 MV: Experimental validation based on activation foils

    NASA Astrophysics Data System (ADS)

    Vagena, E.; Stoulos, S.; Manolopoulou, M.

    2016-03-01

    The operation of a medical linear accelerator was simulated using the Geant4 code regarding to study the characteristics of an 18 MeV photon beam. Simulations showed that (a) the photon spectrum at the isocenter is not influenced by changes of the primary electron beam's energy distribution and spatial spread (b) 98% of the photon energy fluence scored at the isocenter is primary photons that have only interacted with the target (c) the number of contaminant electrons is not negligible since it fluctuated around 5×10-5 per primary electron or 2.40×10-3 per photon at the isocenter (d) the number of neutrons that are created by (γ, n) reactions is 3.13×10-6 per primary electron or 1.50×10-3 per photon at the isocenter (e) a flattening filter free beam needs less primary electrons in order to deliver the same photon fluence at the isocenter than a normal flattening filter operation (f) there is no significant increase of the surface dose due to the contaminant electrons by removing the flattening filter (g) comparing the neutron fluences per incident electron for the flattened and unflattened beam, the neutron fluencies is 7% higher for the unflattened beams. To validate the simulations results, the total neutron and photon fluence at the isocenter field were measured using nickel, indium, and natural uranium activation foils. The percentage difference between simulations and measurements was 1.26% in case of uranium and 2.45% in case of the indium foil regarding photon fluencies while for neutrons the discrepancy is higher up to 8.0%. The photon and neutron fluencies of the simulated experiments fall within a range of ±1 and ±2 sigma error, respectively, compared to the ones obtained experimentally.

  6. Monte Carlo study of the energy and angular dependence of the response of plastic scintillation detectors in photon beams

    PubMed Central

    Wang, Lilie L. W.; Klein, David; Beddar, A. Sam

    2010-01-01

    Purpose: By using Monte Carlo simulations, the authors investigated the energy and angular dependence of the response of plastic scintillation detectors (PSDs) in photon beams. Methods: Three PSDs were modeled in this study: A plastic scintillator (BC-400) and a scintillating fiber (BCF-12), both attached by a plastic-core optical fiber stem, and a plastic scintillator (BC-400) attached by an air-core optical fiber stem with a silica tube coated with silver. The authors then calculated, with low statistical uncertainty, the energy and angular dependences of the PSDs’ responses in a water phantom. For energy dependence, the response of the detectors is calculated as the detector dose per unit water dose. The perturbation caused by the optical fiber stem connected to the PSD to guide the optical light to a photodetector was studied in simulations using different optical fiber materials. Results: For the energy dependence of the PSDs in photon beams, the PSDs with plastic-core fiber have excellent energy independence within about 0.5% at photon energies ranging from 300 keV (monoenergetic) to 18 MV (linac beam). The PSD with an air-core optical fiber with a silica tube also has good energy independence within 1% in the same photon energy range. For the angular dependence, the relative response of all the three modeled PSDs is within 2% for all the angles in a 6 MV photon beam. This is also true in a 300 keV monoenergetic photon beam for PSDs with plastic-core fiber. For the PSD with an air-core fiber with a silica tube in the 300 keV beam, the relative response varies within 1% for most of the angles, except in the case when the fiber stem is pointing right to the radiation source in which case the PSD may over-response by more than 10%. Conclusions: At ±1% level, no beam energy correction is necessary for the response of all three PSDs modeled in this study in the photon energy ranges from 200 keV (monoenergetic) to 18 MV (linac beam). The PSD would be even closer

  7. Monte Carlo estimation of photoneutrons spectra and dose equivalent around an 18 MV medical linear accelerator

    NASA Astrophysics Data System (ADS)

    Alem-Bezoubiri, A.; Bezoubiri, F.; Badreddine, A.; Mazrou, H.; Lounis-Mokrani, Z.

    2014-04-01

    A fully detailed Monte Carlo geometrical model of an 18 MV Varian Clinac 2100C medical linear accelerator, lodged at Blida Anti-Cancer Centre in Algeria, was developed during this study to estimate the photoneutrons spectra and doses at the patient table in a radiotherapy treatment room, for radiation protection purposes.

  8. Monte Carlo source model for photon beam radiotherapy: photon source characteristics

    SciTech Connect

    Fix, Michael K.; Keall, Paul J.; Dawson, Kathryn; Siebers, Jeffrey V.

    2004-11-01

    A major barrier to widespread clinical implementation of Monte Carlo dose calculation is the difficulty in characterizing the radiation source within a generalized source model. This work aims to develop a generalized three-component source model (target, primary collimator, flattening filter) for 6- and 18-MV photon beams that match full phase-space data (PSD). Subsource by subsource comparison of dose distributions, using either source PSD or the source model as input, allows accurate source characterization and has the potential to ease the commissioning procedure, since it is possible to obtain information about which subsource needs to be tuned. This source model is unique in that, compared to previous source models, it retains additional correlations among PS variables, which improves accuracy at nonstandard source-to-surface distances (SSDs). In our study, three-dimensional (3D) dose calculations were performed for SSDs ranging from 50 to 200 cm and for field sizes from 1x1 to 30x30 cm{sup 2} as well as a 10x10 cm{sup 2} field 5 cm off axis in each direction. The 3D dose distributions, using either full PSD or the source model as input, were compared in terms of dose-difference and distance-to-agreement. With this model, over 99% of the voxels agreed within {+-}1% or 1 mm for the target, within 2% or 2 mm for the primary collimator, and within {+-}2.5% or 2 mm for the flattening filter in all cases studied. For the dose distributions, 99% of the dose voxels agreed within 1% or 1 mm when the combined source model--including a charged particle source and the full PSD as input--was used. The accurate and general characterization of each photon source and knowledge of the subsource dose distributions should facilitate source model commissioning procedures by allowing scaling the histogram distributions representing the subsources to be tuned.

  9. Effect of Photon Beam Energy, Gold Nanoparticle Size and Concentration on the Dose Enhancement in Radiation Therapy

    PubMed Central

    Mesbahi, Asghar; Jamali, Farideh; garehaghaji, Nahideh

    2013-01-01

    Introduction Gold nanoparticles have been used as radiation dose enhancing materials in recent investigations. In the current study, dose enhancement effect of gold nanoparticles on tumor cells was evaluated using Monte Carlo (MC) simulation. Methods We used MCNPX code for MC modeling in the current study. A water phantom and a tumor region with a size of 1×1×1 cm3 loaded with gold nanoparticles were simulated. The macroscopic dose enhancement factor was calculated for gold nanoparticles with sizes of 30, 50, and 100 nm. Also, we simulated different photon beams including mono-energetic beams (50-120 keV), a Cobalt-60 beam, 6 & 18 MV photon beams of a conventional linear accelerator. Results We found a dose enhancement factor (DEF) of from 1.4 to 3.7 for monoenergetic kilovoltage beams, while the DEFs for megavoltage beams were negligible and less than 3% for all GNP sizes and concentrations. The optimum energy for higher DEF was found to be the 90 keV monoenergetic beam. The effect of GNP size was not considerable, but the GNP concentration had a substantial impact on achieved DEF in GNP-based radiation therapy. Conclusion The results were in close agreement with some previous studies considering the effect of photon energy and GNP concentration on observed DEF. Application of GNP-based radiation therapy using kilovoltage beams is recommended. PMID:23678467

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

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    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 (γ) 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 × 10 cm2 field at the first density interface from tissue to lung equivalent material. Small fields (2 × 2 cm2) 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

  11. SU-E-T-560: Monte Carlo Simulation of the Neutron Radiation Field Around a Medical 18 MV Linac

    SciTech Connect

    Horst, F; Czarnecki, D; Zink, K

    2015-06-15

    Purpose: Today the majority of radiation therapy treatments are performed at medical electron linear accelerators (linacs). The accelerated electrons are used for the generation of bremsstrahlung photons. The use of higher electron respectively photon energies has some advantages over lower energies such as the longer dose build-up. However photons with energies higher than ∼7 MeV can additionally to the interaction with bound electrons undergo inelastic reactions with nuclei. These photonuclear reactions lead to the emission of fast neutrons which contaminate the primary photon field. The neutrons might penetrate through the collimators and deliver out-of-field dose to the patient. Furthermore the materials inside the linac head as well as the air inside the treatment room get activated which might deliver dose to the medical employees even when the linac is not in operation. A detailed knowledge of these effects is essential for adequate radiation protection of the employees and an optimal patient treatment. Methods: It is a common method to study the radiation fields of such linacs by means of Monte Carlo simulations. For the investigation of the effects caused by photonuclear reactions a typical linac in high energy mode (Varian Clinac 18 MV-X) as well as the surrounding bunker were modelled and simulated using the Monte Carlo code FLUKA which includes extensive nuclear reaction and neutron transport models additional to electron-photon transport as well as capabilities for a detailed study of effective dose distributions and activation yields. Results: Neutron spectra as well as neutron effective dose distributions within the bunker were obtained, reaching up to some mSv/Gy in the patient’s plane. The results are normalized per Gy in the depth dose maximum at 10×10 cm{sup 2} field size. Therefore an absolute interpretation is possible. Conclusion: The obtained data gives a better understanding of the photonuclear reaction caused effects.

  12. Modulated photon radiotherapy (XMRT): an algorithm for the simultaneous optimization of photon beamlet energy and intensity in external beam radiotherapy (EBRT) planning

    NASA Astrophysics Data System (ADS)

    McGeachy, Philip; Villarreal-Barajas, Jose Eduardo; Zinchenko, Yuriy; Khan, Rao

    2016-02-01

    This is a proof of principle study on an algorithm for optimizing external beam radiotherapy in terms of both photon beamlet energy and fluence. This simultaneous beamlet energy and fluence optimization is denoted modulated photon radiotherapy (XMRT). XMRT is compared with single-energy intensity modulated radiotherapy (IMRT) for five clinically relevant test geometries to determine whether treating beamlet energy as a decision variable improves the dose distributions. All test geometries were modelled in a cylindrical water phantom. XMRT optimized the fluence for 6 and 18 MV beamlets while IMRT optimized with only 6 MV and only 18 MV. CERR (computational environment for radiotherapy research) was used to calculate the dose deposition matrices and the resulting dose for XMRT and IMRT solutions. Solutions were compared via their dose volume histograms and dose metrics, such as the mean, maximum, and minimum doses for each structure. The homogeneity index (HI) and conformity number (CN) were calculated to assess the quality of the target dose coverage. Complexity of the resulting fluence maps was minimized using the sum of positive gradients technique. The results showed XMRT’s ability to improve healthy-organ dose reduction while yielding comparable coverage of the target relative to IMRT for all geometries. All three energy-optimization approaches yielded similar HI and CNs for all geometries, as well as a similar degree of fluence map complexity. The dose reduction provided by XMRT was demonstrated by the relative decrease in the dose metrics for the majority of the organs at risk (OARs) in all geometries. Largest reductions ranged between 5% to 10% in the mean dose to OARs for two of the geometries when compared with both single-energy IMRT schemes. XMRT has shown potential dosimetric benefits through improved OAR sparing by allowing beam energy to act as a degree of freedom in the EBRT optimization process.

  13. Modulated photon radiotherapy (XMRT): an algorithm for the simultaneous optimization of photon beamlet energy and intensity in external beam radiotherapy (EBRT) planning.

    PubMed

    McGeachy, Philip; Villarreal-Barajas, Jose Eduardo; Zinchenko, Yuriy; Khan, Rao

    2016-02-21

    This is a proof of principle study on an algorithm for optimizing external beam radiotherapy in terms of both photon beamlet energy and fluence. This simultaneous beamlet energy and fluence optimization is denoted modulated photon radiotherapy (XMRT). XMRT is compared with single-energy intensity modulated radiotherapy (IMRT) for five clinically relevant test geometries to determine whether treating beamlet energy as a decision variable improves the dose distributions. All test geometries were modelled in a cylindrical water phantom. XMRT optimized the fluence for 6 and 18 MV beamlets while IMRT optimized with only 6 MV and only 18 MV. CERR (computational environment for radiotherapy research) was used to calculate the dose deposition matrices and the resulting dose for XMRT and IMRT solutions. Solutions were compared via their dose volume histograms and dose metrics, such as the mean, maximum, and minimum doses for each structure. The homogeneity index (HI) and conformity number (CN) were calculated to assess the quality of the target dose coverage. Complexity of the resulting fluence maps was minimized using the sum of positive gradients technique. The results showed XMRT's ability to improve healthy-organ dose reduction while yielding comparable coverage of the target relative to IMRT for all geometries. All three energy-optimization approaches yielded similar HI and CNs for all geometries, as well as a similar degree of fluence map complexity. The dose reduction provided by XMRT was demonstrated by the relative decrease in the dose metrics for the majority of the organs at risk (OARs) in all geometries. Largest reductions ranged between 5% to 10% in the mean dose to OARs for two of the geometries when compared with both single-energy IMRT schemes. XMRT has shown potential dosimetric benefits through improved OAR sparing by allowing beam energy to act as a degree of freedom in the EBRT optimization process. PMID:26808280

  14. Photon-Electron Interaction and Condense Beams

    SciTech Connect

    Chattopadhyay, S.

    1998-11-01

    We discuss beams of charged particles and radiation from multiple perspectives. These include fundamental acceleration and radiation mechanisms, underlying electron-photon interaction, various classical and quantum phase-space concepts and fluctuational interpretations.

  15. Nuclear astrophysics with intense photon beam

    SciTech Connect

    Shizuma, Toshiyuki

    2012-07-09

    Quasi-monochromatic photon beams generated by inverse Compton scattering of laser light with high energy electrons can be used for precise measurements of photoneutrons and resonant scattered {gamma} rays. Extremely high intensity and small energy spreading width of the photon beam expected at the ELI Nuclear Physics facility would increase the experimental sensitivities considerably. Possible photonuclear reaction measurements relevant to the p-process nucleosynthesis are discussed.

  16. Validation of a new grid-based Boltzmann equation solver for dose calculation in radiotherapy with photon beams

    NASA Astrophysics Data System (ADS)

    Vassiliev, Oleg N.; Wareing, Todd A.; McGhee, John; Failla, Gregory; Salehpour, Mohammad R.; Mourtada, Firas

    2010-02-01

    A new grid-based Boltzmann equation solver, Acuros™, was developed specifically for performing accurate and rapid radiotherapy dose calculations. In this study we benchmarked its performance against Monte Carlo for 6 and 18 MV photon beams in heterogeneous media. Acuros solves the coupled Boltzmann transport equations for neutral and charged particles on a locally adaptive Cartesian grid. The Acuros solver is an optimized rewrite of the general purpose Attila© software, and for comparable accuracy levels, it is roughly an order of magnitude faster than Attila. Comparisons were made between Monte Carlo (EGSnrc) and Acuros for 6 and 18 MV photon beams impinging on a slab phantom comprising tissue, bone and lung materials. To provide an accurate reference solution, Monte Carlo simulations were run to a tight statistical uncertainty (σ ≈ 0.1%) and fine resolution (1-2 mm). Acuros results were output on a 2 mm cubic voxel grid encompassing the entire phantom. Comparisons were also made for a breast treatment plan on an anthropomorphic phantom. For the slab phantom in regions where the dose exceeded 10% of the maximum dose, agreement between Acuros and Monte Carlo was within 2% of the local dose or 1 mm distance to agreement. For the breast case, agreement was within 2% of local dose or 2 mm distance to agreement in 99.9% of voxels where the dose exceeded 10% of the prescription dose. Elsewhere, in low dose regions, agreement for all cases was within 1% of the maximum dose. Since all Acuros calculations required less than 5 min on a dual-core two-processor workstation, it is efficient enough for routine clinical use. Additionally, since Acuros calculation times are only weakly dependent on the number of beams, Acuros may ideally be suited to arc therapies, where current clinical algorithms may incur long calculation times.

  17. Variation of sensitometric curves of radiographic films in high energy photon beams.

    PubMed

    Danciu, C; Proimos, B S; Rosenwald, J C; Mijnheer, B J

    2001-06-01

    Film dosimetry is an important tool for the verification of irradiation techniques. The shape of the sensitometric curve depends on the type of film as well as on the irradiation and processing conditions. Existing data concerning the influence of irradiation geometry on the sensitometric curve are conflicting. In particular the variation of optical density, OD, with field size and depth in a phantom shows large differences in magnitude between various authors. This variation, as well as the effect of beam energy and film plane orientation on OD, was therefore investigated for two types of film, Kodak X-Omat V and Agfa Structurix D2. Films were positioned in a solid phantom, either perpendicular or (almost) parallel to the beam axis, and irradiated to different dose levels using various photon beams (Co-60, 6 MV, 15 MV, 18 MV, 45 MV). It was found that the sensitometric curves of the Kodak film derived at different depths are almost identical for the four x-ray beams. For the Kodak film the differences in OD with depth are less than 2%, except for the Co-60 beam, where the difference is about 4% at 10 cm depth for a 15 cm x 15 cm field. The slope of the sensitometric curve of the Agfa film is somewhat more dependent on photon beam energy, depth and field size. The sensitometric curves of both types of film are almost independent of the film plane orientation, except for shallow depths. For Co-60 and for the same dose, the Kodak and Agfa films gave at dose maximum an OD lower by 4% and 6%, respectively, for the parallel compared to the perpendicular geometry. Good dosimetric results can be obtained if films from the same batch are irradiated with small to moderate field sizes (up to about 15 cm x 15 cm), at moderate depths (up to about 15 cm), using a single calibration curve, e.g., for a 10 cm x 10 cm field. PMID:11439493

  18. Ambient neutron dose equivalent outside concrete vault rooms for 15 and 18 MV radiotherapy accelerators.

    PubMed

    Martínez-Ovalle, S A; Barquero, R; Gómez-Ros, J M; Lallena, A M

    2012-03-01

    In this work, the ambient dose equivalent, H*(10), due to neutrons outside three bunkers that house a 15- and a 18-MV Varian Clinac 2100C/D and a 15-MV Elekta Inor clinical linacs, has been calculated. The Monte Carlo code MCNPX (v. 2.5) has been used to simulate the neutron production and transport. The complete geometries including linacs and full installations have been built up according to the specifications of the manufacturers and the planes provided by the corresponding medical physical services of the hospitals where the three linacs operate. Two of these installations, those lodging the Varian linacs, have an entrance door to the bunker while the other one does not, although it has a maze with two bends. Various treatment orientations were simulated in order to establish plausible annual equivalent doses. Specifically anterior-posterior, posterior-anterior, left lateral, right lateral orientations and an additional one with the gantry rotated 30° have been studied. Significant dose rates have been found only behind the walls and the door of the bunker, near the entrance and the console, with a maximum of 12 µSv h(-1). Dose rates per year have been calculated assuming a conservative workload for the three facilities. The higher dose rates in the corresponding control areas were 799 µSv y(-1), in the case of the facility which operates the 15-MV Clinac, 159 µSv y(-1), for that with the 15-MV Elekta, and 21 µSv y(-1) for the facility housing the 18-MV Varian. A comparison with measurements performed in similar installations has been carried out and a reasonable agreement has been found. The results obtained indicate that the neutron contamination does not increase the doses above the legal limits and does not produce a significant enhancement of the dose equivalent calculated. When doses are below the detection limits provided by the measuring devices available today, MCNPX simulation provides an useful method to evaluate neutron dose equivalents based

  19. Monte Carlo calculations of correction factors for plastic phantoms in clinical photon and electron beam dosimetry.

    PubMed

    Araki, Fujio; Hanyu, Yuji; Fukuoka, Miyoko; Matsumoto, Kenji; Okumura, Masahiko; Oguchi, Hiroshi

    2009-07-01

    The purpose of this study is to calculate correction factors for plastic water (PW) and plastic water diagnostic-therapy (PWDT) phantoms in clinical photon and electron beam dosimetry using the EGSnrc Monte Carlo code system. A water-to-plastic ionization conversion factor k(pl) for PW and PWDT was computed for several commonly used Farmer-type ionization chambers with different wall materials in the range of 4-18 MV photon beams. For electron beams, a depth-scaling factor c(pl) and a chamber-dependent fluence correction factor h(pl) for both phantoms were also calculated in combination with NACP-02 and Roos plane-parallel ionization chambers in the range of 4-18 MeV. The h(pl) values for the plane-parallel chambers were evaluated from the electron fluence correction factor phi(pl)w and wall correction factors P(wall,w) and P(wall,pl) for a combination of water or plastic materials. The calculated k(pl) and h(pl) values were verified by comparison with the measured values. A set of k(pl) values computed for the Farmer-type chambers was equal to unity within 0.5% for PW and PWDT in photon beams. The k(pl) values also agreed within their combined uncertainty with the measured data. For electron beams, the c(pl) values computed for PW and PWDT were from 0.998 to 1.000 and from 0.992 to 0.997, respectively, in the range of 4-18 MeV. The phi(pl)w values for PW and PWDT were from 0.998 to 1.001 and from 1.004 to 1.001, respectively, at a reference depth in the range of 4-18 MeV. The difference in P(wall) between water and plastic materials for the plane-parallel chambers was 0.8% at a maximum. Finally, h(pl) values evaluated for plastic materials were equal to unity within 0.6% for NACP-02 and Roos chambers. The h(pl) values also agreed within their combined uncertainty with the measured data. The absorbed dose to water from ionization chamber measurements in PW and PWDT plastic materials corresponds to that in water within 1%. Both phantoms can thus be used as a

  20. On beam quality and flatness of radiotherapy megavoltage photon beams

    PubMed Central

    Hossain, Murshed; Rhoades, Jeffrey

    2015-01-01

    Ratio of percentage depth dose (PDD) at two depths, PDD at a depth of 10 cm (PDD10), and beam flatness are monitored regularly for radiotherapy beams for quality assurance. The purpose of this study is to understand the effects of changes in one of these parameters on the other. Is it possible to monitor only the beam flatness and not PDD? The investigation has two components. Naturally occurring i.e., unintended changes in PDD ratio and in-plane flatness for 6 and 10 MV photon beams for one particular Siemens Artiste Linac are monitored for a period of about 4 years. Secondly, deliberate changes in the beam parameters are induced by changing the bending magnet current (BMI). Relationships between various beam parameters for unintended changes as well as deliberate changes are characterized. Long term unintentional changes of PDD ratio are found to have no systematic trend. The flatness in the inplane direction for 6 and 10 MV beams show slow increase of 0.43% and 0.75% respectively in about 4 years while the changes in the PDD ratio show no such trend. Over 10% changes in BMI are required to induce changes in the beam quality indices at 2% level. PDD ratio for the 10 MV beam is found to be less sensitive, while the depth of maximum dose, dmax, is more sensitive to the changes in BMI compared to the 6 MV beam. Tolerances are more stringent for PDD10 than PDD ratio for the 10 MV beam. PDD ratio, PDD10, and flatness must be monitored independently. Furthermore, off axis ratio alone cannot be used to monitor flatness. The effect of beam quality change in the absolute dose is clinically insignificant. PMID:26634604

  1. Verification of the pure alanine in PMMA tube dosimeter applicability for dosimetry of radiotherapy photon beams: a feasibility study.

    PubMed

    Al-Karmi, Anan M; Ayaz, Ali Asghar H; Al-Enezi, Mamdouh S; Abdel-Rahman, Wamied; Dwaikat, Nidal

    2015-09-01

    Alanine dosimeters in the form of pure alanine powder in PMMA plastic tubes were investigated for dosimetry in a clinical application. Electron paramagnetic resonance (EPR) spectroscopy was used to measure absorbed radiation doses by detection of signals from radicals generated in irradiated alanine. The measurements were performed for low-dose ranges typical for single-fraction doses often used in external photon beam radiotherapy. First, the dosimeters were irradiated in a solid water phantom to establish calibration curves in the dose range from 0.3 to 3 Gy for 6 and 18 MV X-ray beams from a clinical linear accelerator. Next, the dosimeters were placed at various locations in an anthropomorphic pelvic phantom to measure the dose delivery of a conventional four-field box technique treatment plan to the pelvis. Finally, the doses measured with alanine dosimeters were compared against the doses calculated with a commercial treatment planning system (TPS). The results showed that the alanine dosimeters have a highly sensitive dose response with good linearity and no energy dependence in the dose range and photon beams used in this work. Also, a fairly good agreement was found between the in-phantom dose measurements with alanine dosimeters and the TPS dose calculations. The mean value of the ratios of measured to calculated dose values was found to be near unity. The measured points in the in-field region passed dose-difference acceptance criterion of 3% and those in the penumbral region passed distance-to-agreement acceptance criterion of 3 mm. These findings suggest that the pure alanine powder in PMMA tube dosimeter is a suitable option for dosimetry of radiotherapy photon beams. PMID:26138456

  2. Multiple beam splitter for single photons

    SciTech Connect

    Wang Tun; Kostrun, Marijan; Yelin, S.F.

    2004-11-01

    We propose a method using 'light storage' and fractional stimulated Raman adiabatic passage (F-STIRAP) to get entangled multiple Fock states from a single photon. A light storage technique is used to store the quantum information of a single-photon pulse in atoms. F-STIRAP pulses then split the stored coherence, such that reading pulses retrieve the quantum information from this new coherence. Since each reading pulse only retrieves part of the total coherence, we can obtain entangled multiple Fock states with arbitrary relative amplitude. This method to create entanglement is versatile for obtaining frequency, time, and/or spatial entanglement. Indeed, we obtain a multiple beam splitter with easily adjustable parameters.

  3. Effect of Gold Nanoparticles on Prostate Dose Distribution under Ir-192 Internal and 18 MV External Radiotherapy Procedures Using Gel Dosimetry and Monte Carlo Method

    PubMed Central

    Khosravi, H.; Hashemi, B.; Mahdavi, S. R.; Hejazi, P.

    2015-01-01

    Background Gel polymers are considered as new dosimeters for determining radiotherapy dose distribution in three dimensions. Objective The ability of a new formulation of MAGIC-f polymer gel was assessed by experimental measurement and Monte Carlo (MC) method for studying the effect of gold nanoparticles (GNPs) in prostate dose distributions under the internal Ir-192 and external 18MV radiotherapy practices. Method A Plexiglas phantom was made representing human pelvis. The GNP shaving 15 nm in diameter and 0.1 mM concentration were synthesized using chemical reduction method. Then, a new formulation of MAGIC-f gel was synthesized. The fabricated gel was poured in the tubes located at the prostate (with and without the GNPs) and bladder locations of the phantom. The phantom was irradiated to an Ir-192 source and 18 MV beam of a Varian linac separately based on common radiotherapy procedures used for prostate cancer. After 24 hours, the irradiated gels were read using a Siemens 1.5 Tesla MRI scanner. The absolute doses at the reference points and isodose curves resulted from the experimental measurement of the gels and MC simulations following the internal and external radiotherapy practices were compared. Results The mean absorbed doses measured with the gel in the presence of the GNPs in prostate were 15% and 8 % higher than the corresponding values without the GNPs under the internal and external radiation therapies, respectively. MC simulations also indicated a dose increase of 14 % and 7 % due to presence of the GNPs, for the same experimental internal and external radiotherapy practices, respectively. Conclusion There was a good agreement between the dose enhancement factors (DEFs) estimated with MC simulations and experiment gel measurements due to the GNPs. The results indicated that the polymer gel dosimetry method as developed and used in this study, can be recommended as a reliable method for investigating the DEF of GNPs in internal and external

  4. Two-photon flow cytometer with laser scanning Bessel beams

    NASA Astrophysics Data System (ADS)

    Wang, Yongdong; Ding, Yu; Ray, Supriyo; Paez, Aurelio; Xiao, Chuan; Li, Chunqiang

    2016-03-01

    Flow cytometry is an important technique in biomedical discovery for cell counting, cell sorting and biomarker detection. In vivo flow cytometers, based on one-photon or two-photon excited fluorescence, have been developed for more than a decade. One drawback of laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is fairly small due to the short Rayleigh range of a focused Gaussian beam. Hence, the sampling volume is much smaller than one-photon flow cytometry, which makes it challenging to count or detect rare circulating cells in vivo. Bessel beams have narrow intensity profiles with an effective spot size (FWHM) as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making it an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Bessel beams rather than a Gaussian beam is the fact that Bessel beams have small concentric side rings that contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using scanned Bessel beams to form a light sheet that intersects the micro fluidic channel.

  5. Photonic crystal devices formed by a charged-particle beam

    DOEpatents

    Lin, Shawn-Yu; Koops, Hans W. P.

    2000-01-01

    A photonic crystal device and method. The photonic crystal device comprises a substrate with at least one photonic crystal formed thereon by a charged-particle beam deposition method. Each photonic crystal comprises a plurality of spaced elements having a composition different from the substrate, and may further include one or more impurity elements substituted for spaced elements. Embodiments of the present invention may be provided as electromagnetic wave filters, polarizers, resonators, sources, mirrors, beam directors and antennas for use at wavelengths in the range from about 0.2 to 200 microns or longer. Additionally, photonic crystal devices may be provided with one or more electromagnetic waveguides adjacent to a photonic crystal for forming integrated electromagnetic circuits for use at optical, infrared, or millimeter-wave frequencies.

  6. A photon beam position monitor for SSRL beamline 9

    SciTech Connect

    Cerino, J.A.; Rabedeau, T.; Bowen, W.

    1995-10-01

    We present here the concept of a simple one dimensional photon beam position monitor for use with high power synchrotron radiation beams. It has micron resolution, reasonable linearity in an inexpensive design. Most important, is its insensitivity to diffusely scattered low energy radiation from components upstream of the monitor.

  7. Optical microscope using an interferometric source of two-color, two-beam entangled photons

    DOEpatents

    Dress, William B.; Kisner, Roger A.; Richards, Roger K.

    2004-07-13

    Systems and methods are described for an optical microscope using an interferometric source of multi-color, multi-beam entangled photons. A method includes: downconverting a beam of coherent energy to provide a beam of multi-color entangled photons; converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; transforming at least a portion of the converged multi-color entangled photon beam by interaction with a sample to generate an entangled photon specimen beam; and combining the entangled photon specimen beam with an entangled photon reference beam within a single beamsplitter. An apparatus includes: a multi-refringent device providing a beam of multi-color entangled photons; a condenser device optically coupled to the multi-refringent device, the condenser device converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; a beam probe director and specimen assembly optically coupled to the condenser device; and a beam splitter optically coupled to the beam probe director and specimen assembly, the beam splitter combining an entangled photon specimen beam from the beam probe director and specimen assembly with an entangled photon reference beam.

  8. Clad photon sieve for generating localized hollow beams

    NASA Astrophysics Data System (ADS)

    Cheng, Yiguang; Tong, Junmin; Zhu, Jiangping; Liu, Junbo; Hu, Song; He, Yu

    2016-02-01

    A novel photon sieve structure called clad photon sieve is proposed to generate localized hollow beams and its design principle and focusing properties are studied. The clad photon sieve is composed of the internal zone and external zone with pinholes being positioned on the dark zones. Pinholes in the internal zone and in the external zone give destructive interference to the focus, leading to localized hollow beams being generated on the focal plane. Focusing properties of clad photon sieve with different focal lengths, zone numbers and modulation factors are also studied by theoretical calculations, numerical simulations and experiments, showing that the central dark spot size can be controlled by the focal length and rings number, and the intensity of the central dark spot varies with different modulation factors related with the internal zone and the external zone. This photon sieve can be useful for trapping and manipulating of particles and cooling of atoms.

  9. Fast IMRT with narrow high energy scanned photon beams

    SciTech Connect

    Andreassen, Bjoern; Straaring t, Sara Janek; Holmberg, Rickard; Naefstadius, Peder; Brahme, Anders

    2011-08-15

    Purpose: Since the first publications on intensity modulated radiation therapy (IMRT) in the early 1980s almost all efforts have been focused on fairly time consuming dynamic or segmental multileaf collimation. With narrow fast scanned photon beams, the flexibility and accuracy in beam shaping increases, not least in combination with fast penumbra trimming multileaf collimators. Previously, experiments have been performed with full range targets, generating a broad bremsstrahlung beam, in combination with multileaf collimators or material compensators. In the present publication, the first measurements with fast narrow high energy (50 MV) scanned photon beams are presented indicating an interesting performance increase even though some of the hardware used were suboptimal. Methods: Inverse therapy planning was used to calculate optimal scanning patterns to generate dose distributions with interesting properties for fast IMRT. To fully utilize the dose distributional advantages with scanned beams, it is necessary to use narrow high energy beams from a thin bremsstrahlung target and a powerful purging magnet capable of deflecting the transmitted electron beam away from the generated photons onto a dedicated electron collector. During the present measurements the scanning system, purging magnet, and electron collimator in the treatment head of the MM50 racetrack accelerator was used with 3-6 mm thick bremsstrahlung targets of beryllium. The dose distributions were measured with diodes in water and with EDR2 film in PMMA. Monte Carlo simulations with geant4 were used to study the influence of the electrons transmitted through the target on the photon pencil beam kernel. Results: The full width at half-maximum (FWHM) of the scanned photon beam was 34 mm measured at isocenter, below 9.5 cm of water, 1 m from the 3 mm Be bremsstrahlung target. To generate a homogeneous dose distribution in a 10 x 10 cm{sup 2} field, the authors used a spot matrix of 100 equal intensity

  10. Calculation of effective doses for broad parallel photon beams.

    PubMed

    Kim, C H; Reece, W D; Poston, J W

    1999-02-01

    Values of effective dose (E) were calculated for the entire range of incident directions of broad parallel photon beams for selected photon energies using the Monte Carlo N-Particle (MCNP) transport code with a hermaphroditic phantom. The calculated results are presented in terms of conversion coefficients transforming air kerma to effective dose. This study also compared the numerical values of E and H(E) over the entire range of incident beam directions. E was always less than H(E) considering all beam directions and photon energies, but the differences were not significant except when a photon beam approaches some specific directions (overhead and underfoot). This result suggests that the current H(E) values can be directly interpreted as E or, at least, as a conservative value of E without knowing the details of irradiation geometries. Finally, based on the distributions of H(E) and E over the beam directions, this study proposes ideal angular response factors for personal dosimeters that can be used to improve the angular response properties of personal dosimeters for off-normal incident photons. PMID:9929126

  11. Fast resonant target vibrating wire scanner for photon beam

    NASA Astrophysics Data System (ADS)

    Arutunian, S. G.; Chung, M.; Harutyunyan, G. S.; Margaryan, A. V.; Lazareva, E. G.; Lazarev, L. M.; Shahinyan, L. A.

    2016-02-01

    We propose a new type of wire scanner for beam profile measurements, based on the use of a vibrating wire as a scattering target. Synchronous measurements with the wire oscillation allow to detect only the signal coming from the scattering of the beam on the wire. This resonant method enables fast beam profiling in the presence of a high level of background. The developed wire scanner, called resonant target vibrating wire scanner, is applied to photon beam profiling, in which the photons reflected on the wire are measured by a fast photodiode. In addition, the proposed measurement principle is expected to monitor other types of beams as well, such as neutrons, protons, electrons, and ions.

  12. Fast resonant target vibrating wire scanner for photon beam.

    PubMed

    Arutunian, S G; Chung, M; Harutyunyan, G S; Margaryan, A V; Lazareva, E G; Lazarev, L M; Shahinyan, L A

    2016-02-01

    We propose a new type of wire scanner for beam profile measurements, based on the use of a vibrating wire as a scattering target. Synchronous measurements with the wire oscillation allow to detect only the signal coming from the scattering of the beam on the wire. This resonant method enables fast beam profiling in the presence of a high level of background. The developed wire scanner, called resonant target vibrating wire scanner, is applied to photon beam profiling, in which the photons reflected on the wire are measured by a fast photodiode. In addition, the proposed measurement principle is expected to monitor other types of beams as well, such as neutrons, protons, electrons, and ions. PMID:26931835

  13. A general photon source model for clinical linac heads in photon mode

    NASA Astrophysics Data System (ADS)

    González, W.; García-Ferreira, I.-B.; Anguiano, M.; Lallena, A. M.

    2015-12-01

    In this work a general photon source model has been developed to describe clinical linac heads when operating in photon mode. Six different linacs (three operating at 6 MV, one at 15 MV and two at 18 MV) have been studied. The construction of the model as well as its validation have been carried out on the base of the virtual linac approach in which the complete linac geometries have been simulated with the Monte Carlo code PENELOPE. The model includes a primary and a secondary sources whose geometrical characteristics are determined from a set of simulated fluence distributions in air. The photon energy distributions are obtained from the Monte Carlo energy distributions of the photons moving along the beam axis, using a softening function that depends on the nominal energy of the beam and a Compton-like correction. To verify the model, output factors, percentage depth doses and transverse profiles in water obtained from a calculation performed with the complete geometry are compared to those found with the source model. A reasonable agreement is obtained in all cases analyzed except for the 18 MV Mevatron KDS linac for the 20 cm× 20 cm field.

  14. Photon beam characterization and modelling for Monte Carlo treatment planning

    NASA Astrophysics Data System (ADS)

    Deng, Jun; Jiang, Steve B.; Kapur, Ajay; Li, Jinsheng; Pawlicki, Todd; Ma, C.-M.

    2000-02-01

    Photon beams of 4, 6 and 15 MV from Varian Clinac 2100C and 2300C/D accelerators were simulated using the EGS4/BEAM code system. The accelerators were modelled as a combination of component modules (CMs) consisting of a target, primary collimator, exit window, flattening filter, monitor chamber, secondary collimator, ring collimator, photon jaws and protection window. A full phase space file was scored directly above the upper photon jaws and analysed using beam data processing software, BEAMDP, to derive the beam characteristics, such as planar fluence, angular distribution, energy spectrum and the fractional contributions of each individual CM. A multiple-source model has been further developed to reconstruct the original phase space. Separate sources were created with accurate source intensity, energy, fluence and angular distributions for the target, primary collimator and flattening filter. Good agreement (within 2%) between the Monte Carlo calculations with the source model and those with the original phase space was achieved in the dose distributions for field sizes of 4 cm × 4 cm to 40 cm × 40 cm at source surface distances (SSDs) of 80-120 cm. The dose distributions in lung and bone heterogeneous phantoms have also been found to be in good agreement (within 2%) for 4, 6 and 15 MV photon beams for various field sizes between the Monte Carlo calculations with the source model and those with the original phase space.

  15. Exit Dose Measurement in Therapeutic High Energy Photon Beams and Cobalt-60 Gamma Rays

    NASA Astrophysics Data System (ADS)

    Sathiyan, S.; Ravikumar, M.

    2007-01-01

    To estimate the skin dose to the patient from the treatment planning, the knowledge about exit dose is essential, which is calculated from the percentage depth dose. In this study 6 MV and 18 MV beams from linear accelerator and cobalt-60 beams were used. The ionometric measurements were carried out with parallel plate chamber of sensitive volume 0.16 cc. Parallel plate chamber was fitted in to 30 x 30 cm2 polystyrene phantom at a fixed FSD with the measuring entrance window facing farther from the source. The field size for this measuring condition was maintained at 10 x 10 cm2. The ionization measurements were also carried out by changing the thickness of the polystyrene phantom at the entrance side of the point of measurement. In order to find out the variation of relative exit dose (RED) with field size the measurements were carried out without and with the full back-scattering material (27.2 gm/cm2) placed beyond the entrance window of the chamber. The measurements were also done for the entrance polystyrene phantom thicknesses of 10, 20 and 30 cm for the field size ranging from 5 x 5 cm2 to 30 x 30 cm2. The dose at the exit surface with no backscatter material is about 4.4%, 3.7% and 5.8% less than the dose with the full backscatter material present beyond the point of measurement for 6 MV, 18 MV X-rays and cobalt-60 gamma rays. The reduction in exit dose does not depend much of the phantom thickness through which the beam traverses before exiting at the chamber side. Dose enhancements of about 1.03 times were observed for a field size of 5 x 5 cm2 for 6 MV, 18 MV X-rays and cobalt-60 gamma rays. The dose enhancement factor (DEF) values were noticed to vary with field size beyond 15 x 15 cm2 for all the energies studied. Also it can be observed that the dose enhancement factor (DEF) values do not depend on the thickness of the phantom material through which the beam has traversed. The DEF values were found to vary marginally for different phantom material

  16. Monte Carlo study of photon fields from a flattening filter-free clinical accelerator

    SciTech Connect

    Vassiliev, Oleg N.; Titt, Uwe; Kry, Stephen F.; Poenisch, Falk; Gillin, Michael T.; Mohan, Radhe

    2006-04-15

    In conventional clinical linear accelerators, the flattening filter scatters and absorbs a large fraction of primary photons. Increasing the beam-on time, which also increases the out-of-field exposure to patients, compensates for the reduction in photon fluence. In recent years, intensity modulated radiation therapy has been introduced, yielding better dose distributions than conventional three-dimensional conformal therapy. The drawback of this method is the further increase in beam-on time. An accelerator with the flattening filter removed, which would increase photon fluence greatly, could deliver considerably higher dose rates. The objective of the present study is to investigate the dosimetric properties of 6 and 18 MV photon beams from an accelerator without a flattening filter. The dosimetric data were generated using the Monte Carlo programs BEAMnrc and DOSXYZnrc. The accelerator model was based on the Varian Clinac 2100 design. We compared depth doses, dose rates, lateral profiles, doses outside collimation, total and collimator scatter factors for an accelerator with and without a flatteneing filter. The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.

  17. Synchrotron beam test with a photon-counting pixel detector.

    PubMed

    Brönnimann, C; Florin, S; Lindner, M; Schmitt, B; Schulze-Briese, C

    2000-09-01

    Synchrotron beam measurements were performed with a single-photon-counting pixel detector to investigate the influence of threshold settings on charge sharing. Improvement of image homogeneity by adjusting the threshold of each pixel individually was demonstrated. With a flat-field correction, the homogeneity could be improved. A measurement of the point spread function is reported. PMID:16609212

  18. Measuring the photon energy scale through test beam data

    NASA Astrophysics Data System (ADS)

    Loureiro, Karina Flavia

    This dissertation aims at measuring the photon energy scale combining specialized Monte Carlo simulation with data taken during the combined ATLAS test beam in 2004. This work explains the steps taken to arrive at the photon energy scale, starting from the knowledge acquired for electrons. The chapters are structured as follows: Chapters 1 and 2 briefly introduce this work and the motivation behind it. Chapter 3 gives an overview of the LHC experiment and the ATLAS detector as a whole. Chapters 4 and 5 address in detail the ATLAS electromagnetic calorimeter and signal reconstruction at the cell level. Chapter 6 concentrates on the setup for the combined test beam with emphasis on the photon run. Chapter 7 details the event selection strategy used for the photon run analysis. Chapter 8 describes the generation and tuning of the special Monte Carlo for the photon run. Chapter 9 focuses on the highly specialized Monte Carlo studies that employed special calibration objects known as calibration hits. Chapter 10 details the methodology behind the measurement of the photon scale and evaluates it in terms of the electromagnetic calorimeter resolution. Chapters 11 and 12 present a summary of the results and the conclusions, respectively.

  19. Metastable Krypton Beam Source via Two-Photon Pumping Technique

    SciTech Connect

    Wong, W.W.; Young, L.

    2003-01-01

    Metastable beams of rare gas atoms have wide applications in chemical analysis of samples, as well as in aiding understanding of fundamental processes and physical attributes. Most current sources of metastable rare gas atomic beams, however, are limited in their flux density, which greatly reduces their utility in applications such as low level trace analysis and precision measurements. Previous work has demonstrated feasibility of metastable krypton production via two-photon pumping, and this paper extends that possibility into beam form. Further optimization on this scheme, moreover, promises 100-fold increase of metastable krypton flux density over that of an rf-driven discharge.

  20. Radial Moment Calculations of Coupled Electron-Photon Beams

    SciTech Connect

    FRANKE,BRIAN C.; LARSEN,EDWARD W.

    2000-07-19

    The authors consider the steady-state transport of normally incident pencil beams of radiation in slabs of material. A method has been developed for determining the exact radial moments of 3-D beams of radiation as a function of depth into the slab, by solving systems of 1-D transport equations. They implement these radial moment equations in the ONEBFP discrete ordinates code and simulate energy-dependent, coupled electron-photon beams using CEPXS-generated cross sections. Modified P{sub N} synthetic acceleration is employed to speed up the iterative convergence of the 1-D charged particle calculations. For high-energy photon beams, a hybrid Monte Carlo/discrete ordinates method is examined. They demonstrate the efficiency of the calculations and make comparisons with 3-D Monte Carlo calculations. Thus, by solving 1-D transport equations, they obtain realistic multidimensional information concerning the broadening of electron-photon beams. This information is relevant to fields such as industrial radiography, medical imaging, radiation oncology, particle accelerators, and lasers.

  1. Fundamental limits on beam stability at the Advanced Photon Source.

    SciTech Connect

    Decker, G. A.

    1998-06-18

    Orbit correction is now routinely performed at the few-micron level in the Advanced Photon Source (APS) storage ring. Three diagnostics are presently in use to measure and control both AC and DC orbit motions: broad-band turn-by-turn rf beam position monitors (BPMs), narrow-band switched heterodyne receivers, and photoemission-style x-ray beam position monitors. Each type of diagnostic has its own set of systematic error effects that place limits on the ultimate pointing stability of x-ray beams supplied to users at the APS. Limiting sources of beam motion at present are magnet power supply noise, girder vibration, and thermal timescale vacuum chamber and girder motion. This paper will investigate the present limitations on orbit correction, and will delve into the upgrades necessary to achieve true sub-micron beam stability.

  2. CVD diamond screens for photon beam imaging at PETRA III

    NASA Astrophysics Data System (ADS)

    Degenhardt, M.; Aprigliano, G.; Schulte-Schrepping, H.; Hahn, U.; Grabosch, H.-J.; Wörner, E.

    2013-03-01

    PETRA III, the most brilliant storage-ring-based synchrotron radiation source in the world, started its operation in 2009. It features 14 undulator beamlines and will be extended by further 10 beamlines in the PETRA III extension project. During the startup phase of the 14 PETRA III beamlines, fluorescence monitors based on CVD diamond screens have proven to be a very powerful tool for the monitoring of the attenuated undulator beams and for the commissioning of the optical components, e.g. slit systems and monochromators. They served as the essential instrument for the initial setup of the positron beam orbit to align the undulator photon beam along the beamline. The application of CVD diamond screens for the beam imaging at PETRA III beamlines is presented. Images taken during the beam adjustment and the beamline commissioning are shown.

  3. High intensity X/γ photon beams for nuclear physics and photonics

    NASA Astrophysics Data System (ADS)

    Serafini, L.; Alesini, D.; Bacci, N.; Bliss, N.; Cassou, K.; Curatolo, C.; Drebot, I.; Dupraz, K.; Giribono, A.; Petrillo, V.; Palumbo, L.; Vaccarezza, C.; Variola, A.; Zomer, F.

    2016-05-01

    In this manuscript we review the challenges of Compton backscattering sources in advancing photon beam performances in the 1 - 20 MeV energy range, underlining the design criteria bringing to maximum spectral luminosity and briefly describing the main achievements in conceiving and developing new devices (multi-bunch RF cavities and Laser recirculators) for the case of ELI-NP Gamma Beam System (ELI-NP-GBS).

  4. Integral window/photon beam position monitor and beam flux detectors for x-ray beams

    DOEpatents

    Shu, Deming; Kuzay, Tuncer M.

    1995-01-01

    A monitor/detector assembly in a synchrotron for either monitoring the position of a photon beam or detecting beam flux may additionally function as a vacuum barrier between the front end and downstream segment of the beamline in the synchrotron. A base flange of the monitor/detector assembly is formed of oxygen free copper with a central opening covered by a window foil that is fused thereon. The window foil is made of man-made materials, such as chemical vapor deposition diamond or cubic boron nitrate and in certain configurations includes a central opening through which the beams are transmitted. Sensors of low atomic number materials, such as aluminum or beryllium, are laid on the window foil. The configuration of the sensors on the window foil may be varied depending on the function to be performed. A contact plate of insulating material, such as aluminum oxide, is secured to the base flange and is thereby clamped against the sensor on the window foil. The sensor is coupled to external electronic signal processing devices via a gold or silver lead printed onto the contact plate and a copper post screw or alternatively via a copper screw and a copper spring that can be inserted through the contact plate and coupled to the sensors. In an alternate embodiment of the monitor/detector assembly, the sensors are sandwiched between the window foil of chemical vapor deposition diamond or cubic boron nitrate and a front foil made of similar material.

  5. Photon Beam Diagnostics for VISA FEL

    SciTech Connect

    Murokh, A.; Pellegrini, C.; Rosenzweig, J.; Frigola, P.; Musumeci, P.; Tremaine, A.; Babzien, M.; Ben-Zvi, I.; Doyuran, A.; Johnson, E.; Skaritka, J.; Wang, X.J.; Van Bibber, K.; Hill, J.M.; LeSage, G.P.; Nguyen, D.; Cornacchia, M.

    1999-11-05

    The VISA (Visible to Infrared SASE Amplifier) project is designed to be a SASE-FEL driven to saturation in the sub-micron wavelength region. Its goal is to test various aspects of the existing theory of Self-Amplified Spontaneous Emission, as well as numerical codes. Measurements include: angular and spectral distribution of the FEL light at the exit and inside of the undulator; electron beam micro-bunching using CTR; single-shot time resolved measurements of the pulse profile, using auto-correlation technique and FROG algorithm. The diagnostics are designed to provide maximum information on the physics of the SASE-FEL process, to ensure a close comparison of the experimental results with theory and simulations.

  6. Chiral separation and twin-beam photonics

    NASA Astrophysics Data System (ADS)

    Bradshaw, David S.; Andrews, David L.

    2016-03-01

    It is well-known that, in a homogeneous fluid medium, most optical means that afford discrimination between molecules of opposite handedness are intrinsically weak effects. The reason is simple: the wide variety of origins for differential response commonly feature real or virtual electronic transitions that break a parity condition. Despite being electric dipole allowed, they manifest the chirality of the material in which they occur by breaking a selection rule that would otherwise preclude the simultaneous involvement of magnetic dipole or electric quadrupole forms of coupling. Although the latter are typically weaker than electric dipole effects by several orders of magnitude, it is the involvement of these weak forms of interaction that are responsible for chiral sensitivity. There have been a number of attempts to cleverly exploit novel optical configurations to enhance the relative magnitude - and hence potentially the efficiency - of chiral discrimination. The prospect of success in any such venture is enticing, because of the huge impact that such an advance might be expected to have in the health, food and medical sectors. Some of these proposals have utilized mirror reflection, and others surface plasmon coupling, or optical binding methods. Several recent works in the literature have drawn attention to a further possibility: the deployment of optical beam interference as a means to achieve chiral separations of sizeable extent. In this paper the underlying theory is fully developed to identify the true scope and limitations of such an approach.

  7. Discrete beam combiners: 3D photonics for future interferometers

    NASA Astrophysics Data System (ADS)

    Minardi, S.; Saviauk, A.; Dreisow, F.; Nolte, S.; Pertsch, T.

    2014-04-01

    We present the results of an experimental research aiming at investigating the potential of three-dimensional (3D) photonics for astronomical interferometry. We found that a simple two dimensional array of evanescently coupled waveguides (the so called Discrete Beam Combiner - DBC) can be used to retrieve the mutual coherence properties of light collected by three telescopes with a precision comparable to state-of-the-art interferometric beam combiners. On the basis of these results, we envisage the future use of DBCs in optical/IR interferometry, with particular attention to large arrays of telescopes.

  8. Projection imaging of photon beams by the Cerenkov effect

    SciTech Connect

    Glaser, Adam K.; Davis, Scott C.; McClatchy, David M.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2013-01-15

    Purpose: A novel technique for beam profiling of megavoltage photon beams was investigated for the first time by capturing images of the induced Cerenkov emission in water, as a potential surrogate for the imparted dose in irradiated media. Methods: A high-sensitivity, intensified CCD camera (ICCD) was configured to acquire 2D projection images of Cerenkov emission from a 4 Multiplication-Sign 4 cm{sup 2} 6 MV linear accelerator (LINAC) x-ray photon beam operating at a dose rate of 400 MU/min incident on a water tank with transparent walls. The ICCD acquisition was gated to the LINAC sync pulse to reduce background light artifacts, and the measurement quality was investigated by evaluating the signal to noise ratio and measurement repeatability as a function of delivered dose. Monte Carlo simulations were used to derive a calibration factor for differences between the optical images and deposited dose arising from the anisotropic angular dependence of Cerenkov emission. Finally, Cerenkov-based beam profiles were compared to a percent depth dose (PDD) and lateral dose profile at a depth of d{sub max} from a reference dose distribution generated from the clinical Varian ECLIPSE treatment planning system (TPS). Results: The signal to noise ratio was found to be 20 at a delivered dose of 66.6 cGy, and proportional to the square root of the delivered dose as expected from Poisson photon counting statistics. A 2.1% mean standard deviation and 5.6% maximum variation in successive measurements were observed, and the Monte Carlo derived calibration factor resulted in Cerenkov emission images which were directly correlated to deposited dose, with some spatial issues. The dose difference between the TPS and PDD predicted by Cerenkov measurements was within 20% in the buildup region with a distance to agreement (DTA) of 1.5-2 mm and {+-}3% at depths beyond d{sub max}. In the lateral profile, the dose difference at the beam penumbra was within {+-}13% with a DTA of 0-2 mm

  9. Characteristics of mobile MOSFET dosimetry system for megavoltage photon beams.

    PubMed

    Kumar, A Sathish; Sharma, S D; Ravindran, B Paul

    2014-07-01

    The characteristics of a mobile metal oxide semiconductor field effect transistor (mobile MOSFET) detector for standard bias were investigated for megavoltage photon beams. This study was performed with a brass alloy build-up cap for three energies namely Co-60, 6 and 15 MV photon beams. The MOSFETs were calibrated and the performance characteristics were analyzed with respect to dose rate dependence, energy dependence, field size dependence, linearity, build-up factor, and angular dependence for all the three energies. A linear dose-response curve was noted for Co-60, 6 MV, and 15 MV photons. The calibration factors were found to be 1.03, 1, and 0.79 cGy/mV for Co-60, 6 MV, and 15 MV photon energies, respectively. The calibration graph has been obtained to the dose up to 600 cGy, and the dose-response curve was found to be linear. The MOSFETs were found to be energy independent both for measurements performed at depth as well as on the surface with build-up. However, field size dependence was also analyzed for variable field sizes and found to be field size independent. Angular dependence was analyzed by keeping the MOSFET dosimeter in parallel and perpendicular orientation to the angle of incidence of the radiation with and without build-up on the surface of the phantom. The maximum variation for the three energies was found to be within ± 2% for the gantry angles 90° and 270°, the deviations without the build-up for the same gantry angles were found to be 6%, 25%, and 60%, respectively. The MOSFET response was found to be independent of dose rate for all three energies. The dosimetric characteristics of the MOSFET detector make it a suitable in vivo dosimeter for megavoltage photon beams. PMID:25190992

  10. Characteristics of mobile MOSFET dosimetry system for megavoltage photon beams

    PubMed Central

    Kumar, A. Sathish; Sharma, S. D.; Ravindran, B. Paul

    2014-01-01

    The characteristics of a mobile metal oxide semiconductor field effect transistor (mobile MOSFET) detector for standard bias were investigated for megavoltage photon beams. This study was performed with a brass alloy build-up cap for three energies namely Co-60, 6 and 15 MV photon beams. The MOSFETs were calibrated and the performance characteristics were analyzed with respect to dose rate dependence, energy dependence, field size dependence, linearity, build-up factor, and angular dependence for all the three energies. A linear dose-response curve was noted for Co-60, 6 MV, and 15 MV photons. The calibration factors were found to be 1.03, 1, and 0.79 cGy/mV for Co-60, 6 MV, and 15 MV photon energies, respectively. The calibration graph has been obtained to the dose up to 600 cGy, and the dose-response curve was found to be linear. The MOSFETs were found to be energy independent both for measurements performed at depth as well as on the surface with build-up. However, field size dependence was also analyzed for variable field sizes and found to be field size independent. Angular dependence was analyzed by keeping the MOSFET dosimeter in parallel and perpendicular orientation to the angle of incidence of the radiation with and without build-up on the surface of the phantom. The maximum variation for the three energies was found to be within ± 2% for the gantry angles 90° and 270°, the deviations without the build-up for the same gantry angles were found to be 6%, 25%, and 60%, respectively. The MOSFET response was found to be independent of dose rate for all three energies. The dosimetric characteristics of the MOSFET detector make it a suitable in vivo dosimeter for megavoltage photon beams. PMID:25190992

  11. Application of spherical diodes for megavoltage photon beams dosimetry

    SciTech Connect

    Barbés, Benigno; Azcona, Juan D.; Burguete, Javier; Martí-Climent, Josep M.

    2014-01-15

    Purpose: External beam radiation therapy (EBRT) usually uses heterogeneous dose distributions in a given volume. Designing detectors for quality control of these treatments is still a developing subject. The size of the detectors should be small to enhance spatial resolution and ensure low perturbation of the beam. A high uniformity in angular response is also a very important feature in a detector, because it has to measure radiation coming from all the directions of the space. It is also convenient that detectors are inexpensive and robust, especially to performin vivo measurements. The purpose of this work is to introduce a new detector for measuring megavoltage photon beams and to assess its performance to measure relative dose in EBRT. Methods: The detector studied in this work was designed as a spherical photodiode (1.8 mm in diameter). The change in response of the spherical diodes is measured regarding the angle of incidence, cumulated irradiation, and instantaneous dose rate (or dose per pulse). Additionally, total scatter factors for large and small fields (between 1 × 1 cm{sup 2} and 20 × 20 cm{sup 2}) are evaluated and compared with the results obtained from some commercially available ionization chambers and planar diodes. Additionally, the over-response to low energy scattered photons in large fields is investigated using a shielding layer. Results: The spherical diode studied in this work produces a high signal (150 nC/Gy for photons of nominal energy of 15 MV and 160 for 6 MV, after 12 kGy) and its angular dependence is lower than that of planar diodes: less than 5% between maximum and minimum in all directions, and 2% around one of the axis. It also has a moderated variation with accumulated dose (about 1.5%/kGy for 15 MV photons and 0.7%/kGy for 6 MV, after 12 kGy) and a low variation with dose per pulse (±0.4%), and its behavior is similar to commercial diodes in total scatter factor measurements. Conclusions: The measurements of relative dose

  12. Consistency check of photon beam physical data after recommissioning process

    NASA Astrophysics Data System (ADS)

    Kadman, B.; Chawapun, N.; Ua-apisitwong, S.; Asakit, T.; Chumpu, N.; Rueansri, J.

    2016-03-01

    In radiotherapy, medical linear accelerator (Linac) is the key system used for radiation treatments delivery. Although, recommissioning was recommended after major modification of the machine by AAPM TG53, but it might not be practical in radiotherapy center with heavy workloads. The main purpose of this study was to compare photon beam physical data between initial commissioning and recommissioning of 6 MV Elekta Precise linac. The parameters for comparing were the percentage depth dose (PDD) and beam profiles. The clinical commissioning test cases followed IAEA-TECDOC-1583 were planned on REF 91230 IMRT Dose Verification Phantom by Philips’ Pinnacle treatment planning system. The Delta4PT was used for dose distribution verification with 90% passing criteria of the gamma index (3%/3mm). Our results revealed that the PDDs and beam profiles agreed within a tolerance limit recommended by TRS430. Most of the point doses and dose distribution verification passed the acceptance criteria. This study showed the consistency of photon beam physical data after recommissioning process. There was a good agreement between initial commissioning and recommissioning within a tolerance limit, demonstrated that the full recommissioning process might not be required. However, in the complex treatment planning geometry, the initial data should be applied with great caution.

  13. Intermediate Megavoltage Photon Beams for Improved Lung Cancer Treatments

    PubMed Central

    Zhang, Ying; Feng, Yuanming; Ahmad, Munir; Ming, Xin; Zhou, Li; Deng, Jun

    2015-01-01

    The goal of this study is to evaluate the effects of intermediate megavoltage (3-MV) photon beams on SBRT lung cancer treatments. To start with, a 3-MV virtual beam was commissioned on a commercial treatment planning system based on Monte Carlo simulations. Three optimized plans (6-MV, 3-MV and dual energy of 3- and 6-MV) were generated for 31 lung cancer patients with identical beam configuration and optimization constraints for each patient. Dosimetric metrics were evaluated and compared among the three plans. Overall, planned dose conformity was comparable among three plans for all 31 patients. For 21 thin patients with average short effective path length (< 10 cm), the 3-MV plans showed better target coverage and homogeneity with dose spillage index R50% = 4.68±0.83 and homogeneity index = 1.26±0.06, as compared to 4.95±1.01 and 1.31±0.08 in the 6-MV plans (p < 0.001). Correspondingly, the average/maximum reductions of lung volumes receiving 20 Gy (V20Gy), 5 Gy (V5Gy), and mean lung dose (MLD) were 7%/20%, 9%/30% and 5%/10%, respectively in the 3-MV plans (p < 0.05). The doses to 5% volumes of the cord, esophagus, trachea and heart were reduced by 9.0%, 10.6%, 11.4% and 7.4%, respectively (p < 0.05). For 10 thick patients, dual energy plans can bring dosimetric benefits with comparable target coverage, integral dose and reduced dose to the critical structures, as compared to the 6-MV plans. In conclusion, our study indicated that 3-MV photon beams have potential dosimetric benefits in treating lung tumors in terms of improved tumor coverage and reduced doses to the adjacent critical structures, in comparison to 6-MV photon beams. Intermediate megavoltage photon beams (< 6-MV) may be considered and added into current treatment approaches to reduce the adjacent normal tissue doses while maintaining sufficient tumor dose coverage in lung cancer radiotherapy. PMID:26672752

  14. Deconfinement of Quarks with TeV Attosecond Photon Beams

    NASA Astrophysics Data System (ADS)

    Stefan, V. Alexander

    2010-02-01

    Recently, I have proposed a novel heuristic method for the deconfinement of quarks.footnotetextM. Gell-Mann. The Quark and the Jaguar: Adventures in the Simple and the Complex (New York, NY: W.H. Freeman and Co., 1994) [cf. M. Gell-Mann, The Garden of Live Flowers in: V. Stefan (Editor), Physics and Society. Essays Honoring Victor Frederick Weisskopf (Springer, 1998), pp. 109-121]. It proceeds in two phases.footnotetextV. Alexander Stefan, On a Heuristic Point of View About Inertial Deconfinement of Quarks, American Physical Society, 2009 APS April Meeting, May 2-5, 2009, abstract #E1.038. Firstly, a frozen hydrogen pellet is inertially confined by the ultra-intense lasers up to a solid state density. Secondly, a solid state nano-pellet is ``punched'' by the photon beam created in the beat wave driven free electron laser (BW-FEL), leading to the ``rapture'' (in a ``karate chop'' model) of the ``MIT Bag''footnotetextJ. I. Friedman and H. Kendall, Viki, in: V. Stefan (Editor), Physics and Society. (Springer, 1998), pp. 103-108]. before the asymptotically free quarks move apart. Hereby, I propose TeV, a few 100s attosecond, photon beams in interaction with the nano-pellet. The threshold ``rapture force'' of the TeV attosecond photon is 10^7 N. )

  15. Analysis and control of the photon beam position at PLS-II

    PubMed Central

    Ko, J.; Kim, I.-Y.; Kim, C.; Kim, D.-T.; Huang, J.-Y.; Shin, S.

    2016-01-01

    At third-generation light sources, the photon beam position stability is a critical issue for user experiments. In general, photon beam position monitors are developed to detect the real photon beam position, and the position is controlled by a feedback system in order to maintain the reference photon beam position. At Pohang Light Source II, a photon beam position stability of less than 1 µm r.m.s. was achieved for a user service period in the beamline, where the photon beam position monitor is installed. Nevertheless, a detailed analysis of the photon beam position data was necessary in order to ensure the performance of the photon beam position monitor, since it can suffer from various unknown types of noise, such as background contamination due to upstream or downstream dipole radiation, and undulator gap dependence. This paper reports the results of a start-to-end study of the photon beam position stability and a singular value decomposition analysis to confirm the reliability of the photon beam position data. PMID:26917132

  16. Cardiac single-photon emission-computed tomography using combinedcone-beam/fan-beam collimation

    SciTech Connect

    Gullberg, Grant T.; Zeng, Gengsheng L.

    2004-12-03

    The objective of this work is to increase system sensitivity in cardiac single-photon emission-computed tomography (SPECT) studies without increasing patient imaging time. For imaging the heart, convergent collimation offers the potential of increased sensitivity over that of parallel-hole collimation. However, if a cone-beam collimated gamma camera is rotated in a planar orbit, the projection data obtained are not complete. Two cone-beam collimators and one fan-beam collimator are used with a three-detector SPECT system. The combined cone-beam/fan-beam collimation provides a complete set of data for image reconstruction. The imaging geometry is evaluated using data acquired from phantom and patient studies. For the Jaszazck cardiac torso phantom experiment, the combined cone-beam/fan-beam collimation provided 1.7 times greater sensitivity than standard parallel-hole collimation (low-energy high-resolution collimators). Also, phantom and patient comparison studies showed improved image quality. The combined cone-beam/fan-beam imaging geometry with appropriate weighting of the two data sets provides improved system sensitivity while measuring sufficient data for artifact free cardiac images.

  17. Some results of the advanced photon source beam lifetime studies

    SciTech Connect

    Bizek, H.M.

    1997-06-01

    Total beam lifetime consists of two components: the residual-gas-scattering lifetime and Touschek lifetime. The residual-gas lifetime is comprised of the elastic and inelastic scattering on electrons and elastic and inelastic scattering on nuclei. Touschek scattering involves scattering of particles within the bunch. One usually calculates only the elastic scattering on nuclei (single Coulomb scattering) and inelastic scattering on nuclei (bremsstrahlung) of the residual-gas-scattering lifetime component. Experience gained from computing the beam lifetime in the Advanced Photon Source (APS) storage ring shows that the electron scattering should not be neglected, particularly the inelastic contribution. Given the measured quantities from the APS storage ring, one can compare theoretical predictions with experimental results. Uncertainties in calculating the various contributions to lifetime will be discussed.

  18. Reduction of metal artifacts: beam hardening and photon starvation effects

    NASA Astrophysics Data System (ADS)

    Yadava, Girijesh K.; Pal, Debashish; Hsieh, Jiang

    2014-03-01

    The presence of metal-artifacts in CT imaging can obscure relevant anatomy and interfere with disease diagnosis. The cause and occurrence of metal-artifacts are primarily due to beam hardening, scatter, partial volume and photon starvation; however, the contribution to the artifacts from each of them depends on the type of hardware. A comparison of CT images obtained with different metallic hardware in various applications, along with acquisition and reconstruction parameters, helps understand methods for reducing or overcoming such artifacts. In this work, a metal beam hardening correction (BHC) and a projection-completion based metal artifact reduction (MAR) algorithms were developed, and applied on phantom and clinical CT scans with various metallic implants. Stainless-steel and Titanium were used to model and correct for metal beam hardening effect. In the MAR algorithm, the corrupted projection samples are replaced by the combination of original projections and in-painted data obtained by forward projecting a prior image. The data included spine fixation screws, hip-implants, dental-filling, and body extremity fixations, covering range of clinically used metal implants. Comparison of BHC and MAR on different metallic implants was used to characterize dominant source of the artifacts, and conceivable methods to overcome those. Results of the study indicate that beam hardening could be a dominant source of artifact in many spine and extremity fixations, whereas dental and hip implants could be dominant source of photon starvation. The BHC algorithm could significantly improve image quality in CT scans with metallic screws, whereas MAR algorithm could alleviate artifacts in hip-implants and dentalfillings.

  19. The Pair Beam Production Spectrum from Photon-Photon Annihilation in Cosmic Voids

    NASA Astrophysics Data System (ADS)

    Schlickeiser, R.; Elyiv, A.; Ibscher, D.; Miniati, F.

    2012-10-01

    Highly beamed relativistic e ±-pair energy distributions result in double photon collisions of the beamed gamma rays from TeV blazars at cosmological distances with the isotropically distributed extragalactic background light (EBL) in the intergalactic medium. The typical energies k 0 ~= 10-7 in units of mec 2 of the EBL are more than 10 orders of magnitude smaller than the observed gamma-ray energies k 1 >= 107. Using the limit k 0 Lt k 1, we demonstrate that the angular distribution of the generated pairs in the lab frame is highly beamed in the direction of the initial gamma-ray photons. For the astrophysically important case of power-law distributions of the emitted gamma-ray beam up to the maximum energy M interacting with Wien-type N(k 0)vpropkq 0exp (- k 0/Θ) soft photon distributions with total number density N 0, we calculate analytical approximations for the electron production spectrum. For distant objects with luminosity distances dL Gt r 0 = (σ T N 0)-1 = 0.49N -1 0 Mpc (with Thomson cross section σ T ), the implied large values of the optical depth τ0 = dL /r 0 indicate that the electron production spectra differ at energies inside and outside the interval [(Θln τ0)-1, τ0/Θ], given the maximum gamma-ray energy M Gt Θ-1. In the case M Gt Θ-1, the production spectrum is strongly peaked near E ~= Θ-1, being exponentially reduced at small energies and decreasing with the steep power law vpropE -1 - p up to the maximum energy E = M - (1/2).

  20. VMC++ versus BEAMnrc: A comparison of simulated linear accelerator heads for photon beams

    SciTech Connect

    Hasenbalg, F.; Fix, M. K.; Born, E. J.; Mini, R.; Kawrakow, I.

    2008-04-15

    BEAMnrc, a code for simulating medical linear accelerators based on EGSnrc, has been benchmarked and used extensively in the scientific literature and is therefore often considered to be the gold standard for Monte Carlo simulations for radiotherapy applications. However, its long computation times make it too slow for the clinical routine and often even for research purposes without a large investment in computing resources. VMC++ is a much faster code thanks to the intensive use of variance reduction techniques and a much faster implementation of the condensed history technique for charged particle transport. A research version of this code is also capable of simulating the full head of linear accelerators operated in photon mode (excluding multileaf collimators, hard and dynamic wedges). In this work, a validation of the full head simulation at 6 and 18 MV is performed, simulating with VMC++ and BEAMnrc the addition of one head component at a time and comparing the resulting phase space files. For the comparison, photon and electron fluence, photon energy fluence, mean energy, and photon spectra are considered. The largest absolute differences are found in the energy fluences. For all the simulations of the different head components, a very good agreement (differences in energy fluences between VMC++ and BEAMnrc <1%) is obtained. Only a particular case at 6 MV shows a somewhat larger energy fluence difference of 1.4%. Dosimetrically, these phase space differences imply an agreement between both codes at the <1% level, making VMC++ head module suitable for full head simulations with considerable gain in efficiency and without loss of accuracy.

  1. Packaging consideration of two-dimensional polymer-based photonic crystals for laser beam steering

    NASA Astrophysics Data System (ADS)

    Dou, Xinyuan; Chen, Xiaonan; Chen, Maggie Yihong; Wang, Alan Xiaolong; Jiang, Wei; Chen, Ray T.

    2009-02-01

    In this paper, we report the theoretical study of polymer-based photonic crystals for laser beam steering which is based on the superprism effect as well as the experiment fabrication of the two dimensional photonic crystals for the laser beam steering. Superprism effect, the principle for beam steering, was separately studied in details through EFC (Equifrequency Contour) analysis. Polymer based photonic crystals were fabricated through double exposure holographic interference method using SU8-2007. The experiment results were also reported.

  2. Detector dose response in megavoltage small photon beams. II. Pencil beam perturbation effects

    SciTech Connect

    Bouchard, Hugo Duane, Simon; Kamio, Yuji; Palmans, Hugo; Seuntjens, Jan

    2015-10-15

    Purpose: To quantify detector perturbation effects in megavoltage small photon fields and support the theoretical explanation on the nature of quality correction factors in these conditions. Methods: In this second paper, a modern approach to radiation dosimetry is defined for any detector and applied to small photon fields. Fano’s theorem is adapted in the form of a cavity theory and applied in the context of nonstandard beams to express four main effects in the form of perturbation factors. The pencil-beam decomposition method is detailed and adapted to the calculation of perturbation factors and quality correction factors. The approach defines a perturbation function which, for a given field size or beam modulation, entirely determines these dosimetric factors. Monte Carlo calculations are performed in different cavity sizes for different detection materials, electron densities, and extracameral components. Results: Perturbation effects are detailed with calculated perturbation functions, showing the relative magnitude of the effects as well as the geometrical extent to which collimating or modulating the beam impacts the dosimetric factors. The existence of a perturbation zone around the detector cavity is demonstrated and the approach is discussed and linked to previous approaches in the literature to determine critical field sizes. Conclusions: Monte Carlo simulations are valuable to describe pencil beam perturbation effects and detail the nature of dosimetric factors in megavoltage small photon fields. In practice, it is shown that dosimetric factors could be avoided if the field size remains larger than the detector perturbation zone. However, given a detector and beam quality, a full account for the detector geometry is necessary to determine critical field sizes.

  3. Photon stimulated desorption measurement of an extruded aluminum beam chamber for the Advanced Photon Source

    SciTech Connect

    Foerster, C.L.; Lanni, C.; Noonan, J.R.; Rosenberg, R.A.

    1995-12-31

    The Advanced Photon Source (APS), presently being commisioned, will produce X-ray s of unprecedented brightness. The high energy ring of the APS is a 7 GeV positron storage ring, 1104 meters in circumference designed to operate at less than 10{sup {minus}9} Torr with 300 ma of beam and a greater than 10 hour lifetime. The storage ring vacuum chamber is constructed from an extruded 6063 aluminum alloy. During the construction phase, a 2.34 m long section of the APS extruded aluminum chamber was set up on National Synchrotron Light Source (NSLS) X-ray Beamlline X28A and Photon Stimulated Desorption (PSD) was measured. Cleaning and preparation of the chamber was identical to that of the APS construction. In addition to the chamber, small samples of M, Be, and Cu were also exposed to white light having a critical energy of 5 keV. In addition to PSD, measurements were made of specular and diffuse scattering of photons. The chamber and samples were each exposed to a dose greater than 10{sup 23} photons per meter. Desorption yields for H{sub 2}, CO, CO{sub 2}, CH{sub 4} and H{sub 2}0 are reported as a function of accumulated flux, critical energy, incidence angle, and preparation. These results are compared with previous results for aluminum on NSLS Beamlline U1OB and PSD results of other laboratories published for aluminum.

  4. Photon stimulated desorption measurement of an extruded aluminum beam chamber for the Advanced Photon Source

    SciTech Connect

    Foerster, C.L.; Lanni, C.; Noonan, J.R.; Rosenberg, R.A.

    1996-05-01

    The Advanced Photon Source (APS), presently being commissioned, will produce x rays of unprecedented brightness. The high energy ring of the APS is a 7 GeV positron storage ring, 1104 m in circumference designed to operate at less than 10{sup {minus}9} Torr with 300 mA of beam and a greater than 10 h lifetime. The storage ring vacuum chamber is constructed from an extruded 6063 aluminum alloy. During the construction phase, a 2.34-m-long section of the APS extruded aluminum chamber was set up on National Synchrotron Light Source (NSLS) X-ray Beamline X28A and photon stimulated desorption (PSD) was measured. Cleaning and preparation of the chamber was identical to that of the APS construction. In addition to the chamber, small samples of Al, Be, and Cu were also exposed to white light having a critical energy of 5 keV. In addition to PSD, measurements were made of the specular and diffuse scattering of photons. The chamber and samples were each exposed to a dose greater than 10{sup 23} photons per m. Desorption yields for H{sub 2}, CO, CO{sub 2}, CH{sub 4}, and H{sub 2}O are reported as a function of accumulated flux, critical energy, incidence angle, and preparation. These results are compared with previous results for aluminum on NSLS Beamline U10B and PSD results of other laboratories published for aluminum. {copyright} {ital 1996 American Vacuum Society}

  5. Interferometric source of multi-color, multi-beam entangled photons with mirror and mixer

    DOEpatents

    Dress, William B.; Kisner, Roger A.; Richards, Roger K.

    2004-06-01

    53 Systems and methods are described for an interferometric source of multi-color, multi-beam entangled photons. An apparatus includes: a multi-refringent device optically coupled to a source of coherent energy, the multi-refringent device providing a beam of multi-color entangled photons; a condenser device optically coupled to the multi-refringent device, the condenser device i) including a mirror and a mixer and ii) converging two spatially resolved portions of the beam of multi-color entangled photons into a converged multi-color entangled photon beam; a tunable phase adjuster optically coupled to the condenser device, the tunable phase adjuster changing a phase of at least a portion of the converged multi-color entangled photon beam to generate a first interferometeric multi-color entangled photon beam; and a beam splitter optically coupled to the condenser device, the beam splitter combining the first interferometeric multi-color entangled photon beam with a second interferometric multi-color entangled photon beam.

  6. Beam position feedback system for the Advanced Photon Source

    SciTech Connect

    Chung, Y.

    1993-12-31

    The Advanced Photon Source (APS) will implement both global and local beam position feedback systems to stabilize the particle and X-ray beams for the storage ring. The systems consist of 20 VME crates distributed around the ring, each running multiple digital signal processors (DSP) running at 4kHz sampling rate with a proportional, integral, and derivative (PID) control algorithm. The particle and X-ray beam position data is shared by the distributed processors through networked reflective memory. A theory of closed orbit correction using the technique of singular value decomposition (SVD) of the response matrix and simulation of its application to the APS storage ring will be discussed. This technique combines the global and local feedback systems and resolves the conflict among multiple local feedback systems due to local bump closure error. Maximum correction efficiency is achieved by feeding back the global orbit data to the local feedback systems. The effect of the vacuum chamber eddy current induced by the AC corrector magnet field for local feedback systems is compensated by digital filters. Results of experiments conducted on the X-ray ring of the National Synchrotron Light Source and the SPEAR at Stanford Synchrotron Radiation Laboratory will be presented.

  7. Polarization beam splitters based on a two-dimensional photonic crystal of negative refraction.

    PubMed

    Ao, Xianyu; He, Sailing

    2005-08-15

    A two-dimensional metallo-dielectric photonic crystal of negative refraction was designed for the application of polarization beam splitters. To match the refractive index of air, the effective refractive index of the designed photonic crystal is -1 for TE polarization and +1 for TM polarization. Two types of polarization beam splitter are presented. PMID:16127940

  8. Key comparison BIPM.RI(I)-K6 of the standards for absorbed dose to water of the ARPANSA, Australia and the BIPM in accelerator photon beams

    NASA Astrophysics Data System (ADS)

    Picard, S.; Burns, D. T.; Roger, P.; Harty, P. D.; Ramanathan, G.; Lye, J. E.; Wright, T.; Butler, D. J.; Cole, A.; Oliver, C.; Webb, D. V.

    2014-01-01

    A comparison of the dosimetry for accelerator photon beams was carried out between the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and the Bureau International des Poids et Mesures (BIPM) in September and October 2012. The comparison was based on the determination of absorbed dose to water for three radiation qualities at the ARPANSA. Following receipt of the provisional comparison results, the ARPANSA decided to verify the geometry of the jacket and calorimeter core. This resulted in a change in the conversion factors applied by the ARPANSA to convert from absorbed dose to graphite to absorbed dose to water which was implemented after the comparison. The results for the revised standard, reported as a ratio of the ARPANSA and the BIPM evaluations, are 0.9965 at 6 MV, 0.9924 at 10 MV and 0.9932 at 18 MV, with a combined standard uncertainty of 5.5 parts in 103, 6.0 parts in 103 and 5.9 parts in 103, respectively. This result is the fifth in the on-going BIPM.RI(I)-K6 series of comparisons, and the first to be based solely on graphite calorimetry. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  9. a Photon Tag Calibration Beam for the Agile Satellite

    NASA Astrophysics Data System (ADS)

    Hasan, S.; Prest, M.; Foggetta, L.; Pontoni, C.; Mozzanica, A.; Barbiellini, G.; Basset, M.; Liello, F.; Longo, F.; Vallazza, E.; Buonomo, G.; Mazzitelli, G.; Quintieri, L.; Valente, P.; Boffelli, F.; Cattaneo, P.; Mauri, F.

    2006-04-01

    The AGILE satellite will be launched in 2006 for the study of gamma rays in the energy range 30 MeV-50 GeV. The satellite has to be calibrated using gamma rays of known energy. The calibration facility is being developed at the Beam Test Facility (BTF) at the INFN Laboratories in Frascati. The photons are produced by bremsstrahlung of electrons with a maximum momentum of 750 MeV/c. The electrons are tagged using a dipole magnet whose internal walls are covered by microstrip silicon detectors: depending on the energy loss, they impinge on a different strip once the dipole current has been set to a given value. The correlation between the direction of the electron measured by a pair of x-y silicon chambers and the impinging position on the tagging module inside the magnet allows the tagging of the photon. The paper describes the calibration layout and tests and the results, compared with the Montecarlo simulation, in terms of production rate and energy resolution.

  10. Salivary Gland. Photon beam and particle radiotherapy: Present and future.

    PubMed

    Orlandi, Ester; Iacovelli, Nicola Alessandro; Bonora, Maria; Cavallo, Anna; Fossati, Piero

    2016-09-01

    Salivary gland cancers (SGCs) are rare diseases and their treatment depends upon histology, stage and site of origin. Radical surgery is the mainstay of treatment but radiotherapy (RT) plays a key role in both the postoperative and the inoperable setting, as well as in recurrent disease. In the absence of prospective randomized trials, a wide retrospective literature suggests postoperative RT (PORT) in patients with high risk pathological features. SGCs, and adenoid cystic carcinoma (ACC) in particular, are known to be radio-resistant tumors and should therefore respond well to particle beam therapy. Recently, excellent outcome has been reported with radical carbon ion RT (CIRT) in particular for ACC. Both modern photon- and hadron-based treatments are effective and are characterized by a favourable toxicity profile. But it is not clear whether one modality is superior to the other for disease control, due to the differences in patients' selection, techniques, fractionation schedules and outcome measurements among clinical experiences. In this paper, we review the role of photon and particle RT for malignant SGCs, discussing the difference between modalities in terms of biological and technical characteristics. RT dose and target volumes for different histologies (ACC versus non-ACC) have also been taken into consideration. PMID:27394087

  11. THE PAIR BEAM PRODUCTION SPECTRUM FROM PHOTON-PHOTON ANNIHILATION IN COSMIC VOIDS

    SciTech Connect

    Schlickeiser, R.; Ibscher, D.; Elyiv, A.; Miniati, F. E-mail: ibscher@tp4.rub.de E-mail: fm@phys.ethz.ch

    2012-10-20

    Highly beamed relativistic e {sup {+-}}-pair energy distributions result in double photon collisions of the beamed gamma rays from TeV blazars at cosmological distances with the isotropically distributed extragalactic background light (EBL) in the intergalactic medium. The typical energies k {sub 0} {approx_equal} 10{sup -7} in units of m{sub e}c {sup 2} of the EBL are more than 10 orders of magnitude smaller than the observed gamma-ray energies k {sub 1} {>=} 10{sup 7}. Using the limit k {sub 0} << k {sub 1}, we demonstrate that the angular distribution of the generated pairs in the lab frame is highly beamed in the direction of the initial gamma-ray photons. For the astrophysically important case of power-law distributions of the emitted gamma-ray beam up to the maximum energy M interacting with Wien-type N(k {sub 0}){proportional_to}k{sup q} {sub 0}exp (- k {sub 0}/{Theta}) soft photon distributions with total number density N {sub 0}, we calculate analytical approximations for the electron production spectrum. For distant objects with luminosity distances d{sub L} >> r {sub 0} = ({sigma} {sub T} N {sub 0}){sup -1} = 0.49N {sup -1} {sub 0} Mpc (with Thomson cross section {sigma} {sub T}), the implied large values of the optical depth {tau}{sub 0} = d{sub L} /r {sub 0} indicate that the electron production spectra differ at energies inside and outside the interval [({Theta}ln {tau}{sub 0}){sup -1}, {tau}{sub 0}/{Theta}], given the maximum gamma-ray energy M >> {Theta}{sup -1}. In the case M >> {Theta}{sup -1}, the production spectrum is strongly peaked near E {approx_equal} {Theta}{sup -1}, being exponentially reduced at small energies and decreasing with the steep power law {proportional_to}E {sup -1-p} up to the maximum energy E = M - (1/2).

  12. On the conversion of infrared radiation from fission reactor-based photon engine into parallel beam

    NASA Astrophysics Data System (ADS)

    Gulevich, Andrey V.; Levchenko, Vladislav E.; Loginov, Nicolay I.; Kukharchuk, Oleg F.; Evtodiev, Denis A.; Zrodnikov, Anatoly V.

    2002-01-01

    The efficiency of infrared radiation conversion from photon engine based on fission reactor into parallel photon beam is discussed. Two different ways of doing that are considered. One of them is to use the parabolic mirror to convert of infrared radiation into parallel photon beam. The another one is based on the use of special lattice consisting of numerous light conductors. The experimental facility and some results are described. .

  13. TOPICAL REVIEW: Monte Carlo modelling of external radiotherapy photon beams

    NASA Astrophysics Data System (ADS)

    Verhaegen, Frank; Seuntjens, Jan

    2003-11-01

    An essential requirement for successful radiation therapy is that the discrepancies between dose distributions calculated at the treatment planning stage and those delivered to the patient are minimized. An important component in the treatment planning process is the accurate calculation of dose distributions. The most accurate way to do this is by Monte Carlo calculation of particle transport, first in the geometry of the external or internal source followed by tracking the transport and energy deposition in the tissues of interest. Additionally, Monte Carlo simulations allow one to investigate the influence of source components on beams of a particular type and their contaminant particles. Since the mid 1990s, there has been an enormous increase in Monte Carlo studies dealing specifically with the subject of the present review, i.e., external photon beam Monte Carlo calculations, aided by the advent of new codes and fast computers. The foundations for this work were laid from the late 1970s until the early 1990s. In this paper we will review the progress made in this field over the last 25 years. The review will be focused mainly on Monte Carlo modelling of linear accelerator treatment heads but sections will also be devoted to kilovoltage x-ray units and 60Co teletherapy sources.

  14. Monte Carlo modelling of external radiotherapy photon beams.

    PubMed

    Verhaegen, Frank; Seuntjens, Jan

    2003-11-01

    An essential requirement for successful radiation therapy is that the discrepancies between dose distributions calculated at the treatment planning stage and those delivered to the patient are minimized. An important component in the treatment planning process is the accurate calculation of dose distributions. The most accurate way to do this is by Monte Carlo calculation of particle transport, first in the geometry of the external or internal source followed by tracking the transport and energy deposition in the tissues of interest. Additionally, Monte Carlo simulations allow one to investigate the influence of source components on beams of a particular type and their contaminant particles. Since the mid 1990s, there has been an enormous increase in Monte Carlo studies dealing specifically with the subject of the present review, i.e., external photon beam Monte Carlo calculations, aided by the advent of new codes and fast computers. The foundations for this work were laid from the late 1970s until the early 1990s. In this paper we will review the progress made in this field over the last 25 years. The review will be focused mainly on Monte Carlo modelling of linear accelerator treatment heads but sections will also be devoted to kilovoltage x-ray units and 60Co teletherapy sources. PMID:14653555

  15. Two-Photon-Absorption Scheme for Optical Beam Tracking

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo G.; Farr, William H.

    2011-01-01

    A new optical beam tracking approach for free-space optical communication links using two-photon absorption (TPA) in a high-bandgap detector material was demonstrated. This tracking scheme is part of the canonical architecture described in the preceding article. TPA is used to track a long-wavelength transmit laser while direct absorption on the same sensor simultaneously tracks a shorter-wavelength beacon. The TPA responsivity was measured for silicon using a PIN photodiode at a laser beacon wavelength of 1,550 nm. As expected, the responsivity shows a linear dependence with incident power level. The responsivity slope is 4.5 x 10(exp -7) A/W2. Also, optical beam spots from the 1,550-nm laser beacon were characterized on commercial charge coupled device (CCD) and complementary metal-oxide semiconductor (CMOS) imagers with as little as 13.7 microWatts of optical power (see figure). This new tracker technology offers an innovative solution to reduce system complexity, improve transmit/receive isolation, improve optical efficiency, improve signal-to-noise ratio (SNR), and reduce cost for free-space optical communications transceivers.

  16. Absolute calibration of photon-number-resolving detectors with an analog output using twin beams

    NASA Astrophysics Data System (ADS)

    Peřina, Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria

    2014-01-01

    A method for absolute calibration of a photon-number resolving detector producing analog signals as the output is developed using a twin beam. The method gives both analog-to-digital conversion parameters and quantum detection efficiency for the photon fields. Characteristics of the used twin beam are also obtained. A simplified variant of the method applicable to fields with high signal to noise ratios and suitable for more intense twin beams is suggested.

  17. Absolute calibration of photon-number-resolving detectors with an analog output using twin beams

    SciTech Connect

    Peřina, Jan; Haderka, Ondřej; Allevi, Alessia; Bondani, Maria

    2014-01-27

    A method for absolute calibration of a photon-number resolving detector producing analog signals as the output is developed using a twin beam. The method gives both analog-to-digital conversion parameters and quantum detection efficiency for the photon fields. Characteristics of the used twin beam are also obtained. A simplified variant of the method applicable to fields with high signal to noise ratios and suitable for more intense twin beams is suggested.

  18. Dosimetric dependences of bone heterogeneity and beam angle on the unflattened and flattened photon beams: A Monte Carlo comparison

    NASA Astrophysics Data System (ADS)

    Chow, James C. L.; Owrangi, Amir M.

    2014-08-01

    The variations of depth and surface dose on the bone heterogeneity and beam angle were compared between unflattened and flattened photon beams using Monte Carlo simulations. Phase-space files of the 6 MV photon beams with field size of 10×10 cm2 were generated with and without the flattening filter based on a Varian TrueBeam linac. Depth and surface doses were calculated in a bone and water phantoms using Monte Carlo simulations (the EGSnrc-based code). Dose calculations were repeated with angles of the unflattened and flattened beams turned from 0° to 15°, 30°, 45°, 60°, 75° and 90° in the bone and water phantoms. Monte Carlo results of depth doses showed that compared to the flattened beam the unflattened photon beam had a higher dose in the build-up region but lower dose beyond the depth of maximum dose. Dose ratios of the unflattened to flattened beams were calculated in the range of 1.6-2.6 with beam angle varying from 0° to 90° in water. Similar results were found in the bone phantom. In addition, higher surface doses of about 2.5 times were found with beam angles equal to 0° and 15° in the bone and water phantoms. However, surface dose deviation between the unflattened and flattened beams became smaller with increasing beam angle. Dose enhancements due to the bone backscatter were also found at the water-bone and bone-water interfaces for both the unflattened and flattened beams in the bone phantom. With Monte Carlo beams cross-calibrated to the monitor unit in simulations, variations of depth and surface dose on the bone heterogeneity and beam angle were investigated and compared using Monte Carlo simulations. For the unflattened and flattened photon beams, the surface dose and range of depth dose ratios (unflattened to flattened beam) decreased with increasing beam angle. The dosimetric comparison in this study is useful in understanding the characteristics of unflattened photon beam on the depth and surface dose with bone heterogeneity.

  19. Photon diagnostics for the study of electron beam properties of a VUV SASE-FEL

    NASA Astrophysics Data System (ADS)

    Gerth, Ch.; Faatz, B.; Lokajczyk, T.; Treusch, R.; Feldhaus, J.

    2001-12-01

    A single-pass free-electron laser operating in the self-amplified spontaneous-emission (SASE) mode at around 100 nm is currently under test at the TESLA Test Facility at DESY. After first observation of SASE in February 2000, the photon beam has been characterized by different techniques. We present the methods of VUV photon diagnostics that were used to measure the spectral and angular distribution of the photon beam and how these properties are affected by the electron beam energy and orbit in the undulator.

  20. A review on photoneutrons characteristics in radiation therapy with high-energy photon beams

    PubMed Central

    Naseri, Alireza; Mesbahi, Asghar

    2010-01-01

    In radiation therapy with high-energy photon beams (E > 10 MeV) neutrons are generated mainly in linacs head thorough (γ,n) interactions of photons with nuclei of high atomic number materials that constitute the linac head and the beam collimation system. These neutrons affect the shielding requirements in radiation therapy rooms and also increase the out-of-field radiation dose of patients undergoing radiation therapy with high-energy photon beams. In the current review, the authors describe the factors influencing the neutron production for different medical linacs based on the performed measurements and Monte Carlo studies in the literature. PMID:24376940

  1. Determination of the beam quality index of high-energy photon beams under nonstandard reference conditions

    SciTech Connect

    Palmans, Hugo

    2012-09-15

    Purpose: At some modern radiotherapy machines it is not possible to achieve reference conditions for the measurement of beam quality indices used in dosimetry codes of practice, such as IAEA TRS-398 and AAPM TG-51. This work aims at providing self-consistent and simpler expressions and more accurate fits for a limited range of beams of interest than have been proposed previously for deriving these beam quality indices from measurements. Methods: The starting point is a formula proposed by Sauer [Med. Phys. 36, 4168-4172 (2009)] for deriving the beam quality index used in IAEA TRS-398, TPR{sub 20,10}, from a measurement of the tissue phantom ratio at depths of 20 cm and 10 cm in water for an s Multiplication-Sign s cm{sup 2} (equivalent) square field, TPR{sub 20,10}(s). First, a self-consistent version of this formula is established followed by a simpler version by making a linear approximation. A similar approach is proposed to derive the beam quality index used in AAPM TG-51, %dd(10){sub X}, from a measurement of PDD{sub 10}(s), the percentage depth dose at 10 cm for a square field with size s. All models were fitted to subsets of relevant data from BJR supplement 25. Results: The linear models for TPR{sub 20,10}(s) and exponential models for PDD{sub 10}(s) as a function of the (equivalent) square field size can reproduce the beam quality within 0.3% and beam quality correction factors within 0.05% for square field sizes ranging from 4 cm to 12 cm and nominal photon energies from 4 MV to 12 MV. For higher energy beams the errors are only slightly worse but for %dd(10){sub X}, an additional uncertainty component has to be considered for the electron contamination correction. Conclusions: The models proposed here can be used in practical recommendations for the dosimetry of small and nonstandard fields.

  2. Photon-number statistics of twin beams: Self-consistent measurement, reconstruction, and properties

    SciTech Connect

    Peřina, Jan Jr.; Haderka, Ondřej; Michálek, Václav

    2014-12-04

    A method for the determination of photon-number statistics of twin beams using the joint signal-idler photocount statistics obtained by an iCCD camera is described. It also provides absolute quantum detection efficiency of the camera. Using the measured photocount statistics, quasi-distributions of integrated intensities are obtained. They attain negative values occurring in characteristic strips an a consequence of pairing of photons in twin beams.

  3. Thomson scattering of polarized photons in an intense laser beam

    SciTech Connect

    Byung Yunn

    2006-02-21

    We present a theoretical analysis of the Thomson scattering of linearly and circularly polarized photons from a pulsed laser by electrons. The analytical expression for the photon distribution functions presented in this paper should be useful to designers of Thomson scattering experiments.

  4. Gaussian beam in two-photon fluorescence imaging of rat brain microvessel

    PubMed Central

    Shi, Lingyan; Rodríguez-Contreras, Adrián; Alfano, Robert R.

    2014-01-01

    Abstract. The critical optical properties of a Gaussian laser beam in two-photon or multiphoton fluorescence imaging, including the beam spot size, depth of focus, and intensity profile, are investigated for spatially locating nanoscale solutes in and surrounding the microvessels of rat brain. PMID:25490048

  5. A Polarimeter for GeV Linearly-polarized Photon Beams

    NASA Astrophysics Data System (ADS)

    Wood, M. H.; Tedeschi, D.; Wojtsekhowski, B.; Abbott, D.; Nelyubin, V.; Vlahovic, B.; Asai, J.; Feldman, G.; O'Rielly, G.; Khandaker, Mahbub; Hotta, T.; Kohri, H.; Matsumura, T.; Mibe, T.; Nakano, T.; Yorita, T.; Rudge, A.; Weilhammer, P.; Zegers, R.

    2003-04-01

    We have built a polarimeter for linearly-polarized photon beams in the few GeV photon-energy range. The technique is to detect an electron-positron pair produced from a photon incident on a thin converter. The orientation and the distance separating the e^+ and e^- are measured accurately with silicon-microstrip detectors. The polarimeter was calibrated at the SPring-8 facility using a compton-backscattered photon beam in the energy range of 1.5 GeV ≤ E_γ ≤ 2.4 GeV. This measurement was the first made for the process at these energies. Results will be presented of the measured asymmetry between horizontally and vertically polarized beams.

  6. Out-of-field photon and neutron dose equivalents from step-and-shoot intensity-modulated radiation therapy

    SciTech Connect

    Kry, Stephen F.; Salehpour, Mohammad . E-mail: msalehpour@mdanderson.org; Followill, David S.; Stovall, Marilyn; Kuban, Deborah A.; White, R. Allen; Rosen, Isaac I.

    2005-07-15

    Purpose: To measure the photon and neutron out-of-treatment-field dose equivalents to various organs from different treatment strategies (conventional vs. intensity-modulated radiation therapy [IMRT]) at different treatment energies and delivered by different accelerators. Methods and Materials: Independent measurements were made of the photon and neutron out-of-field dose equivalents resulting from one conventional and six IMRT treatments for prostate cancer. The conventional treatment used an 18-MV beam from a Clinac 2100; the IMRT treatments used 6-MV, 10-MV, 15-MV, and 18-MV beams from a Varian Clinac 2100 accelerator and 6-MV and 15-MV beams from a Siemens Primus accelerator. Photon doses were measured with thermoluminescent dosimeters in a Rando phantom, and neutron fluence was measured with gold foils. Dose equivalents to the colon, liver, stomach, lung, esophagus, thyroid, and active bone marrow were determined for each treatment approach. Results: For each treatment approach, the relationship between dose equivalent per MU, distance from the treatment field, and depth in the patient was examined. Photon dose equivalents decreased approximately exponentially with distance from the treatment field. Neutron dose equivalents were independent of distance from the treatment field and decreased with increasing tissue depth. Neutrons were a significant contributor to the out-of field dose equivalent for beam energies {>=}15 MV. Conclusions: Out-of-field photon and neutron dose equivalents can be estimated to any point in a patient undergoing a similar treatment approach from the distance of that point to the central axis and from the tissue depth. This information is useful in determining the dose to critical structures and in evaluating the risk of associated carcinogenesis.

  7. Monte Carlo simulation estimates of neutron doses to critical organs of a patient undergoing 18 MV x-ray LINAC-based radiotherapy

    SciTech Connect

    Barquero, R.; Edwards, T.M.; Iniguez, M. P.; Vega-Carrillo, H.R.

    2005-12-15

    Absorbed photoneutron dose to patients undergoing 18 MV x-ray therapy was studied using Monte Carlo simulations based on the MCNPX code. Two separate transport simulations were conducted, one for the photoneutron contribution and another for neutron capture gamma rays. The phantom model used was of a female patient receiving a four-field pelvic box treatment. Photoneutron doses were determinate to be higher for organs and tissues located inside the treatment field, especially those closest to the patient's skin. The maximum organ equivalent dose per x-ray treatment dose achieved within each treatment port was 719 {mu}Sv/Gy to the rectum (180 deg. field), 190 {mu}Sv/Gy to the intestine wall (0 deg. field), 51 {mu}Sv/Gy to the colon wall (90 deg. field), and 45 {mu}Sv/Gy to the skin (270 deg. field). The maximum neutron equivalent dose per x-ray treatment dose received by organs outside the treatment field was 65 {mu}Sv/Gy to the skin in the antero-posterior field. A mean value of 5{+-}2 {mu}Sv/Gy was obtained for organs distant from the treatment field. Distant organ neutron equivalent doses are all of the same order of magnitude and constitute a good estimate of deep organ neutron equivalent doses. Using the risk assessment method of the ICRP-60 report, the greatest likelihood of fatal secondary cancer for a 70 Gy dose is estimated to be 0.02% for the pelvic postero-anterior field, the rectum being the organ representing the maximum contribution of 0.011%.

  8. Photonic guiding structures in lithium niobate crystals produced by energetic ion beams

    NASA Astrophysics Data System (ADS)

    Chen, Feng

    2009-10-01

    A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimensions, to realize photonic bandgap crystals in LiNbO3, or directly write surface waveguides or other guiding devices in the crystal. Ion beam-enhanced etching has been extensively applied for micro- or nanostructuring of LiNbO3 surfaces. Methods developed to fabricate a range of photonic guiding structures in LiNbO3 are introduced. Modifications of LiNbO3 through the use of various energetic ion beams, including changes in refractive index and properties related to the photonic guiding structures as well as to the materials (i.e., electro-optic, nonlinear optic, luminescent, and photorefractive features), are overviewed in detail. The application of these LiNbO3 photonic guiding structures in both micro- and nanophotonics are briefly summarized.

  9. Estimation of photoneutron intensities around radiotherapy linear accelerator 23-MV photon beam.

    PubMed

    Shweikani, R; Anjak, O

    2015-05-01

    CR-39 solid-state nuclear track detectors (SSNTDs) were used to study the variations of fast neutron relative intensities around a high-energy (23MV) linear accelerator (Varian 21EX) photon beam. The variations were determined on the patient plane at 0, 50, 100, 150 and 200cm from the isocenter of the photon beam. In addition, photoneutron intensities and distributions at isocenter level with field size of 40×40cm(2) at Source Axis Distance (SAD)=100cm around 23MV photon beam were also determined. The results showed that the photoneutron intensities decreased rapidly by increasing the distance from the center of the x-ray beam towards the periphery, for the open fields. PMID:25770858

  10. Matching extended-SSD electron beams to multileaf collimated photon beams in the treatment of head and neck cancer

    SciTech Connect

    Steel, Jared; Stewart, Allan; Satory, Philip

    2009-09-15

    Purpose: Matching the penumbra of a 6 MeV electron beam to the penumbra of a 6 MV photon beam is a dose optimization challenge, especially when the electron beam is applied from an extended source-to-surface distance (SSD), as in the case of some head and neck treatments. Traditionally low melting point alloy blocks have been used to define the photon beam shielding over the spinal cord region. However, these are inherently time consuming to construct and employ in the clinical situation. Multileaf collimators (MLCs) provide a fast and reproducible shielding option but generate geometrically nonconformal approximations to the desired beam edge definition. The effects of substituting Cerrobend for the MLC shielding mode in the context of beam matching with extended-SSD electron beams are the subject of this investigation. Methods: Relative dose beam data from a Varian EX 2100 linear accelerator were acquired in a water tank under the 6 MeV electron beam at both standard and extended-SSD and under the 6 MV photon beam defined by Cerrobend and a number of MLC stepping regimes. The effect of increasing the electron beam SSD on the beam penumbra was assessed. MLC stepping was also assessed in terms of the effects on both the mean photon beam penumbra and the intraleaf dose-profile nonuniformity relative to the MLC midleaf. Computational techniques were used to combine the beam data so as to simulate composite relative dosimetry in the water tank, allowing fine control of beam abutment gap variation. Idealized volumetric dosimetry was generated based on the percentage depth-dose data for the beam modes and the abutment geometries involved. Comparison was made between each composite dosimetry dataset and the relevant ideal dosimetry dataset by way of subtraction. Results: Weighted dose-difference volume histograms (DDVHs) were produced, and these, in turn, summed to provide an overall dosimetry score for each abutment and shielding type/angle combination. Increasing the

  11. Photon fluence perturbation correction factors for solid state detectors irradiated in kilovoltage photon beams

    NASA Astrophysics Data System (ADS)

    Mobit, Paul N.; Sandison, George A.; Nahum, Alan E.

    2000-02-01

    Dose perturbation correction factors, gamma (p ), for LiF, CaF2 and Li2 B4 O7 solid state detectors have been determined using the EGS4 Monte Carlo code. Each detector was simulated in the form of a disc of diameter 3.61 mm and thickness 1 mm irradiated in a clinical kilovoltage photon beam at a depth of 1 cm in a water phantom. The perturbation correction factor gamma (p ) is defined as the deviation of the absorbed dose ratio from the average mass energy absorption coefficient ratio of water to the detector material, (mubar en /rho )med,det , which is evaluated assuming that the photon fluence spectrum in the medium and in the detector material are identical. We define another mass energy absorption coefficient ratio, (kappabar en /rho )med,det , which is evaluated using the actual photon fluence spectrum in the medium and detector for LiF and CaF2 rather than assuming they are identical. (kappabar en /rho )med,det predicts the average absorbed dose ratio of the medium to the detector material within 0.3%. When the difference in atomic number between the cavity and the phantom material is large then their photon fluence spectra will differ substantially resulting in a difference between (kappabar en /rho )med,det and (

  12. The influence of neutron contamination on dosimetry in external photon beam radiotherapy

    SciTech Connect

    Horst, Felix Czarnecki, Damian; Zink, Klemens

    2015-11-15

    Purpose: Photon fields with energies above ∼7 MeV are contaminated by neutrons due to photonuclear reactions. Their influence on dosimetry—although considered to be very low—is widely unexplored. Methods: In this work, Monte Carlo based investigations into this issue performed with FLUKA and EGSNRC are presented. A typical Linac head in 18 MV-X mode was modeled equivalently within both codes. EGSNRC was used for the photon and FLUKA for the neutron production and transport simulation. Water depth dose profiles and the response of different detectors (Farmer chamber, TLD-100, TLD-600H, and TLD-700H chip) in five representative depths were simulated and the neutrons’ impact (neutron absorbed dose relative to photon absorbed dose) was calculated. To take account of the neutrons’ influence, a theoretically required correction factor was defined and calculated for five representative water depths. Results: The neutrons’ impact on the absorbed dose to water was found to be below 0.1% for all depths and their impact on the response of the Farmer chamber and the TLD-700H chip was found to be even less. For the TLD-100 and the TLD-600H chip it was found to be up to 0.3% and 0.7%, respectively. The theoretical correction factors to be applied to absorbed dose to water values measured with these four detectors in a depth different from the reference/calibration depth were calculated and found to be below 0.05% for the Farmer chamber and the TLD-700H chip, but up to 0.15% and 0.35% for the TLD-100 and TLD-600H chips, respectively. In thermoluminescence dosimetry the neutrons’ influence (and therefore the additional inaccuracy in measurement) was found to be higher for TLD materials whose {sup 6}Li fraction is high, such as TLD-100 and TLD-600H, resulting from the thermal neutron capture reaction on {sup 6}Li. Conclusions: The impact of photoneutrons on the absorbed dose to water and on the response of a typical ionization chamber as well as three different types

  13. Hollow Gaussian beam generation through nonlinear interaction of photons with orbital angular momentum

    PubMed Central

    Chaitanya, N. Apurv; Jabir, M. V.; Banerji, J.; Samanta, G. K.

    2016-01-01

    Hollow Gaussian beams (HGB) are a special class of doughnut shaped beams that do not carry orbital angular momentum (OAM). Such beams have a wide range of applications in many fields including atomic optics, bio-photonics, atmospheric science, and plasma physics. Till date, these beams have been generated using linear optical elements. Here, we show a new way of generating HGBs by three-wave mixing in a nonlinear crystal. Based on nonlinear interaction of photons having OAM and conservation of OAM in nonlinear processes, we experimentally generated ultrafast HGBs of order as high as 6 and power >180 mW at 355 nm. This generic concept can be extended to any wavelength, timescales (continuous-wave and ultrafast) and any orders. We show that the removal of azimuthal phase of vortices does not produce Gaussian beam. We also propose a new and only method to characterize the order of the HGBs. PMID:27581625

  14. Hollow Gaussian beam generation through nonlinear interaction of photons with orbital angular momentum.

    PubMed

    Chaitanya, N Apurv; Jabir, M V; Banerji, J; Samanta, G K

    2016-01-01

    Hollow Gaussian beams (HGB) are a special class of doughnut shaped beams that do not carry orbital angular momentum (OAM). Such beams have a wide range of applications in many fields including atomic optics, bio-photonics, atmospheric science, and plasma physics. Till date, these beams have been generated using linear optical elements. Here, we show a new way of generating HGBs by three-wave mixing in a nonlinear crystal. Based on nonlinear interaction of photons having OAM and conservation of OAM in nonlinear processes, we experimentally generated ultrafast HGBs of order as high as 6 and power >180 mW at 355 nm. This generic concept can be extended to any wavelength, timescales (continuous-wave and ultrafast) and any orders. We show that the removal of azimuthal phase of vortices does not produce Gaussian beam. We also propose a new and only method to characterize the order of the HGBs. PMID:27581625

  15. Surface dose measurements and comparison of unflattened and flattened photon beams.

    PubMed

    Sigamani, Ashokkumar; Nambiraj, Arunai; Yadav, Girigesh; Giribabu, Ananda; Srinivasan, Karthikeyan; Gurusamy, Venkadamanickam; Raman, Kothanda; Karunakaran, Kaviarasu; Thiyagarajan, Rajesh

    2016-01-01

    The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs. PMID:27217619

  16. Surface dose measurements and comparison of unflattened and flattened photon beams

    PubMed Central

    Sigamani, Ashokkumar; Nambiraj, Arunai; Yadav, Girigesh; Giribabu, Ananda; Srinivasan, Karthikeyan; Gurusamy, Venkadamanickam; Raman, Kothanda; Karunakaran, Kaviarasu; Thiyagarajan, Rajesh

    2016-01-01

    The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs. PMID:27217619

  17. Investigation of photon beam models in heterogeneous media of modern radiotherapy.

    PubMed

    Ding, W; Johnston, P N; Wong, T P Y; Bubb, I F

    2004-06-01

    This study investigates the performance of photon beam models in dose calculations involving heterogeneous media in modern radiotherapy. Three dose calculation algorithms implemented in the CMS FOCUS treatment planning system have been assessed and validated using ionization chambers, thermoluminescent dosimeters (TLDs) and film. The algorithms include the multigrid superposition (MGS) algorithm, fast Fourier Transform Convolution (FFTC) algorithm and Clarkson algorithm. Heterogeneous phantoms used in the study consist of air cavities, lung analogue and an anthropomorphic phantom. Depth dose distributions along the central beam axis for 6 MV and 10 MV photon beams with field sizes of 5 cm x 5 cm and 10 cm x 10 cm were measured in the air cavity phantoms and lung analogue phantom. Point dose measurements were performed in the anthropomorphic phantom. Calculated results with three dose calculation algorithms were compared with measured results. In the air cavity phantoms, the maximum dose differences between the algorithms and the measurements were found at the distal surface of the air cavity with a 10 MV photon beam and a 5 cm x 5 cm field size. The differences were 3.8%. 24.9% and 27.7% for the MGS. FFTC and Clarkson algorithms. respectively. Experimental measurements of secondary electron build-up range beyond the air cavity showed an increase with decreasing field size, increasing energy and increasing air cavity thickness. The maximum dose differences in the lung analogue with 5 cm x 5 cm field size were found to be 0.3%. 4.9% and 6.9% for the MGS. FFTC and Clarkson algorithms with a 6 MV photon beam and 0.4%. 6.3% and 9.1% with a 10 MV photon beam, respectively. In the anthropomorphic phantom, the dose differences between calculations using the MGS algorithm and measurements with TLD rods were less than +/-4.5% for 6 MV and 10 MV photon beams with 10 cm x 10 cm field size and 6 MV photon beam with 5 cm x 5 cm field size, and within +/-7.5% for 10 MV with 5 cm

  18. A fast profile monitor with scintillating fiber hodoscopes for high-intensity photon beams

    NASA Astrophysics Data System (ADS)

    Ishikawa, T.; Fujimura, H.; Hamano, H.; Hashimoto, R.; Honda, Y.; Ishida, T.; Kaida, S.; Kanda, H.; Kido, S.; Matsumura, Y.; Miyabe, M.; Mizutani, K.; Nagasawa, I.; Nakamura, A.; Nanbu, K.; Nawa, K.; Ogushi, S.; Shibasaki, Y.; Shimizu, H.; Sugai, H.; Suzuki, K.; Takahashi, K.; Takahashi, S.; Taniguchi, Y.; Tokiyasu, A. O.; Tsuchikawa, Y.; Yamazaki, H.

    2016-03-01

    A fast beam-profile monitor has been developed for high-energy photon beamlines at the Research Center for Electron Photon Science, Tohoku University. The position of the photon converted into an electron-positron pair in a 0.5 mm-thick aluminum plate is measured with two hodoscopes made of scintillating fibers with cross-sections of 3 × 3mm2. Events in which charged particles are produced upstream are rejected with a charge veto plastic scintillator placed in front of the plate, and pair-production events are identified with a trigger plastic scintillator placed behind the plate. The position is determined by a developed logic module with a field-programmable gate array. The dead time for processing an event is 35 ns, and a high data acquisition efficiency (~ 100 %) can be achieved with this monitor for high-intensity photon beams corresponding to 20 MHz tagging signals.

  19. A closed-loop photon beam control study for the Advanced Light Source

    SciTech Connect

    Portmann, G.; Bengtsson, J.

    1993-05-01

    The third generation Advanced Light Source (ALS) will produce extremely bright photon beams using undulators and wigglers. In order to position the photon beams accurate to the micron level, a closed-loop feedback system is being developed. Using photon position monitors and dipole corrector magnets, a closed-loop system can automatically compensate for modeling uncertainties and exogenous disturbances. The following paper will present a dynamics model for the perturbations of the closed orbit of the electron beam in the ALS storage ring including the vacuum chamber magnetic field penetration effects. Using this reference model, two closed-loop feedback algorithms will be compared -- a classical PI controller and a two degree-of-freedom approach. The two degree-of-freedom method provides superior disturbance rejection while maintaining the desired performance goals. Both methods will address the need to gain schedule the controller due to the time varying dynamics introduced by changing field strengths when scanning the insertion devices.

  20. Applying a polynomial formula to photon beam output and equivalent square field.

    PubMed

    Chen, F S

    1990-01-01

    The polynomial formula proposed by Chen [Med. Phys. 15, 348 (1988)] in calculating the electron beam output from a Therac 20 linear accelerator has been applied to generating the output factor of various machines with photon energies ranging from 100 kVp to 18 MeV. The calculated outputs are within 1% of the measured values. This formula can be very useful to the physicist in preparing an output table of photon beams or electron beams for a therapeutic unit. An equation is derived from this formula to calculate the equivalent square. The derivation shows that only under special circumstances is the equivalent square field equivalent to 2ab/(a + b); otherwise the equivalent square field depends on the formula's parameters as well as the sides of the rectangular field. These parameters, in turn, are dependent on the photon energy, the medium irradiated, and the collimator design. PMID:2117228

  1. Effects of vertical aperture on beam lifetime at the Advanced Photon Source (APS) storage ring

    SciTech Connect

    Bizek, H.M.

    1995-06-01

    When a positron`s energy deviation {delta}E/E exceeds the rf acceptance, or when it receives an angular kick for the betatron motion that exceeds some limiting admittance, the positron will be lost. The main contributions to the total beam lifetime come from single Coulomb and Touschek scattering. In this report we investigate the dependence of the residual gas pressure and the vertical aperture of the Advanced Photon Source storage ring on the total beam. lifetime. We present results of calculating the total beam lifetime as a function of vertical aperture for varying average ring pressure, beam current, and coupling coefficient.

  2. Dose conformation of intensity-modulated stereotactic photon beams, proton beams, and intensity-modulated proton beams for intracranial lesions

    SciTech Connect

    Baumert, Brigitta G. . E-mail: brigitta.baumert@maastro.nl; Norton, Ian A.; Lomax, Antony J.; Davis, J.B.

    2004-11-15

    Purpose: This study evaluates photon beam intensity-modulated stereotactic radiotherapy (IMSRT) based on dynamic leaf motion of a micromultileaf collimator (mMLC), proton beams, and intensity-modulated proton therapy (IMPT) with respect to target coverage and organs at risk. Methods and materials: Dose plans of 6 stereotactically treated patients were recalculated for IMSRT by use of the same field setup and an inverse planning algorithm. Proton and IMPT plans were calculated anew. Three different tumor shapes, multifocal, ovoid, and irregular, were analyzed, as well as dose to organs-at-risk (OAR) in the vicinity of the planning target volume (PTV). Dose distributions were calculated from beam-setup data for a manual mMLC for stereotactically guided conformal radiotherapy (SCRT), a dynamic mMLC for IMSRT, the spot-scanning technique for protons, and a modified spot-scanning technique for IMPT. SCRT was included for a part of the comparison. Criteria for assessment were PTV coverage, dose-volume histograms (DVH), volumes of specific isodoses, and the dose to OAR. Results: Dose conformation to the PTV is equally good for all three techniques and tumor shapes considered. The volumes of the 90% and 80% isodose were comparable for all techniques. For the 50% isodose volume, a divergence between the two modes was seen. In 3 cases, this volume is smaller for IMSRT, and in the 3 other cases, it is smaller for IMPT. This difference was even more pronounced for the volumes of the 30% isodose; IMPT shows further improvement over conventional protons. OAR in concavities (e.g., the brainstem) were similarly well spared by protons and IMSRT. IMPT spares critical organs best. Fewer proton beams are required to achieve similar results. Conclusions: The addition of intensity modulation improves the conformality of mMLC-based SCRT. Conformation of dose to the PTV is comparable for IMSRT, protons, and IMPT. Concerning the sparing of OAR, IMSRT is equivalent to IMPT, and IMPT is

  3. Calculation of the characteristics of clinical high-energy photon beams with EGS5-MPI

    NASA Astrophysics Data System (ADS)

    Shimizu, M.; Morishita, Y.; Kato, M.; Kurosawa, T.; Tanaka, T.; Takata, N.; Saito, N.

    2014-03-01

    A graphite calorimeter has been developed as a Japanese primary standard of absorbed dose to water in the high-energy photon beams from a clinical linac. To obtain conversion factors for the graphite calorimeter, the beam characteristics of the high-energy photon beams from the clinical linac at National Metrology Institute of Japan were calculated with the EGS5 Monte Carlo simulation code. To run the EGS5 code on High Performance Computing machines that have more than 1000 CPU cores, we developed the EGS5 parallelisation package "EGS5-MPI" by implementing a message-passing interface. We calculated the photon energy spectra, which are in good agreement with those previously calculated by D. Sheikh-Bagheri and D. W. O. Rogers (Med. Phys. 29 3). We also estimated the percentage-depth-dose distributions of photon beams from the linac using the calculated photon energy spectra. These calculated percentage-depth-dose distributions were compared with our measured distributions and were found they are in good agreement as well. We will calculate conversion factors for the graphite calorimeter using our results.

  4. TU-A-BRE-01: The Relative Biological Effectiveness of Proton Beams Relative to Photon Beams

    SciTech Connect

    Paganetti, H; Stewart, R; Carabe-Fernandez, A

    2014-06-15

    Proton therapy patients receive a 10% lower physical dose than the dose administered using photons, i.e. the proton relative biological effectiveness (RBE) is 1.1 in comparison to high-energy photons. The use of a generic, spatially invariant RBE within tumor targets and normal tissue structures disregards a large body of evidence indicating that proton RBE tends to increase with increasing linear energy transfer (LET). Because the doseaveraged proton LET in the distal edge of a spread out Bragg peak (SOBP) is larger than the LET in the plateau region or proximal edge of a SOBP, the use of a spatially invariant RBE is not well justified from a mechanistic point of view. On the other hand, the available clinical data on local tumor control rates and early or late side effects do not provide strong evidence against the continued use of a constant and spatially invariant clinical RBE. The only potential downside to the ongoing use of a constant RBE of 1.1 seems to be that we are missing a potential opportunity to enhance the therapeutic ratio, i.e., design proton therapy treatments in ways that exploit, rather than mitigate, spatial variations in proton RBE. Speakers in this symposium will: 1-review the laboratory and clinical evidence for and against the continued use of a spatially invariant RBE of 1.1, 2-examine some of the putative mechanisms connecting spatial variations in particle LET to estimates of the proton RBE at the molecular, cellular and tissue levels 3-assess the possible clinical significance of incorporating models for spatial variations in proton RBE into treatment planning systems. 4-discuss treatment planning and delivery techniques that will exploit the spatial variations of RBE within proton beams. Learning Objectives: To review laboratory and clinical evidence for and against the continued use of a constant RBE of 1.1 To understand major mechanisms connecting proton LET to RBE at the molecular, cellular and tissue levels. To quantify the

  5. Determination of the neutron and photon spectra of a clinical fast neutron beam.

    PubMed

    Moyers, M F; Horton, J L

    1990-01-01

    A simple technique to determine the neutron and photon spectra of a clinical fast neutron beam is described. This technique involves making narrow beam attenuation measurements with a pair of ionization chambers and an iterative fitting program to analyze the data. A method is also described for determining the first-guess neutron spectrum for input into the iterative program. The results of the analysis yield spectra suitable for use in dose calculation algorithms and dosimetry protocols. Presented here is the first-known published photon spectrum from a clinical machine. PMID:2120558

  6. Measurement of Electron Beam Polarization from Unstrained Bulk GaAs via Two Photon Photoemission

    SciTech Connect

    J L McCarter, T J Gay, J Hansknecht, M Poelker, M L Stutzman

    2011-06-01

    This paper describes measurements of the beam polarization and quantum efficiency for photoemission using two-photon excitation from unstrained bulk GaAs illuminated with pulsed, high intensity 1560nm laser light. Quantum efficiency is linearly proportional to 1560nm peak laser intensity, which was varied in three independent ways, indicating that the emitted electrons are promoted from the valence to the conduction band via two-photon absorption. Beam polarization was measured using a microMott polarimeter, with a value of 16.8(4)% polarization at 1560nm, which is roughly half the measured value of 33.4(8)% using 778 nm light.

  7. Genetic algorithms optimization of photonic crystal fibers for half diffraction angle reduction of output beam.

    PubMed

    Lu, Jyun-Hong; Cai, Dong-Po; Tsai, Ya-Lun; Chen, Chii-Chang; Lin, Chu-En; Yen, Ta-Jen

    2014-09-22

    In this work, we optimize the structure of the photonic crystal fibers by using genetic algorithms to provide strong light confinement in fiber and small half diffraction angle of output beam. Furthermore, this article shows the potentials of this study, such as optimizing three purposes at the same time and the arbitrary structure design is achieved. We report two optimized results obtained by different optimization conditions. The results show that the half diffraction angle of the output beam of the photonic crystal fibers can be reduced. PMID:25321728

  8. Atom Interferometry with up to 24-Photon-Momentum-Transfer Beam Splitters

    SciTech Connect

    Mueller, Holger; Chiow, Sheng-wey; Long, Quan; Herrmann, Sven; Chu, Steven

    2008-05-09

    We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Borde (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel.

  9. Photon reflectivity distributions from the LHC beam screen and their implications on the arc beam vacuum system

    NASA Astrophysics Data System (ADS)

    Mahne, N.; Baglin, V.; Collins, I. R.; Giglia, A.; Pasquali, L.; Pedio, M.; Nannarone, S.; Cimino, R.

    2004-07-01

    In particle accelerators with intense positively charged bunched beams, an electron cloud may induce beam instabilities and the related beam induced electron multipacting (BIEM) can result in an undesired pressure rise. In a cryogenic machine such as the large hadron collider (LHC), the BIEM will introduce additional heat load. When present, synchrotron radiation (SR) may generate a significant number of photoelectrons, that may play a role in determining the onset and the detailed properties of the electron cloud related instability. Since electrons are constrained to move along field lines, those created on the accelerator equator in a strong vertical (dipole) field cannot participate in the e-cloud build-up. Therefore, for the LHC there has been a continuous effort to find solutions to absorb the photons on the equator. The solution adopted for the LHC dipole beam screens is a saw-tooth structure on the illuminated equator. SR from a bending magnet beamline at ELETTRA, Italy (BEAR) has been used to measure the reflectivities (forward, back-scattered and diffuse), for a flat and a saw-tooth structured Cu co-laminated surface using both white light SR, similar to the one emitted by LHC, and monochromatic light. Our data show that the saw-tooth structure does reduce the total reflectivity and modifies the photon energy distribution of the reflected photons. The implications of these results on the LHC arc vacuum system are discussed.

  10. Spectral reconstruction of high energy photon beams for kernel based dose calculations.

    PubMed

    Hinson, William H; Bourland, J Daniel

    2002-08-01

    A kernel-based dose computation method with finite-size pencil beams (FSPBs) requires knowledge of the photon spectrum. Published methods of indirect spectral measurements using transmission measurements through beam attenuators use mathematical fits with a large number of parameters and constraints. In this study, we examine a simple strategy for fitting transmission data that models important physical characteristics of photon beams produced in clinical linear accelerators. The shape of an unattenuated bremsstrahlung spectrum is known, varying linearly from a maximum at zero energy to a value of zero at a maximum energy. This unattenuated spectrum is altered primarily by absorption of low energy photons by the flattening filter, causing the true spectrum to roll off to zero at low photon energies. A fitting equation models this behavior and has these advantages over previous methods: (1) the equation describes the shape of a bremsstrahlung spectrum based on physical expectations; and (2) only three fit parameters are required with a single constraint. Results for 4 MV and 6 MV accelerators for central axis and off-axis beams show good agreement with the maximum, average and modal energies for known spectra. Previously published models, representations of beam fluence (energy fluence, dN/dE), experimental methods, and the fitting process are discussed. PMID:12201426

  11. A microwave beam waveguide undulator for a brilliant above 100 keV photon source.

    SciTech Connect

    Kang, Y. W.

    1999-04-19

    For generation of photons above 100-keV with a magnetic field strength in the range 0.2-0.5 Tesla, an undulator wavelength {lambda}{sub u} shorter than 5 mm may be needed with beam in the Advanced Photon Source (APS) storage ring. A microwave beam waveguide undulator system has been investigated for generation of such light. The waveguide structure consists of two parallel reflector surfaces that can be derived from an elliptically cylindrical waveguide. The structure can support deflecting TE{sub m0} modes with very low microwave loss. A microwave ring resonator circuit employing the beam waveguide is considered to construct an undulator with the above requirement. Microwave properties of the beam waveguide structure have been investigated, and the design criteria for a microwave undulator are discussed.

  12. Cascaded two-photon spectroscopy of Yb atoms with a transportable effusive atomic beam apparatus.

    PubMed

    Song, Minsoo; Yoon, Tai Hyun

    2013-02-01

    We present a transportable effusive atomic beam apparatus for cascaded two-photon spectroscopy of the dipole-forbidden transition (6s(2)(1)S0↔ 6s7s (1)S0) of Yb atoms. An ohmic-heating effusive oven is designed to have a reservoir volume of 1.6 cm(3) and a high degree of atomic beam collimation angle of 30 mrad. The new atomic beam apparatus allows us to detect the spontaneously cascaded two-photons from the 6s7s(1)S0 state via the intercombination 6s6p(3)P1 state with a high signal-to-noise ratio even at the temperature of 340 °C. This is made possible in our apparatus because of the enhanced atomic beam flux and superior detection solid angle. PMID:23464193

  13. Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy

    SciTech Connect

    Fogliata, A.; Garcia, R.; Knoeoes, T.; Nicolini, G.; Clivio, A.; Vanetti, E.; Khamphan, C.; Cozzi, L.

    2012-10-15

    Purpose: Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medical linacs in radiotherapy. Methods: The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. Results: Definitions for dose profile parameters are suggested starting from the renormalization of the FFF with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of 'unflatness' and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. Conclusions: Ideas for quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines.

  14. Monte Carlo based beam model using a photon MLC for modulated electron radiotherapy

    SciTech Connect

    Henzen, D. Manser, P.; Frei, D.; Volken, W.; Born, E. J.; Vetterli, D.; Chatelain, C.; Fix, M. K.; Neuenschwander, H.; Stampanoni, M. F. M.

    2014-02-15

    Purpose: Modulated electron radiotherapy (MERT) promises sparing of organs at risk for certain tumor sites. Any implementation of MERT treatment planning requires an accurate beam model. The aim of this work is the development of a beam model which reconstructs electron fields shaped using the Millennium photon multileaf collimator (MLC) (Varian Medical Systems, Inc., Palo Alto, CA) for a Varian linear accelerator (linac). Methods: This beam model is divided into an analytical part (two photon and two electron sources) and a Monte Carlo (MC) transport through the MLC. For dose calculation purposes the beam model has been coupled with a macro MC dose calculation algorithm. The commissioning process requires a set of measurements and precalculated MC input. The beam model has been commissioned at a source to surface distance of 70 cm for a Clinac 23EX (Varian Medical Systems, Inc., Palo Alto, CA) and a TrueBeam linac (Varian Medical Systems, Inc., Palo Alto, CA). For validation purposes, measured and calculated depth dose curves and dose profiles are compared for four different MLC shaped electron fields and all available energies. Furthermore, a measured two-dimensional dose distribution for patched segments consisting of three 18 MeV segments, three 12 MeV segments, and a 9 MeV segment is compared with corresponding dose calculations. Finally, measured and calculated two-dimensional dose distributions are compared for a circular segment encompassed with a C-shaped segment. Results: For 15 × 34, 5 × 5, and 2 × 2 cm{sup 2} fields differences between water phantom measurements and calculations using the beam model coupled with the macro MC dose calculation algorithm are generally within 2% of the maximal dose value or 2 mm distance to agreement (DTA) for all electron beam energies. For a more complex MLC pattern, differences between measurements and calculations are generally within 3% of the maximal dose value or 3 mm DTA for all electron beam energies. For the

  15. White Beam Slits and Pink Beam Slits for the Hard X-ray Nanoprobe Beamline at the Advanced Photon Source

    NASA Astrophysics Data System (ADS)

    Benson, C.; Jaski, Y.; Maser, J.; Powers, T.; Schmidt, O.; Rossi, E.

    2007-01-01

    A new type of slit has been designed for use in the hard x-ray nanoprobe beamline at the Advanced Photon Source (APS). The design incorporates monolithic GlidCop slit bodies mounted to commercially available x-y drive systems. Long, tapered apertures with adjacent water-cooling channels intercept the x-ray beam, removing the high heat load produced by two collinear APS undulators. The apertures are L-shaped and provide both horizontal and vertical slits. The beam-defining edges, positioned at the end of the tapered surfaces, consist of two sets of tungsten blades. These blades produce an exit beam with sharp corners and assure a clean cut-off for the white beam edges. The slit assembly is designed to allow overlap of the slit edges to stop the beam. The white beam slit design accommodates 3100 W of total power with a peak power density of 763 W/mm2. The pink beam slit design accommodates 400 W of total power with a peak power density of 180 W/mm2. Detailed thermal analyses were performed to verify the slits' accuracy under full beam loading. The new concept allows beamline operations to 180 mA with a simplified design approach.

  16. White beam slits and pink beam slits for the hard x-ray nanoprobe beamline at the Advanced Photon Source.

    SciTech Connect

    Benson, C.; Jaski, Y.; Maser, J.; Powers, T.; Schmidt, O.; Rossi, E.

    2007-01-01

    A new type of slit has been designed for use in the hard x-ray nanoprobe beamline at the Advanced Photon Source (APS). The design incorporates monolithic GlidCop slit bodies mounted to commercially available x-y drive systems. Long, tapered apertures with adjacent water-cooling channels intercept the x-ray beam, removing the high heat load produced by two collinear APS undulators. The apertures are L-shaped and provide both horizontal and vertical slits. The beam-defining edges, positioned at the end of the tapered surfaces, consist of two sets of tungsten blades. These blades produce an exit beam with sharp corners and assure a clean cut-off for the white beam edges. The slit assembly is designed to allow overlap of the slit edges to stop the beam. The white beam slit design accommodates 3100 W of total power with a peak power density of 763 W/mm2. The pink beam slit design accommodates 400 W of total power with a peak power density of 180 W/mm2. Detailed thermal analyses were performed to verify the slits accuracy under full beam loading. The new concept allows beamline operations to 180 mA with a simplified design approach.

  17. White Beam Slits and Pink Beam Slits for the Hard X-ray Nanoprobe Beamline at the Advanced Photon Source

    SciTech Connect

    Benson, C.; Jaski, Y.; Powers, T.; Schmidt, O.; Rossi, E.; Maser, J.

    2007-01-19

    A new type of slit has been designed for use in the hard x-ray nanoprobe beamline at the Advanced Photon Source (APS). The design incorporates monolithic GlidCop slit bodies mounted to commercially available x-y drive systems. Long, tapered apertures with adjacent water-cooling channels intercept the x-ray beam, removing the high heat load produced by two collinear APS undulators. The apertures are L-shaped and provide both horizontal and vertical slits. The beam-defining edges, positioned at the end of the tapered surfaces, consist of two sets of tungsten blades. These blades produce an exit beam with sharp corners and assure a clean cut-off for the white beam edges. The slit assembly is designed to allow overlap of the slit edges to stop the beam.The white beam slit design accommodates 3100 W of total power with a peak power density of 763 W/mm2. The pink beam slit design accommodates 400 W of total power with a peak power density of 180 W/mm2. Detailed thermal analyses were performed to verify the slits' accuracy under full beam loading. The new concept allows beamline operations to 180 mA with a simplified design approach.

  18. Polarity correction factor for flattening filter free photon beams in several cylindrical ionization chambers.

    PubMed

    Ogata, Toshiyuki; Uehara, Kazuyuki; Nakayama, Masao; Tsudou, Shinji; Masutani, Takashi; Okayama, Takanobu

    2016-07-01

    In this study, we aimed to compare the polarity correction factor in ionization chambers for flattening filter free (FFF) photon beams and flattening filter (FF) beams. Measurements were performed with both 6 and 10 MV FFF and FF beams. Five commercial ionization chambers were evaluated: PTW TN30013; IBA Dosimetry CC01, CC04, and CC13; and Exradin A12S. Except for the CC01 ionization chamber, the other four chambers showed less than a 0.3 % difference in the polarity effect between the FFF and the FF beams. The CC01 chamber showed a strong field-size-dependence, unlike the other chambers. The polarity effect for all chambers with FFF beams did not change with the dose rate. Except in the case of the CC01 chamber, the difference in the polarity effect between FFF and FF beams was not significant. PMID:26873138

  19. Fano resonance of self-collimated beams in two-dimensional photonic crystals.

    PubMed

    Lee, Sun-Goo; Park, Jong-Moon; Kee, Chul-Sik

    2014-11-17

    We report that the Fano resonance of self-collimated beams can be achieved in a two-dimensional photonic crystal by introducing a Fano resonator that is composed of zigzag line defects. An asymmetric Fano line shape in a transmission spectrum is generated by the interference between radiated light beams from the resonator and self-collimated beams that directly pass through the resonator without resonance. It is shown that the Fano profile increases in sharpness as the number of zigzag line defects increases because the phase values of the radiated light beams change more rapidly when the number of defects increases. The Fano resonance of self-collimated beams could provide an efficient approach to manipulate light propagation and increase the possibility of application of self-collimated beams. PMID:25402134

  20. Laser scanning stereomicroscopy for fast volumetric imaging with two-photon excitation and scanned Bessel beams

    NASA Astrophysics Data System (ADS)

    Yang, Yanlong; Zhou, Xing; Li, Runze; Van Horn, Mark; Peng, Tong; Lei, Ming; Wu, Di; Chen, Xun; Yao, Baoli; Ye, Tong

    2015-03-01

    Bessel beams have been used in many applications due to their unique optical properties of maintaining their intensity profiles unchanged during propagation. In imaging applications, Bessel beams have been successfully used to provide extended focuses for volumetric imaging and uniformed illumination plane in light-sheet microscopy. Coupled with two-photon excitation, Bessel beams have been successfully used in realizing fluorescence projected volumetric imaging. We demonstrated previously a stereoscopic solution-two-photon fluorescence stereomicroscopy (TPFSM)-for recovering the depth information in volumetric imaging with Bessel beams. In TPFSM, tilted Bessel beams were used to generate stereoscopic images on a laser scanning two-photon fluorescence microscope; upon post image processing we could successfully provide 3D perception of acquired volume images by wearing anaglyph 3D glasses. However, tilted Bessel beams were generated by shifting either an axicon or an objective laterally; the slow imaging speed and severe aberrations made it hard to use in real-time volume imaging. In this article, we report recent improvements of TPFSM with newly designed scanner and imaging software, which allows 3D stereoscopic imaging without moving any of the optical components on the setup. This improvement has dramatically improved focusing qualities and imaging speed so that the TPFSM can be performed potentially in real-time to provide 3D visualization in scattering media without post image processing.

  1. Comparison of Techniques to Reduce Bremsstrahlung Background Radiation from Monoenergetic Photon Beams

    SciTech Connect

    Johnson, M; McNabb, D

    2006-06-29

    An important applied technology is a tunable mono-energetic photon source [1]. These sources are made of relativistic electron accelerators coupled to low-energy lasers, which produce high-energy, mono-energetic-rays. One challenge associated with systems such as this is a continuum of bremsstrahlung background created when an electron beam passes through an aperture of some sort and the electron bunch or its halo impinges on the aperture pictured in figure 1. For instance, in the current T-REX [1] design for the interaction point between the laser- and electron-beam, the electron-beam passes through the center of a mirror used to reflect the laser. There is a potential with this design that bremsstrahlung radiation may be produced at the edges of the mirror openings and contaminate the mono-energetic photon beam. Certain applications [2] may be sensitive to this contamination. To reduce the bremsstrahlung contaminate a collimator (thickness {approx}24in. (calculated from XCOM database [3]) to attenuate by a factor of 10{sup -3} the 112MeV photons expected in the T-REX demonstration [1]) is situated between the aperture and target. To maximize the brightness of the photon-beam, the collimator opening must be no less than the size of the photon-beam spot size expected to be about 1mm. This fixes the collimator opening. a priori the aperture size must be greater than the collimator opening and is a function distance between the aperture and collimator. In this paper we focus on two approaches to estimate the aperture size, given a collimator and a target whose sizes and distances from the aperture are given. In the next section we will discuss these approaches.

  2. Photon beams for radiosurgery produced by laser Compton backscattering from relativistic electrons

    NASA Astrophysics Data System (ADS)

    Girolami, B.; Larsson, B.; Preger, M.; Schaerf, C.; Stepanek, J.

    1996-09-01

    The frontal collisions of a laser beam with relativistic electrons result in Compton-backscattered photons. The energy of these photons is dependent on the laser and electron energy in the range from kilo-electron-volts to tens of mega-electron-volts. In a sufficiently narrow backscattering angle the photons are nearly monochromatic. Over the past 30 years there have been several attempts to produce photon beams by laser backscattering from relativistic electrons stored in magnetic ring structures. One aim is to produce photons in the high mega-electron-volt energy range with fluxes useful for nuclear physics research; another is to produce photons in the high kilo-electron-volt energy range, which would be useful for medical applications, such as coronary angiography or treatment of tumour. Our present interest is to investigate the possibility of using 34 keV to 10 MeV photon beams for applications in stereotactic functional radiosurgery. We foresee the possibility of neurosurgical operations through the intact skull with precise and effective destruction of deeply lying millimetre-sized targets with minimal effects on intervening structures, high reproducibility and good prediction of the results. Our paper presents: a Monte Carlo study of radiosurgery based on cross firing with 34 keV to 100 MeV photon beams and 200 and 580 MeV proton beams, a theoretical description of the kinematics of Compton backscattering and estimates of the backscattered photon flux from several combinations of laser cavities at Nd:YAG (1.17 eV) and (0.117 eV) laser energies and electron storage rings energies in the range 0.1 - 1.3 GeV. As examples, existing magnetic structures, such as the Accumulator in the lower energy range and the Trieste Synchrotron Light Source ELETTRA in the higher energy range have been utilized in the

  3. Study of dose perturbation parameters for eye shielding in megavoltage photon beam therapy

    SciTech Connect

    Das, I.J.; Kase, K.R.; Fitzgerald, T.J.; Ligon, D.A. )

    1990-08-01

    Shielding blocks are frequently used to minimize dose and shield sensitive organs in radiation therapy. The blocks, which are made of high atomic number materials, produce significant dose perturbations in megavoltage photon beams. The effects of these perturbations are studied with special interest in the eye shielding in the treatment of head and neck malignancies. Optimum parameters for the treatment are suggested.

  4. Determination of ion recombination correction factors for a liquid ionization chamber in megavoltage photon beams

    NASA Astrophysics Data System (ADS)

    Choi, Sang Hyoun; Kim, Kum-Bae; Ji, Young Hoon; Kim, Chan Hyeong; Kim, Seonghoon; Huh, Hyun Do

    2015-05-01

    The aim of this study is to determine the ion recombination correction factor for a liquid ionization chamber in a high energy photon beam by using our experimental method. The ion recombination correction factors were determined by using our experimental method and were compared with theoretical and experimental methods proposed by using the theoretical method (Greening, Johansson) and the two-dose rate method in a cobalt beam and a high energy photon beam. In order to apply the liquid ionization chamber in a reference and small field dosimetry, we acquired the absorbed dose to water correction coefficient, the beam quality correction factor, and the influence quantities for the microLion chamber according to the TRS-398 protocol and applied the results to a high energy photon beam used in clinical fields. As a result, our experimental method for ion recombination in a cobalt beam agreed with the results from the heoretical method (Greening theory) better than it did with the results from the two-dose rate method. For high energy photon beams, the two-dose rate and our experimental methods were in good agreement, less than 2% deviation, while the theoretical general collection efficiency (Johansson et al.) deviated greatly from the experimental values. When we applied the factors for the absorbed dose to water measurement, the absorbed dose to water for the microLion chamber was in good agreement, within 1%, compared with the values for the PTW 30013 chamber in 6 and 10 MV Clinac iX and 6 and 15 MV Oncor impression. With these results, not only can the microLion ionization chamber be used to measure the absorbed dose to water in a reference condition, it can also be used to a the chamber for small, non-standard field dosimetry.

  5. Measurement of electron beam polarization from unstrained GaAs via two-photon photoemission

    SciTech Connect

    McCarter, James L.; Afanasev, A.; Gay, T. J.; Hansknecht, John C.; Kechiantz, A.; Poelker, B. Matthew

    2014-02-01

    Two-photon absorption of 1560 nm light was used to generate polarized electron beams from unstrained GaAs photocathodes of varying thickness: 625 {mu}m, 0.32 {mu}m, and 0.18 {mu}m. For each photocathode, the degree of spin polarization of the photoemitted beam was less than 50%, contradicting earlier predictions based on simple quantum mechanical selection rules for spherically-symmetric systems but consistent with the more sophisticated model of Bhat et al. (Phys. Rev. B 71 (2005) 035209). Polarization via two-photon absorption was the highest from the thinnest photocathode sample and comparable to that obtained via one-photon absorption (using 778 nm light), with values 40.3 +- 1.0% and 42.6 +- 1.0%, respectively.

  6. Two-photon polymerization of cylinder microstructures by femtosecond Bessel beams

    SciTech Connect

    Yang, Liang; El-Tamer, Ayman; Hinze, Ulf; Chichkov, Boris N; Li, Jiawen Hu, Yanlei; Huang, Wenhao; Chu, Jiaru

    2014-07-28

    In this work, we present an approach to modulate femtosecond laser beams into Bessel beams with a spatial light modulator (SLM) for two-photon polymerization applications. Bessel beams with different parameters are generated and annular optical fields are produced at the focal plane of the objective. Uniform cylinder microstructures are fabricated by a single illumination during a few seconds without stage translation. By modulating the holograms encoded on the SLM, the diameters of the fabricated annular structures can be flexibly controlled in a wide range with no need of changing the optical elements and realignment of the optical path.

  7. Absorbed dose measurements in the build-up region of flattened versus unflattened megavoltage photon beams.

    PubMed

    De Puysseleyr, Annemieke; Lechner, Wolfgang; De Neve, Wilfried; Georg, Dietmar; De Wagter, Carlos

    2016-06-01

    This study evaluated absorbed dose measurements in the build-up region of conventional (FF) versus flattening filter-free (FFF) photon beams. The absorbed dose in the build-up region of static 6 and 10MV FF and FFF beams was measured using radiochromic film and extrapolation chamber dosimetry for single beams with a variety of field sizes, shapes and positions relative to the central axis. Removing the flattening filter generally resulted in slightly higher relative build-up doses. No considerable impact on the depth of maximum dose was found. PMID:27020966

  8. Two-photon polymerization of a three dimensional structure using beams with orbital angular momentum

    SciTech Connect

    Zhang, Shi-Jie; Li, Yan Liu, Zhao-Pei; Ren, Jin-Li; Xiao, Yun-Feng; Yang, Hong; Gong, Qihuang

    2014-08-11

    The focus of a beam with orbital angular momentum exhibits internal structure instead of an elliptical intensity distribution of a Gaussian beam, and the superposition of Gauss-Laguerre beams realized by two-dimensional phase modulation can generate a complex three-dimensional (3D) focus. By taking advantage of the flexibility of this 3D focus tailoring, we have fabricated a 3D microstructure with high resolution by two-photon polymerization with a single exposure. Furthermore, we have polymerized an array of double-helix structures that demonstrates optical chirality.

  9. A diamond detector in the dosimetry of high-energy electron and photon beams

    NASA Astrophysics Data System (ADS)

    Laub, Wolfram U.; Kaulich, Theodor W.; Nüsslin, Fridtjof

    1999-09-01

    A diamond detector type 60003 (PTW Freiburg) was examined for the purpose of dosimetry with 4-20 MeV electron beams and 4-25 MV photon beams. Results were compared with those obtained by using a Markus chamber for electron beams and an ionization chamber for photon beams. Dose distributions were measured in a water phantom with the detector connected to a Unidos electrometer (PTW Freiburg). After a pre-irradiation of about 5 Gy the diamond detector shows a stability in response which is better than that of an ionization chamber. The current of the diamond detector was measured under variation of photon beam dose rate between 0.1 and 7 Gy min-1. Different FSDs were chosen. Furthermore the pulse repetition frequency and the depth of the detector were changed. The electron beam dose rate was varied between 0.23 and 4.6 Gy min-1 by changing the pulse-repetition frequency. The response shows no energy dependence within the covered photon-beam energy range. Between 4 MeV and 18 MeV electron beam energy it shows only a small energy dependence of about 2%, as expected from theory. For smaller electron energies the response increases significantly and an influence of the contact material used for the diamond detector can be surmised. A slight sublinearity of the current and dose rate was found. Detector current and dose rate are related by the expression ipropto(dotD)Delta, where i is the detector current, (dotD) is the dose rate and Delta is a correction factor of approximately 0.963. Depth-dose curves of photon beams, measured with the diamond detector, show a slight overestimation compared

  10. Liquid ionization chamber measurements of dose distributions in small 6 MV photon beams

    NASA Astrophysics Data System (ADS)

    Dasu, Alexandru; Löfroth, Per-Olov; Wickman, Göran

    1998-01-01

    A new liquid ionization chamber (LIC) design optimized for high spatial resolution was used for measurements of dose distributions in radiation fields intended for stereotactic radiosurgery (SRS). This work was mainly focused on the properties of this detector in radiation fields from linear accelerators for clinical radiotherapy (pulsed radiation with dose rates from approximately 0.5 to and beam diameters down to 8 mm). The narrow beams used in stereotactic radiosurgery require detectors with small sizes in order to provide a good spatial resolution. The LIC is investigated to see whether it can be used as a detector for dose measurements in beams currently used for stereotactic radiosurgery. Its properties are compared with those of silicon diodes. The comparisons include output factor (OF), depth dose and profile measurements in 6 MV photon fields of different sizes. For OF measurements, an NACP air ionization chamber was also used in the comparison. The dependence of the response on the detector orientation in the photon beam is also investigated for the diodes and the LIC. The results suggest that LICs can provide better properties than diodes for measuring dose distributions in narrow photon beams.

  11. Two-photon excitation in living cells induced by low-power cw laser beams

    NASA Astrophysics Data System (ADS)

    Koenig, Karsten; Krasieva, Tatiana B.; Liu, Yagang; Berns, Michael W.; Tromberg, Bruce J.

    1996-05-01

    We demonstrate multi-photon excitation in optically-trapped living cells. Intracellular non- resonant two-photon excitation of endogenous and exogenous chromophores was induced by CW near infrared (NIR) trapping beams of 105 mW power. In the case of fluorescent chromophores, detection of NIR-excited visible fluorescence was achieved by imaging and spectroscopy methods. Trap-induced, two-photon excited fluorescence was employed as a novel diagnostic method to monitor intracellular redox state and cell vitality of single motile spermatozoa and Chinese hamster ovary cells. We found, that nonlinear absorption of NIR photons < 800 nm may lead to oxidative stress and severe cell damage. Biological response was amplified in multimode CW lasers due to longitudinal mode-beating and partial mode- locking. As a result, we recommend the use of longwavelength-NIR, single-frequency traps (`optical tweezers') for micromanipulation of vital cells.

  12. Collinear Photon Exchange in the Beam Normal Polarization Asymmetry of Elastic Electron-Proton Scattering

    SciTech Connect

    Andrei Afanasev; N.P. Merenkov

    2004-07-01

    The parity-conserving single-spin beam asymmetry of elastic electron-proton scattering is induced by an absorptive part of the two-photon exchange amplitude. We demonstrate that this asymmetry has logarithmic and double-logarithmic enhancement due to contributions of hard collinear quasi-real photons. An optical theorem is used to evaluate the asymmetry in terms of the total photoproduction cross section on the proton, predicting its magnitude at 20-30 parts per million for high electron beam energies and small scattering angles. At fixed 4-momentum transfers, the asymmetry is rising logarithmically with increasing electron beam energy, following the high-energy diffractive behavior of total photoproduction cross section on the proton.

  13. Photon spectra calculation for an Elekta linac beam using experimental scatter measurements and Monte Carlo techniques.

    PubMed

    Juste, B; Miro, R; Campayo, J M; Diez, S; Verdu, G

    2008-01-01

    The present work is centered in reconstructing by means of a scatter analysis method the primary beam photon spectrum of a linear accelerator. This technique is based on irradiating the isocenter of a rectangular block made of methacrylate placed at 100 cm distance from surface and measuring scattered particles around the plastic at several specific positions with different scatter angles. The MCNP5 Monte Carlo code has been used to simulate the particles transport of mono-energetic beams to register the scatter measurement after contact the attenuator. Measured ionization values allow calculating the spectrum as the sum of mono-energetic individual energy bins using the Schiff Bremsstrahlung model. The measurements have been made in an Elekta Precise linac using a 6 MeV photon beam. Relative depth and profile dose curves calculated in a water phantom using the reconstructed spectrum agree with experimentally measured dose data to within 3%. PMID:19163410

  14. Resonant photonuclear isotope detection using medium-energy photon beam

    NASA Astrophysics Data System (ADS)

    Ejiri, Hiroyasu; Shima, Tatsushi

    2012-02-01

    Resonant photonuclear isotope detection (RPID) is a nondestructive detection/assay of nuclear isotopes by measuring γ rays following photonuclear reaction products. Medium-energy wideband photons of Eγ=12-16MeV are used for the photonuclear (γ,n) reactions and γ rays characteristic of the reaction products are measured by means of high-sensitivity Ge detectors. Impurities of stable and radioactive isotopes of the orders of μgr—ngr and ppm—ppb are investigated. RPID is used to study nuclear isotopes of astronuclear and particle physics interests and those of geological and historical interests. It is used to identify radioactive isotopes of fission products as well.

  15. SU-E-T-221: Investigation of Lower Energy (< 6 MV) Photon Beams for Cancer Radiotherapy

    SciTech Connect

    Zhang, Y; Ming, X; Feng, Y; Zhou, L; Ahmad, M; Deng, J; Nguyen, K; Griffin, M

    2014-06-01

    Purpose: To study the potential applications of the lower energy (< 6MV) photon beams in the radiotherapeutic management of pediatric cancer and lung cancer patients. Methods: Photon beams of 2, 3, 4, 5 and 6MV were first simulated with EGS4/BEAM and then used for Monte-Carlo dose calculations. For four pediatric patients with abdominal and brain lesions, six 3D-conformal radiotherapy (3DCRT) plans were generated using single photon energy (2 to 6MV) or mixed energies (3 and 6MV). Furthermore, a virtual machine of 3 and 6MV was commissioned in a treatment planning system (TPS) based on Monte-Carlo simulated data. Three IMRT plans of a lung cancer patient were generated on this virtual machine. All plans were normalized to D95% of target dose for 6MV plan and then compared in terms of integral dose and OAR sparing. Results: For the four pediatric patients, the integral dose for the 2, 3, 4 and 5MV plans increased by 9%, 5%, 3.5%, 1.7%, respectively as compared to 6MV. Almost all OARs in the 2MV plan received more than 10% more doses than 6MV. Mixed energy 3DCRT plans were of the same quality as 6MV plans. For the lung IMRT plans, both the 3MV plan and the mixed beam plan showed better OAR sparing in comparison to 6MV plan. Specifically, the maximum and mean doses to the spinal cord in the mixed energy plan were lower by 21% and 16%, respectively. Conclusion: Single lower energy photon beam was found to be inferior to 6MV in the radiotherapy of pediatric patients and lung cancer patients when the integral doses and the doses to the OARs were considered. However, mixed energy plans combining low with high energy beams showed significant OAR sparing while maintaining the same PTV coverage. Investigation with more patient data is ongoing for further confirmation.

  16. Spatial-mode two-photon interference at a beam splitter

    SciTech Connect

    Deng, L.-P.; Dang, G.-F.; Wang, K.

    2006-12-15

    We present a general theory on the interference of a two-photon wave packet associated with spatial modes at a beam splitter. We find that the topological symmetry of the two-photon angular spectrum governs the nature of the two-photon interference. We distinguish between the coalescence interference and anticoalescence interference according to the decrease or increase of the coincidence probability in the absence of interference, respectively, and demonstrate that the symmetric and antisymmetric two-photon angular spectra are responsible for perfect coalescence interference and anticoalescence interference, respectively. Then we prove that anticoalescence interference never occurs for two independent photons, and it turns out that anticoalescence interference is the signature of two-photon entanglement. On the basis of this feature, we propose a special Mach-Zehnder interferometer, incorporated with two spiral phase plates, which can change the interference from a coalescence to an anticoalescence type only for a two-photon entangled state. The scheme is simple and straightforward compared with a test of Bell's inequality.

  17. Experimental validation of the dual parameter beam quality specifier for reference dosimetry in flattening-filter-free (FFF) photon beams.

    PubMed

    Simpson, Emma; Gajewski, Romuald; Flower, Emily; Stensmyr, Rachel

    2015-07-21

    Removal of the flattening filter alters the energy spectrum of the photon beam such that current beam quality specifiers may not correctly account for this change when predicting the Spencer-Attix restricted water-to-air mass collision stopping-power ratio, (L/ρ)(water)(air). Johnsson et al (2000 Phys. Med. Biol. 45 2733-45) proposed a beam quality specifier, known as the dual parameter beam quality specifier, which was calculated via Monte Carlo (MC) simulations using transmission data of primary kerma through two differing thicknesses of water material. Ceberg et al (2010 Med. Phys. 37 1164-8) extended this MC study to include relevant flattening filter free (FFF) beam data. Experimental investigations of this dual parameter beam quality specifier have not previously been published, therefore the purpose of this work was to validate that the dual parameter beam quality specifier could be measured experimentally for clinical beams (both with a flattening filter (WFF) and without (FFF)). Transmission measurements of primary kerma were performed by employing the setup outlined in Johnsson et al (1999 Phys. Med. Biol. 44 2445-50). Varying absorber thicknesses, in 5 cm increments from 5 to 40 cm, were placed at isocentre with the chamber positioned at an extended source to chamber distance of 300 cm. Experimental setup for TPR20,10 and %dd(10)x followed the methodology outlined in IAEA TRS398 (2004) and TG-51 (1999) with AAPM Addendum to TG-51 (2014) respectively. The maximum difference of (L/ρ)(water)(air) determined using the different beam quality specifiers was found to be 0.35%. Analysis of the absorber thickness combination found that small thicknesses (<10 cm) for the first absorber and absorbers similar in thickness (<10 cm) should be avoided. Stopping-power ratios of the beams investigated were determined using three different beam quality specifiers. The results demonstrated successful experimental determination of the dual parameter beam quality

  18. Experimental validation of the dual parameter beam quality specifier for reference dosimetry in flattening-filter-free (FFF) photon beams

    NASA Astrophysics Data System (ADS)

    Simpson, Emma; Gajewski, Romuald; Flower, Emily; Stensmyr, Rachel

    2015-07-01

    Removal of the flattening filter alters the energy spectrum of the photon beam such that current beam quality specifiers may not correctly account for this change when predicting the Spencer-Attix restricted water-to-air mass collision stopping-power ratio, ~≤ft({\\bar{\\text L}}/ρ \\right)\\text{air}\\text{water} . Johnsson et al (2000 Phys. Med. Biol. 45 2733-45) proposed a beam quality specifier, known as the dual parameter beam quality specifier, which was calculated via Monte Carlo (MC) simulations using transmission data of primary kerma through two differing thicknesses of water material. Ceberg et al (2010 Med. Phys. 37 1164-8) extended this MC study to include relevant flattening filter free (FFF) beam data. Experimental investigations of this dual parameter beam quality specifier have not previously been published, therefore the purpose of this work was to validate that the dual parameter beam quality specifier could be measured experimentally for clinical beams (both with a flattening filter (WFF) and without (FFF)). Transmission measurements of primary kerma were performed by employing the setup outlined in Johnsson et al (1999 Phys. Med. Biol. 44 2445-50). Varying absorber thicknesses, in 5 cm increments from 5 to 40 cm, were placed at isocentre with the chamber positioned at an extended source to chamber distance of 300 cm. Experimental setup for TPR20,10 and %dd(10)x followed the methodology outlined in IAEA TRS398 (2004) and TG-51 (1999) with AAPM Addendum to TG-51 (2014) respectively. The maximum difference of ~≤ft({\\bar{\\text L}}/ρ \\right)\\text{air}\\text{water} determined using the different beam quality specifiers was found to be 0.35%. Analysis of the absorber thickness combination found that small thicknesses (<10 cm) for the first absorber and absorbers similar in thickness (<10 cm) should be avoided. Stopping-power ratios of the beams investigated were determined using three different beam quality specifiers. The results

  19. A comparison of phantom scatter from flattened and flattening filter free high-energy photon beams

    SciTech Connect

    Richmond, Neil; Allen, Vince; Daniel, Jim; Dacey, Rob; Walker, Chris

    2015-04-01

    Flattening filter free (FFF) photon beams have different dosimetric properties from those of flattened beams. The aim of this work was to characterize the collimator scatter (S{sub c}) and total scatter (S{sub cp}) from 3 FFF beams of differing quality indices and use the resulting mathematical fits to generate phantom scatter (S{sub p}) data. The similarities and differences between S{sub p} of flattened and FFF beams are described. S{sub c} and S{sub cp} data were measured for 3 flattened and 3 FFF high-energy photon beams (Varian 6 and 10 MV and Elekta 6 MV). These data were fitted to logarithmic power law functions with 4 numerical coefficients. The agreement between our experimentally determined flattened beam S{sub p} and published data was within ± 1.2% for all 3 beams investigated and all field sizes from 4 × 4 to 40 × 40 cm{sup 2}. For the FFF beams, S{sub p} was only within 1% of the same flattened beam published data for field sizes between 6 × 6 and 14 × 14 cm{sup 2}. Outside this range, the differences were much greater, reaching − 3.2%, − 4.5%, and − 4.3% for the fields of 40 × 40 cm{sup 2} for the Varian 6-MV, Varian 10-MV, and Elekta 6-MV FFF beams, respectively. The FFF beam S{sub p} increased more slowly with increasing field size than that of the published and measured flattened beam of a similar reference field size quality index, i.e., there is less Phantom Scatter than that found with flattened beams for a given field size. This difference can be explained when the fluence profiles of the flattened and FFF beams are considered. The FFF beam has greatly reduced fluence off axis, especially as field size increases, compared with the flattened beam profile; hence, less scatter is generated in the phantom reaching the central axis.

  20. Laboratory Astrophysics Using High Intensity Particle and Photon Beams

    SciTech Connect

    Chen, Pisin

    2001-12-12

    History has shown that the symbiosis between direct observations and laboratory studies is instrumental in the progress of astrophysics. Recent years have seen growing interests in the laboratory investigation of astrophysical phenomena that can be addressed by high densities and advancement of technologies in lasers as well as high-energy particle beams. We will give examples on how frontier phenomena such as black holes, supernovae, gamma ray bursts, ultra high-energy cosmic rays, etc., can be investigated in the laboratory setting. Finally, we describe a possible laboratory astrophysics facility to be developed at SLAC.

  1. Laboratory Astrophysics Using High Intensity Particle and Photon Beams

    SciTech Connect

    Chen, Pisin

    2009-12-12

    History has shown that the symbiosis between direct observations and laboratory studies is instrumental in the progress of astrophysics. Recent years have seen growing interests in the laboratory investigation of astrophysical phenomena that can be addressed by high densities and advancement of technologies in lasers as well as high-energy particle beams. We will give examples on how frontier phenomena such as black holes, supernovae, gamma ray bursts, ultra high-energy cosmic rays, etc., can be investigated in the laboratory setting. Finally, we describe a possible laboratory astrophysics facility to be developed at SLAC.

  2. A beam position fiber counter with scintillation fibers and multi-pixel photon counter for high intensity beam operation

    NASA Astrophysics Data System (ADS)

    Honda, R.; Miwa, K.; Matsumoto, Y.; Chiga, N.; Hasegawa, S.; Imai, K.

    2015-07-01

    A beam position fiber counter consisting of the scintillation fiber (Kuraray SCSF-78 M) and a multi-pixel photon counter (HPK S10362-11-100P) was developed in order to handle a 10 MHz secondary pion beam in the J-PARC E40 experiment. This counter was installed at the entrance of the beam line spectrometer at the K1.8 experimental area in J-PARC and used for the momentum reconstruction. In order to suppress the accidental background and reconstruct the beam momentum, a good timing resolution better than 0.8 ns (σ) and a good position resolution better than 200 μm were simultaneously required for the counter. These requirements were well achieved by reading the 320 fibers with a diameter of 1 mm, which were arranged in a staggered position, with MPPC fiber by fiber. The signal induced from each MPPC was handled with an Extended Analogue SiPM Integrated ReadOut Chip (EASIROC) developed by Omega/IN2P3 in France. In addition, the timing of the discriminated signals from EASIROC was measured by a FPGA-based multi-hit TDC implemented into Spartan-6. Finally, we obtained the timing resolution of 0.68 ns (σ) and the position resolution of 190 μm (σ) under the 9 MHz beam condition using a pion beam.

  3. Monte Carlo study of photon beams from medical linear accelerators: Optimization, benchmark and spectra

    NASA Astrophysics Data System (ADS)

    Sheikh-Bagheri, Daryoush

    1999-12-01

    BEAM is a general purpose EGS4 user code for simulating radiotherapy sources (Rogers et al. Med. Phys. 22, 503-524, 1995). The BEAM code is optimized by first minimizing unnecessary electron transport (a factor of 3 improvement in efficiency). The efficiency of the uniform bremsstrahlung splitting (UBS) technique is assessed and found to be 4 times more efficient. The Russian Roulette technique used in conjunction with UBS is substantially modified to make simulations additionally 2 times more efficient. Finally, a novel and robust technique, called selective bremsstrahlung splitting (SBS), is developed and shown to improve the efficiency of photon beam simulations by an additional factor of 3-4, depending on the end- point considered. The optimized BEAM code is benchmarked by comparing calculated and measured ionization distributions in water from the 10 and 20 MV photon beams of the NRCC linac. Unlike previous calculations, the incident e - energy is known independently to 1%, the entire extra-focal radiation is simulated and e- contamination is accounted for. Both beams use clinical jaws, whose dimensions are accurately measured, and which are set for a 10 x 10 cm2 field at 110 cm. At both energies, the calculated and the measured values of ionization on the central-axis in the buildup region agree within 1% of maximum dose. The agreement is well within statistics elsewhere on the central-axis. Ionization profiles match within 1% of maximum dose, except at the geometrical edges of the field, where the disagreement is up to 5% of dose maximum. Causes for this discrepancy are discussed. The benchmarked BEAM code is then used to simulate beams from the major commercial medical linear accelerators. The off-axis factors are matched within statistical uncertainties, for most of the beams at the 1 σ level and for all at the 2 σ level. The calculated and measured depth-dose data agree within 1% (local dose), at about 1% (1 σ level) statistics, at all depths past

  4. Monte Carlo treatment planning for photon and electron beams

    NASA Astrophysics Data System (ADS)

    Reynaert, N.; van der Marck, S. C.; Schaart, D. R.; Van der Zee, W.; Van Vliet-Vroegindeweij, C.; Tomsej, M.; Jansen, J.; Heijmen, B.; Coghe, M.; De Wagter, C.

    2007-04-01

    During the last few decades, accuracy in photon and electron radiotherapy has increased substantially. This is partly due to enhanced linear accelerator technology, providing more flexibility in field definition (e.g. the usage of computer-controlled dynamic multileaf collimators), which led to intensity modulated radiotherapy (IMRT). Important improvements have also been made in the treatment planning process, more specifically in the dose calculations. Originally, dose calculations relied heavily on analytic, semi-analytic and empirical algorithms. The more accurate convolution/superposition codes use pre-calculated Monte Carlo dose "kernels" partly accounting for tissue density heterogeneities. It is generally recognized that the Monte Carlo method is able to increase accuracy even further. Since the second half of the 1990s, several Monte Carlo dose engines for radiotherapy treatment planning have been introduced. To enable the use of a Monte Carlo treatment planning (MCTP) dose engine in clinical circumstances, approximations have been introduced to limit the calculation time. In this paper, the literature on MCTP is reviewed, focussing on patient modeling, approximations in linear accelerator modeling and variance reduction techniques. An overview of published comparisons between MC dose engines and conventional dose calculations is provided for phantom studies and clinical examples, evaluating the added value of MCTP in the clinic. An overview of existing Monte Carlo dose engines and commercial MCTP systems is presented and some specific issues concerning the commissioning of a MCTP system are discussed.

  5. Compact terahertz wave polarization beam splitter using photonic crystal.

    PubMed

    Mo, Guo-Qiang; Li, Jiu-Sheng

    2016-09-01

    Electromagnetic polarization conveys valuable information for signal processing. Manipulation of a terahertz wave polarization state exhibits tremendous potential in developing applications of terahertz science and technology. We propose an approach to efficiently split transverse-electric and transverse-magnetic polarized terahertz waves into different propagation directions over the frequency range from 0.9998 to 1.0007 THz. Both the plane wave expansion method and the finite-difference time-domain method are used to calculate and analyze the transmission characteristics of the proposed device. The present device is very compact and the total size is 1.02  mm×0.99  mm. This polarization beam splitter performance indicates that the structure has a potential application for forthcoming terahertz-wave integrated circuit fields. PMID:27607286

  6. Physical approach to depth dose distributions in a water phantom irradiated by a teleisotope photon beam

    SciTech Connect

    Ahuja, S.D.; Stroup, S.L.; Bolin, M.G.; Gibbs, S.J.

    1980-03-01

    The physical basis of deposition of radiation dose within a homogeneous phantom irradiated by a monoenergetic photon beam has been studied in terms of photon attenuation and energy-absorption properties of the phantom material. A semi-empirical model based on the Klein--Nishina formula for Compton scattering, and the ratio of multiply scattered to singly scattered photon fluences, has been developed for the scatter dose component within a realistic phantom to determine the central-axial percent depth dose (PDD) and off-central-axis ratios (OCR). Differences between the predicted and measured values of PDD and OCR for cobalt-60 and cesium-137 beams are less than 3% for fields of equivalent-square-side less than 20 cm, and less than 5% for larger fields. Beam profiles of all field sizes can be well simulated by this model and reasonable agreement has been found between the predicted and tabulated values of scatter functions and the backscatter factor for cobalt-60 beams. This formulation involves no variable parameters, and is valid for all values of the source-to-surface distance, field length and width, and field shape. However, the algorithm developed is not suitable for routine multiple-field treatment planning because it requires large computer memory size.

  7. Generation and modelling of megavoltage photon beams for contrast-enhanced radiation therapy

    NASA Astrophysics Data System (ADS)

    Robar, J. L.

    2006-11-01

    Contrast-enhanced radiation therapy (CERT) is a treatment approach involving the irradiation of tumours containing high atomic number (Z) contrast media, using low-quality x-ray beams. This work describes the experimental generation of x-ray beams using a linear accelerator with low-Z target materials (beryllium and aluminium), in order to produce photon energy spectra appropriate for CERT. Measurements were made to compare the experimental beams to conventional linear accelerator photon beams in terms of per cent depth dose. Monte Carlo simulation was used to model the generation of each beam, and models were validated against experimental measurement. Validated models were used to demonstrate changes in photon spectra as well as to quantify the variation of tumour dose enhancement with iodinated contrast medium concentration in a simulated tumour volume. Finally, the ratio of the linear attenuation coefficient for iodinated contrast medium relative to water was determined experimentally as a function of iodine concentration. Beams created with low-Z targets show significant changes in energy spectra compared to conventional beams. For the 4 MeV/Be beam, for example, 33% of photons have energies below 60 keV. Measurements and calculation show that both the linear attenuation coefficient ratio and dose enhancement factor (DEF) increase most rapidly at concentrations below 46 mg I ml-1. There is a significant dependence of DEF on electron energy and a lesser dependence on target material. The 4 MeV/Be beam is the most promising in terms of magnitude of DEF—for example, DEF values of 1.16 and 1.29 are obtained for concentrations of 20 mg I ml-1 and 50 mg I ml-1, respectively. DEF will increase or decrease, respectively, for shallower or deeper tumours at a rate of approximately 1.1% cm-1. In summary, we show that significant dose enhancement is possible by altering the linear accelerator target and filtration, but the magnitude is highly dependent on contrast

  8. Combining tissue-phantom ratios to provide a beam-quality specifier for flattening filter free photon beams

    SciTech Connect

    Dalaryd, Mårten Knöös, Tommy; Ceberg, Crister

    2014-11-01

    Purpose: There are currently several commercially available radiotherapy treatment units without a flattening filter in the beam line. Unflattened photon beams have an energy and lateral fluence distribution that is different from conventional beams and, thus, their attenuation properties differ. As a consequence, for flattening filter free (FFF) beams, the relationship between the beam-quality specifier TPR{sub 20,10} and the Spencer–Attix restricted water-to-air mass collision stopping-power ratios, (L{sup -}/ρ){sub air}{sup water}, may have to be refined in order to be used with equivalent accuracy as for beams with a flattening filter. The purpose of this work was twofold. First, to study the relationship between TPR{sub 20,10} and (L{sup -}/ρ){sub air}{sup water} for FFF beams, where the flattening filter has been replaced by a metal plate as in most clinical FFF beams. Second, to investigate the potential of increasing the accuracy in determining (L{sup -}/ρ){sub air}{sup water} by adding another beam-quality metric, TPR{sub 10,5}. The relationship between (L{sup -}/ρ){sub air}{sup water} and %dd(10){sub x} for beams with and without a flattening filter was also included in this study. Methods: A total of 24 realistic photon beams (10 with and 14 without a flattening filter) from three different treatment units have been used to calculate (L{sup -}/ρ){sub air}{sup water}, TPR{sub 20,10}, and TPR{sub 10,5} using the EGSnrc Monte Carlo package. The relationship between (L{sup -}/ρ){sub air}{sup water} and the dual beam-quality specifier TPR{sub 20,10} and TPR{sub 10,5} was described by a simple bilinear equation. The relationship between the photon beam-quality specifier %dd(10){sub x} used in the AAPM’s TG-51 dosimetry protocol and (L{sup -}/ρ){sub air}{sup water} was also investigated for the beams used in this study, by calculating the photon component of the percentage depth dose at 10 cm depth with SSD 100 cm. Results: The calculated (L{sup -}/

  9. Lyoluminescence dosimetry in photon and fast neutron beams.

    PubMed

    Puite, K J; Crebolder, D L

    1977-11-01

    The lyoluminescence (LL) technique using mannose, a monosaccharide, is described. Dose-response curves for 60Co-gamma-rays (5 rad to 120 krad), fission neutrons, 5.3 MeV and 15 MeV neutrons (100 rad to 20 krad) have been measured. The close tissue-equivalence of mannose makes this material well suited for dosimetric use in low energy X-ray fields for radiotherapy and radiobiology. It also provides a cheap, simple and reproducible dosemeter in industrial applications of radiation (sprouting inhibition of onions and potatoes; control of insect infestation). After correction for the gamma contamination of the neutron beam the LL signal per rad in ICRU muscle tissue from the neutron irradiations has been derived and the relative effectiveness of the LL signal for fast neutrons in mannose has been calculated as 0.34 +/- 0.03 (fission neutrons), 0.63 +/- 0.07 (5.3 MeV neutrons) and 0.74 +/- 0.05 (15 MeV neutrons). These results are compared with data from other systems. It is concluded that mannose can be used as a transfer system in neutron dosimetry, if its variation in sensitivity with neutron energy is taken into account. PMID:594143

  10. An analytical formalism to calculate phantom scatter factors for flattening filter free (FFF) mode photon beams

    NASA Astrophysics Data System (ADS)

    Chung, Heeteak; Prado, Karl L.; Yi, Byong Yong

    2014-02-01

    Phantom Scatter Factors, Sp in the Khan formalism (Khan et al 1980 J. Radiat. Oncol. Biol. Phys. 6 745-51) describe medium-induced changes in photon-beam intensity as a function of size of the beam. According to the British Journal of Radiology, Supplement 25, megavoltage phantom scatter factors are invariant as a function of photon-beam energy. However, during the commissioning of an accelerator with flattening filter free (FFF) photon beams (Varian TrueBeamTM 6-MV FFF and 10-MV FFF), differences were noted in phantom scatter between the filtered beams and FFF-mode beams. The purpose of this work was to evaluate this difference and provide an analytical formalism to explain the phantom scatter differences between FFF-mode and the filtered mode. An analytical formalism was devised to demonstrate the source of phantom scatter differences between the filtered and the FFF-mode beams. The reason for the differences in the phantom scatter factors between the filtered and the FFF-mode beams is hypothesized to be the non-uniform beam profiles of the FFF-mode beams. The analytical formalism proposed here is based on this idea, taking the product of the filtered phantom scatter factors and the ratio of the off-axis ratio between the FFF-mode and the filtered beams. All measurements were performed using a Varian TrueBeamTM linear accelerator with photon energies of 6-MV and 10-MV in both filtered and FFF-modes. For all measurements, a PTW Farmer type chamber and a Scanditronix CC04 cylindrical ionization were used. The in-water measurements were made at depth dose maximum and 100 cm source-to-axis distance. The in-air measurements were done at 100 cm source-to-axis distance with appropriate build-up cap. From these measurements, the phantom scatter factors were derived for the filtered beams and the FFF-mode beams for both energies to be evaluated against the phantoms scatter factors calculated using the proposed algorithm. For 6-MV, the difference between the measured and

  11. An analytical formalism to calculate phantom scatter factors for flattening filter free (FFF) mode photon beams.

    PubMed

    Chung, Heeteak; Prado, Karl L; Yi, Byong Yong

    2014-02-21

    Phantom Scatter Factors, Sp in the Khan formalism (Khan et al 1980 J. Radiat. Oncol. Biol. Phys. 6 745-51) describe medium-induced changes in photon-beam intensity as a function of size of the beam. According to the British Journal of Radiology, Supplement 25, megavoltage phantom scatter factors are invariant as a function of photon-beam energy. However, during the commissioning of an accelerator with flattening filter free (FFF) photon beams (Varian TrueBeam(TM) 6-MV FFF and 10-MV FFF), differences were noted in phantom scatter between the filtered beams and FFF-mode beams. The purpose of this work was to evaluate this difference and provide an analytical formalism to explain the phantom scatter differences between FFF-mode and the filtered mode. An analytical formalism was devised to demonstrate the source of phantom scatter differences between the filtered and the FFF-mode beams. The reason for the differences in the phantom scatter factors between the filtered and the FFF-mode beams is hypothesized to be the non-uniform beam profiles of the FFF-mode beams. The analytical formalism proposed here is based on this idea, taking the product of the filtered phantom scatter factors and the ratio of the off-axis ratio between the FFF-mode and the filtered beams. All measurements were performed using a Varian TrueBeam(TM) linear accelerator with photon energies of 6-MV and 10-MV in both filtered and FFF-modes. For all measurements, a PTW Farmer type chamber and a Scanditronix CC04 cylindrical ionization were used. The in-water measurements were made at depth dose maximum and 100 cm source-to-axis distance. The in-air measurements were done at 100 cm source-to-axis distance with appropriate build-up cap. From these measurements, the phantom scatter factors were derived for the filtered beams and the FFF-mode beams for both energies to be evaluated against the phantoms scatter factors calculated using the proposed algorithm. For 6-MV, the difference between the measured

  12. Surface Dose Investigation of the Flattening Filter-Free Photon Beams

    SciTech Connect

    Wang Yuenan; Khan, Mohammad K.; Ting, Joseph Y.; Easterling, Stephen B.

    2012-06-01

    Purpose: Flattening filter-free (FFF) x-rays can provide more efficient use of photons and a significant increase of dose rate compared with conventional flattened x-rays, features that are especially beneficial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). The available data on the entrance doses of the FFF photon beams remain limited. The purpose of this study was to investigate the entrance dose of FFF photons in the buildup region and to compare it with that of conventional flattened photons. Methods and Materials: A Varian TrueBeam linear accelerator has been in full clinical operation with 6-MV and 10-MV FFF and flattened x-ray photons. Entrance dose at the surface was measured using a parallel plate ionization chamber in a solid water phantom with buildup depth = 0{approx}15 mm for 6X and 0{approx}25 mm for 10X. Different field size (FS) patterns were created in the Eclipse Treatment Planning System by multileaf collimator (MLC) rather than jaws (FS = 2 Multiplication-Sign 2, 3 Multiplication-Sign 3, 4 Multiplication-Sign 4, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2} by MLC and jaw size = 2.2 Multiplication-Sign 2.2, 3.2 Multiplication-Sign 3.2, 4.2 Multiplication-Sign 4.2, 6 Multiplication-Sign 6, and 10 Multiplication-Sign 10 cm{sup 2}). The smallest FS was about four times larger than the ion chamber dimension. All buildup dose measurements were normalized to FS = 10 Multiplication-Sign 10 cm{sup 2} at the depth of dose maximum (dmax). Results: Good repeatability was demonstrated and surface dose increased linearly with FS for both flattened and FFF photons. The entrance dose of the FFF photons was modestly larger than that of the corresponding flattened photons for both 6X and 10X for different FS ranging from 2 Multiplication-Sign 2 cm{sup 2} to 10 Multiplication-Sign 10 cm{sup 2}. Conclusions: The FFF photons have a higher entrance dose than that of the corresponding flattened photons for FS

  13. Projection imaging of photon beams using Čerenkov-excited fluorescence

    NASA Astrophysics Data System (ADS)

    Glaser, Adam K.; Davis, Scott C.; Voigt, William H. A.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2013-02-01

    Full 3D beam profiling and quality assurance (QA) of therapeutic megavoltage linear accelerator (LINAC) x-ray photon beams is not routinely performed due to the slow point-by-point measurement nature of conventional scanning ionization chamber systems. In this study we explore a novel optical-based dose imaging approach using a standard commercial camera, water tank, and fluorescent dye, which when excited by the Čerenkov emission induced by the radiation beam, allows 2D projection imaging in a fast timeframe, potentially leading toward 3D tomographic beam profiling. Detailed analysis was carried out to optimize the imaging parameters in the experimental setup. The results demonstrate that the captured images are linear with delivered dose, independent of dose rate, and comparison of experimentally captured images to a reference dose distribution for a 4 × 4 cm2 6 MV x-ray photon beam yielded results with improved accuracy over a previous study which used direct imaging and Monte Carlo calibration of the Čerenkov emission itself. The agreement with the reference dose distribution was within 1-2% in the lateral direction, and ±3% in the depth direction. The study was restricted to single 2D image projection, with the eventual goal of creating full 3D profiles after tomographic reconstruction from multiple projections. Given the increasingly complex advances in radiation therapy, and the increased emphasis on patient-specific treatment plans, further refinement of the technique could prove to be an important tool for fast and robust QA of x-ray photon LINAC beams.

  14. Projection imaging of photon beams using Čerenkov-excited fluorescence.

    PubMed

    Glaser, Adam K; Davis, Scott C; Voigt, William H A; Zhang, Rongxiao; Pogue, Brian W; Gladstone, David J

    2013-02-01

    Full 3D beam profiling and quality assurance (QA) of therapeutic megavoltage linear accelerator (LINAC) x-ray photon beams is not routinely performed due to the slow point-by-point measurement nature of conventional scanning ionization chamber systems. In this study we explore a novel optical-based dose imaging approach using a standard commercial camera, water tank, and fluorescent dye, which when excited by the Čerenkov emission induced by the radiation beam, allows 2D projection imaging in a fast timeframe, potentially leading toward 3D tomographic beam profiling. Detailed analysis was carried out to optimize the imaging parameters in the experimental setup. The results demonstrate that the captured images are linear with delivered dose, independent of dose rate, and comparison of experimentally captured images to a reference dose distribution for a 4 × 4 cm(2) 6 MV x-ray photon beam yielded results with improved accuracy over a previous study which used direct imaging and Monte Carlo calibration of the Čerenkov emission itself. The agreement with the reference dose distribution was within 1-2% in the lateral direction, and ±3% in the depth direction. The study was restricted to single 2D image projection, with the eventual goal of creating full 3D profiles after tomographic reconstruction from multiple projections. Given the increasingly complex advances in radiation therapy, and the increased emphasis on patient-specific treatment plans, further refinement of the technique could prove to be an important tool for fast and robust QA of x-ray photon LINAC beams. PMID:23318469

  15. Projection imaging of photon beams using Čerenkov-excited fluorescence

    PubMed Central

    Glaser, Adam K.; Davis, Scott C.; Voigt, William H.A.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2013-01-01

    Full 3D beam profiling and quality assurance (QA) of therapeutic megavoltage linear accelerator (LINAC) x-ray photon beams is not routinely performed due to the slow point-by-point measurement nature of conventional scanning ionization chamber systems. In this study we explore a novel optical-based dose imaging approach using a standard commercial camera, water tank, and fluorescent dye, which when excited by the Čerenkov emission induced by the radiation beam, allows 2D projection imaging in a fast timeframe, potentially leading towards 3D tomographic beam profiling. Detailed analysis was done to optimize the imaging parameters in the experimental setup. The results demonstrate that the captured images are linear with delivered dose, independent of dose rate, and comparison of experimentally captured images to a reference dose distribution for a 4×4 cm 6 MV x-ray photon beam yielded results with improved accuracy over a previous study which used direct imaging and Monte Carlo calibration of the Čerenkov emission itself. The agreement with the reference dose distribution was within 1-2% in the lateral direction, and ± 3 % in the depth direction. The study was restricted to single 2D image projection, with the eventual goal of creating full 3D profiles after tomographic reconstruction from multiple projections. Given the increasingly complex advances in radiation therapy, and the increased emphasis on patient-specific treatment plans, further refinement of the technique could prove to be an important tool for fast and robust QA of x-ray photon LINAC beams. PMID:23318469

  16. Design of mechanically-tunable photonic crystal split-beam nanocavity.

    PubMed

    Lin, Tong; Tian, Feng; Shi, Peng; Chau, Fook Siong; Zhou, Guangya; Tang, Xiaosong; Deng, Jie

    2015-08-01

    Photonic crystal split-beam nanocavities allow for ultra-sensitive optomechanical transductions but are degraded due to their relatively low optical quality factors. We have proposed and experimentally demonstrated a new type of one-dimensional photonic crystal split-beam nanocavity optimized for an ultra-high optical-quality factor. The design is based on the combination of the deterministic method and hill-climbing algorithm. The latter is the simplest and most straightforward method of the local search algorithm that provides the local maximum of the chosen quality factors. This split-beam nanocavity is made up of two mechanical uncoupled cantilever beams with Bragg mirrors patterned onto it and separated by a 75-nm air gap. Experimental results emphasize that the quality factor of the second-order TE mode can be as high as 1.99×10(4). Additionally, one beam of the device is actuated in the lateral direction with the aid of a NEMS actuator, and the quality factor maintains quite well even if there is a lateral offset up to 64 nm. Potentially promising applications, such as sensitive optomechanical torque sensor, local tuning of Fano resonance, all-optical-reconfigurable filters, etc., are foreseen. PMID:26258343

  17. Determination of scatter factor parameters and electron disequilibrium for monoenergetic photon beams.

    PubMed

    McDonough, J; Bloch, P; Bjärngard, B E

    1999-02-01

    The tissue-phantom-ratio (TPR) is expressed as the product of the phantom scatter factor (SF), an electron disequilibrium factor, and an attenuation factor, equal to the zero-area TPR. The scatter factor, as a function of depth d and field size s, has been described by two parameters a and w, SF(d,s) = 1 + asd/(ws + d). We have determined the parameters a and w for 20 monoenergetic photon beams between 1 and 20 MeV. Pencil-beam energy-deposition kernels were obtained using Monte Carlo simulations. The kernels were used to calculate broad-beam depth-dose data, which were converted to TPR and fitted to the equation above using an iterative search over a-w space. The parameter a is nearly equal to the attenuation coefficient for all energies while the parameter w increases with energy. The resulting a and w compare favorably to values determined for clinical photon beams, as a function of the measured attenuation coefficient. With the scatter factor determined, we isolated the electron disequilibrium factor for each monoenergetic beam. It can be characterized as a quadratic function of the depth. The coefficients of the quadratic function can be related to the range of the most energetic secondary electron produced. PMID:10076974

  18. Spectral reconstruction by scatter analysis for a linear accelerator photon beam.

    PubMed

    Jalbout, Wassim T; Spyrou, Nicholas M

    2006-05-01

    Pre-existing methods for photon beam spectral reconstruction are briefly reviewed. An alternative reconstruction method by scatter analysis for linear accelerators is introduced. The method consists in irradiating a small plastic phantom at standard 100 cm SSD and inferring primary beam energy spectral information based on the measurement with a standard Farmer chamber of scatter around the phantom at several specific scatter angles: a scatter curve is measured which is indicative of the primary spectrum at hand. A Monte Carlo code is used to simulate the scatter measurement set-up and predict the relative magnitude of scatter measurements for mono-energetic primary beams. Based on mono-energetic primary scatter data, measured scatter curves are analysed and the spectrum unfolded as the sum of mono-energetic individual energy bins using the Schiff bremsstrahlung model. The method is applied to an Elekta/SL18 6 MV photon beam. The reconstructed spectrum matches the Monte Carlo calculated spectrum for the same beam within 6.2% (average error when spectra are compared bin by bin). Depth dose values calculated for the reconstructed spectrum agree with physically measured depth dose data to within 1%. Scatter analysis is preliminarily shown to have potential as a practical spectral reconstruction method requiring few measurements under standard 100 cm SSD and feasible in any radiotherapy department using a phantom and a Farmer chamber. PMID:16625037

  19. One- and two-photon absorption in solution: The effects of a passive auxiliary beam

    SciTech Connect

    Ford, J. S.; Andrews, D. L.

    2014-07-21

    The efficiencies of one- and two-photon absorption by chromophores in solution may be significantly modified by a sufficiently intense beam of off-resonant light. A molecular analysis based on quantum electrodynamics (QED) fully accounts for this phenomenon of laser-modified absorption. A time-dependent perturbation-theory treatment describes the process in terms of stimulated forward Rayleigh-scattering of the auxiliary beam occurring simultaneously with the absorption interaction(s). Our formulation accommodates media modifications to the basic character of light-matter interactions, taking into account the refractive and dispersive properties of a solution-phase environment. This introduces the bulk refractive index of the solvent directly into the QED framework. The measurable electronic response of molecules freely rotating in solution is defined by an average of all orientations. We explicitly derive fixed-orientation and rotationally averaged calculations for the Fermi-rule rate of laser-modified one- and two-photon absorption. For a given beam polarization geometry, the solution-phase molecular response is expressible as a set of natural invariant scalars. These results reveal details of the dependence on the beam polarisations and on the rotationally averaged molecular response: we illustrate the breadth of variation available via geometric manipulation of beam polarization, and raise new possibilities for quantum weak measurements of laser states.

  20. Projection imaging of photon beams by the Čerenkov effect

    PubMed Central

    Glaser, Adam K.; Davis, Scott C.; McClatchy, David M.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2013-01-01

    Purpose: A novel technique for beam profiling of megavoltage photon beams was investigated for the first time by capturing images of the induced Čerenkov emission in water, as a potential surrogate for the imparted dose in irradiated media. Methods: A high-sensitivity, intensified CCD camera (ICCD) was configured to acquire 2D projection images of Čerenkov emission from a 4 × 4 cm2 6 MV linear accelerator (LINAC) x-ray photon beam operating at a dose rate of 400 MU/min incident on a water tank with transparent walls. The ICCD acquisition was gated to the LINAC sync pulse to reduce background light artifacts, and the measurement quality was investigated by evaluating the signal to noise ratio and measurement repeatability as a function of delivered dose. Monte Carlo simulations were used to derive a calibration factor for differences between the optical images and deposited dose arising from the anisotropic angular dependence of Čerenkov emission. Finally, Čerenkov-based beam profiles were compared to a percent depth dose (PDD) and lateral dose profile at a depth of dmax from a reference dose distribution generated from the clinical Varian ECLIPSE treatment planning system (TPS). Results: The signal to noise ratio was found to be 20 at a delivered dose of 66.6 cGy, and proportional to the square root of the delivered dose as expected from Poisson photon counting statistics. A 2.1% mean standard deviation and 5.6% maximum variation in successive measurements were observed, and the Monte Carlo derived calibration factor resulted in Čerenkov emission images which were directly correlated to deposited dose, with some spatial issues. The dose difference between the TPS and PDD predicted by Čerenkov measurements was within 20% in the buildup region with a distance to agreement (DTA) of 1.5–2 mm and ±3% at depths beyond dmax. In the lateral profile, the dose difference at the beam penumbra was within ±13% with a DTA of 0–2 mm, ±5% in the central beam region

  1. The use of intensity-modulated radiation therapy photon beams for improving the dose uniformity of electron beams shaped with MLC

    SciTech Connect

    Mosalaei, Homeira; Karnas, Scott; Shah, Sheel; Van Doodewaard, Sharon; Foster, Tim; Chen, Jeff

    2012-04-01

    Electrons are ideal for treating shallow tumors and sparing adjacent normal tissue. Conventionally, electron beams are collimated by cut-outs that are time-consuming to make and difficult to adapt to tumor shape throughout the course of treatment. We propose that electron cut-outs can be replaced using photon multileaf collimator (MLC). Two major problems of this approach are that the scattering of electrons causes penumbra widening because of a large air gap, and available commercial treatment planning systems (TPSs) do not support MLC-collimated electron beams. In this study, these difficulties were overcome by (1) modeling electron beams collimated by photon MLC for a commercial TPS, and (2) developing a technique to reduce electron beam penumbra by adding low-energy intensity-modulated radiation therapy (IMRT) photons (4 MV). We used blocks to simulate MLC shielding in the TPS. Inverse planning was used to optimize boost photon beams. This technique was applied to a parotid and a central nervous system (CNS) clinical case. Combined photon and electron plans were compared with conventional plans and verified using ion chamber, film, and a 2D diode array. Our studies showed that the beam penumbra for mixed beams with 90 cm source to surface distance (SSD) is comparable with electron applicators and cut-outs at 100 cm SSD. Our mixed-beam technique yielded more uniform dose to the planning target volume and lower doses to various organs at risk for both parotid and CNS clinical cases. The plans were verified with measurements, with more than 95% points passing the gamma criteria of 5% in dose difference and 5 mm for distance to agreement. In conclusion, the study has demonstrated the feasibility and potential advantage of using photon MLC to collimate electron beams with boost photon IMRT fields.

  2. The use of intensity-modulated radiation therapy photon beams for improving the dose uniformity of electron beams shaped with MLC.

    PubMed

    Mosalaei, Homeira; Karnas, Scott; Shah, Sheel; Van Doodewaard, Sharon; Foster, Tim; Chen, Jeff

    2012-01-01

    Electrons are ideal for treating shallow tumors and sparing adjacent normal tissue. Conventionally, electron beams are collimated by cut-outs that are time-consuming to make and difficult to adapt to tumor shape throughout the course of treatment. We propose that electron cut-outs can be replaced using photon multileaf collimator (MLC). Two major problems of this approach are that the scattering of electrons causes penumbra widening because of a large air gap, and available commercial treatment planning systems (TPSs) do not support MLC-collimated electron beams. In this study, these difficulties were overcome by (1) modeling electron beams collimated by photon MLC for a commercial TPS, and (2) developing a technique to reduce electron beam penumbra by adding low-energy intensity-modulated radiation therapy (IMRT) photons (4 MV). We used blocks to simulate MLC shielding in the TPS. Inverse planning was used to optimize boost photon beams. This technique was applied to a parotid and a central nervous system (CNS) clinical case. Combined photon and electron plans were compared with conventional plans and verified using ion chamber, film, and a 2D diode array. Our studies showed that the beam penumbra for mixed beams with 90 cm source to surface distance (SSD) is comparable with electron applicators and cut-outs at 100 cm SSD. Our mixed-beam technique yielded more uniform dose to the planning target volume and lower doses to various organs at risk for both parotid and CNS clinical cases. The plans were verified with measurements, with more than 95% points passing the gamma criteria of 5% in dose difference and 5 mm for distance to agreement. In conclusion, the study has demonstrated the feasibility and potential advantage of using photon MLC to collimate electron beams with boost photon IMRT fields. PMID:21925867

  3. Photon beam quality variations of a flattening filter free linear accelerator

    SciTech Connect

    Georg, Dietmar; Kragl, Gabriele; Wetterstedt, Sacha af; McCavana, Patrick; McClean, Brendan; Knoeoes, Tommy

    2010-01-15

    Purpose: Recently, there has been an increasing interest in operating conventional linear accelerators without a flattening filter. The aim of this study was to determine beam quality variations as a function of off-axis ray angle for unflattened beams. In addition, a comparison was made with the off-axis energy variation in flattened beams. Methods: Two Elekta Precise linear accelerators were modified in order to enable radiation delivery with and without the flattening filter in the beam line. At the Medical University Vienna (Vienna, Austria), half value layer (HVL) measurements were performed for 6 and 10 MV with an in-house developed device that can be easily mounted on the gantry. At St. Luke's Hospital (Dublin, Ireland), measurements were performed at 6 MV in narrow beam geometry with the gantry tilted around 270 deg. with pinhole collimators, an attenuator, and the chamber positioned on the table. All attenuation measurements were performed with ionization chambers and a buildup cap (2 mm brass) or a PMMA mini phantom (diameter 3 cm, measurement depth 2.5 cm). Results: For flattened 6 and 10 MV photon beams from the Elekta linac the relative HVL({theta}) varies by about 11% for an off-axis ray angle {theta}=10 deg. These results agree within {+-}2% with a previously proposed generic off-axis energy correction. For unflattened beams, the variation was less than 5% in the whole range of off-axis ray angles up to 10 deg. The difference in relative HVL data was less than 1% for unflattened beams at 6 and 10 MV. Conclusions: Off-axis energy variation is rather small in unflattened beams and less than half the one for flattened beams. Thus, ignoring the effect of off-axis energy variation for dose calculations in unflattened beams can be clinically justified.

  4. Physical characteristics of photon beam from a CLINAC-DBX single energy accelerator

    NASA Astrophysics Data System (ADS)

    Umbarkar, Rahul; Supe, Sanjay; Pandey, Manoy; Ashok, Jayanty

    2011-01-01

    Commissioning beam data are treated as a reference and ultimately used by treatment planning systems, therefore, it is vitally important that the collected data are of the highest quality, in order to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. High-energy photon and electron beams from different accelerators of the same nominal energy may have different dosimetric characteristics due to differences in target and flattening filter materials, accelerator guide and collimator designs. In the present study, clinically pertinent data for the available photon energy were investigated. For making measurements in water, first time in India, a three dimensional radiation field analyzer RFA (CRS- Scan -O-Plan) was used. For absolute dosimetry and other measurements like relative output factors, wedge factors etc., a DOSE1 electrometer (Scanditronix Wellhofer) in a white polystyrene was employed. All the measured data were utilized as an input to the ECLIPSE treatment planning system for further clinical use.

  5. Automated Sample Exchange Robots for the Structural Biology Beam Lines at the Photon Factory

    SciTech Connect

    Hiraki, Masahiko; Watanabe, Shokei; Yamada, Yusuke; Matsugaki, Naohiro; Igarashi, Noriyuki; Gaponov, Yurii; Wakatsuki, Soichi

    2007-01-19

    We are now developing automated sample exchange robots for high-throughput protein crystallographic experiments for onsite use at synchrotron beam lines. It is part of the fully automated robotics systems being developed at the Photon Factory, for the purposes of protein crystallization, monitoring crystal growth, harvesting and freezing crystals, mounting the crystals inside a hutch and for data collection. We have already installed the sample exchange robots based on the SSRL automated mounting system at our insertion device beam lines BL-5A and AR-NW12A at the Photon Factory. In order to reduce the time required for sample exchange further, a prototype of a double-tonged system was developed. As a result of preliminary experiments with double-tonged robots, the sample exchange time was successfully reduced from 70 seconds to 10 seconds with the exception of the time required for pre-cooling and warming up the tongs.

  6. Atom interferometry with up to 24-photon-momentum-transfer beam splitters.

    PubMed

    Müller, Holger; Chiow, Sheng-wey; Long, Quan; Herrmann, Sven; Chu, Steven

    2008-05-01

    We present up to 24-photon Bragg diffraction as a beam splitter in light-pulse atom interferometers to achieve the largest splitting in momentum space so far. Relative to the 2-photon processes used in the most sensitive present interferometers, these large momentum transfer beam splitters increase the phase shift 12-fold for Mach-Zehnder (MZ) and 144-fold for Ramsey-Bordé (RB) geometries. We achieve a high visibility of the interference fringes (up to 52% for MZ or 36% for RB) and long pulse separation times that are possible only in atomic fountain setups. As the atom's internal state is not changed, important systematic effects can cancel. PMID:18518355

  7. Direct megavoltage photon calibration service in Australia

    PubMed Central

    Ramanathan, G.; Oliver, C.; Cole, A.; Lye, J.; Harty, P. D.; Wright, T.; Webb, D. V.; Followill, D. S.

    2014-01-01

    The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) maintains the Australian primary standard of absorbed dose. Until recently, the standard was used to calibrate ionisation chambers only in 60Co gamma rays. These chambers are then used by radiotherapy clinics to determine linac output, using a correction factor (kQ) to take into account the different spectra of 60Co and the linac. Over the period 2010–2013, ARPANSA adapted the primary standard to work in megavoltage linac beams, and has developed a calibration service at three photon beams (6, 10 and 18 MV) from an Elekta Synergy linac. We describe the details of the new calibration service, the method validation and the use of the new calibration factors with the International Atomic Energy Agency’s TRS-398 dosimetry Code of Practice. The expected changes in absorbed dose measurements in the clinic when shifting from 60Co to the direct calibration are determined. For a Farmer chamber (model 2571), the measured chamber calibration coefficient is expected to be reduced by 0.4, 1.0 and 1.1 % respectively for these three beams when compared to the factor derived from 60Co. These results are in overall agreement with international absorbed dose standards and calculations by Muir and Rogers in 2010 of kQ factors using Monte Carlo techniques. The reasons for and against moving to the new service are discussed in the light of the requirements of clinical dosimetry. PMID:25146559

  8. Direct megavoltage photon calibration service in Australia.

    PubMed

    Butler, D J; Ramanathan, G; Oliver, C; Cole, A; Lye, J; Harty, P D; Wright, T; Webb, D V; Followill, D S

    2014-12-01

    The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) maintains the Australian primary standard of absorbed dose. Until recently, the standard was used to calibrate ionisation chambers only in (60)Co gamma rays. These chambers are then used by radiotherapy clinics to determine linac output, using a correction factor (k Q) to take into account the different spectra of (60)Co and the linac. Over the period 2010-2013, ARPANSA adapted the primary standard to work in megavoltage linac beams, and has developed a calibration service at three photon beams (6, 10 and 18 MV) from an Elekta Synergy linac. We describe the details of the new calibration service, the method validation and the use of the new calibration factors with the International Atomic Energy Agency's TRS-398 dosimetry Code of Practice. The expected changes in absorbed dose measurements in the clinic when shifting from (60)Co to the direct calibration are determined. For a Farmer chamber (model 2571), the measured chamber calibration coefficient is expected to be reduced by 0.4, 1.0 and 1.1 % respectively for these three beams when compared to the factor derived from (60)Co. These results are in overall agreement with international absorbed dose standards and calculations by Muir and Rogers in 2010 of k Q factors using Monte Carlo techniques. The reasons for and against moving to the new service are discussed in the light of the requirements of clinical dosimetry. PMID:25146559

  9. Strong enhancing effect of correlations of photon trajectories on laser beam scintillations

    NASA Astrophysics Data System (ADS)

    Chumak, O. O.; Baskov, R. A.

    2016-03-01

    To provide a detailed description of the dynamics of laser beam propagation in the atmosphere we use the method of the photon distribution function in the phase space, which reduces the analysis to consideration of photon trajectories and their correlations. The scintillation index σ2 is calculated for the range of moderate and strong turbulence, which is the most challenging for analytical consideration. The considerable growth of σ2 (by two to three times) found for moderate turbulence is shown to be due to correlations between photon trajectories. Our calculations demonstrate that the maximum of σ2 can be considerably decreased by an increase of the source aperture or the use of the fast phase diffuser.

  10. A SiPM based real time dosimeter for radiotherapic beams

    NASA Astrophysics Data System (ADS)

    Berra, A.; Conti, V.; Lietti, D.; Milan, L.; Novati, C.; Ostinelli, A.; Prest, M.; Romanó, C.; Vallazza, E.

    2015-02-01

    This paper describes the development of a scintillator dosimeter prototype for radiotherapic applications based on plastic scintillating fibers readout by Silicon PhotoMultipliers. The dosimeter, whose probes are water equivalent, could be used for quality control measurements, beam characterization and in vivo dosimetry, allowing a real time measurement of the dose spatial distribution. This paper describes the preliminary percentual depth dose scan performed with clinical 6 and 18 MV photon beams, comparing the results with a reference curve. The measurements were performed using a Varian Clinac iX linear accelerator at the Radiotherapy Department of the St. Anna Hospital in Como (IT). The prototype has given promising results, allowing real time measurements of relative dose without applying any correction factors.

  11. Timelike deeply virtual Compton scattering with a linearly polarized real (or quasi-real) photon beam

    NASA Astrophysics Data System (ADS)

    Goritschnig, A.; Pire, B.; Wagner, J.

    We calculate timelike virtual Compton scattering amplitudes in the generalized Bjorken scaling regime and focus on a new polarization asymmetry in the scattering process with a linearly polarized photon beam in the medium energy range, which will be studied intensely at JLab12 experiments. We demonstrate that new observables help us to access the polarized quark and gluon generalized parton distributions $\\tilde H(x, \\xi, t)$ and $ \\tilde E(x, \\xi, t)$.

  12. Measurements of photon and neutron leakage from medical linear accelerators and Monte Carlo simulation of tenth value layers of concrete used for intensity modulated radiation therapy treatment

    NASA Astrophysics Data System (ADS)

    Jaradat, Adnan Khalaf

    The x ray leakage from the housing of a therapy x ray source is regulated to be <0.1% of the useful beam exposure at a distance of 1 m from the source. The x ray leakage in the backward direction has been measured from linacs operating at 4, 6, 10, 15, and 18 MV using a 100 cm3 ionization chamber and track-etch detectors. The leakage was measured at nine different positions over the rear wall using a 3 x 3 matrix with a 1 m separation between adjacent positions. In general, the leakage was less than the canonical value, but the exact value depends on energy, gantry angle, and measurement position. Leakage at 10 MV for some positions exceeded 0.1%. Electrons with energy greater than about 9 MeV have the ability to produce neutrons. Neutron leakage has been measured around the head of electron accelerators at a distance 1 m from the target at 0°, 46°, 90°, 135°, and 180° azimuthal angles; for electron energies of 9, 12, 15, 16, 18, and 20 MeV and 10, 15, and 18 MV x ray photon beam, using a neutron bubble detector of type BD-PND and using Track-Etch detectors. The highest neutron dose equivalent per unit electron dose was at 0° for all electron energies. The neutron leakage from photon beams was the highest between all the machines. Intensity modulated radiation therapy (IMRT) delivery consists of a summation of small beamlets having different weights that make up each field. A linear accelerator room designed exclusively for IMRT use would require different, probably lower, tenth value layers (TVL) for determining the required wall thicknesses for the primary barriers. The first, second, and third TVL of 60Co gamma rays and photons from 4, 6, 10, 15, and 18 MV x ray beams by concrete have been determined and modeled using a Monte Carlo technique (MCNP version 4C2) for cone beams of half-opening angles of 0°, 3°, 6°, 9°, 12°, and 14°.

  13. The influence of bowtie filtration on x-ray photons distribution in cone beam CT

    NASA Astrophysics Data System (ADS)

    Jiang, Shanghai; Feng, Peng; Wei, Biao; He, Peng; Deng, Luzhen; Zhang, Wei

    2015-10-01

    Bowtie filters are used to modulate an incoming x-ray beam as a function of the angle of the x-ray to balance the photon flux on a detector array. Because of their key roles in radiation dose reduction and multi-energy imaging, bowtie filters have attracted a major attention in modern X-ray computed tomography (CT). However, few researches are concerned on the effects of the structure and materials for the bowtie filter in the Cone Beam CT (CBCT). In this study, the influence of bowtie filters' structure and materials on X-ray photons distribution are analyzed using Monte Carlo (MC) simulations by MCNP5 code. In the current model, the phantom was radiated by virtual X-ray source (its' energy spectrum calculated by SpekCalc program) filtered using bowtie, then all photons were collected through array photoncounting detectors. In the process above, two bowtie filters' parameters which include center thickness (B), edge thickness (controlled by A), changed respectively. Two kinds of situation are simulated: 1) A=0.036, B=1, 2, 3, 4, 5, 6mm and the material is aluminum; 2) A=0.016, 0.036, 0.056, 0.076, 0.096, B=2mm and the material is aluminum. All the X-ray photons' distribution are measured through MCNP. The results show that reduction in center thickness and edge thickness can reduce the number of background photons in CBCT. Our preliminary research shows that structure parameters of bowtie filter can influence X-ray photons, furthermore, radiation dose distribution, which provide some evidences in design of bowtie filter for reducing radiation dose in CBCT.

  14. Nonlinear Interaction of the Beat-Photon Beams with the Brain Neurocenters: Laser Neurophysics

    NASA Astrophysics Data System (ADS)

    Stefan, V. Alexander

    2010-03-01

    I propose a novel mechanism for laser-brain interaction: Nonlinear interaction of ultrashort pulses of beat-photon, (φ1-- φ2), or double-photon, (φ1+φ2), footnotetextMaria Goeppert-Mayer, "Uber Elementarakte mit zwei Quantenspr"ungen, Ann Phys 9, 273, 95. (1931). beams with the corrupted brain neurocenters, causing a particular neurological disease. The open-scull cerebral tissue can be irradiated with the beat-photon pulses in the range of several 100s fs, with the laser irradiances in the range of a few mW/cm^2, repetition rate of a few 100s Hz, and in the frequency range of 700-1300nm generated in the beat-wave driven free electron laser.footnotetextV. Alexander Stefan, The Interaction of Photon Beams with the DNA Molecules: Genomic Medical Physics. American Physical Society, 2009 APS March Meeting, March 16-20, 2009, abstract #K1.276; V. Stefan, B. I. Cohen, and C. Joshi, Nonlinear Mixing of Electromagnetic Waves in Plasmas Science 27 January 1989:Vol. 243. no. 4890, pp. 494 -- 500 (January 1989). This method may prove to be an effective mechanism in the treatment of neurological diseases: Parkinson's, Lou Gehrig's, and others.

  15. Vector meson and associated strangeness production using a linearly polarized photon beam at Jefferson Lab

    SciTech Connect

    Philip L. Cole

    2004-09-01

    The set of experiments forming the g8a run took place in the summer of 2001 in Hall B of Jefferson Lab. The g8a run was the commissioning experiment for the linearly-polarized photon beam at CLAS. The aim of these experiments is to improve the understanding of the underlying symmetry of the quark degrees of freedom in the nucleon, the nature of the parity exchange between the incident photon and the target nucleon, and the mechanism of associated strangeness production in electromagnetic reactions. A beam of tagged and collimated linearly polarized photons (energy range 1.8-2.2 GeV) in conjunction with the large solid angle coverage of CLAS make possible the extraction of the differential cross-sections and polarization observables for the photoproduction of vector mesons and kaons. The reaction channels are under investigation to search for possibly missing nucleon resonances. An overview of the experiment and preliminary results on the measurement of the photon asymmetries of the aforementioned reactions will be presented in this paper.

  16. Photon spectral characteristics of dissimilar 6 MV linear accelerators.

    PubMed

    Hinson, William H; Kearns, William T; deGuzman, Allan F; Bourland, J Daniel

    2008-05-01

    This work measures and compares the energy spectra of four dosimetrically matched 6 MV beams, generated from four physically different linear accelerators. The goal of this work is twofold. First, this study determines whether the spectra of dosimetrically matched beams are measurably different. This study also demonstrates that the spectra of clinical photon beams can be measured as a part of the beam data collection process for input to a three-dimensional (3D) treatment planning system. The spectra of 6 MV beams that are dosimetrically matched for clinical use were studied to determine if the beam spectra are similarly matched. Each of the four accelerators examined had a standing waveguide, but with different physical designs. The four accelerators were two Varian 2100C/Ds (one 6 MV/18 MV waveguide and one 6 MV/10 MV waveguide), one Varian 600 C with a vertically mounted waveguide and no bending magnet, and one Siemens MD 6740 with a 6 MV/10 MV waveguide. All four accelerators had percent depth dose curves for the 6 MV beam that were matched within 1.3%. Beam spectra were determined from narrow beam transmission measurements through successive thicknesses of pure aluminum along the central axis of the accelerator, made with a graphite Farmer ion chamber with a Lucite buildup cap. An iterative nonlinear fit using a Marquardt algorithm was used to find each spectrum. Reconstructed spectra show that all four beams have similar energy distributions with only subtle differences, despite the differences in accelerator design. The measured spectra of different 6 MV beams are similar regardless of accelerator design. The measured spectra show excellent agreement with those found by the auto-modeling algorithm in a commercial 3D treatment planning system that uses a convolution dose calculation algorithm. Thus, beam spectra can be acquired in a clinical setting at the time of commissioning as a part of the routine beam data collection. PMID:18561644

  17. Dosimetric characterization of CyberKnife radiosurgical photon beams using polymer gels

    SciTech Connect

    Pantelis, E.; Antypas, C.; Petrokokkinos, L.; Karaiskos, P.; Papagiannis, P.; Kozicki, M.; Georgiou, E.; Sakelliou, L.; Seimenis, I.

    2008-06-15

    Dose distributions registered in water equivalent, polymer gel dosimeters were used to measure the output factors and off-axis profiles of the radiosurgical photon beams employed for CyberKnife radiosurgery. Corresponding measurements were also performed using a shielded silicon diode commonly employed for CyberKnife commissioning, the PinPoint ion chamber, and Gafchromic EBT films, for reasons of comparison. Polymer gel results of this work for the output factors of the 5, 7.5, and 10 mm diameter beams are (0.702{+-}0.029), (0.872{+-}0.039), and (0.929{+-}0.041), respectively. Comparison of polymer gel and diode measurements shows that the latter overestimate output factors of the two small beams (5% for the 5 mm beam and 3% for the 7.5 mm beams). This is attributed to the nonwater equivalence of the high atomic number silicon material of the diode detector. On the other hand, the PinPoint chamber is found to underestimate output factors up to 10% for the 5 mm beam due to volume averaging effects. Polymer gel and EBT film output factor results are found in close agreement for all beam sizes, emphasizing the importance of water equivalence and fine detector sensitive volume for small field dosimetry. Relative off-axis profile results are in good agreement for all dosimeters used in this work, with noticeable differences observed only in the PinPoint estimate of the 80%-20% penumbra width, which is relatively overestimated.

  18. Broad beam attenuation of kilovoltage photon beams: effect of ion chambers.

    PubMed

    Das, I J

    1998-01-01

    In kilovoltage X-ray treatment, beam shaping and shielding normal tissue are accomplished by thin sheets of lead cutout, the thickness of which is selected based upon either published data or measurements. Available broad beam attenuation (BBA) data are found to be unsatisfactory and are the subject of this investigation. BBA is defined as the ratio of intensity with (I) and without (I0) attenuating medium for a large field in a phantom. BBA = I(x,t,E)/I0(x,0,E), where x is the depth of measurement, t is the thickness of attenuator, and E is the beam energy. The depth x should be zero for kilovoltage beams and dmax for megavoltage beams. Unfortunately, x is limited by the window thickness which is the core of this study. A Farmer-type cylindrical ion chamber and three parallel plate ion chambers (Capintec, PS-033; Markus; and Holt) were used to measure BBA for kilovoltage beams from a Siemens Stabilipan unit. Results indicate that attenuation is strongly dependent on the window thickness. For the 240 kVp beam, the thickness of lead for 5% and 1% transmissions are 3.1 mm, and 5.2 mm, respectively, with the Capintec chamber. The corresponding values of lead thickness for the Markus chamber are 2.3 mm and 4.0 mm; for the Holt chamber the values are 1.1 mm and 2.2 mm; and for the cylindrical chambers the values are 1.1 mm and 2.3 mm, respectively. Similar variabilities in lead thickness with ion chambers were also noted for the other kilovoltage beams. The large differences in lead thicknesses produce enormous clinical errors, especially for shielding eye and other critical structures. For small thickness of lead (< 0.1 mm), a 20-fold increase in surface dose could be observed instead of usual beam attenuation. This is due to intense low energy photoelectrons liberated from lead sheets in the contact with tissue. It is concluded that the lead thickness required to shield normal tissue varies with ion chamber. Until national or international guidelines for broad beam

  19. The water equivalence of solid phantoms for low energy photon beams

    SciTech Connect

    Hill, Robin; Kuncic, Zdenka; Baldock, Clive

    2010-08-15

    Purpose: To compare and evaluate the dosimetric water equivalence of several commonly used solid phantoms for low energy photon beams. Methods: A total of ten different solid phantom materials was used in the study. The PENELOPE Monte Carlo code was used to calculate depth doses and beam profiles in all the phantom materials as well as the dose to a small water voxel at the surface of the solid phantom. These doses were compared to the corresponding doses calculated in a water phantom. The primary photon beams used ranged in energy from 50 to 280 kVp. Results: A number of phantom materials had excellent agreement in dose compared to water for all the x-ray beam energies studied. RMI457 Solid Water, Virtual Water, PAGAT, A150, and Plastic Water DT all had depth doses that agreed with those in water to within 2%. For these same phantom materials, the dose changes in the water voxel at the surface of the solid phantom were within 2%, except for A150, which agreed to within 2.7%. By comparison, the largest differences in depth doses occurred for Plastic Water (-21.7%) and polystyrene (17.6%) for the 50 kVp energy photon beam and 8 cm diameter field size. Plastic Water gave the largest difference in the normalized beam profiles with differences of up to 3.5% as compared to water. Surface dose changes, due to the presence of the solid phantom acting as the backscatter material, were found to be up to 9.1% for polystyrene with significant differences also found for Plastic Water, PMMA, and RW3 phantoms. Conclusions: The following solid phantoms can be considered water equivalent and are recommended for relative dosimetry of low energy photon beams: A150, PAGAT, Plastic Water DT, RMI457 Solid Water, and Virtual Water. However, the following solid phantoms give significant differences, compared to water, in depth doses, profiles, and/or in surface doses due to backscatter changes: Plastic Water, PMMA, polystyrene, PRESAGE, and RW3.

  20. Production and dosimetry of simultaneous therapeutic photons and electrons beam by linear accelerator: A Monte Carlo study

    SciTech Connect

    Khledi, Navid; Sardari, Dariush; Arbabi, Azim; Ameri, Ahmad; Mohammadi, Mohammad

    2015-02-24

    Depending on the location and depth of tumor, the electron or photon beams might be used for treatment. Electron beam have some advantages over photon beam for treatment of shallow tumors to spare the normal tissues beyond of the tumor. In the other hand, the photon beam are used for deep targets treatment. Both of these beams have some limitations, for example the dependency of penumbra with depth, and the lack of lateral equilibrium for small electron beam fields. In first, we simulated the conventional head configuration of Varian 2300 for 16 MeV electron, and the results approved by benchmarking the Percent Depth Dose (PDD) and profile of the simulation and measurement. In the next step, a perforated Lead (Pb) sheet with 1mm thickness placed at the top of the applicator holder tray. This layer producing bremsstrahlung x-ray and a part of the electrons passing through the holes, in result, we have a simultaneous mixed electron and photon beam. For making the irradiation field uniform, a layer of steel placed after the Pb layer. The simulation was performed for 10×10, and 4×4 cm2 field size. This study was showed the advantages of mixing the electron and photon beam by reduction of pure electron's penumbra dependency with the depth, especially for small fields, also decreasing of dramatic changes of PDD curve with irradiation field size.

  1. Production and dosimetry of simultaneous therapeutic photons and electrons beam by linear accelerator: A Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Khledi, Navid; Arbabi, Azim; Sardari, Dariush; Mohammadi, Mohammad; Ameri, Ahmad

    2015-02-01

    Depending on the location and depth of tumor, the electron or photon beams might be used for treatment. Electron beam have some advantages over photon beam for treatment of shallow tumors to spare the normal tissues beyond of the tumor. In the other hand, the photon beam are used for deep targets treatment. Both of these beams have some limitations, for example the dependency of penumbra with depth, and the lack of lateral equilibrium for small electron beam fields. In first, we simulated the conventional head configuration of Varian 2300 for 16 MeV electron, and the results approved by benchmarking the Percent Depth Dose (PDD) and profile of the simulation and measurement. In the next step, a perforated Lead (Pb) sheet with 1mm thickness placed at the top of the applicator holder tray. This layer producing bremsstrahlung x-ray and a part of the electrons passing through the holes, in result, we have a simultaneous mixed electron and photon beam. For making the irradiation field uniform, a layer of steel placed after the Pb layer. The simulation was performed for 10×10, and 4×4 cm2 field size. This study was showed the advantages of mixing the electron and photon beam by reduction of pure electron's penumbra dependency with the depth, especially for small fields, also decreasing of dramatic changes of PDD curve with irradiation field size.

  2. Correlation study of a beam-position monitor and a photon-beam-position monitor in the PLS-II

    NASA Astrophysics Data System (ADS)

    Kim, Changbum; Shin, Seunghwan; Hwang, Ilmoon; Lee, Byung-Joon; Joo, Young-Do; Ha, Taekyun; Yoon, Jong Chel; Kim, Ghyung Hwa; Kim, Mungyung; Lee, Eun Hee; Kim, Ilyou; Huang, Jung-Yun

    2015-01-01

    The beam stability is one of the most important issues for the user service of the synchrotron radiation facility. After the upgrade of the Pohang Light Source (PLS-II), the electron-beam orbit is maintained within a root-mean-squred (rms) 1- μm range by using an orbit feedback system. However, that does not guarantee the radiation stability at the end of the beamline because unknown factors, such as focusing mirrors and double-crystal monocrometers, are present in the beamline. As a first step to solve this problem, photon-beam-position monitors (PBPMs) are installed in the front ends of the beamline to monitor the radiation stability. If the radiation is stable at the starting point of the beamline, we can move to the other components downstream that make the radiation unstable. In this paper, a correlation study will be presented between the beam-position monitor (BPM) and the PBPM. In addition, the effect of the orbit feedback system on the correlation will be described.

  3. The bremsstrahlung tagged photon beam in Hall B at the Jefferson Laboratory

    SciTech Connect

    Daniel I. Sober; Hall Crannell; Alberto Longhi; Scott Matthews; James T. O'Brien; Barry L. Berman; William Briscoe; Philip L. Cole; James Connelly; W.R. Dodge; Luc Y. Murphy; S.A. Phillips; Michael Dugger; David Lawrence; Barry G. Ritchie; Elton Smith; J.M. Lambert; Eric P.M. Anciant; Gerad Audit; Thierry Auger; Claude Marchand; Michael Klusman; James Napolitano; M.A. Khandaker; Carlos Salgado; Adam Sarty

    2000-02-01

    We describe the design and commissioning of the photon tagging beamline installed in experimental Hall B at the Thomas Jefferson National Accelerator Facility (Jlab). This system can tag photon energies over a range from 20% to 95% of the incident electron energy, and is capable of operation with beam energies up to 6.1 GeV. A single dipole magnet is combined with a hodoscope containing two planar arrays of plastic scintillators to detect energy-degraded electrons from a thin bremsstrahlung radiator. The first layer of 384 partially overlapping small scintillators provides photon energy resolution, while the second layer of 61 larger scintillators provides the timing resolution necessary to form a coincidence with the corresponding nuclear interaction triggered by the tagged photon. The definitions of overlap channels in the first counter plane and of geometric correlation between the two planes are determined using digitized time information from the individual counters. Auxiliary beamline devices are briefly described, and performance results to date under real operating conditions are presented. The entire photon-tagging system has met or exceeded its design goals.

  4. The FiR 1 photon beam model adjustment according to in-air spectrum measurements with the Mg(Ar) ionization chamber.

    PubMed

    Koivunoro, H; Schmitz, T; Hippeläinen, E; Liu, Y-H; Serén, T; Kotiluoto, P; Auterinen, I; Savolainen, S

    2014-06-01

    The mixed neutron-photon beam of FiR 1 reactor is used for boron-neutron capture therapy (BNCT) in Finland. A beam model has been defined for patient treatment planning and dosimetric calculations. The neutron beam model has been validated with an activation foil measurements. The photon beam model has not been thoroughly validated against measurements, due to the fact that the beam photon dose rate is low, at most only 2% of the total weighted patient dose at FiR 1. However, improvement of the photon dose detection accuracy is worthwhile, since the beam photon dose is of concern in the beam dosimetry. In this study, we have performed ionization chamber measurements with multiple build-up caps of different thickness to adjust the calculated photon spectrum of a FiR 1 beam model. PMID:24588987

  5. Verification of total body photon irradiation dosimetry techniques

    SciTech Connect

    Kirby, T.H.; Hanson, W.F.; Cates, D.A.

    1988-05-01

    A method of verifying the dosimetry of patients undergoing total body irradiation (TBI) with photon beams having energies from cobalt-60 to 25 MV is presented. A simple set of spot checks at the TBI axis has been used to verify data used for TBI dosimetry. Calculations to verify dose delivered to TBI patients are done in the same manner as those irradiated at standard treatment distances. A simple method of effective field size determination for various anatomical locations in a typical adult is presented. Measurements in an Alderson phantom with thermoluminescent dosimeters and an ion chamber at several anatomical locations indicate that this calculational method can predict the dose along the patient axis to within 4% for /sup 60/Co and 18-MV photon beams, provided the dosimetry data are appropriate (as determined by the spot checks). Results of intercomparisons of TBI beam calibration, off-axis and depth-dose data at various institutions visited by the Radiological Physics Center are also presented.

  6. Dosimetric impact of monoenergetic photon beams in the small-animal irradiation with inhomogeneities: A Monte Carlo evaluation

    NASA Astrophysics Data System (ADS)

    Chow, James C. L.

    2013-05-01

    This study investigated the variations of the dose and dose distribution in a small-animal irradiation due to the photon beam energy and presence of inhomogeneity. Based on the same mouse computed tomography image set, three Monte Carlo phantoms namely, inhomogeneous, homogeneous and bone-tissue phantoms were used in this study. These phantoms were generated by overriding the relative electron density of no voxel (inhomogeneous), all voxel (homogeneous) and the bone voxel (bone-tissue) to one. 360° photon arcs with beam energies of 50-1250 kV were used in mouse irradiations. Doses in the above phantoms were calculated using the EGSnrc-based DOSXYZnrc code through the DOSCTP. It was found that the dose conformity increased with the increase of the photon beam energy from the kV to MV range. For the inhomogeneous mouse phantom, increasing the photon beam energy from 50 kV to 1250 kV increased about 21 times the dose deposited at the isocenter. For the bone dose enhancement, the mean dose was 1.4 times higher when the bone inhomogeneity was not neglected using the 50 kV photon beams in the mouse irradiation. Bone dose enhancement affecting the mean dose in the mouse irradiation can be found in the photon beams with energy range of 50-200 kV, and the dose enhancement decreases with an increase of the beam energy. Moreover, the MV photon beam has a higher dose at the isocenter, and a better dose conformity compared to the kV beam.

  7. Monte Carlo simulation on pre-clinical irradiation: A heterogeneous phantom study on monoenergetic kilovoltage photon beams

    NASA Astrophysics Data System (ADS)

    Chow, James C. L.

    2012-10-01

    This study investigated radiation dose variations in pre-clinical irradiation due to the photon beam energy and presence of tissue heterogeneity. Based on the same mouse computed tomography image dataset, three phantoms namely, heterogeneous, homogeneous and bone homogeneous were used. These phantoms were generated by overriding the relative electron density of no voxel (heterogeneous), all voxel (homogeneous) and the bone voxel (bone homogeneous) to one. 360° photon arcs with beam energies of 50 - 1250 keV were used in mouse irradiations. Doses in the above phantoms were calculated using the EGSnrc-based DOSXYZnrc code through the DOSCTP. Monte Carlo simulations were carried out in parallel using multiple nodes in a high-performance computing cluster. It was found that the dose conformity increased with the increase of the photon beam energy from the keV to MeV range. For the heterogeneous mouse phantom, increasing the photon beam energy from 50 keV to 1250 keV increased seven times the dose deposited at the isocenter. For the bone dose enhancement, the mean dose was 2.7 times higher when the bone heterogeneity was not neglected using the 50 keV photon beams in the mouse irradiation. Bone dose enhancement affecting the mean dose was found in the photon beams with energy range of 50 - 200 keV and the dose enhancement decreased with an increase of the beam energy. Moreover, the MeV photon beam had a higher dose at the isocenter, and a better dose conformity compared to the keV beam.

  8. Energy dependence and dose response of Gafchromic EBT2 film over a wide range of photon, electron, and proton beam energies

    SciTech Connect

    Arjomandy, Bijan; Tailor, Ramesh; Anand, Aman; Sahoo, Narayan; Gillin, Michael; Prado, Karl; Vicic, Milos

    2010-05-15

    Purpose: Since the Gafchromic film EBT has been recently replaced by the newer model EBT2, its characterization, especially energy dependence, has become critically important. The energy dependence of the dose response of Gafchromic EBT2 film is evaluated for a broad range of energies from different radiation sources used in radiation therapy. Methods: The beams used for this study comprised of kilovoltage x rays (75, 125, and 250 kVp), {sup 137}Cs gamma (662 KeV), {sup 60}Co gamma (1.17-1.33 MeV), megavoltage x rays (6 and 18 MV), electron beams (6 and 20 MeV), and proton beams (100 and 250 MeV). The film's response to each of the above energies was measured over the dose range of 0.4-10 Gy, which corresponds to optical densities ranging from 0.05 to 0.74 for the film reader used. Results: The energy dependence of EBT2 was found to be relatively small within measurement uncertainties (1{sigma}={+-}4.5%) for all energies and modalities. Conclusion: For relative and absolute dosimetry of radiation therapy beams, the weak energy dependence of the EBT2 makes it most suitable for clinical use compared to other films.

  9. Cerenkov light spectrum in an optical fiber exposed to a photon or electron radiation therapy beam

    SciTech Connect

    Lambert, Jamil; Yin Yongbai; McKenzie, David R.; Law, Sue; Suchowerska, Natalka

    2009-06-20

    A Cerenkov signal is generated when energetic charged particles enter the core of an optical fiber. The Cerenkov intensity can be large enough to interfere with signals transmitted through the fiber. We determine the spectrum of the Cerenkov background signal generated in a poly(methyl methacrylate) optical fiber exposed to photon and electron therapeutic beams from a linear accelerator. This spectral measurement is relevant to discrimination of the signal from the background, as in scintillation dosimetry using optical fiber readouts. We find that the spectrum is approximated by the theoretical curve after correction for the wavelength dependent attenuation of the fiber. The spectrum does not depend significantly on the angle between the radiation beam and the axis of the fiber optic but is dependent on the depth in water at which the fiber is exposed to the beam.

  10. Ant colony algorithm implementation in electron and photon Monte Carlo transport: Application to the commissioning of radiosurgery photon beams

    SciTech Connect

    Garcia-Pareja, S.; Galan, P.; Manzano, F.; Brualla, L.; Lallena, A. M.

    2010-07-15

    Purpose: In this work, the authors describe an approach which has been developed to drive the application of different variance-reduction techniques to the Monte Carlo simulation of photon and electron transport in clinical accelerators. Methods: The new approach considers the following techniques: Russian roulette, splitting, a modified version of the directional bremsstrahlung splitting, and the azimuthal particle redistribution. Their application is controlled by an ant colony algorithm based on an importance map. Results: The procedure has been applied to radiosurgery beams. Specifically, the authors have calculated depth-dose profiles, off-axis ratios, and output factors, quantities usually considered in the commissioning of these beams. The agreement between Monte Carlo results and the corresponding measurements is within {approx}3%/0.3 mm for the central axis percentage depth dose and the dose profiles. The importance map generated in the calculation can be used to discuss simulation details in the different parts of the geometry in a simple way. The simulation CPU times are comparable to those needed within other approaches common in this field. Conclusions: The new approach is competitive with those previously used in this kind of problems (PSF generation or source models) and has some practical advantages that make it to be a good tool to simulate the radiation transport in problems where the quantities of interest are difficult to obtain because of low statistics.

  11. Validation of the Pinnacle³ photon convolution-superposition algorithm applied to fast neutron beams.

    PubMed

    Kalet, Alan M; Sandison, George A; Phillips, Mark H; Parvathaneni, Upendra

    2013-01-01

    We evaluate a photon convolution-superposition algorithm used to model a fast neutron therapy beam in a commercial treatment planning system (TPS). The neutron beam modeled was the Clinical Neutron Therapy System (CNTS) fast neutron beam produced by 50 MeV protons on a Be target at our facility, and we implemented the Pinnacle3 dose calculation model for computing neutron doses. Measured neutron data were acquired by an IC30 ion chamber flowing 5 cc/min of tissue equivalent gas. Output factors and profile scans for open and wedged fields were measured according to the Pinnacle physics reference guide recommendations for photon beams in a Wellhofer water tank scanning system. Following the construction of a neutron beam model, computed doses were then generated using 100 monitor units (MUs) beams incident on a water-equivalent phantom for open and wedged square fields, as well as multileaf collimator (MLC)-shaped irregular fields. We compared Pinnacle dose profiles, central axis doses, and off-axis doses (in irregular fields) with 1) doses computed using the Prism treatment planning system, and 2) doses measured in a water phantom and having matching geometry to the computation setup. We found that the Pinnacle photon model may be used to model most of the important dosimetric features of the CNTS fast neutron beam. Pinnacle-calculated dose points among open and wedged square fields exhibit dose differences within 3.9 cGy of both Prism and measured doses along the central axis, and within 5 cGy difference of measurement in the penumbra region. Pinnacle dose point calculations using irregular treatment type fields showed a dose difference up to 9 cGy from measured dose points, although most points of comparison were below 5 cGy. Comparisons of dose points that were chosen from cases planned in both Pinnacle and Prism show an average dose difference less than 0.6%, except in certain fields which incorporate both wedges and heavy blocking of the central axis. All

  12. The Interaction of Photon Beams with the DNA Molecules: Genomic Medical Physics

    NASA Astrophysics Data System (ADS)

    Stefan, V. Alexander

    2009-03-01

    I propose a novel method for the modification of the corrupted human DNAootnotetextJ.D. Watson and F. H. C. Crick, Nature, 171, 737-738 (1953). code that causes particular genetic disease. The method is based on the nonlinear interaction between the DNA molecule and the ``modulation photons'' generated in beat wave driven free electron laser, BW-FEL.ootnotetextV. Alexander Stefan. Beat Wave Driven Free Electron Laser (S-U-Press, 2002, La Jolla, CA)[cf. V. Stefan, et al., Bull. Am. Phys. Soc. 32, No. 9, 1713 (1987)] The BW-FEL frequency is given by ν˜γ^2nφe (γ is the free electron beam relativistic factor, n is the harmonic number of the electron Bernstein plasma mode, and φe is the electron cyclotron frequency). The meV ``carrier photons'' are focused on the area of the brain, the source-center of a genetic disease. For the BW-FEL parameters: the free electron beam guiding d.c. magnetic field ˜ 1kG, γ˜10^3, and n=10, the keV ``modulation photons'' are generated, which are easily focused on the nucleotides. By modulating the frequency of the BW-FEL, the parametric resonance with the different DNA (sub-DNA) eigen molecular oscillation-modes are achieved, leading to the ``knock-on'' of the unwanted (corrupted) nucleotides.

  13. Ultrashort coherence times in partially polarized stationary optical beams measured by two-photon absorption.

    PubMed

    Shevchenko, Andriy; Roussey, Matthieu; Friberg, Ari T; Setälä, Tero

    2015-11-30

    We measure the recently introduced electromagnetic temporal degree of coherence of a stationary, partially polarized, classical optical beam. Instead of recording the visibility of intensity fringes, the spectrum, or the polarization characteristics, we introduce a novel technique based on two-photon absorption. Using a Michelson interferometer equipped with polarizers and a specific GaAs photocount tube, we obtain the two fundamental quantities pertaining to the fluctuations of light: the degree of coherence and the degree of polarization. We also show that the electromagnetic intensity-correlation measurements with two-photon absorption require that the polarization dynamics, i.e., the time evolution of the instantaneous polarization state, is properly taken into account. We apply the technique to unpolarized and polarized sources of amplified spontaneous emission (Gaussian statistics) and to a superposition of two independent, narrow-band laser beams of different mid frequencies (non-Gaussian statistics). For these two sources femtosecond-range coherence times are found that are in good agreement with the traditional spectral measurements. Although previously employed for laser pulses, two-photon absorption provides a new physical principle to study electromagnetic coherence phenomena in classical and quantum continuous-wave light at extremely short time scales. PMID:26698754

  14. A depth dependence determination of the wedge transmission factor for 4-10 MV photon beams.

    PubMed

    McCullough, E C; Gortney, J; Blackwell, C R

    1988-01-01

    The depth dependence (up to 25 cm) of the in-phantom wedge transmission factor (WTF) has been determined for three medical linear accelerator x-ray beams with energies of 4, 6, and 10 MV containing 15 degrees-60 degrees (nominal) brass wedges. All measurements were made with a cylindrical ionization chamber in water, for a field size of 10 X 10 cm2 with a source-skin distance of 80 or 100 cm. We conclude that, for the accelerators studied, the WTF factor at depth is less than 2% different from that determined at dmax (for the nominal wedge angles and photon energies studied) unless the depth of interest is greater than 10 cm. Up to the maximum depth studied (25 cm) the relative wedge factor--that is, wedge factor at depth compared to that determined at dmax--was about equal to or less than 1.02 for the 15 degrees and 30 degrees wedges and any of the photon beam energies studied. For the seldom utilized combination of a nominal wedge angle in excess of 45 degrees with a depth greater than 10 cm, the WTF at depth can differ from the WTF determined at dmax, by up to 5%. Since the wedge transmission factor is reflective of relative percent dose data, our results also indicate that it is in error to use open field percent depth doses for certain combinations of wedge angle, photon energy, and depth. PMID:3211057

  15. Beam related response of in vivo diode detectors for external radiotherapy

    NASA Astrophysics Data System (ADS)

    Baci, Syrja; Telhaj, Ervis; Malkaj, Partizan

    2016-03-01

    In Vivo Dosimetry (IVD) is a set of methods used in cancer treatment clinics to determine the real dose of radiation absorbed by target volume in a patient's body. IVD has been widely implemented in radiotherapy treatment centers and is now recommended part of Quality Assurance program by many International health and radiation organizations. Because of cost and lack of specialized personnel, IVD has not been practiced as yet, in Albanian radiotherapy clinics. At Hygeia Hospital Tirana, patients are irradiated with high energy photons generated by Elekta Synergy Accelerators. We have recently started experimenting with the purpose of establishing an IVD practice at this hospital. The first set of experiments was aimed at calibration of diodes that are going to be used for IVD. PMMA, phantoms by PTW were used to calibrate p - type Si, semiconductor diode dosimeters, made by PTW Freiburg for entrance dose. Response of the detectors is affected by energy of the beam, accumulated radiation dose, dose rate, temperature, angle against the beam axis, etc. Here we present the work done for calculating calibration factor and correction factors of source to surface distance, field size, and beam incidence for the entrance dose for both 6 MV photon beam and 18 MV photon beam. Dependence of dosimeter response was found to be more pronounced with source to surface distance as compared to other variables investigated.

  16. Investigations of high mobility single crystal chemical vapor deposition diamond for radiotherapy photon beam monitoring

    SciTech Connect

    Tromson, D.; Descamps, C.; Tranchant, N.; Bergonzo, P.; Nesladek, M.; Isambert, A.

    2008-03-01

    The intrinsic properties of diamond make this material theoretically very suitable for applications in medical physics. Until now ionization chambers have been fabricated from natural stones and are commercialized by PTW, but their fairly high costs and long delivery times have often limited their use in hospital. The properties of commercialized intrinsic polycrystalline diamond were investigated in the past by many groups. The results were not completely satisfactory due to the nature of the polycrystalline material itself. In contrast, the recent progresses in the growth of high mobility single crystal synthetic diamonds prepared by chemical vapor deposition (CVD) technique offer new alternatives. In the framework of the MAESTRO project (Methods and Advanced Treatments and Simulations for Radio Oncology), the CEA-LIST is studying the potentialities of synthetic diamond for new techniques of irradiation such as intensity modulated radiation therapy. In this paper, we present the growth and characteristics of single crystal diamond prepared at CEA-LIST in the framework of the NoRHDia project (Novel Radiation Hard CVD Diamond Detector for Hadrons Physics), as well as the investigations of high mobility single crystal CVD diamond for radiotherapy photon beam monitoring: dosimetric analysis performed with the single crystal diamond detector in terms of stability and repeatability of the response signal, signal to noise ratio, response speed, linearity of the signal versus the absorbed dose, and dose rate. The measurements performed with photon beams using radiotherapy facilities demonstrate that single crystal CVD diamond is a good alternative for air ionization chambers for beam quality control.

  17. Liquid scintillator for 2D dosimetry for high-energy photon beams

    SciTech Connect

    Poenisch, Falk; Archambault, Louis; Briere, Tina Marie; Sahoo, Narayan; Mohan, Radhe; Beddar, Sam; Gillin, Michael T.

    2009-05-15

    Complex radiation therapy techniques require dosimetric verification of treatment planning and delivery. The authors investigated a liquid scintillator (LS) system for application for real-time high-energy photon beam dosimetry. The system was comprised of a transparent acrylic tank filled with liquid scintillating material, an opaque outer tank, and a CCD camera. A series of images was acquired when the tank with liquid scintillator was irradiated with a 6 MV photon beam, and the light data measured with the CCD camera were filtered to correct for scattering of the optical light inside the liquid scintillator. Depth-dose and lateral profiles as well as two-dimensional (2D) dose distributions were found to agree with results from the treatment planning system. Further, the corrected light output was found to be linear with dose, dose rate independent, and is robust for single or multiple acquisitions. The short time needed for image acquisition and processing could make this system ideal for fast verification of the beam characteristics of the treatment machine. This new detector system shows a potential usefulness of the LS for 2D QA.

  18. An alternative approach to compensators design for photon beams used in radiotherapy

    NASA Astrophysics Data System (ADS)

    Jurković, S.; Žauhar, G.; Bistrović, M.; Faj, D.; Kaliman, Z.; Smilović Radojčić, Đ.

    2007-09-01

    The use of compensators in order to achieve desired dose distribution has a long history and is a well-established technique in radiation therapy planning. There are several different calculation methods for determining a compensator's thickness. An alternative method that is based on the Cunningham's modification of Clarkson's method to calculate scattered radiation in beams with an inhomogeneous cross-section is proposed. It is well known that the total dose distribution of radiotherapy photon beam consists of the contributions of the primary beam, attenuated by the tissue layer, and the scattered radiation generated by the primary radiation in single and multiple photon scatter events. The scattered component can be represented as a function of the primary radiation. The central point of our method is the numerical estimation of the primary distribution required to achieve the desired total distribution. Now using the calculated primary distribution, the shape of the modulator could be determined. In this way the contribution of the scattered component is validated in a more accurate way than using effective attenuation coefficients, which is a common practice. The method is verified in various clinical situations and compared with the standard method. The accuracy, although dependent on geometry, was improved by at least 2%. With more complex geometries there is an even higher gain in accuracy with our method when compared to the standard method.

  19. Experimental study on photon-beam peripheral doses, their components and some possibilities for their reduction

    NASA Astrophysics Data System (ADS)

    Chofor, Ndimofor; Harder, Dietrich; Rühmann, Antje; Willborn, Kay C.; Wiezorek, Tilo; Poppe, Björn

    2010-07-01

    The component analysis of the peripheral doses produced at typical accelerators such as the Siemens Primus 6/15 is regarded as an approach enabling technical strategies towards the reduction of second malignancies associated with photon beam radiotherapy. Suitable phantom and detector arrangements have been applied to show that the unavoidable peripheral dose contribution due to photon scattering from the directly irradiated part of the body or phantom does not constitute the entirety of the peripheral doses. Rather, there are peripheral dose contributions due to beam head leakage and to extrafocal radiation which can be regarded as partly avoidable. Simple methods of reducing beam head leakage from the Siemens Primus 6/15 linac are, for the crossplane direction, to install a pair of adjustable shielding blocks in the accessory holder and, for the inplane direction, to close all out-of-field leaf pairs of the multileaf collimator via the treatment planning system software. The relative efficiency of these shielding measures is largest in the case of small unavoidable dose contributions, i.e. for small fields and small depths. Methods of avoiding doses coming from extrafocal radiation are also envisaged for future research.

  20. Cerenkov emission induced by external beam radiation stimulates molecular fluorescence

    SciTech Connect

    Axelsson, Johan; Davis, Scott C.; Gladstone, David J.; Pogue, Brian W.

    2011-07-15

    Purpose: Cerenkov emission is induced when a charged particle moves faster than the speed of light in a given medium. Both x-ray photons and electrons produce optical Cerenkov photons in everyday radiation therapy of tissue; yet, this phenomenon has never been fully documented. This study quantifies the emissions and also demonstrates that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. Methods: In this study, Cerenkov emission induced by radiation from a clinical linear accelerator is investigated. Biological mimicking phantoms were irradiated with x-ray photons, with energies of 6 or 18 MV, or electrons at energies 6, 9, 12, 15, or 18 MeV. The Cerenkov emission and the induced molecular fluorescence were detected by a camera or a spectrometer equipped with a fiber optic cable. Results: It is shown that both x-ray photons and electrons, at MeV energies, produce optical Cerenkov photons in tissue mimicking media. Furthermore, we demonstrate that the Cerenkov emission can excite a fluorophore, protoporphyrin IX (PpIX), embedded in biological phantoms. Conclusions: The results here indicate that molecular fluorescence monitoring during external beam radiotherapy is possible.

  1. Dosimetric properties of equivalent-quality flattening filter-free (FFF) and flattened photon beams of Versa HD linear accelerator.

    PubMed

    Meshram, Mukesh N; Pramanik, Srimanta; Ranjith, C P; Gopal, Saravana K; Dobhal, Rishabh

    2016-01-01

    This study presents the basic dosimetric properties of photon beams of a Versa HD linear accelerator (linac), which is capable of delivering flattening filter-free (FFF) beams with a beam quality equivalent to the corresponding flattened beams based on comprehensive beam data measurement. The analyzed data included the PDDs, profiles, penumbra, out-of-field doses, surface doses, output factors, head and phantom scatter factors, and MLC transmissions for both FFF and flattened beams of 6 MV and 10 MV energy from an Elekta Versa HD linac. The 6MVFFF and 10MVFFF beams had an equivalent mean energy to the flattened beams and showed less PDD variations with the field sizes. Compared with their corresponding flattened beams, Dmax was deeper for FFF beams for all field sizes; the ionization ratio variations with the field size were lower for FFF beams; the out-of-field doses were lower and the penumbras were sharper for the FFF beams; the off-axis profile variations with the depths were lesser for the FFF beams. Further, the 6MVFFF and 10MVFFF beams had 35.7% and 40.9% less variations in output factor with the field size, respectively. The collimator exchange effect was reduced in the FFF mode. The head scatter factor showed 59.1% and 73.6% less variations, on average, for the 6MVFFF and 10MVFFF beams, respectively; the variations in the phantom scatter factor were also smaller. The surface doses for all beams increased linearly with the field size. The 6MVFFF and 10MVFFF beams had higher surface doses than the corresponding flattened beams for field sizes of up to 10 ×10cm2 but had lower surface doses for larger fields. Both FFF beams had lower average MLC transmissions than the flattened beams. The finding that the FFF beams were of equivalent quality to the corresponding flattened beams indicates a significant dif-ference from the data on unmatched FFF beams. PMID:27167293

  2. Proton beam writing of long, arbitrary structures for micro/nano photonics and fluidics applications

    NASA Astrophysics Data System (ADS)

    Udalagama, Chammika; Teo, E. J.; Chan, S. F.; Kumar, V. S.; Bettiol, A. A.; Watt, F.

    2011-10-01

    The last decade has seen proton beam writing maturing into a versatile lithographic technique able to produce sub-100 nm, high aspect ratio structures with smooth side walls. However, many applications in the fields of photonics and fluidics require the fabrication of structures with high spatial resolution that extends over several centimetres. This cannot be achieved by purely magnetic or electrostatic beam scanning due to the large off-axis beam aberrations in high demagnification systems. As a result, this has limited us to producing long straight structures using a combination of beam and stage scanning. In this work we have: (1) developed an algorithm to include any arbitrary pattern into the writing process by using a more versatile combination of beam and stage scanning while (2) incorporating the use of the ubiquitous AutoCAD DXF (drawing exchange format) into the design process. We demonstrate the capability of this approach in fabricating structures such as Y-splitters, Mach-Zehnder modulators and microfluidic channels that are over several centimetres in length, in polymer. We also present optimisation of such parameters as scanning speed and scanning loops to improve on the surface roughness of the structures. This work opens up new possibilities of using CAD software in PBW for microphotonics and fluidics device fabrication.

  3. A dosimetric intercomparison of megavoltage photon beams in UK radiotherapy centres.

    PubMed

    Thwaites, D I; Williams, J R; Aird, E G; Klevenhagen, S C; Williams, P C

    1992-02-01

    A dosimetry intercomparison has been carried out for all 64 radiotherapy centres in the UK. Doses were measured with an ionization chamber in an epoxy resin water-substitute phantom of relatively simple geometry. Reference-point measurements were made for all MV photon beams. For 61 Co-60 beams, a mean ratio of measured-to-stated dose of 1.002 was observed with a standard deviation of 0.014, whilst for 100 MV x-ray beams, the corresponding figures were 1.003 and 0.015. 97% of beams lay within a +/- 3% deviation. One measurement was instrumental in discovering a large discrepancy. Doses were also investigated in two planned three-field distributions at one beam quality in each centre. One of these was in a homogeneous phantom, whilst the second included a lung-equivalent insert. Doses were measured at the central point and at four other points in the high dose volume. In both situations, the mean ratio of measured-to-calculated doses for all points was 1.008, with standard deviations of 0.027 and 0.035 for the uniform and non-uniform phantoms, respectively. Discrepancies over 5% were followed up. The work must be viewed in the context of other international intercomparisons and is an essential part of wider radiotherapy audit processes. PMID:1553393

  4. Collimated Blue and Infrared Beams Generated by Two-Photon Excitation in Rubidium Vapor

    NASA Astrophysics Data System (ADS)

    Gearba, Alina; Sell, Jerry; Olesen, Robert; Knize, Randy

    2016-05-01

    Utilizing nonlinear optical processes in Rb vapor we describe the generation of optical fields at 420 nm, 1.32 μm, and 1.37 μm. Input laser beams at 780 nm and 776 nm enter a heated Rb vapor cell collinear and circularly polarized. Rubidium atoms are excited to the 5D5 / 2 state, with blue light generated by four-wave mixing through the 6P3 / 2 --> 5S1 / 2 states, while infrared beams at 1.37 μm and 1.32 μm are generated by cascading decays through the 6S1 / 2 --> 5P3 / 2 and 6S1 / 2 --> 5P1 / 2 states, respectively. While the blue beam emission from four-wave mixing has been studied in detail, the mechanisms responsible for generating the infrared beams are still under investigation. We will present our results for the conditions which give rise to infrared beam generation by two-photon excitation in rubidium vapor.

  5. Therapeutic dose simulation of a 6 MV Varian Linac photon beam using GEANT4

    NASA Astrophysics Data System (ADS)

    Salama, E.; Ali, A. S.; Khaled, N. E.; Radi, A.

    2015-10-01

    A developed program in C++ language using GEANT4 libraries was used to simulate the gantry of a 6 MV high energy photon linear accelerator (Linac). The head of a clinical linear accelerator based on the manufacturer's detailed information is simulated. More than 2× 109 primary electrons are used to create the phase space file. Evaluation of the percentage depth dose (PDD) and flatness symmetry (lateral dose profiles) in water phantom were performed. Comparisons between experimental and simulated data were carried out for three field sizes; 5 × 5, 10 × 10 and 15 × 15 cm2. A relatively good agreement appeared between computed and measured PDD. Electron contamination and spatial distribution for both photons and electrons in the simulated beam are evaluated. Moreover, the obtained lateral dose profiles at 15, 50, and 100 mm depth are compatible with the measured values. The obtained results concluded that, GEANT4 code is a promising applicable Monte Carlo program in radiotherapy applications.

  6. 3D imaging using combined neutron-photon fan-beam tomography: A Monte Carlo study.

    PubMed

    Hartman, J; Yazdanpanah, A Pour; Barzilov, A; Regentova, E

    2016-05-01

    The application of combined neutron-photon tomography for 3D imaging is examined using MCNP5 simulations for objects of simple shapes and different materials. Two-dimensional transmission projections were simulated for fan-beam scans using 2.5MeV deuterium-deuterium and 14MeV deuterium-tritium neutron sources, and high-energy X-ray sources, such as 1MeV, 6MeV and 9MeV. Photons enable assessment of electron density and related mass density, neutrons aid in estimating the product of density and material-specific microscopic cross section- the ratio between the two provides the composition, while CT allows shape evaluation. Using a developed imaging technique, objects and their material compositions have been visualized. PMID:26953978

  7. Photon beam dose distributions for patients with implanted temporary tissue expanders

    NASA Astrophysics Data System (ADS)

    Asena, A.; Kairn, T.; Crowe, S. B.; Trapp, J. V.

    2015-01-01

    This study examines the effects of temporary tissue expanders (TTEs) on the dose distributions of photon beams in breast cancer radiotherapy treatments. EBT2 radiochromic film and ion chamber measurements were taken to quantify the attenuation and backscatter effects of the inhomogeneity. Results illustrate that the internal magnetic port present in a tissue expander causes a dose reduction of approximately 25% in photon tangent fields immediately downstream of the implant. It was also shown that the silicone elastomer shell of the tissue expander reduced the dose to the target volume by as much as 8%. This work demonstrates the importance for an accurately modelled high-density implant in the treatment planning system for post-mastectomy breast cancer patients.

  8. BEAM EXPOSURE DEPENDENCE AND MECHANISMS OF PHOTON-STIMULATED DESORPTION FROM ALKALI FLUORIDES

    SciTech Connect

    Parks, C.C.; Shirley, D.A.; Loubriel, G.

    1983-11-01

    Photon-stimulated desorption experiments were performed on the (001) face of LiF for photon energies near the F(2s) and Li(ls) edges (from 37 to 72 eV). There are structures in the F{sup +} yield above the F(2s) edge which are absent in the Li{sup +} spectrum, differences in detail in the Li{sup +} and F{sup +} yields near the Li(1s) edge, and considerable broadening of the desorption yields as compared to the bulk photoabsorption spectrum. The first observation of a strong x-ray, and visible, beam exposure dependence of ion yields from LiF and NaF is also presented. These results are discussed in terms of electronic and defect properties of alkali halides.

  9. Why diamond dimensions and electrode geometry are crucial for small photon beam dosimetry

    SciTech Connect

    Marsolat, F.; Tromson, D.; Tranchant, N.; Pomorski, M.; Bergonzo, P.; Bassinet, C.; Huet, C.; Buchheit, I.; Marchesi, V.; Gaudaire-Josset, S.; Lisbona, A.; Lazaro, D.; Hugon, R.

    2015-12-21

    Recent use of very small photon beams (down to 4 mm) in stereotactic radiotherapy requires new detectors to accurately determine the delivered dose. Diamond detectors have been presented in the literature as an attractive candidate for this application, due to their small detection volume and the diamond atomic number (Z = 6) which is close to water effective atomic number (Zeff ∼ 7.42). However, diamond exhibits a density 3.51 times greater than that of water and recent studies using Monte Carlo simulations have demonstrated the drawback of a high-density detector on small beam output factors. The current study focuses on geometrical parameters of diamond detector, namely, the diamond dimensions and the electrode geometry, in order to solve the dosimetric issues still observed in small photon beams with diamond detectors. To give better insights to these open questions, we have used both computational method and experimental analysis. This study highlighted that reducing diamond dimensions is crucial for small beam output factor measurements and to limit the influence of its high density. Furthermore, electrodes covering the whole diamond surface were essential for a dose rate independence of the diamond detector. The optimal dosimeter derived from this work presented small diamond dimensions of approximately 1 × 1 × 0.15 mm{sup 3}, with diamond-like-carbon electrodes covering the whole diamond surface. A dose rate independence of this diamond detector (better than 0.5% over a wide range of dose rates available on a stereotactic dedicated facility) was obtained due to the electrode geometry. Concerning the output factor measurements, a good agreement (better than 1.1%) was observed between this carbon material detector and two types of passive dosimeters (LiF microcubes and EBT2 radiochromic films) for all beam sizes except the smallest field of 0.6 × 0.6 cm{sup 2} with a deviation of 2.6%. This new study showed the high performance

  10. SU-E-T-142: Effect of the Bone Heterogeneity On the Unflattened and Flattened Photon Beam Dosimetry: A Monte Carlo Comparison

    SciTech Connect

    Chow, J; Owrangi, A

    2014-06-01

    Purpose: This study compared the dependence of depth dose on bone heterogeneity of unflattened photon beams to that of flattened beams. Monte Carlo simulations (the EGSnrc-based codes) were used to calculate depth doses in phantom with a bone layer in the buildup region of the 6 MV photon beams. Methods: Heterogeneous phantom containing a bone layer of 2 cm thick at a depth of 1 cm in water was irradiated by the unflattened and flattened 6 MV photon beams (field size = 10×10 cm{sup 2}). Phase-space files of the photon beams based on the Varian TrueBeam linac were generated by the Geant4 and BEAMnrc codes, and verified by measurements. Depth doses were calculated using the DOSXYZnrc code with beam angles set to 0° and 30°. For dosimetric comparison, the above simulations were repeated in a water phantom using the same beam geometry with the bone layer replaced by water. Results: Our results showed that the beam output of unflattened photon beams was about 2.1 times larger than the flattened beams in water. Comparing the water phantom to the bone phantom, larger doses were found in water above and below the bone layer for both the unflattened and flattened photon beams. When both beams were turned 30°, the deviation of depth dose between the bone and water phantom became larger compared to that with beam angle equal to 0°. Dose ratio of the unflattened and flattened photon beams showed that the unflattened beam has larger depth dose in the buildup region compared to the flattened beam. Conclusion: Although the unflattened photon beam had different beam output and quality compared to the flattened, dose enhancements due to the bone scatter were found similar. However, we discovered that depth dose deviation due to the presence of bone was sensitive to the beam obliquity.

  11. Efficiency improvements for ion chamber calculations in high energy photon beams.

    PubMed

    Wulff, J; Zink, K; Kawrakow, I

    2008-04-01

    This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross-section enhancement (XCSE), an intermediate phase-space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results-in combination with a Russian Roulette game for electrons that cannot reach the cavity volume-in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor Pcel can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the Pcel variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase-space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs_chamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs_chamber code are presented. PMID:18491527

  12. Efficiency improvements for ion chamber calculations in high energy photon beams

    SciTech Connect

    Wulff, J.; Zink, K.; Kawrakow, I.

    2008-04-15

    This article presents the implementation of several variance reduction techniques that dramatically improve the simulation efficiency of ion chamber dose and perturbation factor calculations. The cavity user code for the EGSnrc Monte Carlo code system is extended by photon cross-section enhancement (XCSE), an intermediate phase-space storage (IPSS) technique, and a correlated sampling (CS) scheme. XCSE increases the density of photon interaction sites inside and in the vicinity of the chamber and results - in combination with a Russian Roulette game for electrons that cannot reach the cavity volume - in an increased efficiency of up to a factor of 350 for calculating dose in a Farmer type chamber placed at 10 cm depth in a water phantom. In combination with the IPSS and CS techniques, the efficiency for the calculation of the central electrode perturbation factor P{sub cel} can be increased by up to three orders of magnitude for a single chamber location and by nearly four orders of magnitude when considering the P{sub cel} variation with depth or with distance from the central axis in a large field photon beam. The intermediate storage of the phase-space properties of particles entering a volume that contains many possible chamber locations leads to efficiency improvements by a factor larger than 500 when computing a profile of chamber doses in the field of a linear accelerator photon beam. All techniques are combined in a new EGSnrc user code egs{sub c}hamber. Optimum settings for the variance reduction parameters are investigated and are reported for a Farmer type ion chamber. A few example calculations illustrating the capabilities of the egs{sub c}hamber code are presented.

  13. Detector dose response in megavoltage small photon beams. I. Theoretical concepts

    SciTech Connect

    Bouchard, Hugo Duane, Simon; Seuntjens, Jan; Kamio, Yuji; Palmans, Hugo

    2015-10-15

    Purpose: To explain the reasons for significant quality correction factors in megavoltage small photon fields and clarify the underlying concepts relevant to dosimetry under such conditions. Methods: The validity of cavity theory and the requirement of charged particle equilibrium (CPE) are addressed from a theoretical point of view in the context of nonstandard beams. Perturbation effects are described into four main subeffects, explaining their nature and pointing out their relative importance in small photon fields. Results: It is demonstrated that the failure to meet classical cavity theory requirements, such as CPE, is not the reason for significant quality correction factors. On the contrary, it is shown that the lack of CPE alone cannot explain these corrections and that what matters most, apart from volume averaging effects, is the relationship between the lack of CPE in the small field itself and the density of the detector cavity. The density perturbation effect is explained based on Fano’s theorem, describing the compensating effect of two main contributions to cavity absorbed dose. Using the same approach, perturbation effects arising from the difference in atomic properties of the cavity medium and the presence of extracameral components are explained. Volume averaging effects are also discussed in detail. Conclusions: Quality correction factors of small megavoltage photon fields are mainly due to differences in electron density between water and the detector medium and to volume averaging over the detector cavity. Other effects, such as the presence of extracameral components and differences in atomic properties of the detection medium with respect to water, can also play an accentuated role in small photon fields compared to standard beams.

  14. Design and fabrication of Si-based photonic crystal stamps with electron beam lithography (EBL)

    NASA Astrophysics Data System (ADS)

    Jannesary, Reyhaneh; Bergmair, Iris; Zamiri, Saeid; Hingerl, Kurt; Hubbard, Graham; Abbott, Steven; Chen, Qin; Allsopp, Duncan

    2009-05-01

    The quest for mass replication has established technologies like nanoimprinting via hard stamps or PDMS stamps, where the stamps are usually produced via Electron Beam Lithography (EBL) for applications in the microelectronic industry. On the other hand, nanopatterning with self ordered structures1 or via holographic patterns provide the basis for large area imprints for applications for example, antireflection coatings based on biomimetic motheyes2. In this work we report on a technology for enabling the mass replication of custom-designed and e-beam lithographically prepared structures via establishing novel roll to roll nanoimprint processes for pattern transfer into UV curable pre-polymers. The new nano-fabrication technology is based on the concept of Disposal Master Technology (DMT) capable of patterning areas up to 1 x 1 m2 and is suitable for mass volume manufacturing of large area arrays of sub-wavelength photonic elements. As an example to show the potential of the application of the new nanoimprint technologies, we choose the fabrication of a photonic crystal (PhC) structure with integrated light coupling devices for low loss interconnection between PhC lightwave circuits and optical fibre systems. We present two methods for fabrication of nanoimprint lithography stamps in Si substrate. In the first method optimized electron beam lithography (EBL) and lift-off patterning of a 15-nm thick Cr mask, and then the pattern transfer into Si using reacting ion etching (RIE) with SF6 as etch gas. In the first method, we use 200nm of positive resist PMMA 950K for EBL exposure. In this method, resist thickness, exposure dose, development time and parameter for etching have been optimized and a photonic crystal of Si-rods in air was fabricated. In the second method lift-off has not been performed and metal mask has been used as master. The subsequent steps for fabricating the master will be presented in detail.

  15. SU-E-T-577: Commissioning of a Deterministic Algorithm for External Photon Beams

    SciTech Connect

    Zhu, T; Finlay, J; Mesina, C; Liu, H

    2014-06-01

    Purpose: We report commissioning results for a deterministic algorithm for external photon beam treatment planning. A deterministic algorithm solves the radiation transport equations directly using a finite difference method, thus improve the accuracy of dose calculation, particularly under heterogeneous conditions with results similar to that of Monte Carlo (MC) simulation. Methods: Commissioning data for photon energies 6 – 15 MV includes the percentage depth dose (PDD) measured at SSD = 90 cm and output ratio in water (Spc), both normalized to 10 cm depth, for field sizes between 2 and 40 cm and depths between 0 and 40 cm. Off-axis ratio (OAR) for the same set of field sizes was used at 5 depths (dmax, 5, 10, 20, 30 cm). The final model was compared with the commissioning data as well as additional benchmark data. The benchmark data includes dose per MU determined for 17 points for SSD between 80 and 110 cm, depth between 5 and 20 cm, and lateral offset of up to 16.5 cm. Relative comparisons were made in a heterogeneous phantom made of cork and solid water. Results: Compared to the commissioning beam data, the agreement are generally better than 2% with large errors (up to 13%) observed in the buildup regions of the FDD and penumbra regions of the OAR profiles. The overall mean standard deviation is 0.04% when all data are taken into account. Compared to the benchmark data, the agreements are generally better than 2%. Relative comparison in heterogeneous phantom is in general better than 4%. Conclusion: A commercial deterministic algorithm was commissioned for megavoltage photon beams. In a homogeneous medium, the agreement between the algorithm and measurement at the benchmark points is generally better than 2%. The dose accuracy for a deterministic algorithm is better than a convolution algorithm in heterogeneous medium.

  16. Instrumentation and beam dynamics study of advanced electron-photon facility in Indiana University

    NASA Astrophysics Data System (ADS)

    Luo, Tianhuan

    The Advanced eLectron-PHoton fAcility (ALPHA) is a compact electron accelerator under construction and being commissioned at the Indiana University Center for Exploration of Energy and Matter (CEEM). In this thesis, we have studied the refurbished Cooler Injector Synchrotron (CIS) RF cavity using both the transmission line model and SUPERFISH simulation. Both low power and high power RF measurements have been carried out to characterize the cavity. Considering the performance limit of ferrite, we have designed a new ferrite loaded, co-axial quarter wave like cavity with similar structure but a more suitable ferrite material. We have also designed a traveling wave stripline kicker for fast extraction by POISSON and Microwave Studio. The strips' geometry is trimmed to maximize the uniformity of the kicking field and match the impedance of the power cables. The time response simulation shows the kicker is fast enough for machine operation. The pulsed power supply requirement has also been speci ed. For the beam diagnosis in the longitudinal direction, we use a wideband Wall Gap Monitor (WGM) served in CIS. With proper shielding and amplification to get good WGM signal, we have characterized the injected and extracted beam signal in single pass commissioning, and also verified the debunching effect of the ALPHA storage ring. A modulation-demodulation signal processing method is developed to measure the current and longitudinal profile of injected beam. By scanning the dipole strength in the injection line, we have reconstructed the tomography of the longitudinal phase space of the LINAC beam. In the accumulation mode, ALPHA will be operated under a low energy and high current condition, where intra beam scattering (IBS) becomes a dominant effect on the beam emittance. A self consistent simulation, including IBS effect, gas scattering and linear coupling, has been carried out to calculate the emittance of the stored beam.

  17. Instrumentation and Beam Dynamics Study of Advanced Electron-Photon Facility in Indiana University

    SciTech Connect

    Luo, Tianhuan

    2011-08-01

    The Advanced eLectron-PHoton fAcility (ALPHA) is a compact electron accelerator under construction and being commissioned at the Indiana University Center for Exploration of Energy and Matter (CEEM). In this thesis, we have studied the refurbished Cooler Injector Synchrotron (CIS) RF cavity using both the transmission line model and SUPERFISH simulation. Both low power and high power RF measurements have been carried out to characterize the cavity. Considering the performance limit of ferrite, we have designed a new ferrite loaded, co-axial quarter wave like cavity with similar structure but a more suitable ferrite material. We have also designed a traveling wave stripline kicker for fast extraction by POISSON and Microwave Studio. The strips geometry is trimmed to maximize the uniformity of the kicking field and match the impedance of the power cables. The time response simulation shows the kicker is fast enough for machine operation. The pulsed power supply requirement has also been specified. For the beam diagnosis in the longitudinal direction, we use a wideband Wall Gap Monitor (WGM) served in CIS. With proper shielding and amplification to get good WGM signal, we have characterized the injected and extracted beam signal in single pass commissioning, and also verified the debunching effect of the ALPHA storage ring. A modulation-demodulation signal processing method is developed to measure the current and longitudinal profile of injected beam. By scanning the dipole strength in the injection line, we have reconstructed the tomography of the longitudinal phase space of the LINAC beam. In the accumulation mode, ALPHA will be operated under a low energy and high current condition, where intra beam scattering (IBS) becomes a dominant effect on the beam emittance. A self consistent simulation, including IBS effect, gas scattering and linear coupling, has been carried out to calculate the emittance of the stored beam.

  18. Dirac leaky-wave antennas for continuous beam scanning from photonic crystals

    NASA Astrophysics Data System (ADS)

    Memarian, Mohammad; Eleftheriades, George V.

    2015-01-01

    Leaky-Wave Antennas (LWAs) enable directive and scannable radiation patterns, which are highly desirable attributes at terahertz, infrared and optical frequencies. However, a LWA is generally incapable of continuous beam scanning through broadside, due to an open stopband in its dispersion characteristic. This issue is yet to be addressed at frequencies beyond microwaves, mainly as existing microwave solutions (for example, transmission line metamaterials) are unavailable at these higher frequencies. Here we report leaky-wave radiation from the interface of a photonic crystal (PC) with a Dirac-type dispersion and air. The resulting Dirac LWA (DLWA) can radiate at broadside, chiefly owing to the closed Γ-point bandgap of the Dirac PC. Thus, the DLWA can continuously scan a directive beam over a wide range of angles by varying the frequency. These DLWAs can be designed at microwave as well as terahertz to optical frequencies, with feasible dimensions and low losses.

  19. Dirac leaky-wave antennas for continuous beam scanning from photonic crystals.

    PubMed

    Memarian, Mohammad; Eleftheriades, George V

    2015-01-01

    Leaky-Wave Antennas (LWAs) enable directive and scannable radiation patterns, which are highly desirable attributes at terahertz, infrared and optical frequencies. However, a LWA is generally incapable of continuous beam scanning through broadside, due to an open stopband in its dispersion characteristic. This issue is yet to be addressed at frequencies beyond microwaves, mainly as existing microwave solutions (for example, transmission line metamaterials) are unavailable at these higher frequencies. Here we report leaky-wave radiation from the interface of a photonic crystal (PC) with a Dirac-type dispersion and air. The resulting Dirac LWA (DLWA) can radiate at broadside, chiefly owing to the closed Γ-point bandgap of the Dirac PC. Thus, the DLWA can continuously scan a directive beam over a wide range of angles by varying the frequency. These DLWAs can be designed at microwave as well as terahertz to optical frequencies, with feasible dimensions and low losses. PMID:25556705

  20. Highly indistinguishable photons from deterministic quantum-dot microlenses utilizing three-dimensional in situ electron-beam lithography

    NASA Astrophysics Data System (ADS)

    Gschrey, M.; Thoma, A.; Schnauber, P.; Seifried, M.; Schmidt, R.; Wohlfeil, B.; Krüger, L.; Schulze, J.-H.; Heindel, T.; Burger, S.; Schmidt, F.; Strittmatter, A.; Rodt, S.; Reitzenstein, S.

    2015-07-01

    The success of advanced quantum communication relies crucially on non-classical light sources emitting single indistinguishable photons at high flux rates and purity. We report on deterministically fabricated microlenses with single quantum dots inside which fulfil these requirements in a flexible and robust quantum device approach. In our concept we combine cathodoluminescence spectroscopy with advanced in situ three-dimensional electron-beam lithography at cryogenic temperatures to pattern monolithic microlenses precisely aligned to pre-selected single quantum dots above a distributed Bragg reflector. We demonstrate that the resulting deterministic quantum-dot microlenses enhance the photon-extraction efficiency to (23+/-3)%. Furthermore we prove that such microlenses assure close to pure emission of triggered single photons with a high degree of photon indistinguishability up to (80+/-7)% at saturation. As a unique feature, both single-photon purity and photon indistinguishability are preserved at high excitation power and pulsed excitation, even above saturation of the quantum emitter.

  1. Photon beam dosimetry in the superficial buildup region using radiochromic EBT film stack.

    PubMed

    Chiu-Tsao, Sou-Tung; Chan, Maria F

    2009-06-01

    It has been a challenge to perform accurate 2D or 3D dosimetry in the surface region with steep dose gradient for megavoltage photon beams. We developed a dosimetry method in the superficial buildup region for the 6 and 15 MV photon beams using a radiochromic EBT film stack. Eight radiochromic EBT film strips (3 x 20 x 0.024 cm3) stacked together formed a 3D dosimeter. The film stack was positioned above a polystyrene phantom and surrounded by Solid Water slabs (0.2 cm) with the top film layer at 100 cm SSD. A 10 x 10 cm2 open field was used to irradiate the film stack with 1000 MU. All films were scanned using Epson 4870 flatbed scanner with transmission mode, 48 bit color, and 150 dpi (0.017 cm pixel resolution). The pixel values were converted to doses using an established calibration curve. This method allowed dose measurement for depths from 0.012 to 0.18 cm with fine spatial resolution (0.017 cm horizontally and 0.024 cm vertically). For each energy modality, we obtained both the central axis percent depth doses and the beam profiles along the central line covering the primary field and peripheral region at each depth. The primary field doses varied steeply with depth, while those in the peripheral region were weakly dependent on depth. For the 6 MV and 15 MV photon beams, (1) the central axis percent depth doses in the eight film layers ranged from 22% to 66% and from 15% to 44%, respectively; (2) the extrapolated percent depth doses at d = 0 were 15% and 14%, respectively. Agreement with the previously reported central axis percent depth doses in this region using parallel plate thin window ion chamber and ultrathin TLD was observed. The percent depth doses and beam profiles data can be incorporated in the treatment planning system for more accurate assessment of the doses to skin and shallow tumors to accomplish more accurate calculation results in the clinical usage. PMID:19610296

  2. Poster — Thur Eve — 37: Respiratory gating with an Elekta flattening filter free photon beam

    SciTech Connect

    Péloquin, S; Furstoss, C; Munger, P; Wierzbicki, W; Carrier, J-F

    2014-08-15

    In cases where surgery is not possible for lung cancer treatment, stereotactic body radiation therapy (SBRT) may be an option. One problem when treating this type of cancer is the motion of the lungs caused by the patient's respiration. It is possible to reduce the impact of this movement with the use of respiratory gating. By combining respiratory gating with a flattening filter free (FFF) photon beam linac, the increased treatment time caused by a reduced beam-on time of respiratory gating methods can be compensated by the inherent increased dose rate of FFF beams. This project's aim is to create hardware and software interfaces allowing free respiration gating on an Elekta Synergy-S linac specially modified to deliver 6 MV FFF photon beams. First, a printed circuit board was created for reading the signal from a Bellows Belt from Philips (a respiration monitor belt) and transmitting an On/Off signal to the accelerator. A software was also developed to visualize patient respiration. Secondly, a FFF model was created with the Pinnacle treatment planning system from Philips. Gamma (Γ) analysis (2%, 2 mm) was used to evaluate model. For fields going from 5.6 × 5.6 to 12 × 12 cm{sup 2}, central axis depth dose model fitting shows an average gamma value of 0.2 and 100% of gamma values remain under the Γ = 1 limit. For smaller fields (0.8 × 0.8 and 1.6 × 1.6 cm{sup 2}), Pinnacle has more trouble trying to fit the measurements, overestimating dose in penumbra and buildup regions.

  3. N-isopropylacrylamide gel dosimeter to evaluate clinical photon beam characteristics.

    PubMed

    Chiu, Chung-Yu; Tsang, Yuk-Wah; Hsieh, Bor-Tsung

    2014-08-01

    The introduction of beam intensity control concept in current radiotherapy techniques has increased treatment planning complexity. Thus, small-field dose measurement has become increasingly vital. Polymer gel dosimetry method is widely studied. It is the only dose measurement tool that provides 3D dose distribution. This study aims to use an N-isopropylacrylamide (NIPAM) gel dosimeter to conduct beam performance measurements of percentage depth dose (PDD), beam flatness, and symmetry for photon beams with field sizes of 3×3 and 4×4 cm(2). Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and Gafchromic™ EBT3 radiochromic film displayed high consistency in the region deeper than the build-up region. The gel dosimeter dose profile had 3% lower flatness and symmetry measurement at 5 cm depth for different fields compared with that of the Gafchromic™ EBT3 film. During gamma evaluation under 3%/3 mm dose difference/distance-to-agreement standard, the pass rates of the polymer gel dosimeter to the TPS and EBT3 film were both higher than 96%. Given that the gel is tissue equivalent, it did not exhibit the energy dependence problems of radiochromic films. Therefore, the practical use of NIPAM polymer gel dosimeters is enhanced in clinical dose verification. PMID:24836904

  4. Coherent beam control through inhomogeneous media in multi-photon microscopy

    NASA Astrophysics Data System (ADS)

    Paudel, Hari Prasad

    Multi-photon fluorescence microscopy has become a primary tool for high-resolution deep tissue imaging because of its sensitivity to ballistic excitation photons in comparison to scattered excitation photons. The imaging depth of multi-photon microscopes in tissue imaging is limited primarily by background fluorescence that is generated by scattered light due to the random fluctuations in refractive index inside the media, and by reduced intensity in the ballistic focal volume due to aberrations within the tissue and at its interface. We built two multi-photon adaptive optics (AO) correction systems, one for combating scattering and aberration problems, and another for compensating interface aberrations. For scattering correction a MEMS segmented deformable mirror (SDM) was inserted at a plane conjugate to the objective back-pupil plane. The SDM can pre-compensate for light scattering by coherent combination of the scattered light to make an apparent focus even at a depths where negligible ballistic light remains (i.e. ballistic limit). This problem was approached by investigating the spatial and temporal focusing characteristics of a broad-band light source through strongly scattering media. A new model was developed for coherent focus enhancement through or inside the strongly media based on the initial speckle contrast. A layer of fluorescent beads under a mouse skull was imaged using an iterative coherent beam control method in the prototype two-photon microscope to demonstrate the technique. We also adapted an AO correction system to an existing in three-photon microscope in a collaborator lab at Cornell University. In the second AO correction approach a continuous deformable mirror (CDM) is placed at a plane conjugate to the plane of an interface aberration. We demonstrated that this "Conjugate AO" technique yields a large field-of-view (FOV) advantage in comparison to Pupil AO. Further, we showed that the extended FOV in conjugate AO is maintained over a

  5. Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets

    SciTech Connect

    Hatchett, Stephen P.; Brown, Curtis G.; Cowan, Thomas E.; Henry, Eugene A.; Johnson, Joy S.; Key, Michael H.; Koch, Jeffrey A.; Langdon, A. Bruce; Lasinski, Barbara F.; Lee, Richard W.

    2000-05-01

    In recent Petawatt laser experiments at Lawrence Livermore National Laboratory, several hundred joules of 1 {mu}m laser light in 0.5-5.0-ps pulses with intensities up to 3x10{sup 20} W cm{sup -2} were incident on solid targets and produced a strongly relativistic interaction. The energy content, spectra, and angular patterns of the photon, electron, and ion radiations have all been diagnosed in a number of ways, including several novel (to laser physics) nuclear activation techniques. About 40%-50% of the laser energy is converted to broadly beamed hot electrons. Their beam centroid direction varies from shot to shot, but the resulting bremsstrahlung beam has a consistent width. Extraordinarily luminous ion beams (primarily protons) almost precisely normal to the rear of various targets are seen--up to 3x10{sup 13} protons with kT{sub ion}{approx}several MeV representing {approx}6% of the laser energy. Ion energies up to at least 55 MeV are observed. The ions appear to originate from the rear target surfaces. The edge of the ion beam is very sharp, and collimation increases with ion energy. At the highest energies, a narrow feature appears in the ion spectra, and the apparent size of the emitting spot is smaller than the full back surface area. Any ion emission from the front of the targets is much less than from the rear and is not sharply beamed. The hot electrons generate a Debye sheath with electrostatic fields of order MV per micron, which apparently accelerate the ions. (c) 2000 American Institute of Physics.

  6. Electron, Photon, and Ion Beams from the Relativistic Interaction of Petawatt Laser Pulses with Solid Targets

    SciTech Connect

    Hatchett, S.P.; Brown, C.G.; Cowan, T.E.; Henry, E.A.; Johnson, J.; Key, M.H.; Koch, J.A.; Langdon, A.B.; Lasinski, B.F.; Lee, R.W.; Mackinnon, A.J.; Pennington, D.M.; Perry, M.D.; Phillips, T.W.; Roth, M.; Sangster, T.C.; Singh, M.S.; Snavely, R.A.; Stoyer, M.A.; Wilks, S.C.; Yasuike, K.

    1999-11-12

    In our Petawatt laser experiments several hundred joules of 1 {micro}m laser light in 0.5-5.0 ps pulses with intensities up to 3 x 10{sup 20}Wcm{sup -2} were incident on solid targets producing a strongly relativistic interaction. The energy content, spectra, and angular patterns of the photon, electron, and ion radiations were diagnosed in a number of ways, including several novel (to laser physics) nuclear activation techniques. From the beamed bremsstrahlung we infer that about 40-50% of the laser energy is converted to broadly beamed hot electrons. Their direction centroid varies from shot to shot, but the beam has a consistent width. Extraordinarily luminous ion beams almost precisely normal to the rear of various targets are seen--up to 3 x 10{sup 13} protons with kT{sub ion} {approx} several MeV representing {approx}6% of the laser energy. We observe ion energies up to at least 55 MeV. The ions appear to originate from the rear target surfaces. The edge of the ion beam is very sharp, and collimation increases with ion energy. At the highest energies, a narrow feature appears in the ion spectra, and the apparent size of the emitting spot is smaller than the full back surface area. Any ion emission from the front of the targets is much less than from the rear and is not sharply beamed. The hot electrons generate a Debye sheath with electrostatic fields of order MV per micron which apparently accelerate the ions.

  7. A comparison of beam characteristics for gated and nongated clinical x-ray beams.

    PubMed

    Ramsey, C R; Cordrey, I L; Oliver, A L

    1999-10-01

    Respiratory gating has only recently been applied to conventional external beam radiotherapy. In order for respiratory gating to be used clinically, an evaluation of the dosimetric effects of small units of delivered dose must be performed. The purpose of this study is to systematically evaluate the effect of various gating sequences on x-ray central axis output, ionization ratios (nominal accelerating potential), beam flatness, and beam symmetry. Measurements were taken for 6 and 18 MV photons on a linear accelerator that generates the gate by using a gridded electron gun to stop the electron flow to the wave-guide. The beam output, energy, flatness, and symmetry did not vary by more than 0.8 percent in most of the gating sequences. The maximum output deviations (0.8 percent), flatness deviations (1.9 percent), and symmetry deviations (0.8 percent) occurred when a low number of monitor units (<5 MU) were delivered in the gating window. Although these deviations are not clinically significant, each linear accelerator should be evaluated carefully before clinical implementation. PMID:10535624

  8. Monte Carlo photon beam modeling and commissioning for radiotherapy dose calculation algorithm.

    PubMed

    Toutaoui, A; Ait chikh, S; Khelassi-Toutaoui, N; Hattali, B

    2014-11-01

    The aim of the present work was a Monte Carlo verification of the Multi-grid superposition (MGS) dose calculation algorithm implemented in the CMS XiO (Elekta) treatment planning system and used to calculate the dose distribution produced by photon beams generated by the linear accelerator (linac) Siemens Primus. The BEAMnrc/DOSXYZnrc (EGSnrc package) Monte Carlo model of the linac head was used as a benchmark. In the first part of the work, the BEAMnrc was used for the commissioning of a 6 MV photon beam and to optimize the linac description to fit the experimental data. In the second part, the MGS dose distributions were compared with DOSXYZnrc using relative dose error comparison and γ-index analysis (2%/2 mm, 3%/3 mm), in different dosimetric test cases. Results show good agreement between simulated and calculated dose in homogeneous media for square and rectangular symmetric fields. The γ-index analysis confirmed that for most cases the MGS model and EGSnrc doses are within 3% or 3 mm. PMID:24947967

  9. Neutron contamination of Varian Clinac iX 10 MV photon beam using Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Yani, S.; Tursinah, R.; Rhani, M. F.; Soh, R. C. X.; Haryanto, F.; Arif, I.

    2016-03-01

    High energy medical accelerators are commonly used in radiotherapy to increase the effectiveness of treatments. As we know neutrons can be emitted from a medical accelerator if there is an incident of X-ray that hits any of its materials. This issue becomes a point of view of many researchers. The neutron contamination has caused many problems such as image resolution and radiation protection for patients and radio oncologists. This study concerns the simulation of neutron contamination emitted from Varian Clinac iX 10 MV using Monte Carlo code system. As neutron production process is very complex, Monte Carlo simulation with MCNPX code system was carried out to study this contamination. The design of this medical accelerator was modelled based on the actual materials and geometry. The maximum energy of photons and neutron in the scoring plane was 10.5 and 2.239 MeV, respectively. The number and energy of the particles produced depend on the depth and distance from beam axis. From these results, it is pointed out that the neutron produced by linac 10 MV photon beam in a typical treatment is not negligible.

  10. Two dimensional thermo-optic beam steering using a silicon photonic optical phased array

    NASA Astrophysics Data System (ADS)

    Mahon, Rita; Preussner, Marcel W.; Rabinovich, William S.; Goetz, Peter G.; Kozak, Dmitry A.; Ferraro, Mike S.; Murphy, James L.

    2016-03-01

    Components for free space optical communication terminals such as lasers, amplifiers, and receivers have all seen substantial reduction in both size and power consumption over the past several decades. However, pointing systems, such as fast steering mirrors and gimbals, have remained large, slow and power-hungry. Optical phased arrays provide a possible solution for non-mechanical beam steering devices that can be compact and lower in power. Silicon photonics is a promising technology for phased arrays because it has the potential to scale to many elements and may be compatible with CMOS technology thereby enabling batch fabrication. For most free space optical communication applications, two-dimensional beam steering is needed. To date, silicon photonic phased arrays have achieved two-dimensional steering by combining thermo-optic steering, in-plane, with wavelength tuning by means of an output grating to give angular tuning, out-of-plane. While this architecture might work for certain static communication links, it would be difficult to implement for moving platforms. Other approaches have required N2 controls for an NxN element phased array, which leads to complexity. Hence, in this work we demonstrate steering using the thermo-optic effect for both dimensions with a simplified steering mechanism requiring only two control signals, one for each steering dimension.

  11. SU-D-213-01: Transparent Photon Detector For The Online Monitoring Of IMRT Beams

    SciTech Connect

    Delorme, R; Arnoud, Y; Fabbro, R; Boyer, B; Rossetto, O; Gallin-Martel, L; Gallin-Martel, M; Pelissier, A; Fonteille, I

    2015-06-15

    Purpose: An innovative Transparent Detector for Radiotherapy (TraDeRa) has been developed. The detector aims at real-time monitoring of modulated beam ahead of the patient during delivery sessions, with a field cover up to 40×40 cm {sup 2}. Methods: TraDeRa consists in a pixelated matrix of ionization chambers with a patented electrodes design. An in-house designed specific integrated circuit allows to extract the signal and provides a real-time map of beam intensity and shape, at the linac pulse-scale. The measurements under irradiation are made with a 6 MV clinical X-Ray beam. Dose calculations are performed with the Monte Carlo code PENELOPE, modeling the full accelerator head and the TraDeRa detector. Results: A 2 % attenuation of the beam was measured in the presence of TraDeRa and the PENELOPE dosimetric study showed no significant modification of the photon beam properties. TraDeRa detects error leaf position as small as 1 mm compared to a reference field, for both static and modulated fields. In addition, measurements are accurate over a large dynamic range from low intensity signals, as inter-leaves leaks, to very high intensities as obtained on the medical line of the European Synchrotron Radiation Facility. The detector is fully operational for conventional and high dose rate beams as FFF modes (up to 2400 MU/min). Conclusion: The current version of TraDeRa shows promising results for IMRT quality assurance (QA), allowing pulse-scale monitoring of the beam and high sensitivity for errors detection. The attenuation is small enough not to hinder the irradiation while keeping the beam upstream of the patient under constant control. A final prototype under development will include 1600 independent electrodes, half of them with a high resolution centered on the beam axis. This compact detector provides an independent set of measurements for a better QA. Funding support : This work was supported by the LABEX PRIMES (ANR-11-LABX-0063) of Universite de Lyon

  12. A controllable single photon beam-splitter as a node of a quantum network

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Gautam, Gaurav; Ghosh, Saikat; Kumar, Deepak; Indian Institute of Technology, Kanpur, India Collaboration; Jawaharlal Nehru University, New Delhi, India Collaboration

    2016-05-01

    A theoretical model for a controlled single-photon beam-splitter is proposed and analysed. It consists of two crossed optical-cavities with overlapping waists, dynamically coupled to a single flying atom. The system is shown to route a single photon with near-unity efficiency in an effective ``weak-coupling'' regime. Furthermore, two such nodes, forming a segment of a quantum network, are shown to perform several controlled quantum operations. All one-qubit operations involve a transfer of a photon from one cavity to another in a single node, while two-qubit operations involve transfer from one node to a next one, coupled via an optical fiber. Novel timing protocols for classical optical fields are found to simplify possible experimental realizations along with achievable effective parameter regime. This model can be extended to various other physical systems including gated quantum dots, circuit-QED or opto-mechanical elements. This work is supported by DST-SERB, and DAE, Government of India.

  13. A controllable single photon beam-splitter as a node of a quantum network

    NASA Astrophysics Data System (ADS)

    Gautam, Gaurav; Kumar, Santosh; Ghosh, Saikat; Kumar, Deepak

    2016-03-01

    A model for a controlled single-photon beam-splitter is proposed and analyzed. It consists of two crossed optical-cavities with overlapping waists, dynamically coupled to a single flying atom. The system is shown to route a single photon with near-unity efficiency in an effective ‘weak-coupling’ regime. Furthermore, two such nodes, forming a segment of a quantum network, are shown to perform several controlled quantum operations. All one-qubit operations involve a transfer of a photon from one cavity to another in a single node, while two-qubit operations involve transfer from one node to a next one, coupled via an optical fiber. Novel timing protocols for classical optical fields are found to simplify possible experimental realizations along with achievable effective parameter regime. Though our analysis here is based on a cavity-QED scenario, basic features of the model can be extended to various other physical systems including gated quantum dots, circuit-QED or opto-mechanical elements.

  14. Integration of a photonic crystal polarization beam splitter and waveguide bend.

    PubMed

    Zheng, Wanhua; Xing, Mingxin; Ren, Gang; Johnson, Steven G; Zhou, Wenjun; Chen, Wei; Chen, Lianghui

    2009-05-11

    In this work, we present the design of an integrated photonic-crystal polarization beam splitter (PC-PBS) and a low-loss photonic-crystal 60 degrees waveguide bend. Firstly, the modal properties of the PC-PBS and the mechanism of the low-loss waveguide bend are investigated by the two-dimensional finite-difference time-domain (FDTD) method, and then the integration of the two devices is studied. It shows that, although the individual devices perform well separately, the performance of the integrated circuit is poor due to the multi-mode property of the PC-PBS. By introducing deformed airhole structures, a single-mode PC-PBS is proposed, which significantly enhance the performance of the circuit with the extinction ratios remaining above 20 dB for both transverse-electric (TE) and transverse-magnetic (TM) polarizations. Both the specific result and the general idea of integration design are promising in the photonic crystal integrated circuits in the future. PMID:19434199

  15. Dysprosium detector for neutron dosimetry in external beam radiotherapy

    NASA Astrophysics Data System (ADS)

    Ostinelli, A.; Berlusconi, C.; Conti, V.; Duchini, M.; Gelosa, S.; Guallini, F.; Vallazza, E.; Prest, M.

    2014-09-01

    Radiotherapy treatments with high-energy (>8 MeV) photon beams are a standard procedure in clinical practice, given the skin and near-target volumes sparing effect, the accurate penetration and the uniform spatial dose distribution. On the other hand, despite these advantages, neutrons may be produced via the photo-nuclear (γ,n) reactions of the high-energy photons with the high-Z materials in the accelerator head, in the treatment room and in the patient, resulting in an unwanted dose contribution which is of concern, given its potential to induce secondary cancers, and which has to be monitored. This work presents the design and the test of a portable Dysprosium dosimeter to be used during clinical treatments to estimate the "in vivo" dose to the patient. The dosimeter has been characterized and validated with tissue-equivalent phantom studies with a Varian Clinical iX 18 MV photon beam, before using it with a group of patients treated at the S. Anna Hospital in Como. The working principle of the dosimeter together with the readout chain and the results in terms of delivered dose are presented.

  16. Commissioning of a Varian Clinac iX 6 MV photon beam using Monte Carlo simulation

    SciTech Connect

    Dirgayussa, I Gde Eka Yani, Sitti; Haryanto, Freddy; Rhani, M. Fahdillah

    2015-09-30

    Monte Carlo modelling of a linear accelerator is the first and most important step in Monte Carlo dose calculations in radiotherapy. Monte Carlo is considered today to be the most accurate and detailed calculation method in different fields of medical physics. In this research, we developed a photon beam model for Varian Clinac iX 6 MV equipped with MilleniumMLC120 for dose calculation purposes using BEAMnrc/DOSXYZnrc Monte Carlo system based on the underlying EGSnrc particle transport code. Monte Carlo simulation for this commissioning head LINAC divided in two stages are design head Linac model using BEAMnrc, characterize this model using BEAMDP and analyze the difference between simulation and measurement data using DOSXYZnrc. In the first step, to reduce simulation time, a virtual treatment head LINAC was built in two parts (patient-dependent component and patient-independent component). The incident electron energy varied 6.1 MeV, 6.2 MeV and 6.3 MeV, 6.4 MeV, and 6.6 MeV and the FWHM (full width at half maximum) of source is 1 mm. Phase-space file from the virtual model characterized using BEAMDP. The results of MC calculations using DOSXYZnrc in water phantom are percent depth doses (PDDs) and beam profiles at depths 10 cm were compared with measurements. This process has been completed if the dose difference of measured and calculated relative depth-dose data along the central-axis and dose profile at depths 10 cm is ≤ 5%. The effect of beam width on percentage depth doses and beam profiles was studied. Results of the virtual model were in close agreement with measurements in incident energy electron 6.4 MeV. Our results showed that photon beam width could be tuned using large field beam profile at the depth of maximum dose. The Monte Carlo model developed in this study accurately represents the Varian Clinac iX with millennium MLC 120 leaf and can be used for reliable patient dose calculations. In this commissioning process, the good

  17. Commissioning of a Varian Clinac iX 6 MV photon beam using Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Dirgayussa, I. Gde Eka; Yani, Sitti; Rhani, M. Fahdillah; Haryanto, Freddy

    2015-09-01

    Monte Carlo modelling of a linear accelerator is the first and most important step in Monte Carlo dose calculations in radiotherapy. Monte Carlo is considered today to be the most accurate and detailed calculation method in different fields of medical physics. In this research, we developed a photon beam model for Varian Clinac iX 6 MV equipped with MilleniumMLC120 for dose calculation purposes using BEAMnrc/DOSXYZnrc Monte Carlo system based on the underlying EGSnrc particle transport code. Monte Carlo simulation for this commissioning head LINAC divided in two stages are design head Linac model using BEAMnrc, characterize this model using BEAMDP and analyze the difference between simulation and measurement data using DOSXYZnrc. In the first step, to reduce simulation time, a virtual treatment head LINAC was built in two parts (patient-dependent component and patient-independent component). The incident electron energy varied 6.1 MeV, 6.2 MeV and 6.3 MeV, 6.4 MeV, and 6.6 MeV and the FWHM (full width at half maximum) of source is 1 mm. Phase-space file from the virtual model characterized using BEAMDP. The results of MC calculations using DOSXYZnrc in water phantom are percent depth doses (PDDs) and beam profiles at depths 10 cm were compared with measurements. This process has been completed if the dose difference of measured and calculated relative depth-dose data along the central-axis and dose profile at depths 10 cm is ≤ 5%. The effect of beam width on percentage depth doses and beam profiles was studied. Results of the virtual model were in close agreement with measurements in incident energy electron 6.4 MeV. Our results showed that photon beam width could be tuned using large field beam profile at the depth of maximum dose. The Monte Carlo model developed in this study accurately represents the Varian Clinac iX with millennium MLC 120 leaf and can be used for reliable patient dose calculations. In this commissioning process, the good criteria of dose

  18. Depth dependence determination of the wedge transmission factor for 4--10 MV photon beams

    SciTech Connect

    McCullough, E.C.; Gortney, J.; Blackwell, C.R.

    1988-07-01

    The depth dependence (up to 25 cm) of the in-phantom wedge transmission factor (WTF) has been determined for three medical linear accelerator x-ray beams with energies of 4, 6, and 10 MV containing 15/sup 0/--60/sup 0/ (nominal) brass wedges. All measurements were made with a cylindrical ionization chamber in water, for a field size of 10 x 10 cm/sup 2/ with a source--skin distance of 80 or 100 cm. We conclude that, for the accelerators studied, the WTF factor at depth is less than 2% different from that determined at d/sub max/ (for the nominal wedge angles and photon energies studied) unless the depth of interest is greater than 10 cm. Up to the maximum depth studied (25 cm) the relative wedge factor: that is, wedge factor at depth compared to that determined at d/sub max/ : was about equal to or less than 1.02 for the 15/sup 0/ and 30/sup 0/ wedges and any of the photon beam energies studied. For the seldom utilized combination of a nominal wedge angle in excess of 45/sup 0/ with a depth greater than 10 cm, the WTF at depth can differ from the WTF determined at d/sub max/, by up to 5%. Since the wedge transmission factor is reflective of relative percent dose data, our results also indicate that it is in error to use open field percent depth doses for certain combinations of wedge angle, photon energy, and depth.

  19. SU-E-T-597: Parameterization of the Photon Beam Dosimetry for a Commercial Linear Accelerator

    SciTech Connect

    Lebron, S; Lu, B; Yan, G; Kahler, D; Li, J; Barraclough, B; Liu, C

    2015-06-15

    Purpose: In radiation therapy, accurate data acquisition of photon beam dosimetric quantities is important for (1) beam modeling data input into a treatment planning system (TPS), (2) comparing measured and TPS modelled data, (3) a linear accelerator’s (linac) beam characteristics quality assurance process, and (4) establishing a standard data set for data comparison, etcetera. Parameterization of the photon beam dosimetry creates a portable data set that is easy to implement for different applications such as those previously mentioned. The aim of this study is to develop methods to parameterize photon percentage depth doses(PDD), profiles, and total scatter output factors(Scp). Methods: Scp, PDDs and profiles for different field sizes (from 2×2 to 40×40cm{sup 2}), depths and energies were measured in a linac using a three-dimensional water tank. All data were smoothed and profile data were also centered, symmetrized and geometrically scaled. The Scp and PDD data were analyzed using exponential functions. For modelling of open and wedge field profiles, each side was divided into three regions described by exponential, sigmoid and Gaussian equations. The model’s equations were chosen based on the physical principles described by these dosimetric quantities. The equations’ parameters were determined using a least square optimization method with the minimal amount of measured data necessary. The model’s accuracy was then evaluated via the calculation of absolute differences and distance–to–agreement analysis in low gradient and high gradient regions, respectively. Results: All differences in the PDDs’ buildup and the profiles’ penumbra regions were less than 2 mm and 0.5 mm, respectively. Differences in the low gradient regions were 0.20 ± 0.20% and 0.50 ± 0.35% for PDDs and profiles, respectively. For Scp data, all differences were less than 0.5%. Conclusion: This novel analytical model with minimum measurement requirements proved to accurately

  20. Effect of dosimeter type for commissioning small photon beams on calculated dose distribution in stereotactic radiosurgery

    SciTech Connect

    García-Garduño, O. A. E-mail: amanda.garcia.g@gmail.com; Rodríguez-Ponce, M.; Gamboa-deBuen, I.; Rodríguez-Villafuerte, M.; Galván de la Cruz, O. O.; and others

    2014-09-15

    Purpose: To assess the impact of the detector used to commission small photon beams on the calculated dose distribution in stereotactic radiosurgery (SRS). Methods: In this study, six types of detectors were used to characterize small photon beams: three diodes [a silicon stereotactic field diode SFD, a silicon diode SRS, and a silicon diode E], an ionization chamber CC01, and two types of radiochromic film models EBT and EBT2. These detectors were used to characterize circular collimated beams that were generated by a Novalis linear accelerator. This study was conducted in two parts. First, the following dosimetric data, which are of particular interest in SRS, were compared for the different detectors: the total scatter factor (TSF), the tissue phantom ratios (TPRs), and the off-axis ratios (OARs). Second, the commissioned data sets were incorporated into the treatment planning system (TPS) to compare the calculated dose distributions and the dose volume histograms (DVHs) that were obtained using the different detectors. Results: The TSFs data measured by all of the detectors were in good agreement with each other within the respective statistical uncertainties: two exceptions, where the data were systematically below those obtained for the other detectors, were the CC01 results for all of the circular collimators and the EBT2 film results for circular collimators with diameters below 10.0 mm. The OAR results obtained for all of the detectors were in excellent agreement for all of the circular collimators. This observation was supported by the gamma-index test. The largest difference in the TPR data was found for the 4.0 mm circular collimator, followed by the 10.0 and 20.0 mm circular collimators. The results for the calculated dose distributions showed that all of the detectors passed the gamma-index test at 100% for the 3 mm/3% criteria. The aforementioned observation was true regardless of the size of the calculation grid for all of the circular collimators

  1. Photon generator

    DOEpatents

    Srinivasan-Rao, Triveni

    2002-01-01

    A photon generator includes an electron gun for emitting an electron beam, a laser for emitting a laser beam, and an interaction ring wherein the laser beam repetitively collides with the electron beam for emitting a high energy photon beam therefrom in the exemplary form of x-rays. The interaction ring is a closed loop, sized and configured for circulating the electron beam with a period substantially equal to the period of the laser beam pulses for effecting repetitive collisions.

  2. Out-of-plane nano-electro-mechanical tuning of the Fano resonance in photonic crystal split-beam nanocavity

    NASA Astrophysics Data System (ADS)

    Lin, Tong; Zhang, Xingwang; Zou, Yongchao; Chau, Fook Siong; Deng, Jie; Zhou, Guangya

    2015-10-01

    We propose and experimentally demonstrate the use of Fano resonance as a means to improve the Quality factor of photonic crystal split-beam nanocavities. The Fano resonance is triggered by the interference between the second-order quasi-transverse electric resonant mode and the leaky high-order quasi-transverse electric propagation mode of the optimized photonic crystal split-beam nanocavity. Compared with a similar photonic crystal split-beam nanocavity without asymmetric Fano lineshape, the Q-factor is increased up to 3-fold: from 1.99 ×104 to 5.95 ×104 . Additionally, out-of-plane tuning of the Fano resonance is investigated by means of a Nano-Electro-Mechanical Systems based actuator. The maximum centre wavelength shift of the Fano resonance reached 116.69 pm, which is more than 4.5 times the original quasi-Full Width at Half Magnitude.

  3. Study of the penumbra for high-energy photon beams with Gafchromic™ EBT2 films

    NASA Astrophysics Data System (ADS)

    Oh, Se An; Kang, Min Kyu; Yea, Ji Woon; Kim, Sung Kyu; Oh, Young Kee

    2012-06-01

    The penumbra has a major impact on obtaining uniformity of isodose distributions in radiation therapy. The penumbra phenomena of intensity-modulated radiation therapy (IMRT) techniques using multi-leaf collimators (MLCs) has an impact on the dose distributions in the border of the target volumes and the MLC. The aim of this study was to determine the impact of high photon energy (6 MV, 10 MV) on the penumbra for various depths and field sizes by using the Pencil Beam Convolution algorithms (eclipse 8.6) and self-developing Gafchromic™ EBT2 film. For dose calculations and EBT2 measurements, we used an acryl phantom with dimensions 20 × 20 × 20 cm3. The 200 cGy dose was delivered to the central depth (10 cm) of the acryl phantom. The result of this study was that increased energy, field size and depth are rise to an increased penumbra (20% ˜ 80%) width. For a 6 MV photon energy, the penumbra widths (20%-80%) at 1.5 cm, 5 cm, and 10 cm depths were 4.2 mm, 4.4 mm, and 5.7 mm for the eclipse calculations and 2.9 mm, 4.1 mm, and 4.2 mm for the EBT2 film measurements for 10 × 10 cm2 field sizes, respectively. For a 10 MV photon energy, the penumbra widths were 4.5 mm, 4.7 mm, and 6.2 mm for eclipse calculations and 4.1 mm, 4.6 mm, and 4.9 mm for EBT2 film measurements, respectively. As the field size was changed to 3 cm, 5 cm, 7 cm, 10 cm, and 15 cm, the penumbra widths changed to 5.1 mm, 5.3 mm, 5.6 mm, 5.9 mm, and 6.1 mm for eclipse calculations and 2.9 mm, 3.3 mm, 3.6 mm, 4.2 mm, and 5.1 mm for EBT2 measurements, respectively, for 10 cm depths for 6 MV photon energies. In this study, compared to the 10 MV photon energy, the 6 MV photon energy was preferred in treatments such as the 3D conformal radiation therapy and the IMRT for critical organs near the target volume.

  4. Direct calibration in megavoltage photon beams using Monte Carlo conversion factor: validation and clinical implications

    NASA Astrophysics Data System (ADS)

    Wright, Tracy; Lye, Jessica E.; Ramanathan, Ganesan; Harty, Peter D.; Oliver, Chris; Webb, David V.; Butler, Duncan J.

    2015-01-01

    The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has established a method for ionisation chamber calibrations using megavoltage photon reference beams. The new method will reduce the calibration uncertainty compared to a 60Co calibration combined with the TRS-398 energy correction factor. The calibration method employs a graphite calorimeter and a Monte Carlo (MC) conversion factor to convert the absolute dose to graphite to absorbed dose to water. EGSnrc is used to model the linac head and doses in the calorimeter and water phantom. The linac model is validated by comparing measured and modelled PDDs and profiles. The relative standard uncertainties in the calibration factors at the ARPANSA beam qualities were found to be 0.47% at 6 MV, 0.51% at 10 MV and 0.46% for the 18 MV beam. A comparison with the Bureau International des Poids et Mesures (BIPM) as part of the key comparison BIPM.RI(I)-K6 gave results of 0.9965(55), 0.9924(60) and 0.9932(59) for the 6, 10 and 18 MV beams, respectively, with all beams within 1σ of the participant average. The measured kQ values for an NE2571 Farmer chamber were found to be lower than those in TRS-398 but are consistent with published measured and modelled values. Users can expect a shift in the calibration factor at user energies of an NE2571 chamber between 0.4-1.1% across the range of calibration energies compared to the current calibration method.

  5. Direct calibration in megavoltage photon beams using Monte Carlo conversion factor: validation and clinical implications.

    PubMed

    Wright, Tracy; Lye, Jessica E; Ramanathan, Ganesan; Harty, Peter D; Oliver, Chris; Webb, David V; Butler, Duncan J

    2015-01-21

    The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has established a method for ionisation chamber calibrations using megavoltage photon reference beams. The new method will reduce the calibration uncertainty compared to a (60)Co calibration combined with the TRS-398 energy correction factor. The calibration method employs a graphite calorimeter and a Monte Carlo (MC) conversion factor to convert the absolute dose to graphite to absorbed dose to water. EGSnrc is used to model the linac head and doses in the calorimeter and water phantom. The linac model is validated by comparing measured and modelled PDDs and profiles. The relative standard uncertainties in the calibration factors at the ARPANSA beam qualities were found to be 0.47% at 6 MV, 0.51% at 10 MV and 0.46% for the 18 MV beam. A comparison with the Bureau International des Poids et Mesures (BIPM) as part of the key comparison BIPM.RI(I)-K6 gave results of 0.9965(55), 0.9924(60) and 0.9932(59) for the 6, 10 and 18 MV beams, respectively, with all beams within 1σ of the participant average. The measured kQ values for an NE2571 Farmer chamber were found to be lower than those in TRS-398 but are consistent with published measured and modelled values. Users can expect a shift in the calibration factor at user energies of an NE2571 chamber between 0.4-1.1% across the range of calibration energies compared to the current calibration method. PMID:25565406

  6. Features of possible polarized photon beams at high energy and corresponding physics programme or the proton structure function using real photons

    SciTech Connect

    Tannenbaum, M.J.

    1980-01-01

    In the range of electron energies available at Fermilab, 100 GeV less than or equal to E less than or equal to 500 GeV, coherent Bremsstrahlung in crystals, particularly diamond, gives a huge enhancement to the equivalent photon spectrum at large values of x where x = k/E. The photons in this enhancement are polarized. Requirements on electron beam energy spread, angular divergence and spot size imposed by the use of a diamond as a radiator are discussed. The physics program emphasizes hard processes and tests of QCD using polarization.

  7. Lossless backward second-harmonic generation of extremely narrow subdiffractive beams in two-dimensional photonic crystals

    SciTech Connect

    Nistor, C.; Cojocaru, C.; Trull, J.; Karle, T. J.; Raj, R.; Raineri, F.; Staliunas, K.

    2010-09-15

    We report efficient second harmonic generation using extremely narrow beams (with diameter of the order of the wavelength) that propagate in the self-collimation (or nondiffractive) regime in a two-dimensional photonic crystal. We design and numerically test an AlGaAs photonic crystal membrane, where both fundamental and generated second harmonic beams propagate without diffraction and without out-of-plane losses. The characteristics of the generated second harmonic that is mainly propagating in the backward direction and the conversion efficiency of the proposed scheme are obtained by nonlinear finite-difference time-domain numerical simulations.

  8. SU-E-T-637: Age and Batch Dependence of Gafchromic EBT Films in Photon and Proton Beam Dosimetry

    SciTech Connect

    Das, I; Akino, Y

    2014-06-15

    Purpose: Gafchrmoic films have undergone significant changes in characteristic over time reflected by HS, EBT, EBT2, EBT3 name. Interand intra- EBT film variability have been studied and found to be significant. However, age and lot/batch type have not been studied in various radiation beams that are investigated in this study. Methods: Thirteen sets of films; 2 EBT, 6 EBT2 and 5 EBT3 films with different lot number and expiration date were acquired. Films were cut longitudinally in 3 cm width and sandwiched between two solid water slabs that were placed in a water phantom to eliminate air gap. Each set of films were irradiated longitudinally at dmax with 6 and 15 MV photon beams as well as in reference condition (16 cm range, 10 cm SOBP) in our uniform scanning proton beam. Films were scanned using an Epson flatbed scanner (ES-10000G) after 48 hours to achieve full polymerization. The profiles were compared with the depth-dose measured with ionization chamber and net optical density (net OD) were calculated. Results: The net OD versus dose for EBT, EBT2 and EBT3 films of different age showed similar trend but with different slope. Even after calibration, differences are clearly visible in net OD in proton and photon beams. A net OD difference of nearly 0.5 is observed in photon but this was limited to 0.2–0.3 in proton beam. This relates to 20% and 15% dosimetric difference in photon and proton beam respectively over age and type of film. Conclusion: Net OD related to dose is dependent on the age and lot of the film in both photon and proton beams. It is concluded that before any set of film is used, a calibration film should be used for a meaningful dosimetry. The expired films showed larger OD variation compared to unexpired films.

  9. Dose response of BaFBrI:Eu{sup 2+} storage phosphor plates exposed to megavoltage photon beams

    SciTech Connect

    Li, H. Harold; Gonzalez, Albin L.; Ji, Huaying; Duggan, Dennis M.

    2007-01-15

    The BaFBrI:Eu{sup 2+} storage phosphor plate (SPP) is a reusable radiation image detector, widely used in diagnostic computed radiography, x-ray crystallography and radioactive tracer studies. When exposed to ionizing radiation, the SPP stores a latent image until it is scanned with a red reading laser which causes blue photostimulated luminescent (PSL) photons to be emitted. The mechanism of formation of the latent image is still poorly understood, especially for megavoltage photon beams. In order to gain insight into this mechanism and aid applications to high-energy beam dosimetry, the authors have directly determined the SPP generation efficiency, W, the energy required to produce one quantum of emitted PSL when it is irradiated by {sup 60}Co and 6 MV photon beams. This was done in four steps: 1. The SPP, in a water-equivalent plastic (WEP) phantom, was exposed to a {sup 60}Co or 6 MV beam, which had been calibrated to give a known absorbed dose to water in a water phantom at the position of the sensitive layer of the SPP. 2. Monte Carlo simulations were used to calculate the ratio of the dose to the sensitive layer in the WEP phantom to the dose to water at the same position in a water phantom. 3. A bleaching experiment was used to determine the number of photons emitted by a plate given a known dose. 4. The generation efficiency was calculated from the number of photons and the dose. This method is much more direct than previous calculations for kilovoltage x-ray beams based on quantum noise analysis. W was found, within experimental uncertainty, to be 190 eV for {sup 60}Co and 160 eV for 6 MV, independent of dose. The values for kilovoltage x-ray beams determined previously agree, within their large uncertainty, with these values for megavoltage beams.

  10. Analyzing the characteristics of 6 MV photon beam at low monitor unit settings

    PubMed Central

    Nithya, L.; Raj, N. Arunai Nambi; Rathinamuthu, Sasikumar

    2016-01-01

    Analyzing the characteristics of a low monitor unit (MU) setting is essential, particularly for intensity-modulated techniques. Intensity modulation can be achieved through intensity-modulated radiotherapy (IMRT) or volumetric-modulated arc therapy (VMAT). There is possibility for low MUs in the segments of IMRT and VMAT plans. The minimum MU/segment must be set by the physicist in the treatment planning system at the time of commissioning. In this study, the characteristics such as dose linearity, stability, flatness, and symmetry of 6 MV photon beam of a Synergy linear accelerator at low MU settings were investigated for different dose rates. The measurements were performed for Synergy linear accelerator using a slab phantom with a FC65-G chamber and Profiler 2. The MU linearity was studied for 1–100 MU using a field size of 10 cm ×10 cm. The linearity error for 1 MU was 4.2%. Flatness of the beam was deteriorated in 1 MU condition. The beam stability and symmetry was well within the specification. Using this study, we conclude that the treatment delivered with <3 MU may result in uncertainty in dose delivery. To ensure the correct dose delivery with less uncertainty, it is recommended to use ≥3 MU as the minimum MU per segment in IMRT and VMAT plans. PMID:27051168

  11. Measuring linac photon beam energy through EPID image analysis of physically wedged fields

    SciTech Connect

    Dawoud, S. M. Weston, S. J.; Bond, I.; Ward, G. C.; Rixham, P. A.; Mason, J.; Huckle, A.; Sykes, J. R.

    2014-02-15

    Purpose: Electronic portal imaging devices (EPIDs) have proven to be useful tools for measuring several parameters of interest in linac quality assurance (QA). However, a method for measuring linac photon beam energy using EPIDs has not previously been reported. In this report, such a method is devised and tested, based on fitting a second order polynomial to the profiles of physically wedged beams, where the metric of interest is the second order coefficientα. The relationship between α and the beam quality index [percentage depth dose at 10 cm depth (PDD{sub 10})] is examined to produce a suitable calibration curve between these two parameters. Methods: Measurements were taken in a water-tank for beams with a range of energies representative of the local QA tolerances about the nominal value 6 MV. In each case, the beam quality was found in terms of PDD{sub 10} for 100 × 100 mm{sup 2} square fields. EPID images of 200 × 200 mm{sup 2} wedged fields were then taken for each beam and the wedge profile was fitted in MATLAB 2010b (The MathWorks, Inc., Natick, MA). α was then plotted against PDD{sub 10} and fitted with a linear relation to produce the calibration curve. The uncertainty in α was evaluated by taking five repeat EPID images of the wedged field for a beam of 6 MV nominal energy. The consistency of measuring α was found by taking repeat measurements on a single linac over a three month period. The method was also tested at 10 MV by repeating the water-tank crosscalibration for a range of energies centered approximately about a 10 MV nominal value. Finally, the calibration curve from the test linac and that from a separate clinical machine were compared to test consistency of the method across machines in a matched fleet. Results: The relationship betweenα and PDD{sub 10} was found to be strongly linear (R{sup 2} = 0.979) while the uncertainty in α was found to be negligible compared to that associated with measuring PDD{sub 10} in the water-tank (

  12. Development of an efficient scanning and purging magnet system for IMRT with narrow high energy photon beams

    NASA Astrophysics Data System (ADS)

    Andreassen, Björn; Svensson, Roger; Holmberg, Rickard; Danared, Håkan; Brahme, Anders

    2009-12-01

    Due to the clinical advantages of Intensity Modulated Radiation Therapy (IMRT) high flexibility and accuracy in intensity modulated dose delivery is desirable to really maximize treatment outcome. Although it is possible to deliver IMRT by using broad beams in combination with dynamic multileaf collimation the process is rather time consuming and inefficient. By using narrow scanned high energy photon beams the treatment outcome can be improved, the treatment time reduced and accurate 3D in vivo dose delivery monitoring is possible by PET-CT based dose delivery imaging of photo nuclear reactions in human tissues. Narrow photon beams can be produced by directing a low emittance high energy electron beam on a thin target, and then cleaning the therapeutic photon beam from transmitted high energy electrons, and photon generated charged leptons, with a dedicated purging magnet placed directly downstream of the target. To have an effective scanning and purging magnet system the purging magnet should be placed immediately after the bremsstrahlung target to deflect the transmitted electrons to an efficient electron stopper. In the static electron stopper the electrons should be safely collected independent of the desired direction of the therapeutic scanned photon beam. The SID (Source to Isocenter Distance) should preferably be short while retaining the ability to scan over a large area on the patient and consequently there are severe requirements both on the strength and the geometry of the scanning and purging magnets. In the present study an efficient magnet configuration with a purging and scanning magnet assembly is developed for electron energies in the 50-75 MeV range and a SID of 75 cm. For a bremsstrahlung target of 3 mm Be these electron energies produce a photon beam of 25-17 mm FWHM (Full Width Half Maximum) at a SID of 75 cm. The magnet system was examined both in terms of the efficiency in scanning the narrow bremsstrahlung beam and the deflection of

  13. Respiratory gating for proton beam scanning versus photon 3D-CRT for breast cancer radiotherapy.

    PubMed

    Flejmer, Anna M; Edvardsson, Anneli; Dohlmar, Frida; Josefsson, Dan; Nilsson, Mats; Witt Nyström, Petra; Dasu, Alexandru

    2016-05-01

    Background Respiratory gating and proton therapy have both been proposed to reduce the cardiopulmonary burden in breast cancer radiotherapy. This study aims to investigate the additional benefit of proton radiotherapy for breast cancer with and without respiratory gating. Material and methods Twenty left-sided patients were planned on computed tomography (CT)-datasets acquired during enhanced inspiration gating (EIG) and free-breathing (FB), using photon three-dimensional conformal radiation therapy (3D-CRT) and scanned proton beams. Ten patients received treatment to the whole breast only (WBO) and 10 were treated to the breast and the regional lymph nodes (BRN). Dosimetric parameters characterizing the coverage of target volumes and the cardiopulmonary burden were compared using a paired, two-tailed Student's t-test. Results Protons ensured comparable or better target coverage than photons in all patients during both EIG and FB. The heterogeneity index decreased from 12% with photons to about 5% with protons. The mean dose to the ipsilateral lung was reduced in BRN patients from 12 Gy to 7 Gy  (RBE) in EIG and from 14 Gy to 6-7 Gy (RBE) in FB, while for WBO patients all values were about 5-6 Gy (RBE). The mean dose to heart decreased by a factor of four in WBO patients [from 1.1 Gy to 0.3 Gy (RBE) in EIG and from 2.1 Gy to 0.5 Gy (RBE) in FB] and 10 in BRN patients [from 2.1 Gy to 0.2 Gy (RBE) in EIG and from 3.4 Gy to 0.3 Gy (RBE) in FB]. Similarly, the mean and the near maximum dose to the left anterior descending artery (LAD) were significantly lower (p < 0.05) with protons in comparison with photons. Conclusion Proton spot scanning has a high potential to reduce the irradiation of organs at risk and other normal tissues for most patients, beyond what could be achieved with EIG and photon therapy. The largest dose sparing has been seen for BRN patients, both in terms of cardiopulmonary burden and integral dose. PMID:27027913

  14. Commissioning and quality assurance of the Pinnacle(3) radiotherapy treatment planning system for external beam photons.

    PubMed

    Bedford, J L; Childs, P J; Nordmark Hansen, V; Mosleh-Shirazi, M A; Verhaegen, F; Warrington, A P

    2003-03-01

    The commissioning of a Pinnacle(3) treatment planning system is described. Four Elekta linear accelerators were commissioned for external beam photons. Measured data were used to derive parameter values for the Pinnacle(3) beam model by (1). fitting a Monte Carlo model of the accelerator head to measured data and then extracting the parameters for the Pinnacle(3) beam model, and by (2). using the auto-modelling facility within Pinnacle(3). Both of these methods yielded dose distributions in accord with published recommendations. A separate small-field beam model, customized for an in-house compact blocking system, was also created, which satisfied appropriate acceptance criteria for stereotactically guided conformal brain treatments. Inhomogeneous, oblique, asymmetrical and irregular fields were also assessed, with calculated and measured doses agreeing to within +/-3%. Dose-volume histogram calculation was found to be accurate to within +/-5% dose or volume for a grid size of 4 mm x 4 mm x 4 mm, with better accuracy being achieved for finer grids. Isocentric doses were compared between Pinnacle(3)'s collapsed cone convolution algorithm and the Bentley-Milan algorithm within the Target-2 treatment planning system. Dose differences were generally less than 3% in the dose prescribed, with larger values for breast plans, where the Pinnacle(3) algorithm calculated scatter more accurately. Pelvic and thoracic plans were also verified using an anthropomorphic phantom, with local dose differences between calculated and delivered dose of up to 8%, but mainly less than 3%, and with no systematic difference. Ionization chamber verifications using START and RT-01 trial procedures demonstrated differences between calculated and measured doses of less than 2%. Following satisfactory performance in the commissioning process, Pinnacle(3) has now been introduced into routine clinical use. PMID:12684232

  15. Liquid gallium cooling of silicon crystals in high intensity photon beams

    SciTech Connect

    Smither, R. K.; Forster, G. A.; Bilderback, D. H.; Bedzyk, M.; Finkelstein, K.; Henderson, C.; White, J.; Berman, L. E.; Stefan, P.; Oversluizen, T.; and others

    1989-07-01

    The high-brilliance, insertion-device-based photon beams of the next generation of synchrotron sources (Argonne's APS and Grenoble's ESRF) will deliver large thermal loads (1--10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium-cooled silicon diffraction crystals with water-cooled crystals. A six-pole wiggler beam was used to perform these tests on three different Si crystals, two with new cooling geometries and the one presently in use. A special high-pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. In all experiments, the specially cooled crystal was used as the first crystal in a two crystal monochromator. An infrared camera was used to monitor the thermal profiles and correlated them with rocking curve measurements. A second set of cooling experiments were conducted in June of 1988 that used the intense, highly collimated beam from the newly installed ANL/CHESS undulator.

  16. Measurement of skin and target dose in post-mastectomy radiotherapy using 4 and 6 MV photon beams

    PubMed Central

    2013-01-01

    Background For patients with high risk breast cancer and mastectomy, radiotherapy is the treatment of choice to improve survival and local control. Target dose is mainly limited due to skin reactions. The feasibility of using 4 MV beams for chest wall treatment was studied and compared to standard 6 MV bolus radiotherapy. Methods Post-mastectomy IMRT was planned on an Alderson-phantom using 4 and 6 MV photon beams without/with a 0.5 cm thick bolus. Dose was measured using TLDs placed at 8 locations in 1 and 3 mm depth to represent skin and superficial target dose, respectively. Results 4 MV and 6 MV beams with bolus perform equally regarding target coverage. The minimum and mean superficial target dose for the 6 MV and 4 MV were 93.0% and 94.7%, and 93.1% and 94.4%, respectively. Regarding skin dose the 4 MV photon beam was advantageous. The minimum and mean skin dose for the 6 MV and 4 MV was 76.7% and 81.6%, and 69.4% and 72.9%, respectively. The TPS was able to predict dose in the build-up region with a precision of around 5%. Conclusions The use of 4 MV photon beams are a good alternative for treating the thoracic wall without the need to place a bolus on the patient. The main limitation of 4 MV beams is the limited dose rate. PMID:24238366

  17. Investigation of the thermo-optic effect in doubly coupled photonic crystal split-beam nanocavities

    NASA Astrophysics Data System (ADS)

    Lin, Tong; Tao, Jifang; Chau, Fook Siong; Deng, Jie; Zhou, Guangya; Gu, Yuandong

    2016-07-01

    We design and experimentally demonstrate doubly coupled photonic crystal split-beam nanocavities. The thermal response of the coupled nanocavities is characterized by controlling the device temperature: the resonant wavelengths of the odd mode (1557.28 nm) and even mode (1567.18 nm) are both redshifted linearly from 17.4 °C to 46.5 °C. The tuning ratio of the two modes is measured to be 97.4%, implying that they respond almost the same to temperature changes. Therefore, changes of the wavelength difference between this pair of modes can be applied to effectively decouple the thermo-optic effect from the optomechanical effect without on-chip temperature self-referencing. Additionally, the topmost quality-factor approaches 28 300 throughout the thermal tuning. The proposed structure paves the way for studying purely optomechanical actuations.

  18. Light-controlled photonics-based mm-wave beam switch.

    PubMed

    Yurchenko, Vladimir; Ciydem, Mehmet; Gradziel, Marcin; Murphy, Anthony; Altintas, Ayhan

    2016-07-25

    We present experimental investigation of light-controlled photonics-enhanced quasi-optical mm-wave beam switch operating at a resonant frequency in the mm-wave band of 75 to 110 GHz. The switch is implemented as a Bragg structure with a resonant layer of high-resistivity silicon that creates a narrow transmission peak within the mm-wave propagation gap. The peak amplitude is sensitive to the intensity of light pulses illuminating the structure. When using a silicon wafer of 30 KOhm · cm resistivity and light pulses created by a 400W LED-array light source, we achieved mm-wave transmission peak modulation exceeding 15 dB. PMID:27464100

  19. Observation of wakefields in a beam-driven photonic band gap accelerating structure.

    SciTech Connect

    Conde, M.; Yusof, Z.; Power, J. G.; Jing, C.; Gao, F.; Antipov, S.; Xu, P.; Zheng, S.; Chen, H.; Tang, C.; Gai, W.; High Energy Physics; Euclid Techlabs LLC; Tsinghua Univ.

    2009-12-01

    Wakefield excitation has been experimentally studied in a three-cell X-band standing wave photonic band gap (PBG) accelerating structure. Major monopole (TM{sub 01}- and TM{sub 02}-like) and dipole (TM{sub 11}- and TM{sub 12}-like) modes were identified and characterized by precisely controlling the position of beam injection. The quality factor Q of the dipole modes was measured to be {approx}10 times smaller than that of the accelerating mode. A charge sweep, up to 80 nC, has been performed, equivalent to {approx} 30 MV/m accelerating field on axis. A variable delay low charge witness bunch following a high charge drive bunch was used to calibrate the gradient in the PBG structure by measuring its maximum energy gain and loss. Experimental results agree well with numerical simulations.

  20. A phantom study on the behavior of Acuros XB algorithm in flattening filter free photon beams

    PubMed Central

    Muralidhar, K. R.; Pangam, Suresh; Srinivas, P.; Athar Ali, Mirza; Priya, V. Sujana; Komanduri, Krishna

    2015-01-01

    To study the behavior of Acuros XB algorithm for flattening filter free (FFF) photon beams in comparison with the anisotropic analytical algorithm (AAA) when applied to homogeneous and heterogeneous phantoms in conventional and RapidArc techniques. Acuros XB (Eclipse version 10.0, Varian Medical Systems, CA, USA) and AAA algorithms were used to calculate dose distributions for both 6X FFF and 10X FFF energies. RapidArc plans were created on Catphan phantom 504 and conventional plans on virtual homogeneous water phantom 30 × 30 × 30 cm3, virtual heterogeneous phantom with various inserts and on solid water phantom with air cavity. Dose at various inserts with different densities were measured in both AAA and Acuros algorithms. The maximum % variation in dose was observed in (−944 HU) air insert and minimum in (85 HU) acrylic insert in both 6X FFF and 10X FFF photons. Less than 1% variation observed between −149 HU and 282 HU for both energies. At −40 HU and 765 HU Acuros behaved quite contrarily with 10X FFF. Maximum % variation in dose was observed in less HU values and minimum variation in higher HU values for both FFF energies. Global maximum dose observed at higher depths for Acuros for both energies compared with AAA. Increase in dose was observed with Acuros algorithm in almost all densities and decrease at few densities ranging from 282 to 643 HU values. Field size, depth, beam energy, and material density influenced the dose difference between two algorithms. PMID:26500400

  1. Improving the neutron-to-photon discrimination capability of detectors used for neutron dosimetry in high energy photon beam radiotherapy.

    PubMed

    Irazola, L; Terrón, J A; Bedogni, R; Pola, A; Lorenzoli, M; Sánchez-Nieto, B; Gómez, F; Sánchez-Doblado, F

    2016-09-01

    The increasing interest of the medical community to radioinduced second malignancies due to photoneutrons in patients undergoing high-energy radiotherapy, has stimulated in recent years the study of peripheral doses, including the development of some dedicated active detectors. Although these devices are designed to respond to neutrons only, their parasitic photon response is usually not identically zero and anisotropic. The impact of these facts on measurement accuracy can be important, especially in points close to the photon field-edge. A simple method to estimate the photon contribution to detector readings is to cover it with a thermal neutron absorber with reduced secondary photon emission, such as a borated rubber. This technique was applied to the TNRD (Thermal Neutron Rate Detector), recently validated for thermal neutron measurements in high-energy photon radiotherapy. The positive results, together with the accessibility of the method, encourage its application to other detectors and different clinical scenarios. PMID:27337649

  2. Comparison of RTPS and Monte Carlo dose distributions in heterogeneous phantoms for photon beams.

    PubMed

    Nakaguchi, Yuji; Araki, Fujio; Maruyama, Masato; Fukuda, Shogo

    2010-04-20

    The purpose of this study was to compare dose distributions from three different RTPS with those from Monte Carlo (MC) calculations and measurements, in heterogeneous phantoms for photon beams. This study used four algorithms for RTPS: AAA (analytical anisotropic algorithm) implemented in the Eclipse (Varian Medical Systems) treatment planning system, CC (collapsed cone) superposition from the Pinnacle (Philips), and MGS (multigrid superposition) and FFT (fast Fourier transform) convolution from XiO (CMS). The dose distributions from these algorithms were compared with those from MC and measurements in a set of heterogeneous phantoms. Eclipse/AAA underestimated the dose inside the lung region for low energies of 4 and 6 MV. This is because Eclipse/AAA do not adequately account for a scaling of the spread of the pencil (lateral electron transport) based on changes in the electron density at low photon energies. The dose distributions from Pinnacle/CC and XiO/MGS almost agree with those of MC and measurements at low photon energies, but increase errors at high energy of 15 MV, especially for a small field of 3x3 cm(2). The FFT convolution extremely overestimated the dose inside the lung slab compared to MC. The dose distributions from the superposition algorithms almost agree with those from MC as well as measured values at 4 and 6 MV. The dose errors for Eclipse/AAA are lager in lung model phantoms for 4 and 6 MV. It is necessary to use the algorithms comparable to superposition for accuracy of dose calculations in heterogeneous regions. PMID:20625219

  3. EPR dosimetry of radiotherapy photon beams in inhomogeneous media using alanine films

    NASA Astrophysics Data System (ADS)

    Helge Østerås, Bjørn; Olaug Hole, Eli; Rune Olsen, Dag; Malinen, Eirik

    2006-12-01

    In the current work, EPR (electron paramagnetic resonance) dosimetry using alanine films (134 µm thick) was utilized for dose measurements in inhomogeneous phantoms irradiated with radiotherapy photon beams. The main phantom material was PMMA, while either Styrofoam or aluminium was introduced as an inhomogeneity. The phantoms were irradiated to a maximum dose of about 30 Gy with 6 or 15 MV photons. The performance of the alanine film dosimeters was investigated and compared to results from ion chamber dosimetry, Monte Carlo simulations and radiotherapy treatment planning calculations. It was found that the alanine film dosimeters had a linear dose response above approximately 5 Gy, while a background signal obscured the response at lower dose levels. For doses between 5 and 60 Gy, the standard deviation of single alanine film dose estimates was about 2%. The alanine film dose estimates yielded results comparable to those from the Monte Carlo simulations and the ion chamber measurements, with absolute differences between estimates in the order of 1 15%. The treatment planning calculations exhibited limited applicability. The current work shows that alanine film dosimetry is a method suitable for estimating radiotherapeutical doses and for dose measurements in inhomogeneous media.

  4. Modelling lateral beam quality variations in pencil kernel based photon dose calculations

    NASA Astrophysics Data System (ADS)

    Nyholm, T.; Olofsson, J.; Ahnesjö, A.; Karlsson, M.

    2006-08-01

    Standard treatment machines for external radiotherapy are designed to yield flat dose distributions at a representative treatment depth. The common method to reach this goal is to use a flattening filter to decrease the fluence in the centre of the beam. A side effect of this filtering is that the average energy of the beam is generally lower at a distance from the central axis, a phenomenon commonly referred to as off-axis softening. The off-axis softening results in a relative change in beam quality that is almost independent of machine brand and model. Central axis dose calculations using pencil beam kernels show no drastic loss in accuracy when the off-axis beam quality variations are neglected. However, for dose calculated at off-axis positions the effect should be considered, otherwise errors of several per cent can be introduced. This work proposes a method to explicitly include the effect of off-axis softening in pencil kernel based photon dose calculations for arbitrary positions in a radiation field. Variations of pencil kernel values are modelled through a generic relation between half value layer (HVL) thickness and off-axis position for standard treatment machines. The pencil kernel integration for dose calculation is performed through sampling of energy fluence and beam quality in sectors of concentric circles around the calculation point. The method is fully based on generic data and therefore does not require any specific measurements for characterization of the off-axis softening effect, provided that the machine performance is in agreement with the assumed HVL variations. The model is verified versus profile measurements at different depths and through a model self-consistency check, using the dose calculation model to estimate HVL values at off-axis positions. A comparison between calculated and measured profiles at different depths showed a maximum relative error of 4% without explicit modelling of off-axis softening. The maximum relative error

  5. Monitor unit calculations for external photon and electron beams: Report of the AAPM Therapy Physics Committee Task Group No. 71

    SciTech Connect

    Gibbons, John P.; Antolak, John A.; Followill, David S.; Huq, M. Saiful; Klein, Eric E.; Lam, Kwok L.; Palta, Jatinder R.; Roback, Donald M.; Reid, Mark; Khan, Faiz M.

    2014-03-15

    A protocol is presented for the calculation of monitor units (MU) for photon and electron beams, delivered with and without beam modifiers, for constant source-surface distance (SSD) and source-axis distance (SAD) setups. This protocol was written by Task Group 71 of the Therapy Physics Committee of the American Association of Physicists in Medicine (AAPM) and has been formally approved by the AAPM for clinical use. The protocol defines the nomenclature for the dosimetric quantities used in these calculations, along with instructions for their determination and measurement. Calculations are made using the dose per MU under normalization conditions, D{sub 0}{sup ′}, that is determined for each user's photon and electron beams. For electron beams, the depth of normalization is taken to be the depth of maximum dose along the central axis for the same field incident on a water phantom at the same SSD, where D{sub 0}{sup ′} = 1 cGy/MU. For photon beams, this task group recommends that a normalization depth of 10 cm be selected, where an energy-dependent D{sub 0}{sup ′} ≤ 1 cGy/MU is required. This recommendation differs from the more common approach of a normalization depth of d{sub m}, with D{sub 0}{sup ′} = 1 cGy/MU, although both systems are acceptable within the current protocol. For photon beams, the formalism includes the use of blocked fields, physical or dynamic wedges, and (static) multileaf collimation. No formalism is provided for intensity modulated radiation therapy calculations, although some general considerations and a review of current calculation techniques are included. For electron beams, the formalism provides for calculations at the standard and extended SSDs using either an effective SSD or an air-gap correction factor. Example tables and problems are included to illustrate the basic concepts within the presented formalism.

  6. Repeat-until-success distributed quantum computation by using single-photon interference at a beam splitter

    NASA Astrophysics Data System (ADS)

    Feng, Xun-Li; Qian, Jun; Kwek, L. C.; Oh, C. H.

    2008-07-01

    A repeat-until-success (RUS) measurement-based scheme for the implementation of the distributed quantum computation by using single-photon interference at a 50:50 beam splitter is proposed. It is shown that the 50:50 beam splitter can naturally project a suitably encoded matter-photon state to either a desired entangling gate-operated state of the matter qubits or to their initial state when the photon is detected. The recurrence of the initial state permits us to implement the desired entangling gate in a RUS way. To implement a distributed quantum computation we suggest an encoding method by means of the effect of dipole-induced transparency proposed recently [E. Waks and J. Vuckovic, Phys. Rev. Lett. 96, 153601 (2006)]. The effects of the unfavorable factors on our scheme are also discussed.

  7. Experimental determination of beam quality factors, kQ, for two types of Farmer chamber in a 10 MV photon and a 175 MeV proton beam

    NASA Astrophysics Data System (ADS)

    Medin, Joakim; Ross, Carl K.; Klassen, Norman V.; Palmans, Hugo; Grusell, Erik; Grindborg, Jan-Erik

    2006-03-01

    Absorbed doses determined with a sealed water calorimeter operated at 4 °C are compared with the results obtained using ionization chambers and the IAEA TRS-398 code of practice in a 10 MV photon beam (TPR20,10 = 0.734) and a 175 MeV proton beam (at a depth corresponding to the residual range, Rres = 14.7 cm). Three NE 2571 and two FC65-G ionization chambers were calibrated in terms of absorbed-dose-to-water in 60Co at the Swedish secondary standard dosimetry laboratory, directly traceable to the BIPM. In the photon beam quality, calorimetry was found to agree with ionometry within 0.3%, confirming the kQ values tabulated in TRS-398. In contrast, a 1.8% deviation was found in the proton beam at 6 g cm-2 depth, suggesting that the TRS-398 tabulated kQ values for these two ionization chamber types are too high. Assuming no perturbation effect in the proton beam for the ionization chambers, a value for (wair/e)Q of 33.6 J C-1 ± 1.7% (k = 1) can be derived from these measurements. An analytical evaluation of the effect from non-elastic nuclear interactions in the ionization chamber wall indicates a perturbation effect of 0.6%. Including this estimated result in the proton beam would increase the determined (wair/e)Q value by the same amount.

  8. Experimental determination of beam quality factors, kQ, for two types of Farmer chamber in a 10 MV photon and a 175 MeV proton beam.

    PubMed

    Medin, Joakim; Ross, Carl K; Klassen, Norman V; Palmans, Hugo; Grusell, Erik; Grindborg, Jan-Erik

    2006-03-21

    Absorbed doses determined with a sealed water calorimeter operated at 4 degrees C are compared with the results obtained using ionization chambers and the IAEA TRS-398 code of practice in a 10 MV photon beam (TPR(20,10) = 0.734) and a 175 MeV proton beam (at a depth corresponding to the residual range, R(res) = 14.7 cm). Three NE 2571 and two FC65-G ionization chambers were calibrated in terms of absorbed-dose-to-water in (60)Co at the Swedish secondary standard dosimetry laboratory, directly traceable to the BIPM. In the photon beam quality, calorimetry was found to agree with ionometry within 0.3%, confirming the k(Q) values tabulated in TRS-398. In contrast, a 1.8% deviation was found in the proton beam at 6 g cm(-2) depth, suggesting that the TRS-398 tabulated k(Q) values for these two ionization chamber types are too high. Assuming no perturbation effect in the proton beam for the ionization chambers, a value for (w(air)/e)(Q) of 33.6 J C(-1) +/- 1.7% (k = 1) can be derived from these measurements. An analytical evaluation of the effect from non-elastic nuclear interactions in the ionization chamber wall indicates a perturbation effect of 0.6%. Including this estimated result in the proton beam would increase the determined (w(air)/e)(Q) value by the same amount. PMID:16510959

  9. Optical cone beam tomography of Cherenkov-mediated signals for fast 3D dosimetry of x-ray photon beams in water

    SciTech Connect

    Glaser, Adam K. E-mail: Brian.W.Pogue@dartmouth.edu; Andreozzi, Jacqueline M.; Zhang, Rongxiao; Pogue, Brian W. E-mail: Brian.W.Pogue@dartmouth.edu; Gladstone, David J.

    2015-07-15

    Purpose: To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF). Methods: An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp–Davis–Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts. Results: 3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm{sup 3} volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%–99% pass fraction depending on the chosen threshold dose. Conclusions: The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water.

  10. Optical cone beam tomography of Cherenkov-mediated signals for fast 3D dosimetry of x-ray photon beams in water

    PubMed Central

    Glaser, Adam K.; Andreozzi, Jacqueline M.; Zhang, Rongxiao; Pogue, Brian W.; Gladstone, David J.

    2015-01-01

    Purpose: To test the use of a three-dimensional (3D) optical cone beam computed tomography reconstruction algorithm, for estimation of the imparted 3D dose distribution from megavoltage photon beams in a water tank for quality assurance, by imaging the induced Cherenkov-excited fluorescence (CEF). Methods: An intensified charge-coupled device coupled to a standard nontelecentric camera lens was used to tomographically acquire two-dimensional (2D) projection images of CEF from a complex multileaf collimator (MLC) shaped 6 MV linear accelerator x-ray photon beam operating at a dose rate of 600 MU/min. The resulting projections were used to reconstruct the 3D CEF light distribution, a potential surrogate of imparted dose, using a Feldkamp–Davis–Kress cone beam back reconstruction algorithm. Finally, the reconstructed light distributions were compared to the expected dose values from one-dimensional diode scans, 2D film measurements, and the 3D distribution generated from the clinical Varian ECLIPSE treatment planning system using a gamma index analysis. A Monte Carlo derived correction was applied to the Cherenkov reconstructions to account for beam hardening artifacts. Results: 3D light volumes were successfully reconstructed over a 400 × 400 × 350 mm3 volume at a resolution of 1 mm. The Cherenkov reconstructions showed agreement with all comparative methods and were also able to recover both inter- and intra-MLC leaf leakage. Based upon a 3%/3 mm criterion, the experimental Cherenkov light measurements showed an 83%–99% pass fraction depending on the chosen threshold dose. Conclusions: The results from this study demonstrate the use of optical cone beam computed tomography using CEF for the profiling of the imparted dose distribution from large area megavoltage photon beams in water. PMID:26133613

  11. Boosting runtime-performance of photon pencil beam algorithms for radiotherapy treatment planning.

    PubMed

    Siggel, M; Ziegenhein, P; Nill, S; Oelfke, U

    2012-10-01

    Pencil beam algorithms are still considered as standard photon dose calculation methods in Radiotherapy treatment planning for many clinical applications. Despite their established role in radiotherapy planning their performance and clinical applicability has to be continuously adapted to evolving complex treatment techniques such as adaptive radiation therapy (ART). We herewith report on a new highly efficient version of a well-established pencil beam convolution algorithm which relies purely on measured input data. A method was developed that improves raytracing efficiency by exploiting the capability of modern CPU architecture for a runtime reduction. Since most of the current desktop computers provide more than one calculation unit we used symmetric multiprocessing extensively to parallelize the workload and thus decreasing the algorithmic runtime. To maximize the advantage of code parallelization, we present two implementation strategies - one for the dose calculation in inverse planning software, and one for traditional forward planning. As a result, we could achieve on a 16-core personal computer with AMD processors a superlinear speedup factor of approx. 18 for calculating the dose distribution of typical forward IMRT treatment plans. PMID:22071169

  12. Evaluation of Electron Contamination in Cancer Treatment with Megavoltage Photon Beams: Monte Carlo Study

    PubMed Central

    Seif, F.; Bayatiani, M. R.

    2015-01-01

    Background Megavoltage beams used in radiotherapy are contaminated with secondary electrons. Different parts of linac head and air above patient act as a source of this contamination. This contamination can increase damage to skin and subcutaneous tissue during radiotherapy. Monte Carlo simulation is an accurate method for dose calculation in medical dosimetry and has an important role in optimization of linac head materials. The aim of this study was to calculate electron contamination of Varian linac. Materials and Method The 6MV photon beam of Varian (2100 C/D) linac was simulated by Monte Carlo code, MCNPX, based on its company’s instructions. The validation was done by comparing the calculated depth dose and profiles of simulation with dosimetry measurements in a water phantom (error less than 2%). The Percentage Depth Dose (PDDs), profiles and contamination electron energy spectrum were calculated for different therapeutic field sizes (5×5 to 40×40 cm2) for both linacs. Results The dose of electron contamination was observed to rise with increase in field size. The contribution of the secondary contamination electrons on the surface dose was 6% for 5×5 cm2 to 27% for 40×40 cm2, respectively. Conclusion Based on the results, the effect of electron contamination on patient surface dose cannot be ignored, so the knowledge of the electron contamination is important in clinical dosimetry. It must be calculated for each machine and considered in Treatment Planning Systems. PMID:25973409

  13. Evaluation of a computed radiography system for megavoltage photon beam dosimetry.

    PubMed

    Olch, Arthur J

    2005-09-01

    Computed radiography (CR) systems have been gaining adoption as digital replacements for film for diagnostic and therapy imaging. As a result, film processors are being removed from service, leaving a void for the medical physicists who use film and processors for two-dimensional mega-voltage beam dosimetry. This is the first report to evaluate the ability of a commercial CR reader and storage phosphor plate system to accurately quantitate absolute dose and dose distributions from a 6 MV photon beam. There are potential advantages and disadvantages of current CR systems compared to film systems. CR systems inherently produce a linear dose-response over several logs of dose. However, the barium in the storage phosphor has a higher atomic number than the silver in film, resulting in significant energy sensitivity. The purpose of this work is to fully characterize the impact of these and other features of this CR system relevant to dosimetry. The tests performed and reported on in this study include uniformity of readout across a uniform field, geometrical accuracy, intra- and interday reproducibility, signal decay with time and with light exposure, dose-to-signal calibration, high dose effects, obliquity effects, perpendicular and parallel calibration results, field size and depth of measurement effects and the use of lead filters to minimize them, and intensity modulated radiation therapy quality assurance test results compared to that for film. Practical techniques are provided to optimize the accuracy of the system as a dosimetric replacement for film. PMID:16266113

  14. Liquid gallium cooling of silicon crystals in high intensity photon beam

    SciTech Connect

    Smither, R.K.; Forster, G.A.; Bilderback, D.H.; Bedzyk, M.; Finkelstein, K.; Henderson, C.; White, J.; Berman, L.E.; Stefan, P.; Oversluizen, T.

    1988-11-01

    The high-brilliance, insertion-device-based, photon beams of the next generation of synchrotron sources will deliver large thermal loads (1 kW to 10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and new cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in uhv conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium cooled silicon diffraction crystals with water cooled crystals. 2 refs., 16 figs., 1 tab.

  15. Combined modulated electron and photon beams planned by a Monte-Carlo-based optimization procedure for accelerated partial breast irradiation

    NASA Astrophysics Data System (ADS)

    Atriana Palma, Bianey; Ureba Sánchez, Ana; Salguero, Francisco Javier; Arráns, Rafael; Míguez Sánchez, Carlos; Walls Zurita, Amadeo; Romero Hermida, María Isabel; Leal, Antonio

    2012-03-01

    The purpose of this study was to present a Monte-Carlo (MC)-based optimization procedure to improve conventional treatment plans for accelerated partial breast irradiation (APBI) using modulated electron beams alone or combined with modulated photon beams, to be delivered by a single collimation device, i.e. a photon multi-leaf collimator (xMLC) already installed in a standard hospital. Five left-sided breast cases were retrospectively planned using modulated photon and/or electron beams with an in-house treatment planning system (TPS), called CARMEN, and based on MC simulations. For comparison, the same cases were also planned by a PINNACLE TPS using conventional inverse intensity modulated radiation therapy (IMRT). Normal tissue complication probability for pericarditis, pneumonitis and breast fibrosis was calculated. CARMEN plans showed similar acceptable planning target volume (PTV) coverage as conventional IMRT plans with 90% of PTV volume covered by the prescribed dose (Dp). Heart and ipsilateral lung receiving 5% Dp and 15% Dp, respectively, was 3.2-3.6 times lower for CARMEN plans. Ipsilateral breast receiving 50% Dp and 100% Dp was an average of 1.4-1.7 times lower for CARMEN plans. Skin and whole body low-dose volume was also reduced. Modulated photon and/or electron beams planned by the CARMEN TPS improve APBI treatments by increasing normal tissue sparing maintaining the same PTV coverage achieved by other techniques. The use of the xMLC, already installed in the linac, to collimate photon and electron beams favors the clinical implementation of APBI with the highest efficiency.

  16. The curvature of sensitometric curves for Kodak XV-2 film irradiated with photon and electron beams

    SciTech Connect

    Battum, L. J. van; Huizenga, H.

    2006-07-15

    Sensitometric curves of Kodak XV-2 film, obtained in a time period of ten years with various types of equipment, have been analyzed both for photon and electron beams. The sensitometric slope in the dataset varies more than a factor of 2, which is attributed mainly to variations in developer conditions. In the literature, the single hit equation has been proposed as a model for the sensitometric curve, as with the parameters of the sensitivity and maximum optical density. In this work, the single hit equation has been translated into a polynomial like function as with the parameters of the sensitometric slope and curvature. The model has been applied to fit the sensitometric data. If the dataset is fitted for each single sensitometric curve separately, a large variation is observed for both fit parameters. When sensitometric curves are fitted simultaneously it appears that all curves can be fitted adequately with a sensitometric curvature that is related to the sensitometric slope. When fitting each curve separately, apparently measurement uncertainty hides this relation. This relation appears to be dependent only on the type of densitometer used. No significant differences between beam energies or beam modalities are observed. Using the intrinsic relation between slope and curvature in fitting sensitometric data, e.g., for pretreatment verification of intensity-modulated radiotherapy, will increase the accuracy of the sensitometric curve. A calibration at a single dose point, together with a predetermined densitometer-dependent parameter OD{sub max} will be adequate to find the actual relation between optical density and dose.

  17. An institutional experience of quality assurance of a treatment planning system on photon beam

    PubMed Central

    Özgüven, Yıldıray; Yaray, Kadir; Alkaya, Fadime; Yücel, Birsen; Soyuer, Serdar

    2013-01-01

    Aim The purpose of the present study is to show the application of the IAEA TRS-430 QA procedures of Eclipse™v7.5 TPS for photon energies. In addition, the trends of the deviations found in the conducted tests were determined. Background In the past, the lack of complete TPS QA procedures led to some serious accidents. So, QA in the radiotherapy treatment planning process is essential for determination of accuracy in the radiotherapy process and avoidance of treatment errors. Materials and methods The calculations of TPS and measurements of irradiations of the treatment device were compared in the study. As a result, the local dose deviation values (δ1: central beam axis, δ2: penumbra and build up region, δ3: inside field, δ4: outside beam edges, δ50–90: beam fringe, RW50: radiological width) and their confidence limit values (including systematic and random errors) were obtained. Results The confidence limit values of δ4 were detected to increase with expanding field size. The values of δ1 and δ3 of hard wedge were larger than open fields. The values of δ2 and δ50–90 of the inhomogeneity effect test were larger, especially than other tests of this study. The average deviation was showed to increase with the rise of the wedge angle. The values of δ3 and δ4 of lung irradiation were outside tolerance. Conclusions The QA of TPS was done and it was found that there were no reservations in its use in patient treatment. The trend of the deviations is shown. PMID:24936337

  18. Characterization of a new commercial single crystal diamond detector for photon- and proton-beam dosimetry

    PubMed Central

    Akino, Yuichi; Gautam, Archana; Coutinho, Len; Würfel, Jan; Das, Indra J.

    2015-01-01

    A synthetic single crystal diamond detector (SCDD) is commercially available and is characterized for radiation dosimetry in various radiation beams in this study. The characteristics of the commercial SCDD model 60019 (PTW) with 6- and 15-MV photon beams, and 208-MeV proton beams, were investigated and compared with the pre-characterized detectors: Semiflex (model 31010) and PinPoint (model 31006) ionization chambers (PTW), the EDGE diode detector (Sun Nuclear Corp) and the SFD Stereotactic Dosimetry Diode Detector (IBA). To evaluate the effects of the pre-irradiation, the diamond detector, which had not been irradiated on the day, was set up in the water tank, and the response to 100 MU was measured every 20 s. The depth–dose and profiles data were collected for various field sizes and depths. For all radiation types and field sizes, the depth–dose data of the diamond chamber showed identical curves to those of the ionization chambers. The profile of the diamond detector was very similar to those of the EDGE and SFD detectors, although the Semiflex and PinPoint chambers showed volume-averaging effects in the penumbrae region. The temperature dependency was within 0.7% in the range of 4–41°C. A dose of 900 cGy and 1200 cGy was needed to stabilize the chamber to the level within 0.5% and 0.2%, respectively. The PTW type 60019 SCDD detector showed suitable characteristics for radiation dosimetry, for relative dose, depth–dose and profile measurements for a wide range of field sizes. However, at least 1000 cGy of pre-irradiation will be needed for accurate measurements. PMID:26268483

  19. Composite patterns formed by paraxial vortex-beams propagation in one-dimensional multilayer plasma photonic crystals

    NASA Astrophysics Data System (ADS)

    Khamedi, Mohammad; Bahrampour, Ali Reza

    2014-02-01

    Optical properties of twisted electromagnetic beam propagating in one-dimensional binary dielectric-plasma photonic crystal are investigated. Reflection and transmission spectra by using nonlinear Transfer Matrix Method of Degenerate Four-Wave Mixing are calculated. These characteristics are studied in low intensity, high temperature range of plasma, large Rayleigh range and neglecting the pumps depletion. In our calculation, the standard slowly varying field approximation is employed. The results show that the composite vortex patterns in the left of photonic crystal structure is dependent on the beam vortex charge number, the incident beam frequency and plasma temperature. Also, it is indicated that reflection and transmission may be more than unity for the sake of amplifying through the nonlinear medium. In fact, this structure can be exploited for characterization of phase conjugation in multilayer optical structures and optoelectronic.

  20. Two-color interference effect involving three-photon atomic excitation and four-wave mixing in crossed laser beams

    SciTech Connect

    Peet, V.

    2007-09-15

    Through multiphoton ionization measurements, the polarization effects in destructive quantum interference under three-photon resonant excitation have been studied. Recent observations [V. Peet, Phys. Rev. A 74, 033406 (2006)] have indicated that contrary to the well-known pattern of a total suppression of resonance excitation, the destructive interference becomes incomplete if three-photon transition is driven by crossed beams with orthogonal polarization planes. These observations have been tested for a more general case of two-color excitation and very similar polarization-dependent anomalies in the interference character have been registered. It has been shown that the destructive interference is modified and the resonance excitation does occur if two crossed laser beams have opposite circular polarizations. The pressure-induced evolution of the uncanceled ionization peaks has the ratio of blue shift to width close to 0.5 exactly as it is known for resonance ionization peaks registered under excitation by counterpropagating laser beams.

  1. Ray-tracing study on the post-scanner variable beam expansion optics in a two-photon microscopy system

    NASA Astrophysics Data System (ADS)

    Kim, Do-Hyun; Welle, Cristin; Krauthamer, Victor

    2012-03-01

    Due to the low signal levels typical of two-photon microscopy (TPM) in biological samples, optical design optimization is critical. One of the most important factors is overfilling of the back aperture of the objective lens. A variable beam expander is commonly placed before the scanning mirrors to achieve this goal, however, this may cause degradation of image quality due to increased dispersion. Additionally, scanning mirror size restricts the degree of expansion, which often prevents the overfilling of objective lens back aperture. We investigated the implementation of variable beam expansion optics after the scanning mirrors. Ray-tracing analyses confirmed that the post-scanner beam expansion has two key advantages over the conventional pre-scanner beam expansion approach: decreasing the number of optical elements reduces pulse dispersion and reducing the size of the scanning mirror enables faster scanning. Resolution and aberration of a TPM with post-scanner beam expansion optics were analysed.

  2. Fabrication of 4, 5, or 6-fold symmetric 3D photonic structures using single beam and single reflective optical element based holographic lithography

    NASA Astrophysics Data System (ADS)

    George, D.; Lutkenhaus, J.; Lowell, D.; Philipose, U.; Zhang, H.; Poole, Z.; Chen, K.; Lin, Y.

    2015-03-01

    Here we present the holographic fabrication of large area 3D photonic structures using a single reflective optical element (ROE) with a single beam, single exposure process. The ROE consists of a 3D printed plastic support that houses 4, 5, or 6-fold symmetrically arranged reflecting surfaces which redirect a central beam into multiple side beams in an umbrella configuration to be used in multi-beam holography. With a circular polarized beam incident to silicon wafer reflecting surfaces at the Brewster angle, multiple linearly s-polarized side beams are generated. 3D photonic crystal structures of woodpile, Penrose quasi-crystal, and hexagonal symmetry were produced with ROEs that have 4+1, 5+1 and 6+1 beam configurations, respectively. Since the ROE design can be readily changed and implemented for different photonic crystal structures, this fabrication method is more versatile and cost effective than currently comparable single optical methods like prisms and phase masks.

  3. Liquid gallium cooling of silicon crystals in high intensity photon beams (invited)

    NASA Astrophysics Data System (ADS)

    Smither, R. K.; Forster, G. A.; Bilderback, D. H.; Bedzyk, M.; Finkelstein, K.; Henderson, C.; White, J.; Berman, L. E.; Stefan, P.; Oversluizen, T.

    1989-07-01

    The high-brilliance, insertion-device-based photon beams of the next generation of synchrotron sources (Argonne's APS and Grenoble's ESRF) will deliver large thermal loads (1-10 kW) to the first optical elements. Considering the problems that present synchrotron users are experiencing with beams from recently installed insertion devices, new and improved methods of cooling these first optical elements, particularly when they are diffraction crystals, are clearly needed. A series of finite element calculations were performed to test the efficiency of new cooling geometries and various cooling fluids. The best results were obtained with liquid Ga metal flowing in channels just below the surface of the crystal. Ga was selected because of its good thermal conductivity and thermal capacity, low melting point, high boiling point, low kinetic viscosity, and very low vapor pressure. Its very low vapor pressure, even at elevated temperatures, makes it especially attractive in UHV conditions. A series of experiments were conducted at CHESS in February of 1988 that compared liquid gallium-cooled silicon diffraction crystals with water-cooled crystals. A six-pole wiggler beam was used to perform these tests on three different Si crystals, two with new cooling geometries and the one presently in use. A special high-pressure electromagnetic induction pump, recently developed at Argonne, was used to circulate the liquid gallium through the silicon crystals. In all experiments, the specially cooled crystal was used as the first crystal in a two crystal monochromator. An infrared camera was used to monitor the thermal profiles and correlated them with rocking curve measurements. A second set of cooling experiments were conducted in June of 1988 that used the intense, highly collimated beam from the newly installed ANL/CHESS undulator. Tests were performed on two new Ga-cooled Si crystals and compared with the standard water-cooled Si crystal. One of the crystals had cooling

  4. Characterization of megavoltage electron beams delivered through a photon multi-leaf collimator (pMLC)

    NASA Astrophysics Data System (ADS)

    du Plessis, F. C. P.; Leal, A.; Stathakis, S.; Xiong, W.; Ma, C.-M.

    2006-04-01

    A study is presented that characterizes megavoltage electron beams delivered through an existing double-focused photon multi-leaf collimator (pMLC) using film measurements in a solid water phantom. Machine output stability and linearity were evaluated as well as the effect of source-to-surface distance (SSD) and field size on the penumbra for electron energies between 6 and 18 MeV over an SSD range of 60-100 cm. Penumbra variations as a function of field size, depth of measurement and the influence of the jaws were also studied. Field abutment, field flatness and target coverage for segmented beams were also addressed. The measured field size for electrons transported through the pMLC was the same as that for an x-ray beam up to SSDs of 70 cm. At larger SSD, the lower energy electron fields deviated from the projected field. Penumbra data indicated that 60 cm SSD was the most favourable treatment distance. Backprojection of P20-80 penumbra data yielded a virtual source position located at 98.9 cm from the surface for 18 MeV electrons. For 6 MeV electrons, the virtual source position was at a distance of 82.6 cm. Penumbra values were smaller for small beam slits and reached a near-constant value for field widths larger than 5 cm. The influence of the jaws had a small effect on the penumbra. The R90 values ranged from 1.4 to 4.8 cm between 6 and 21 MeV as measured at 60 cm SSD for a 9 × 9 cm2 field. Uniformity and penumbra improvement could be demonstrated using weighted abutted fields especially useful for small segments. No detectable electron leakage through the pMLC was observed. Bremsstrahlung measurements taken at 60 cm SSD for a 9 × 9 cm2 field as shaped by the pMLC compared within 1% to bremsstrahlung measurements taken at 100 cm SSD for a 10 × 10 cm2 electron applicator field at 100 cm SSD.

  5. Low-energy broad-beam photon shielding data for constituents of concrete.

    PubMed

    Ogundare, Folorunso O; Ogundele, Samuel A; Akerele, Olumide O; Balogun, Fatai A

    2012-01-01

    The ability of concrete to attenuate ionizing radiation intensity is assessed using its linear or mass attenuation coefficient. In this work, the broad-beam linear and mass attenuation coefficients of different types of soils and cements used for making concrete were measured at different photon energies (60-1333 keV), nearly spanning the diagnostic photon energy range, using a NaI detector. The mass attenuation coefficients of cement decreased from 0.133 ± 0.002 at 60 keV to 0.047 ± 0.003 at 1332.5 keV. For soils, the mass attenuation coefficient of those collected from the beach was the highest, decreasing from 0.176 ± 0.003 cm²/g at 60 keV to 0.054 ± 0.001 cm²/g at 1332.5 keV. Land soils had the least value, decreasing from 0.124 ± 0.002 cm²/g at 60 keV to 0.044 ± 0.003 cm²/g at 1332.5 keV. Limestone had smaller mass attenuation coefficients than the cement produced using it. The implication of the above is that for making concrete, beach sand should be preferred as the sand component of the concrete. Models of the form μ(L) = A(E) exp[B(E)ρ] and μ(m) = αln(E)+β are proposed for fitting the linear attenuation coefficient and mass attenuation coefficient data, respectively. PMID:22402377

  6. Observation of dielectronic recombination through two-electron-one-photon correlative stabilization in an electron-beam ion trap

    SciTech Connect

    Zou, Y.; Crespo Lopez-Urrutia, J.R.; Ullrich, J.

    2003-04-01

    Dielectronic recombination (DR) for He-like Ar{sup 16+} through both one-electron-one-photon and two-electron-one-photon (TEOP) stabilizations of Li-like states was studied with an electron-beam ion trap (EBIT). It turned out that this is an excellent method to investigate TEOP transitions. Its advantages are a high branching ratio for the TEOP transition and clean conditions under which spectator electrons are controlled. Further, state- and configuration-resolved KLL DR cross sections were obtained due to the unsurpassed electron energy resolution achieved in the EBIT in the energy range around 2 keV.

  7. Optimization of beam quality for photon-counting spectral computed tomography in head imaging: simulation study.

    PubMed

    Chen, Han; Xu, Cheng; Persson, Mats; Danielsson, Mats

    2015-10-01

    Head computed tomography (CT) plays an important role in the comprehensive evaluation of acute stroke. Photon-counting spectral detectors, as promising candidates for use in the next generation of x-ray CT systems, allow for assigning more weight to low-energy x-rays that generally contain more contrast information. Most importantly, the spectral information can be utilized to decompose the original set of energy-selective images into several basis function images that are inherently free of beam-hardening artifacts, a potential advantage for further improving the diagnosis accuracy. We are developing a photon-counting spectral detector for CT applications. The purpose of this work is to determine the optimal beam quality for material decomposition in two head imaging cases: nonenhanced imaging and K-edge imaging. A cylindrical brain tissue of 16-cm diameter, coated by a 6-mm-thick bone layer and 2-mm-thick skin layer, was used as a head phantom. The imaging target was a 5-mm-thick blood vessel centered in the head phantom. In K-edge imaging, two contrast agents, iodine and gadolinium, with the same concentration ([Formula: see text]) were studied. Three parameters that affect beam quality were evaluated: kVp settings (50 to 130 kVp), filter materials ([Formula: see text] to 83), and filter thicknesses [0 to 2 half-value layer (HVL)]. The image qualities resulting from the varying x-ray beams were compared in terms of two figures of merit (FOMs): squared signal-difference-to-noise ratio normalized by brain dose ([Formula: see text]) and that normalized by skin dose ([Formula: see text]). For nonenhanced imaging, the results show that the use of the 120-kVp spectrum filtered by 2 HVL copper ([Formula: see text]) provides the best performance in both FOMs. When iodine is used in K-edge imaging, the optimal filter is 2 HVL iodine ([Formula: see text]) and the optimal kVps are 60 kVp in terms of [Formula: see text] and 75 kVp in terms of [Formula: see text]. A

  8. Diamond detector in absorbed dose measurements in high-energy linear accelerator photon and electron beams.

    PubMed

    Ravichandran, Ramamoorthy; Binukumar, John Pichy; Al Amri, Iqbal; Davis, Cheriyathmanjiyil Antony

    2016-01-01

    Diamond detectors (DD) are preferred in small field dosimetry of radiation beams because of small dose profile penumbras, better spatial resolution, and tissue-equivalent properties. We investigated a commercially available 'microdiamond' detector in realizing absorbed dose from first principles. A microdiamond detector, type TM 60019 with tandem electrometer is used to measure absorbed doses in water, nylon, and PMMA phantoms. With sensitive volume 0.004 mm3, radius 1.1mm, thickness 1 x10(-3) mm, the nominal response is 1 nC/Gy. It is assumed that the diamond detector could collect total electric charge (nC) developed during irradiation at 0 V bias. We found that dose rate effect is less than 0.7% for changing dose rate by 500 MU/min. The reproducibility in obtaining readings with diamond detector is found to be ± 0.17% (1 SD) (n = 11). The measured absorbed doses for 6 MV and 15 MV photons arrived at using mass energy absorption coefficients and stop-ping power ratios compared well with Nd, water calibrated ion chamber measured absorbed doses within 3% in water, PMMA, and nylon media. The calibration factor obtained for diamond detector confirmed response variation is due to sensitivity due to difference in manufacturing process. For electron beams, we had to apply ratio of electron densities of water to carbon. Our results qualify diamond dosimeter as a transfer standard, based on long-term stability and reproducibility. Based on micro-dimensions, we recommend these detectors for pretreatment dose verifications in small field irradiations like stereotactic treatments with image guidance. PMID:27074452

  9. Highly indistinguishable photons from deterministic quantum-dot microlenses utilizing three-dimensional in situ electron-beam lithography

    PubMed Central

    Gschrey, M.; Thoma, A.; Schnauber, P.; Seifried, M.; Schmidt, R.; Wohlfeil, B.; Krüger, L.; Schulze, J. -H.; Heindel, T.; Burger, S.; Schmidt, F.; Strittmatter, A.; Rodt, S.; Reitzenstein, S.

    2015-01-01

    The success of advanced quantum communication relies crucially on non-classical light sources emitting single indistinguishable photons at high flux rates and purity. We report on deterministically fabricated microlenses with single quantum dots inside which fulfil these requirements in a flexible and robust quantum device approach. In our concept we combine cathodoluminescence spectroscopy with advanced in situ three-dimensional electron-beam lithography at cryogenic temperatures to pattern monolithic microlenses precisely aligned to pre-selected single quantum dots above a distributed Bragg reflector. We demonstrate that the resulting deterministic quantum-dot microlenses enhance the photon-extraction efficiency to (23±3)%. Furthermore we prove that such microlenses assure close to pure emission of triggered single photons with a high degree of photon indistinguishability up to (80±7)% at saturation. As a unique feature, both single-photon purity and photon indistinguishability are preserved at high excitation power and pulsed excitation, even above saturation of the quantum emitter. PMID:26179766

  10. Highly indistinguishable photons from deterministic quantum-dot microlenses utilizing three-dimensional in situ electron-beam lithography.

    PubMed

    Gschrey, M; Thoma, A; Schnauber, P; Seifried, M; Schmidt, R; Wohlfeil, B; Krüger, L; Schulze, J-H; Heindel, T; Burger, S; Schmidt, F; Strittmatter, A; Rodt, S; Reitzenstein, S

    2015-01-01

    The success of advanced quantum communication relies crucially on non-classical light sources emitting single indistinguishable photons at high flux rates and purity. We report on deterministically fabricated microlenses with single quantum dots inside which fulfil these requirements in a flexible and robust quantum device approach. In our concept we combine cathodoluminescence spectroscopy with advanced in situ three-dimensional electron-beam lithography at cryogenic temperatures to pattern monolithic microlenses precisely aligned to pre-selected single quantum dots above a distributed Bragg reflector. We demonstrate that the resulting deterministic quantum-dot microlenses enhance the photon-extraction efficiency to (23±3)%. Furthermore we prove that such microlenses assure close to pure emission of triggered single photons with a high degree of photon indistinguishability up to (80±7)% at saturation. As a unique feature, both single-photon purity and photon indistinguishability are preserved at high excitation power and pulsed excitation, even above saturation of the quantum emitter. PMID:26179766

  11. Raman-Free, Noble-Gas-Filled Photonic-Crystal Fiber Source for Ultrafast, Very Bright Twin-Beam Squeezed Vacuum.

    PubMed

    Finger, Martin A; Iskhakov, Timur Sh; Joly, Nicolas Y; Chekhova, Maria V; Russell, Philip St J

    2015-10-01

    We report a novel source of twin beams based on modulational instability in high-pressure argon-filled hollow-core kagome-style photonic-crystal fiber. The source is Raman-free and manifests strong photon-number correlations for femtosecond pulses of squeezed vacuum with a record brightness of ∼2500 photons per mode. The ultra-broadband (∼50  THz) twin beams are frequency tunable and contain one spatial and less than 5 frequency modes. The presented source outperforms all previously reported squeezed-vacuum twin-beam sources in terms of brightness and low mode content. PMID:26551812

  12. Effects of electron beam parameters and velocity spread on radio frequency output of a photonic band gap cavity gyrotron oscillator

    SciTech Connect

    Singh, Ashutosh; Jain, P. K.

    2015-09-15

    In this paper, the effects of electron beam parameters and velocity spread on the RF behavior of a metallic photonic band gap (PBG) cavity gyrotron operating at 35 GHz with TE{sub 041}–like mode have been theoretically demonstrated. PBG cavity is used here to achieve a single mode operation of the overmoded cavity. The nonlinear time-dependent multimode analysis has been used to observe the beam-wave interaction behavior of the PBG cavity gyrotron, and a commercially available PIC code “CST Particle Studio” has been reconfigured to obtain 3D simulation results in order to validate the analytical values. The output power for this typical PBG gyrotron has been obtained ∼108 kW with ∼15.5% efficiency in a well confined TE{sub 041}–like mode, while all other competing modes have significantly low values of power output. The output power and efficiency of a gyrotron depend highly on the electron beam parameters and velocity spread. The influence of several electron beam parameters, e.g., beam voltage, beam current, beam velocity pitch factor, and DC magnetic field, on the PBG gyrotron operations has been investigated. This study would be helpful in optimising the electron beam parameters and estimating accurate RF output power of the high frequency PBG cavity based gyrotron oscillators.

  13. Effects of electron beam parameters and velocity spread on radio frequency output of a photonic band gap cavity gyrotron oscillator

    NASA Astrophysics Data System (ADS)

    Singh, Ashutosh; Jain, P. K.

    2015-09-01

    In this paper, the effects of electron beam parameters and velocity spread on the RF behavior of a metallic photonic band gap (PBG) cavity gyrotron operating at 35 GHz with TE041-like mode have been theoretically demonstrated. PBG cavity is used here to achieve a single mode operation of the overmoded cavity. The nonlinear time-dependent multimode analysis has been used to observe the beam-wave interaction behavior of the PBG cavity gyrotron, and a commercially available PIC code "CST Particle Studio" has been reconfigured to obtain 3D simulation results in order to validate the analytical values. The output power for this typical PBG gyrotron has been obtained ˜108 kW with ˜15.5% efficiency in a well confined TE041-like mode, while all other competing modes have significantly low values of power output. The output power and efficiency of a gyrotron depend highly on the electron beam parameters and velocity spread. The influence of several electron beam parameters, e.g., beam voltage, beam current, beam velocity pitch factor, and DC magnetic field, on the PBG gyrotron operations has been investigated. This study would be helpful in optimising the electron beam parameters and estimating accurate RF output power of the high frequency PBG cavity based gyrotron oscillators.

  14. Compensation for displacement of the focal point in cone beam single photon emission computed tomography reconstruction.

    PubMed

    Cao, Z; Qian, L

    1997-04-01

    This study examined the effects of focal point displacement on image quality in cone beam single photon emission computed tomography (SPECT). A new image reconstruction algorithm that accounts for the focal point shift was derived and three shift geometries were investigated. The geometries included a lateral shift with a fixed focal length but off-center focusing, a linear axial shift with a variable focal length that depends linearly on the distance between a bin of the detector and the center of the detector, and a random axial shift with a randomly varying focal length. Computer simulation was conducted to evaluate the shift effects with a phantom that was composed of 118 small spherical sources. The results demonstrated that the lateral shift of the focal point was more critical to image quality than was the axial shift. With a 0.64 cm (1 pixel) lateral shift, noticeable artifacts was observed, while an axial shift resulted in minimal changes in image quality until it reached 8 cm (12.5 pixels). The derived reconstruction algorithm eliminated most of the artifacts caused by a fixed lateral shift or a linear axial shift of the focal point, but failed to do so for a random axial shift since the linear distribution assumed in image reconstruction did not match the random shift occurred in acquisition of the data. PMID:9291002

  15. Note: Spectrometer with multichannel photon-counting detector for beam emission spectroscopy in magnetic fusion devices

    NASA Astrophysics Data System (ADS)

    Lizunov, A.; Khilchenko, A.; Khilchenko, V.; Kvashnin, A.; Zubarev, P.

    2015-12-01

    A spectrometer based on a linear array photomultiplier tube (PMT) has been developed and calibrated. A 0.635 m focal length Czerny-Turner monochromator combined with a coupling optics provides an image of a narrow 0.5 nm spectral range with a resolution of 0.015 nm/channel on a 32-anode PMT. The system aims at spectroscopy of Dα or Hα lines emitted by a diagnostic atomic beam in a plasma (primarily a motional Stark effect diagnostics). To record a low photon flux of ˜106 s-1 per channel with the time resolution of 100 μs, a pulse counting approach has been used. Wideband amplifiers scale single-electron pulses and transmit them to a digital data processing core hardwired in a programmable logic matrix. Calibrations have shown that the aberration-limited instrument function fits to a single detector channel of 1 mm width. Pilot results of passive measurements of Dα light emission from the plasma confined in a magnetic trap are presented.

  16. Extended calibration range for prompt photon emission in ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Bellini, F.; Boehlen, T. T.; Chin, M. P. W.; Collamati, F.; De Lucia, E.; Faccini, R.; Ferrari, A.; Lanza, L.; Mancini-Terracciano, C.; Marafini, M.; Mattei, I.; Morganti, S.; Ortega, P. G.; Patera, V.; Piersanti, L.; Russomando, A.; Sala, P. R.; Sarti, A.; Sciubba, A.; Solfaroli Camillocci, E.; Voena, C.

    2014-05-01

    Monitoring the dose delivered during proton and carbon ion therapy is still a matter of research. Among the possible solutions, several exploit the measurement of the single photon emission from nuclear decays induced by the irradiation. To fully characterize such emission the detectors need development, since the energy spectrum spans the range above the MeV that is not traditionally used in medical applications. On the other hand, a deeper understanding of the reactions involving gamma production is needed in order to improve the physic models of Monte Carlo codes, relevant for an accurate prediction of the prompt-gamma energy spectrum. This paper describes a calibration technique tailored for the range of energy of interest and reanalyzes the data of the interaction of a 80 MeV/u fully stripped carbon ion beam with a Poly-methyl methacrylate target. By adopting the FLUKA simulation with the appropriate calibration and resolution a significant improvement in the agreement between data and simulation is reported.

  17. Note: Spectrometer with multichannel photon-counting detector for beam emission spectroscopy in magnetic fusion devices

    SciTech Connect

    Lizunov, A.; Khilchenko, A.; Khilchenko, V.; Kvashnin, A.; Zubarev, P.

    2015-12-15

    A spectrometer based on a linear array photomultiplier tube (PMT) has been developed and calibrated. A 0.635 m focal length Czerny-Turner monochromator combined with a coupling optics provides an image of a narrow 0.5 nm spectral range with a resolution of 0.015 nm/channel on a 32-anode PMT. The system aims at spectroscopy of D{sub α} or H{sub α} lines emitted by a diagnostic atomic beam in a plasma (primarily a motional Stark effect diagnostics). To record a low photon flux of ∼10{sup 6} s{sup −1} per channel with the time resolution of 100 μs, a pulse counting approach has been used. Wideband amplifiers scale single-electron pulses and transmit them to a digital data processing core hardwired in a programmable logic matrix. Calibrations have shown that the aberration-limited instrument function fits to a single detector channel of 1 mm width. Pilot results of passive measurements of D{sub α} light emission from the plasma confined in a magnetic trap are presented.

  18. Dose-calculation algorithms in the context of inhomogeneity corrections for high energy photon beams

    SciTech Connect

    Papanikolaou, Niko; Stathakis, Sotirios

    2009-10-15

    Radiation therapy has witnessed a plethora of innovations and developments in the past 15 years. Since the introduction of computed tomography for treatment planning there has been a steady introduction of new methods to refine treatment delivery. Imaging continues to be an integral part of the planning, but also the delivery, of modern radiotherapy. However, all the efforts of image guided radiotherapy, intensity-modulated planning and delivery, adaptive radiotherapy, and everything else that we pride ourselves in having in the armamentarium can fall short, unless there is an accurate dose-calculation algorithm. The agreement between the calculated and delivered doses is of great significance in radiation therapy since the accuracy of the absorbed dose as prescribed determines the clinical outcome. Dose-calculation algorithms have evolved greatly over the years in an effort to be more inclusive of the effects that govern the true radiation transport through the human body. In this Vision 20/20 paper, we look back to see how it all started and where things are now in terms of dose algorithms for photon beams and the inclusion of tissue heterogeneities. Convolution-superposition algorithms have dominated the treatment planning industry for the past few years. Monte Carlo techniques have an inherent accuracy that is superior to any other algorithm and as such will continue to be the gold standard, along with measurements, and maybe one day will be the algorithm of choice for all particle treatment planning in radiation therapy.

  19. Note: Spectrometer with multichannel photon-counting detector for beam emission spectroscopy in magnetic fusion devices.

    PubMed

    Lizunov, A; Khilchenko, A; Khilchenko, V; Kvashnin, A; Zubarev, P

    2015-12-01

    A spectrometer based on a linear array photomultiplier tube (PMT) has been developed and calibrated. A 0.635 m focal length Czerny-Turner monochromator combined with a coupling optics provides an image of a narrow 0.5 nm spectral range with a resolution of 0.015 nm/channel on a 32-anode PMT. The system aims at spectroscopy of D(α) or H(α) lines emitted by a diagnostic atomic beam in a plasma (primarily a motional Stark effect diagnostics). To record a low photon flux of ∼10(6) s(-1) per channel with the time resolution of 100 μs, a pulse counting approach has been used. Wideband amplifiers scale single-electron pulses and transmit them to a digital data processing core hardwired in a programmable logic matrix. Calibrations have shown that the aberration-limited instrument function fits to a single detector channel of 1 mm width. Pilot results of passive measurements of D(α) light emission from the plasma confined in a magnetic trap are presented. PMID:26724090

  20. A liquid ionisation detector for digital radiography of therapeutic megavoltage photon beams.

    PubMed

    Meertens, H; van Herk, M; Weeda, J

    1985-04-01

    Experiments with an ionisation detector were performed in order to determine whether it was possible to obtain high energy photon beam images for radiotherapy treatment verification. A small prototype detector with a field of view of 78 mm X 78 mm and constructed from printed circuit boards was used. The imaging area was a matrix ionisation chamber, filled with air or liquid (2,2,4-trimethylpentane). A minicomputer was used to control the data acquisition electronics and to reconstruct and restore the images. The images were displayed on a viewing console for computed tomography images. The liquid filled detector with a front-rear board separation of 1.0 mm gave the best results. The spatial resolution was about 3.8 mm with a density resolution of 0.5% for a data acquisition time of 120 s. Comparison of the liquid detector images with corresponding metal screen-film detector images showed that the image qualities were the same. An important advantage of the ionisation detector image is that grey scale modification, sharpening and smoothing by digital processing can easily be performed. PMID:3923505

  1. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Golden, Mark; Frantzeskakis, Emmanouil; de Jong, Nick; Huang, Yingkai; Wu, Dong; Pan, Yu; de Visser, Anne; van Heumen, Erik; van Bay, Tran; Zwartsenberg, Berend; Pronk, Pieter; Varier Ramankutty, Shyama; Tytarenko, Alona; Xu, Nan; Plumb, Nick; Shi, Ming; Radovic, Milan; Varkhalov, Andrei

    2015-03-01

    The only states crossing EF in ideal, 3D TIs are topological surface states. Single crystals of Bi2Se3andBi2Te3 are too defective to exhibit bulk-insulating behaviour, and ARPES shows topologically trivial 2DEGs at EF in the surface region due to downward band bending. Ternary & quaternary alloys of Bi /Te /Se /Sb hold promise for obtaining bulk-insulating crystals. Here we report ARPES data from quaternary, bulk-insulating, Bi-based TIs. Shortly after cleavage in UHV, downward band bending pulls the bulk conduction band below EF, once again frustrating the ``topological only'' ambition for the Fermi surface. However, there is light at the end of the tunnel: we show that a super-band-gap photon beam generates a surface photovoltage sufficient to flatten the bands, thereby recovering the ideal, ``topological only'' situation. In our bulk-insulating quaternary TIs, this effect is local in nature, and permits the writing of arbitrary, micron-sized patterns in the topological energy landscape at the surface. Support from FOM, NWO and the EU is gratefully acknowledged.

  2. Diffraction inspired unidirectional and bidirectional beam splitting in defect-containing photonic structures without interface corrugations

    NASA Astrophysics Data System (ADS)

    Colak, Evrim; Serebryannikov, Andriy E.; Usik, P. V.; Ozbay, Ekmel

    2016-05-01

    It is shown that strong diffractions and related dual-beam splitting can be obtained at transmission through the nonsymmetric structures that represent two slabs of photonic crystal (PhC) separated by a single coupled-cavity type defect layer, while there are no grating-like corrugations at the interfaces. The basic operation regimes include unidirectional and bidirectional splitting that occur due to the dominant contribution of the first positive and first negative diffraction orders to the transmission, which is typically connected with different manifestations of the asymmetric transmission phenomenon. Being the main component of the resulting transmission mechanism, diffractions appear owing to the effect exerted by the defect layer that works like an embedded diffractive element. Two mechanisms can co-exist in one structure, which differ, among others, in that whether dispersion allows coupling of zero order to a wave propagating in the regular, i.e., defect-free PhC segments or not. The possibility of strong diffractions and efficient splitting related to it strongly depend on the dispersion properties of the Floquet-Bloch modes of the PhC. Existence of one of the studied transmission scenarios is not affected by location of the defect layer.

  3. Single-photon ionization quadrupole mass spectrometry with an electron beam pumped excimer light source.

    PubMed

    Mühlberger, F; Wieser, J; Morozov, A; Ulrich, A; Zimmermann, R

    2005-04-01

    The application of soft ionization methods for mass spectrometry (MS), such as single-photon ionization (SPI) using vacuum ultraviolet (VUV) light, provides powerful analytical instrumentation for real-time on-line monitoring of organic substances in gaseous matrixes. A compact and mobile quadrupole mass spectrometer (QMS) system using a novel electron beam pumped rare gas VUV lamp for SPI has been developed for on-line analysis of organic trace compounds (ppb concentrations). The VUV radiation of the light source is employed for SPI in the ion source of the QMS. The concept of the interfacing of the VUV light source with the QMS is described and the SPI-QMS is characterized. On-line detection limits down to 50 ppb for benzene, toluene, and m-xylene were achieved. The instrument is well suited for continuous measurements of aromatic and aliphatic trace compounds and can therefore be used for on-line monitoring of trace compounds in dynamically fluctuating process gases. First measurements of gas standards, petrochemical samples, and on-line monitoring of automotive exhaust are presented. PMID:15801756

  4. MOSFET sensitivity dependence on integrated dose from high-energy photon beams.

    PubMed

    Tanyi, James A; Krafft, Shane P; Hagio, Tomoe; Fuss, Martin; Salter, Bill J

    2008-01-01

    The ability of a commercially available dual bias, dual MOSFET dosimetry system to measure therapeutic doses reproducibly throughout its vendor-defined dose-based lifetime has been evaluated by characterizing its sensitivity variation to integrated/cumulative doses from,high-energy (6 and 15 MV) photon radiotherapy beams. The variation of sensitivity as a function of total integrated dose was studied for three different dose-per-fraction levels; namely, 50, 200, and 1200 cGy/fraction. In standard sensitivity mode (i.e., measurements involving dose-per-fraction levels > or =100 cGy), the response of the MOSFET system to identical irradiations increased with integrated dose for both energies investigated. Dose measurement reproducibility for the low (i.e., 50 cGy) dose fractions was within 2.1% (if the system was calibrated before each in-phantom measurement) and 3.1% [if the system was calibrated prior to first use, with no intermediate calibration(s)]. Similarly, dose measurement reproducibility was between 2.2% and 6.6% for the conventional (i.e., 200 cGy) dose fractions and between 1.8% and 7.9% for escalated (i.e., 1200 cGy) dose fractions. The results of this study suggest that, due to the progressively increasing sensitivity resulting from the dual-MOSFET design, frequent calibrations are required to achieve measurement accuracy of < or =3% (within one standard deviation). PMID:18293559

  5. Experimental analysis of general ion recombination in a liquid-filled ionization chamber in high-energy photon beams

    SciTech Connect

    Chung, Eunah; Seuntjens, Jan; Davis, Stephen

    2013-06-15

    Purpose: To study experimentally the general ion recombination effect in a liquid-filled ionization chamber (LIC) in high-energy photon beams. Methods: The general ion recombination effect on the response of a micro liquid ion chamber (microLion) was investigated with a 6 MV photon beam in normal and SRS modes produced from a Varian{sup Registered-Sign} Novalis Tx{sup TM} linear accelerator. Dose rates of the linear accelerator were set to 100, 400, and 1000 MU/min, which correspond to pulse repetition frequencies of 60, 240, and 600 Hz, respectively. Polarization voltages applied to the microLion were +800 and +400 V. The relative collection efficiency of the microLion response as a function of dose per pulse was experimentally measured with changing polarization voltage and pulse repetition frequencies and was compared with the theoretically calculated value. Results: For the 60 Hz pulse repetition frequency, the experimental relative collection efficiency was not different from the theoretical one for a pulsed beam more than 0.3% for both polarization voltages. For a pulsed radiation beam with a higher pulse repetition frequency, the experimental relative collection efficiency converged to the theoretically calculated efficiency for continuous beams. This result indicates that the response of the microLion tends toward the response to a continuous beam with increasing pulse repetition frequency of a pulsed beam because of low ion mobility in the liquid. Conclusions: This work suggests an empirical method to correct for differences in general ion recombination of a LIC between different radiation fields. More work is needed to quantitatively explain the LIC general ion recombination behavior in pulsed beams generated from linear accelerators.

  6. On-ground calibration of AGILE-GRID with a photon beam: results and lessons for the future

    NASA Astrophysics Data System (ADS)

    Cattaneo, P. W.; Rappoldi, A.; Argan, A.; Buonomo, B.; Bulgarelli, A.; Chen, A. W.; D'Ammando, F.; Foggetta, L.; Fuschino, F.; Galli, M.; Gianotti, F.; Giuliani, A.; Longo, F.; Marisaldi, M.; Mazzitelli, G.; Pellizzoni, A.; Prest, M.; Pucella, G.; Quintieri, L.; Tavani, M.; Trifoglio, M.; Trois, A.; Valente, P.; Vallazza, E.; Vercellone, S.; Barbiellini, G.; Caraveo, P.; Costa, E.; De Paris, G.; Del Monte, E.; Di Cocco, G.; Donnarumma, I.; Evangelista, Y.; Ferrari, A.; Feroci, M.; Fiorini, M.; Giusti, M.; Labanti, C.; Lapshov, I.; Lazzarotto, F.; Lipari, P.; Lucarelli, F.; Mereghetti, S.; Morelli, E.; Moretti, E.; Morselli, A.; Pacciani, L.; Perotti, F.; Piano, G.; Picozza, P.; Pilia, M.; Rapisarda, M.; Rubini, A.; Sabatini, S.; Soffitta, P.; Striani, E.; Vittorini, V.; Zanello, D.; Colafrancesco, S.; Giommi, P.; Pittori, C.; Santolamazza, P.; Verrecchia, F.; Salotti, L.

    2012-09-01

    At the core of the AGILE scientific instrument, designed to operate on a satellite, there is the Gamma Ray Imaging Detector (GRID) consisting of a Silicon Tracker (ST), a Cesium Iodide Mini-Calorimeter and an Anti-Coincidence system of plastic scintillator bars. The ST needs an on-ground calibration with a γ-ray beam to validate the simulation used to calculate the energy response function and the effective area versus the energy and the direction of the γ rays. A tagged γ-ray beam line was designed at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali of Frascati (LNF), based on an electron beam generating γ rays through bremsstrahlung in a position-sensitive target. The γ-ray energy is deduced by the difference with the post-bremsstrahlung electron energy1-.2 The electron energy is measured by a spectrometer consisting of a dipole magnet and an array of position sensitive silicon strip detectors, the Photon Tagging System (PTS). The use of the combined BTF-PTS system as tagged photon beam requires understanding the efficiency of γ-ray tagging, the probability of fake tagging, the energy resolution and the relation of the PTS hit position versus the γ-ray energy. This paper describes this study comparing data taken during the AGILE calibration occurred in 2005 with simulation.

  7. [Measurement of peak correction factor of Farmer chamber for calibration of flattening filter free (FFF) clinical photon beams].

    PubMed

    Kontra, Gábor; Major, Tibor; Polgár, Csaba

    2015-06-01

    Farmer-type ionization chambers are considered the most reliable detectors and for this reason they are most frequently used for the calibration of photon beams of medical linear accelerators. Flattening filter free (FFF) photon beams of linear accelerators have recently started to be used in radiotherapy. The dose profile of FFF beams is peaked in the center of the field and the dose distribution will be inhomogeneous along the axis of the 2.3 cm long measuring volume of the Farmer chamber. The peaked radiation field will result in volume averaging effects in the large Farmer chamber, therefore this chamber will underestimate the true central axis dose. Our objective was to determine the value of the peak correction factor (Kp) of Farmer-type chamber with measurements to avoid the underestimation of the central axis dose during the calibration of FFF radiation fields. Measurements were made with 6 MV and 10 MV flattened (6X and 10X) and FFF beams (6XFFF and 10XFFF) of a Varian TrueBeam medical linear accelerator in a solid water phantom at 10 cm depth. The source surface distance (SSD) was 100 cm, the field size was 10×10 cm and the dose rate was always 400 MU/min during the measurements. We delivered 100 MU in each measurement and the absorbed dose to water was calculated according to the IAEA TRS-398 dosimetry protocol. The measured signals of the ionization chambers were always corrected for the ion recombination loss. The ion recombination correction factors (Kr) were determined with the two-voltage method separately for the used ion chambers and for flattened and unflattened beams. First, we measured the dose to water with PTW TM30012 Farmer chamber in 6XFFF and 6X beams, then calculated the ratio of doses of 6XFFF and 6X beams (R6,Farmer). Immediately after this we repeated the above measurements with PTW TM31010 Semiflex chamber and determined the ratio of doses of 6XFFF and 6X beams again (R6,Semiflex). The length of the sensitive volume of the Semiflex

  8. Photon beam quality correction factors for the NE2571A and NE2581A thimble ionization chambers using PENELOPE.

    PubMed

    Erazo, Fabián; Lallena, Antonio M

    2016-01-01

    The beam quality correction factor kQ,Q0 and the perturbation factor pQ for photon beams were calculated for the NE2571A and NE2581A ionization chambers, using the Monte Carlo simulation code PENELOPE. Results are compared to those quoted for the NE2571 and NE2581 chambers in previous works. Both kQ,Q0 and pQ obtained for NE2571A and NE2581A chambers agree with those of their predecessors NE2571 and NE2581 ones. PMID:26602965

  9. Quantum correlations by four-wave mixing in an atomic vapor in a nonamplifying regime: Quantum beam splitter for photons

    SciTech Connect

    Glorieux, Quentin; Guidoni, Luca; Guibal, Samuel; Likforman, Jean-Pierre; Coudreau, Thomas

    2011-11-15

    We study the generation of intensity quantum correlations using four-wave mixing in a rubidium vapor. The absence of cavities in these experiments allows to deal with several spatial modes simultaneously. In the standard amplifying configuration, we measure relative intensity squeezing up to 9.2 dB below the standard quantum limit. We also theoretically identify and experimentally demonstrate an original regime where, despite no overall amplification, quantum correlations are generated. In this regime, a four-wave mixing setup can play the role of a photonic beam splitter with nonclassical properties, that is, a device that splits a coherent state input into two quantum-correlated beams.

  10. Dosimetric variation due to the photon beam energy in the small-animal irradiation: A Monte Carlo study

    SciTech Connect

    Chow, James C. L.; Leung, Michael K. K.; Lindsay, Patricia E.; Jaffray, David A.

    2010-10-15

    Purpose: The impact of photon beam energy and tissue heterogeneities on dose distributions and dosimetric characteristics such as point dose, mean dose, and maximum dose was investigated in the context of small-animal irradiation using Monte Carlo simulations based on the EGSnrc code. Methods: Three Monte Carlo mouse phantoms, namely, heterogeneous, homogeneous, and bone homogeneous were generated based on the same mouse computed tomography image set. These phantoms were generated by overriding the tissue type of none of the voxels (heterogeneous), all voxels (homogeneous), and only the bone voxels (bone homogeneous) to that of soft tissue. Phase space files of the 100 and 225 kVp photon beams based on a small-animal irradiator (XRad225Cx, Precision X-Ray Inc., North Branford, CT) were generated using BEAMnrc. A 360 deg. photon arc was simulated and three-dimensional (3D) dose calculations were carried out using the DOSXYZnrc code through DOSCTP in the above three phantoms. For comparison, the 3D dose distributions, dose profiles, mean, maximum, and point doses at different locations such as the isocenter, lung, rib, and spine were determined in the three phantoms. Results: The dose gradient resulting from the 225 kVp arc was found to be steeper than for the 100 kVp arc. The mean dose was found to be 1.29 and 1.14 times higher for the heterogeneous phantom when compared to the mean dose in the homogeneous phantom using the 100 and 225 kVp photon arcs, respectively. The bone doses (rib and spine) in the heterogeneous mouse phantom were about five (100 kVp) and three (225 kVp) times higher when compared to the homogeneous phantom. However, the lung dose did not vary significantly between the heterogeneous, homogeneous, and bone homogeneous phantom for the 225 kVp compared to the 100 kVp photon beams. Conclusions: A significant bone dose enhancement was found when the 100 and 225 kVp photon beams were used in small-animal irradiation. This dosimetric effect, due to

  11. Spontaneous parametric down conversion of vectorial beams: helicity effects on the orbital angular momentum of the photon pairs

    NASA Astrophysics Data System (ADS)

    Jáuregui, R.

    2015-06-01

    We study the process of spontaneous parametric down conversion of a coherent structured electromagnetic (EM) field into a pair of photons that are also described by structured EM modes. We explore the relevance of a full vectorial description when the pump beam is outside the paraxial regime. A particularly interesting new phenomenon in such a regime corresponds to the conversion of angular momentum of the EM field associated with its polarization (usually referred to as spin angular momentum or SAM) into angular momentum related to optical vortices (usually referred to as orbital angular momentum or OAM). We show that such a conversion can take place using Bessel pump beams and standard nonlinear crystals with their birefringent axis parallel to the vector normal to its surface. Phase matching conditions are studied in detail for this configuration. Signatures of the conversion of SAM into OAM on the angular spectrum of the down converted photons are described.

  12. Implementation status of the global and local beam position feedback systems for the Advanced Photon Source storage ring

    SciTech Connect

    Chung, Y.; Barr, D.; Decker, G.; Galayda, J.; Kirchman, J.; Lenkszus, F.; Lumpkin, A.; Votaw, A.J.

    1995-07-01

    The Advanced Photon Source (APS) is implementing an extensive beam position feedback system for both global and local stabilization of particle and photon beams based on digital signal processing. The description and operational experience of the system will be given in this paper. In particular, we will discuss the underlying fundamental principles, hardware layout, controls interface, and automatic software generation for multiple digital signal processors (DSPS) distributed in 20 VME crates around the ring. The feedback system runs at 4-kHz sampling frequency in order to achieve the correction bandwidth of approximately 100 Hz. For the maximum correction efficiency and resolution of conflicts among multiple local feedback systems due to the local bump closure error, the global and local feedback systems are combined into a single unified system. This novel approach is made possible through data sharing among the global and local systems via the fiber-optically networked reflective memories.

  13. Measurement of therapeutic photon beams-induced Cerenkov radiation generated in PMMA- and PS-based plastic optical fibers

    NASA Astrophysics Data System (ADS)

    Lee, Bongsoo; Shin, Sang Hun; Yoo, Wook Jae; Jang, Kyoung Won

    2016-07-01

    In this study, we characterized Cerenkov radiation generated in polystyrene (PS)- and polymethyl methacrylate (PMMA)-based plastic optical fibers (POFs) to select an adequate optical fiber for producing Cerenkov radiation. To determine the relationship between the absorbed dose and the intensity of Cerenkov radiation, we calculated the energy depositions of photon beams and fluxes of electrons inducing Cerenkov radiation using the Monte Carlo N-Particle eXtended code. Also, intensities of Cerenkov radiation generated in PS- and PMMA-based POFs were measured as functions of dose rate and monitor unit. At last, therapeutic photon beams-induced Cerenkov radiation in PS- and PMMA-based POFs was measured according to depths of solid water phantom.

  14. Evolution of the CaF2:Tm (TLD-300) glow curve as an indicator of beam quality for low-energy photon beams

    NASA Astrophysics Data System (ADS)

    Muñoz, I. D.; Avila, O.; Gamboa-deBuen, I.; Brandan, M. E.

    2015-03-01

    We study the high- to low- temperature signal ratio (HLTR) of the CaF2:Tm glow curve as a function of beam quality for low-energy photon beams with effective energy between 15.2 and 33.6 keV, generated with W, Mo and Rh anodes. CaF2:Tm dosemeters (TLD-300) were exposed to x-rays and 60Co gamma-rays. Glow curves were deconvoluted into 7 peaks, using computerized glow curve deconvolution and HLTR was evaluated. Air kerma and dose in water were between 2.1-15.0 mGy and 49.8-373.8 mGy, respectively. All peaks in the glow curve showed a linear response with respect to air kerma and dose in water. HLTR values decreased monotonically between 1.029  ±  0.010 (at 15.2 keV) and 0.821  ±  0.011 (33.6 keV), and no effects due to the use of different anode/filter combinations were observed. The results indicate a relatively high value of HLTR (about 1 for 17 keV effective energy, or 3 keV μm-1 track-average LET) and a measurable dependence on the photon beam quality. Comparison of these photon data with HLTR for ions shows good quantitative agreement. The reported evolution of the CaF2:Tm glow curve could facilitate the estimation of the effective energy of unknown photon fields by this technique.

  15. Optical beam induced current measurements based on two-photon absorption process in 4H-SiC bipolar diodes

    SciTech Connect

    Hamad, H.; Raynaud, C.; Bevilacqua, P.; Tournier, D.; Planson, D.; Vergne, B.

    2014-02-24

    Using a pulsed green laser with a wavelength of 532 nm, a duration pulse of ∼1 ns, and a mean power varying between 1 and 100 mW, induced photocurrents have been measured in 4H-SiC bipolar diodes. Considering the photon energy (2.33 eV) and the bandgap of 4H-SiC (3.2 eV), the generation of electron-hole pair by the conventional single photon absorption process should be negligible. The intensity of the measured photocurrents depends quadratically on the power beam intensity. This clearly shows that they are generated using two-photon absorption process. As in conventional OBIC (Optical Beam Induced Current), the measurements give an image of the electric field distribution in the structure under test, and the minority carrier lifetime can be extracted from the decrease of the photocurrent at the edge of the structure. The extracted minority carrier lifetime of 210 ns is consistent with results obtained in case of single photon absorption.

  16. Photon desorption measurements of copper and copper plated beam tubes for the SSCL 20 TeV proton collider

    SciTech Connect

    Foerster, C.L.; Lanni, C. ); Maslennikov, I.; Turner, W. )

    1994-07-01

    Relativistic protons circulating in the SSCL 20 TeV collider emit synchrotron radiation (10[sup 16] photons/m/s, [ital E][sub crit]=284 eV). This radiation will photodesorb gases from the walls of the beam tube. The 4.2 K superconducting magnet bore tubes will act as very long distributed pumps. Build up of cryosorbed gases could severely limit collider operation and may require a bore tube liner to hide cryosorbed molecules from the photon flux and to increase the H[sub 2] pumping capacity. To predict collider vacuum performance, photon stimulated desorption experiments have been running at the National Synchrotron Light Source (NSLS) at BNL and on the VEPP2M storage ring at BINP, Novosibirsk, Russia. At the U10B beamline of the VUV ring at NSLS, beam tube samples were exposed to over 10[sup 23] photons/m with [ital E][sub crit]=486 eV and incident angle=12 mrad. Unbaked copper and copper plated stainless steel have been tested. In addition, results have been obtained with a 1100 G dipole magnetic field and with a 350 [degree]C vacuum bake. Results are presented and compared with other measurements at the NSLS and at other laboratories.

  17. A system of beam energy measurement based on the Compton backscattered laser photons for the VEPP-2000 electron-positron collider

    NASA Astrophysics Data System (ADS)

    Abakumova, E. V.; Achasov, M. N.; Berkaev, D. E.; Kaminsky, V. V.; Koop, I. A.; Korol, A. A.; Koshuba, S. V.; Krasnov, A. A.; Muchnoi, N. Yu.; Perevedentsev, E. A.; Pyata, E. E.; Shatunov, P. Yu.; Shatunov, Yu. M.; Shwartz, D. B.

    2014-04-01

    The beam energy measurement system for the VEPP-2000 electron-positron collider is described. The method of Compton backscattering of CO laser photons on the electron beam is used. The relative systematic uncertainty of the beam energy determination is estimated as 6×10-5. It was obtained through comparison of the results of the beam energy measurements using the Compton backscattering and resonance depolarization methods.

  18. Sub-wavelength focusing of cylindrical vector beams by a 1D metallic photonic crystal plano-concave lens

    NASA Astrophysics Data System (ADS)

    Zhong, Yi; Wang, Jin; Xu, Ji

    2014-10-01

    The fine manipulations of cylindrical vector beams (CVBs) based on metallic microstructures, such as sub-wavelength focusing, have entered many interdisciplinary areas, and the important applications have been found in many fields including optical micromanipulation, super-resolution imaging, micro-machining and so on. But so far, the sub-wavelength focusing of azimuthally polarized beams is encountered, since the manipulation mechanisms rely heavily on the excitation of surface plasmon polaritons, which brings the polarization limitation. We theoretically investigated the focusing behavior of CVBs in 1D metallic photonic crystals (MPCs). The simulation results show that a 1D MPC plano-concave lens can focus cylindrical vector beams into scale of sub-wavelength. The negative refraction at the interface between the air and the 1D MPC is analyzed at the frequencies corresponding to the second photonic band, which makes the 1D MPC has the ability to focus higher Fourier components of light beams. The cylindrical plano-concave structure is constructed to focus the radially and azimuthally polarized beams simultaneously. The behavior is demonstrated by Finite Element Method (FEM). The shape of focusing field can be tailored, by changing the polarization ratio of the incident beams. In addition, the effective sub-wavelength focusing phenomenon can also be realized in variety of wave ranges, by choosing the proper materials and adjusting the parameters. We believe that it's the first time to realize the simultaneous sub-wavelength focusing of radially and azimuthally polarized beams, the application of which is quite promising in broad prospects.

  19. Bone and mucosal dosimetry in skin radiation therapy: a Monte Carlo study using kilovoltage photon and megavoltage electron beams

    NASA Astrophysics Data System (ADS)

    Chow, James C. L.; Jiang, Runqing

    2012-06-01

    This study examines variations of bone and mucosal doses with variable soft tissue and bone thicknesses, mimicking the oral or nasal cavity in skin radiation therapy. Monte Carlo simulations (EGSnrc-based codes) using the clinical kilovoltage (kVp) photon and megavoltage (MeV) electron beams, and the pencil-beam algorithm (Pinnacle3 treatment planning system) using the MeV electron beams were performed in dose calculations. Phase-space files for the 105 and 220 kVp beams (Gulmay D3225 x-ray machine), and the 4 and 6 MeV electron beams (Varian 21 EX linear accelerator) with a field size of 5 cm diameter were generated using the BEAMnrc code, and verified using measurements. Inhomogeneous phantoms containing uniform water, bone and air layers were irradiated by the kVp photon and MeV electron beams. Relative depth, bone and mucosal doses were calculated for the uniform water and bone layers which were varied in thickness in the ranges of 0.5-2 cm and 0.2-1 cm. A uniform water layer of bolus with thickness equal to the depth of maximum dose (dmax) of the electron beams (0.7 cm for 4 MeV and 1.5 cm for 6 MeV) was added on top of the phantom to ensure that the maximum dose was at the phantom surface. From our Monte Carlo results, the 4 and 6 MeV electron beams were found to produce insignificant bone and mucosal dose (<1%), when the uniform water layer at the phantom surface was thicker than 1.5 cm. When considering the 0.5 cm thin uniform water and bone layers, the 4 MeV electron beam deposited less bone and mucosal dose than the 6 MeV beam. Moreover, it was found that the 105 kVp beam produced more than twice the dose to bone than the 220 kVp beam when the uniform water thickness at the phantom surface was small (0.5 cm). However, the difference in bone dose enhancement between the 105 and 220 kVp beams became smaller when the thicknesses of the uniform water and bone layers in the phantom increased. Dose in the second bone layer interfacing with air was found to be

  20. Comparison of Head Scatter Factor for 6MV and 10MV flattened (FB) and Unflattened (FFF) Photon Beam using indigenously Designed Columnar Mini Phantom

    PubMed Central

    Ashokkumar, Sigamani; Nambi Raj, N Arunai; Sinha, Sujit Nath; Yadav, Girigesh; Thiyagarajan, Rajesh; Raman, Kothanda; Mishra, Manindra Bhushan

    2014-01-01

    To measure and compare the head scatter factor for flattened (FB) and unflattened (FFF) of 6MV and 10MV photon beam using indigenously designed mini phantom. A columnar mini phantom was designed as recommended by AAPM Task Group 74 with low and high atomic number materials at 10 cm (mini phantom) and at approximately twice the depth of maximum dose water equivalent thickness (brass build-up cap). Scatter in the accelerator (Sc) values of 6MV-FFF photon beams are lesser than that of the 6MV-FB photon beams (0.66-2.8%; Clinac iX, 2300CD) and (0.47-1.74%; True beam) for field sizes ranging from 10 × 10 cm2 to 40 × 40 cm2. Sc values of 10MV-FFF photon beams are lesser (0.61-2.19%; True beam) than that of the 10MV-FB photons beams for field sizes ranging from 10 × 10 cm2 to 40 × 40 cm2. The SSD had no influence on head scatter for both flattened and unflattened beams and irrespective of head design of the different linear accelerators. The presence of field shaping device influences the Sc values. The collimator exchange effect reveals that the opening of the upper jaw increases Sc irrespective of FB or FFF photon beams and different linear accelerators, and it is less significant in FFF beams. Sc values of 6MV-FB square field were in good agreement with that of AAPM, TG-74 published data for Varian (Clinac iX, 2300CD) accelerator. Our results confirm that the removal of flattening filter decreases in the head scatter factor compared to flattened beam. This could reduce the out-of-field dose in advanced treatment delivery techniques. PMID:25190997

  1. Energy calibration of energy-resolved photon-counting pixel detectors using laboratory polychromatic x-ray beams

    NASA Astrophysics Data System (ADS)

    Youn, Hanbean; Han, Jong Chul; Kam, Soohwa; Yun, Seungman; Kim, Ho Kyung

    2014-10-01

    Recently, photon-counting detectors capable of resolving incident x-ray photon energies have been considered for use in spectral x-ray imaging applications. For reliable use of energy-resolved photon-counting detectors (ERPCDs), energy calibration is an essential procedure prior to their use because variations in responses from each pixel of the ERPCD for incident photons, even at the same energy, are inevitable. Energy calibration can be performed using a variety of methods. In all of these methods, the photon spectra with well-defined peak energies are recorded. Every pixel should be calibrated on its own. In this study, we suggest the use of a conventional polychromatic x-ray source (that is typically used in laboratories) for energy calibration. The energy calibration procedure mainly includes the determination of the peak energies in the spectra, flood-field irradiation, determination of peak channels, and determination of calibration curves (i.e., the slopes and intercepts of linear polynomials). We applied a calibration algorithm to a CdTe ERPCD comprised of 128×128 pixels with a pitch of 0.35 mm using highly attenuated polychromatic x-ray beams to reduce the pulse pile-up effect, and to obtain a narrow-shaped spectrum due to beam hardening. The averaged relative error in calibration curves obtained from 16,384 pixels was about 0.56% for 59.6 keV photons from an Americium radioisotope. This pixel-by-pixel energy calibration enhanced the signal- and contrast-to-noise ratios in images, respectively, by a factor of ~5 and 3 due to improvement in image homogeneity, compared to those obtained without energy calibration. One secondary finding of this study was that the x-ray photon spectra obtained using a common algorithm for computing x-ray spectra reasonably described the peaks in the measured spectra, which implies easier peak detection without the direct measurement of spectra using a separate spectrometer. The proposed method will be a useful alternative to

  2. Reference radiochromic film dosimetry in kilovoltage photon beams during CBCT image acquisition

    SciTech Connect

    Tomic, Nada; Devic, Slobodan; DeBlois, Francois; Seuntjens, Jan

    2010-03-15

    Purpose: A common approach for dose assessment during cone beam computed tomography (CBCT) acquisition is to use thermoluminescent detectors for skin dose measurements (on patients or phantoms) or ionization chamber (in phantoms) for body dose measurements. However, the benefits of a daily CBCT image acquisition such as margin reduction in planning target volume and the image quality must be weighted against the extra dose received during CBCT acquisitions. Methods: The authors describe a two-dimensional reference dosimetry technique for measuring dose from CBCT scans using the on-board imaging system on a Varian Clinac-iX linear accelerator that employs the XR-QA radiochromic film model, specifically designed for dose measurements at low energy photons. The CBCT dose measurements were performed for three different body regions (head and neck, pelvis, and thorax) using humanoid Rando phantom. Results: The authors report on both surface dose and dose profiles measurements during clinical CBCT procedures carried out on a humanoid Rando phantom. Our measurements show that the surface doses per CBCT scan can range anywhere between 0.1 and 4.7 cGy, with the lowest surface dose observed in the head and neck region, while the highest surface dose was observed for the Pelvis spot light CBCT protocol in the pelvic region, on the posterior side of the Rando phantom. The authors also present results of the uncertainty analysis of our XR-QA radiochromic film dosimetry system. Conclusions: Radiochromic film dosimetry protocol described in this work was used to perform dose measurements during CBCT acquisitions with the one-sigma dose measurement uncertainty of up to 3% for doses above 1 cGy. Our protocol is based on film exposure calibration in terms of ''air kerma in air,'' which simplifies both the calibration procedure and reference dosimetry measurements. The results from a full Monte Carlo investigation of the dose conversion of measured XR-QA film dose at the surface into

  3. Aspects of radiation beam quality and their effect on the dose response of polymer gels: Photons, electrons and fast neutrons

    NASA Astrophysics Data System (ADS)

    Berg, Andreas; Bayreder, Christian; Georg, Dietmar; Bankamp, Achim; Wolber, Gerd

    2009-05-01

    Polymer gels are generally assumed to exhibit no significant dependence of the dose response on the energy or type of irradiation for clinically used beam qualities. Based on reports on differences in dose response for low energy photons and particle beams with high linear energy transfer (LET) we here investigate the dose response and energy dependence for a normoxic methacrylic acid polymer gel (MAGAT) for X-rays (100 kV), high energy photon beams (E = 1.2 MeV (60Co), 6 MV and 15 MV) and for three different electron energies (4, 12 and 20 MeV). Due to the possible impact also the sensitivity of the dose response to the dose rate is reported. A reduction in polymer gel relaxation rate has been observed for proton and carbon beams due to the high Linear Energy Transfer (LET) of these types of radiations. We here report on the dose response of an acryl-amide polymer gel (PAG) in a fast neutron field along with collimation as proposed for Boron neutron capture therapy (BNCT).

  4. Craniospinal Irradiation Techniques: A Dosimetric Comparison of Proton Beams With Standard and Advanced Photon Radiotherapy

    SciTech Connect

    Yoon, Myonggeun; Shin, Dong Ho; Kim, Jinsung; Kim, Jong Won; Kim, Dae Woong; Park, Sung Yong; Lee, Se Byeong; Kim, Joo Young; Park, Hyeon-Jin; Park, Byung Kiu; Shin, Sang Hoon

    2011-11-01

    Purpose: To evaluate the dosimetric benefits of advanced radiotherapy techniques for craniospinal irradiation in cancer in children. Methods and Materials: Craniospinal irradiation (CSI) using three-dimensional conformal radiotherapy (3D-CRT), tomotherapy (TOMO), and proton beam treatment (PBT) in the scattering mode was planned for each of 10 patients at our institution. Dosimetric benefits and organ-specific radiation-induced cancer risks were based on comparisons of dose-volume histograms (DVHs) and on the application of organ equivalent doses (OEDs), respectively. Results: When we analyzed the organ-at-risk volumes that received 30%, 60%, and 90% of the prescribed dose (PD), we found that PBT was superior to TOMO and 3D-CRT. On average, the doses delivered by PBT to the esophagus, stomach, liver, lung, pancreas, and kidney were 19.4 Gy, 0.6 Gy, 0.3 Gy, 2.5 Gy, 0.2 Gy, and 2.2 Gy for the PD of 36 Gy, respectively, which were significantly lower than the doses delivered by TOMO (22.9 Gy, 4.5 Gy, 6.1 Gy, 4.0 Gy, 13.3 Gy, and 4.9 Gy, respectively) and 3D-CRT (34.6 Gy, 3.6 Gy, 8.0 Gy, 4.6 Gy, 22.9 Gy, and 4.3 Gy, respectively). Although the average doses delivered by PBT to the chest and abdomen were significantly lower than those of 3D-CRT or TOMO, these differences were reduced in the head-and-neck region. OED calculations showed that the risk of secondary cancers in organs such as the stomach, lungs, thyroid, and pancreas was much higher when 3D-CRT or TOMO was used than when PBT was used. Conclusions: Compared with photon techniques, PBT showed improvements in most dosimetric parameters for CSI patients, with lower OEDs to organs at risk.

  5. Assessment of small volume ionization chambers as reference dosimeters in high-energy photon beams

    NASA Astrophysics Data System (ADS)

    Le Roy, M.; de Carlan, L.; Delaunay, F.; Donois, M.; Fournier, P.; Ostrowsky, A.; Vouillaume, A.; Bordy, J. M.

    2011-09-01

    LNE-LNHB is involved in a European project aiming at establishing absorbed dose-to-water standards for photon-radiation fields down to 2 × 2 cm2. This requires the calibration of reference ionization chambers of small volume. Twenty-four ionization chambers of eight different types with volume ranging from 0.007 to 0.057 cm3 were tested in a 60Co beam. For each chamber, two major characteristics were investigated: (1) the stability of the measured current as a function of the irradiation time under continuous irradiation. At LNE-LNHB, the variation of the current should be less than ±0.1% in comparison with its first value (over a 16 h irradiation time); (2) the variation of the ionization current with the applied polarizing voltage and polarity. Leakage currents were also measured. Results show that (1) every tested PTW (31015, 31016 and 31014) and Exradin A1SL chambers demonstrate a satisfying stability under irradiation. Other types of chambers have a stability complying with the stability criterion for some or none of them. (2) IBA CC01, IBA CC04 and Exradin A1SL show a proper response as a function of applied voltage for both polarities. PTW, Exradin A14SL and Exradin A16 do not. Only three types of chambers were deemed suitable as reference chambers according to LNE-LNHB requirements and specifications from McEwen (2010 Med. Phys. 37 2179-93): Exradin A1SL chambers (3/3), IBA CC04 (2/3) and IBA CC01 (1/3). The Exradin A1SL type with an applied polarizing voltage of 150 V was chosen as an LNE-LNHB reference chamber type in 2 × 2 cm2 radiation fields.

  6. A 3D photon superposition/convolution algorithm and its foundation on results of Monte Carlo calculations

    NASA Astrophysics Data System (ADS)

    Ulmer, W.; Pyyry, J.; Kaissl, W.

    2005-04-01

    Based on previous publications on a triple Gaussian analytical pencil beam model and on Monte Carlo calculations using Monte Carlo codes GEANT-Fluka, versions 95, 98, 2002, and BEAMnrc/EGSnrc, a three-dimensional (3D) superposition/convolution algorithm for photon beams (6 MV, 18 MV) is presented. Tissue heterogeneity is taken into account by electron density information of CT images. A clinical beam consists of a superposition of divergent pencil beams. A slab-geometry was used as a phantom model to test computed results by measurements. An essential result is the existence of further dose build-up and build-down effects in the domain of density discontinuities. These effects have increasing magnitude for field sizes <=5.5 cm2 and densities <=0.25 g cm-3, in particular with regard to field sizes considered in stereotaxy. They could be confirmed by measurements (mean standard deviation 2%). A practical impact is the dose distribution at transitions from bone to soft tissue, lung or cavities. This work has partially been presented at WC 2003, Sydney.

  7. Air cavity effects on the radition dose to the larynx using Co-60, 6 MV, and 10 MV photon beams

    SciTech Connect

    Niroomand-Rad, A.; Harter, K.W.; Thobejane, S.; Bertrand, K.

    1994-07-30

    The purpose was to determine the perturbation effect in the surface layers of lesions located in the air-tumor tissues interface of larynx using {sup 60}Co, 6 MV, and 10 MV photon beams. Thermoluminescent dosimeters (TLDs) were embedded at 16 measurement locations in slab no. 8 of a humanoid phantom and exposed to two lateral-opposed beams using standard 7 {times} 7 cm fields. Similarly, radiographic and radiochromic films were placed between slabs no. 7 and no. 8 of the humanoid phantom and exposed to two lateral-opposed radiation beams. The dosimeters were irradiated with {sup 60}Co, 6 MV, and 10 MV photon beams. Computer tomography (CT) treatment planning without inhomogeneity correction was performed. At the tissue-air interface, the average measured percentage dose (% dose{sub m}) is about (108.7 {+-} 4.8%) with TLD data, (96.8 {+-} 2.5%) with radiographic film data, and (100.8 {+-} 4.9%) with radiochromic film data. Similarly, in the central part of the cavity, the % dose{sub m} is (98.4 {+-} 3.1)% with TLD data, (94.3 {+-} 3.3)% with radiographic film data, and (91.7 {+-} 5.0)% with radiochromic film data. Using the CT-based generated dose distribution (without inhomogeneity correction), the average calculated percentage dose (% dose{sub c}) is (98.7 {+-} 1.0%) at the tissue-air interface and 98% in the central part of the air cavity. For the beam energies studied, the variation from the % dose {sub m} at the tissue-air interface for a given dosimetry technique is relatively small and therefore should not be significant in clinical settings. The variation from the % dose{sub m} at the tissue-air interface is more significant for lower energies. This variation is about 4.3% for 10 MV photon beam, therefore, while institutional practice favors lower energy ({sup 60}Co to 6 MV) for node-negative glottic cancers, physical/dosimetric evidence offers no disadvantage to the use of higher energy photons. 10 refs., 7 figs., 2 tabs.

  8. The dosimetric impact of different photon beam energy on RapidArc radiotherapy planning for cervix carcinoma

    PubMed Central

    Kumar, Lalit; Yadav, Girigesh; Raman, Kothanda; Bhushan, Manindra; Pal, Manoj

    2015-01-01

    The main purpose of this study is to know the effect of three different photon energies viz., 6, 10, and 15 mega voltage (MV) on RapidArc (RA) planning for deep-seated cervix tumor and to develop clinically acceptable RA plans with suitable photon energy. RA plans were generated for 6, 10, and 15 MV photon energies for twenty patients reported with cervix carcinoma. RA plans were evaluated in terms of planning target volume (PTV) coverage, dose to organs at risk (OARs), conformity index (CI), homogeneity index (HI), gradient measure, external volume index of dose distribution produced, total number of monitor units (MUs), nontumor integral dose (ID), and low dose volume of normal tissue. A two-sample paired t-test was performed to compare the dosimetric parameters of RA plans. Irrespective of photon energy used for RA planning, plans were dosimetrically similar in terms of PTV coverage, OARs sparing, CI and HI. The numbers of MUs were 13.4 ± 1.4% and 18.2 ± 1.5% higher and IDs were 2.7 ± 0.8% and 3.7 ± 0.9% higher in 6 MV plans in comparison to that in the 10 and 15 MV plans, respectively. V1Gy, V2Gy, V3Gy, and V4Gy were higher in 6 MV plans in comparison to that in 10 and 15 MV plans. Based on this study, 6 MV photon beam is a good choice for RA planning in case of cervix carcinoma, as it does not deliver additional exposure to patients caused by photoneutrons produced in high energy beams. PMID:26865756

  9. On-ground calibration of AGILE-GRID with a photon beam: results and lessons for the future

    NASA Astrophysics Data System (ADS)

    Cattaneo, P. W.; Rappoldi, A.

    2013-06-01

    On the AGILE satellite, there is the Gamma Ray Imaging Detector (GRID) consisting of a Silicon Tracker (ST), a Cesium Iodide Mini-Calorimeter and an Anti-Coincidence system of plastic scintillator bars. The ST needs a calibration with a γ-ray beam to validate the simulation used to calculate the detector response versus the energy and the direction of the γ rays. A tagged γ-ray beam line was designed at the Beam Test Facility of the Laboratori Nazionali of Frascati, generated by an electron beam through bremsstrahlung in a position-sensitive target. The γ-ray energy is deduced by the difference with the post-bremsstrahlung electron energy [P. W. Cattaneo, et al., Characterization of a tagged γ-ray beam line at the daΦne beam test facility, Nucl. Instr. and Meth. A 674 (2012) 55-66; P. W. Cattaneo, et al., First results about on-ground calibration of the silicon tracker for the agile satellite, Nucl. Instr. and Meth. A 630(1) (2011) 251-257.]. The electron energy is measured by a spectrometer consisting of a dipole magnet and an array of position sensitive silicon strip detectors, the Photon Tagging System (PTS). In this paper the setup and the calibration of AGILE performed in 2005 are described.

  10. High-Brightness Beam Generation and Characterization at the Advanced Photon Source Low-Energy Undulator Test Line Linac*

    NASA Astrophysics Data System (ADS)

    Lewellen, John; Biedron, Sandra; Borland, Michael; Hahne, Michael; Harkay, Katherine; Lumpkin, Alex; Milton, Stephen; Sereno, Nicholas; Travish, Gil

    2000-04-01

    Improvements to the Advanced Photon Source injector linac have been made to allow for the production and characterization of high-brightness beams in support of fourth-generation light source research. In particular, effort has been directed at generating beams suitable for use in the low-energy undulator test line (LEUTL) free-electron laser (FEL). We describe the enhancements to the linac operational and diagnostic capabilities that enabled self-amplified spontaneous emission (SASE) operation of the FEL at 530 nm. Electron beam measurement techniques and recent results will be discussed. Beam properties are measured under the same operational conditions as those used for FEL studies. The nominal FEL beam parameters are as follows: 217 MeV beam energy; less than 0.15 mm-mrad normalized emittance; 100 A peak current from a 0.7-nC charge at a 7-psec bunch. * Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38

  11. Photon-stimulated desorption yields from stainless steel and copper-plated beam tubes with various pretreatments

    SciTech Connect

    Foerster, C.L.; Halama, H.; Lanni, C. )

    1990-05-01

    Photon-stimulated desorption (PSD) from the walls of electron storage rings and associated beamlines imposes serious limits on their beam quality and beam lifetimes. Stainless steel (SS) is the most used material for beam lines and its use has become more dominant for dedicated light sources. Copper-plated SS beam pipes have been selected for the superconducting super collider (SSC) project. Three-meter-long tubes of 3, 8.8, and 10 cm diameter were prepared using the following pretreatments common in storage rings. The samples were chemically cleaned only, vacuum baked to 200 {degree}C, vacuum fired to 950 {degree}C, and argon--oxygen glow-discharge conditioned. A dedicated beam line at the National Synchrotron Light Source was used to measure PSD from the samples. Desorption was measured as a function of beam current during exposure to white light having a critical energy of 500 MeV. Our results are presented and compared with PSD from previous work on aluminum and SS here and at other laboratories. Glow-discharged SS yields the lowest PSD.

  12. Producing and measuring setup of the twin photons beams obtained by SPDC phenomenon

    NASA Astrophysics Data System (ADS)

    Rusu, Al.; Rusu, L.

    2012-08-01

    The quantum photon pairs, generated by spontaneous parametric down conversion phenomenon, promise a lot of applications. That's why, a setup including both producing and measuring instrumentation for quantum correlated photon pairs was designed and manufactured in Romania, too. Some significant solved technical challenges are presented. The described measurements and results prove the ability to generate and measure entangled photon pairs. The setup is ready for experimental research and technological development activities.

  13. A direction-selective flattening filter for clinical photon beams. Monte Carlo evaluation of a new concept

    NASA Astrophysics Data System (ADS)

    Chofor, Ndimofor; Harder, Dietrich; Willborn, Kay; Rühmann, Antje; Poppe, Björn

    2011-07-01

    A new concept for the design of flattening filters applied in the generation of 6 and 15 MV photon beams by clinical linear accelerators is evaluated by Monte Carlo simulation. The beam head of the Siemens Primus accelerator has been taken as the starting point for the study of the conceived beam head modifications. The direction-selective filter (DSF) system developed in this work is midway between the classical flattening filter (FF) by which homogeneous transversal dose profiles have been established, and the flattening filter-free (FFF) design, by which advantages such as increased dose rate and reduced production of leakage photons and photoneutrons per Gy in the irradiated region have been achieved, whereas dose profile flatness was abandoned. The DSF concept is based on the selective attenuation of bremsstrahlung photons depending on their direction of emission from the bremsstrahlung target, accomplished by means of newly designed small conical filters arranged close to the target. This results in the capture of large-angle scattered Compton photons from the filter in the primary collimator. Beam flatness has been obtained up to any field cross section which does not exceed a circle of 15 cm diameter at 100 cm focal distance, such as 10 × 10 cm2, 4 × 14.5 cm2 or less. This flatness offers simplicity of dosimetric verifications, online controls and plausibility estimates of the dose to the target volume. The concept can be utilized when the application of small- and medium-sized homogeneous fields is sufficient, e.g. in the treatment of prostate, brain, salivary gland, larynx and pharynx as well as pediatric tumors and for cranial or extracranial stereotactic treatments. Significant dose rate enhancement has been achieved compared with the FF system, with enhancement factors 1.67 (DSF) and 2.08 (FFF) for 6 MV, and 2.54 (DSF) and 3.96 (FFF) for 15 MV. Shortening the delivery time per fraction matters with regard to workflow in a radiotherapy department

  14. Statistical connection of binomial photon counting and photon averaging in high dynamic range beam-scanning microscopy

    PubMed Central

    Muir, Ryan D.; Kissick, David J.; Simpson, Garth J.

    2012-01-01

    Data from photomultiplier tubes are typically analyzed using either counting or averaging techniques, which are most accurate in the dim and bright signal limits, respectively. A statistical means of adjoining these two techniques is presented by recovering the Poisson parameter from averaged data and relating it to the statistics of binomial counting from Kissick et al. [Anal. Chem. 82, 10129 (2010)]. The point at which binomial photon counting and averaging have equal signal to noise ratios is derived. Adjoining these two techniques generates signal to noise ratios at 87% to approaching 100% of theoretical maximum across the full dynamic range of the photomultiplier tube used. The technique is demonstrated in a second harmonic generation microscope. PMID:22535131

  15. Statistical connection of binomial photon counting and photon averaging in high dynamic range beam-scanning microscopy.

    PubMed

    Muir, Ryan D; Kissick, David J; Simpson, Garth J

    2012-04-23

    Data from photomultiplier tubes are typically analyzed using either counting or averaging techniques, which are most accurate in the dim and bright signal limits, respectively. A statistical means of adjoining these two techniques is presented by recovering the Poisson parameter from averaged data and relating it to the statistics of binomial counting from Kissick et al. [Anal. Chem. 82, 10129 (2010)]. The point at which binomial photon counting and averaging have equal signal to noise ratios is derived. Adjoining these two techniques generates signal to noise ratios at 87% to approaching 100% of theoretical maximum across the full dynamic range of the photomultiplier tube used. The technique is demonstrated in a second harmonic generation microscope. PMID:22535131

  16. Determination of the Linear Polarization of the Hall-B Tagged Photon Beam at Jefferson Lab

    SciTech Connect

    Sabintsev, A. A.; Livingston, K.

    2011-10-24

    The JLab CLAS g9a/FROST experiments are double polarization measurements that have accumulated photo-production data using linearly polarized, tagged photons incident on a longitudinally polarized, frozen spin butanol target. The analysis of the resulting coherent peaks was used to determine the photon polarization, which is in agreement with phenomenological calculations.

  17. Determination of the linear polarization of the Hall-B tagged photon beam at Jefferson Lab

    SciTech Connect

    A.A. Sabintsev, K. Livingston

    2011-10-01

    The JLab CLAS g9a/FROST experiments are double polarization measurements that have accumulated photo-production data using linearly polarized, tagged photons incident on a longitudinally polarized, frozen spin butanol target. The analysis of the resulting coherent peaks was used to determine the photon polarization, which is in agreement with phenomenological calculations.

  18. Development of high intensity laser-electron photon beams up to 2.9 GeV at the SPring-8 LEPS beamline

    NASA Astrophysics Data System (ADS)

    Muramatsu, N.; Kon, Y.; Daté, S.; Ohashi, Y.; Akimune, H.; Chen, J. Y.; Fujiwara, M.; Hasegawa, S.; Hotta, T.; Ishikawa, T.; Iwata, T.; Kato, Y.; Kohri, H.; Matsumura, T.; Mibe, T.; Miyachi, Y.; Morino, Y.; Nakano, T.; Nakatsugawa, Y.; Ohkuma, H.; Ohta, T.; Oka, M.; Sawada, T.; Wakai, A.; Yonehara, K.; Yoon, C. J.; Yorita, T.; Yosoi, M.

    2014-02-01

    A laser-Compton backscattering beam, which we call a 'Laser-Electron Photon' beam, was upgraded at the LEPS beamline of SPring-8. We accomplished the gains in backscattered photon beam intensities by factors of 1.5-1.8 with the injection of two adjacent laser beams or a higher power laser beam into the storage ring. The maximum energy of the photon beam was also extended from 2.4 GeV to 2.9 GeV with deep-ultraviolet lasers. The upgraded beams have been utilized for hadron photoproduction experiments at the LEPS beamline. Based on the developed methods, we plan the simultaneous injection of four high power laser beams at the LEPS2 beamline, which has been newly constructed at SPring-8. As a simulation result, we expect an order of magnitude higher intensities close to 107 s-1 and 106 s-1 for tagged photons up to 2.4 GeV and 2.9 GeV, respectively.

  19. Validation of GEANT4 simulations for percentage depth dose calculations in heterogeneous media by using small photon beams from the 6-MV Cyberknife: Comparison with photon beam dosimetry with EBT2 film

    NASA Astrophysics Data System (ADS)

    Lee, Chung Il; Yoon, Sei-Chul; Shin, Jae Won; Hong, Seung-Woo; Suh, Tae Suk; Min, Kyung Joo; Lee, Sang Deok; Chung, Su Mi; Jung, Jae-Yong

    2015-04-01

    Percentage depth dose (PDD) distributions in heterogeneous phantoms with lung and soft bone equivalent media are studied by using the GEANT4 Monte Carlo code. For lung equivalent media, Balsa wood is used, and for soft bone equivalent media, a compound material with epoxy resin, hardener and calcium carbonate is used. Polystyrene slabs put together with these materials are used as a heterogeneous phantom. Dose measurements are performed with Gafchromic EBT2 film by using photon beams from the 6-MV CyberKnife at the Seoul Uridul Hospital. The cone sizes of the photon beams are varied from 5 to 10 to 30 mm. When the Balsa wood is inserted in the phantom, the dose measured with EBT2 film is found to be significantly different from the dose without the EBT2 film in and the dose beyond the Balsa wood region, particularly for small field sizes. On the other hand, when the soft bone equivalent material is inserted in the phantom, the discrepancy between the dose measured with EBT2 film and the dose without EBT2 film can be seen only in the region of the soft bone equivalent material. GEANT4 simulations are done with and without the EBT2 film to compare the simulation results with measurements. The GEANT4 simulations including EBT2 film are found to agree well with the measurements for all the cases within an error of 2.2%. The results of the present study show that GEANT4 gives reasonable results for the PDD calculations in heterogeneous media when using photon beams produced by the 6-MV CyberKnife

  20. Effect of the thermoplastic masks on dose distribution in the build-up region for photon beams

    NASA Astrophysics Data System (ADS)

    Półtorak, Michał; Fujak, Edyta; Kukołowicz, Paweł

    2016-03-01

    The aim of the study was to investigate the influence of thermoplastic masks material (Klarity Medical&Equipment Co., Guangzhou, China) with different diameters of holes (ϕ 0.25 cm and ϕ 0.40 cm) on the dose distribution in the build-up region for photon beams. Measurements were made for external radiation beams produced by the linear accelerator (TrueBeam, Varian Medical Systems, Inc., Palo Alto, CA, USA) using the Markus parallel plane ionization chamber and the Unidos electrometer (both from PTW, Freiburg, Germany). Measurements were made in a solid water phantom for two photon energies 6 MV and 15 MV, at 90 cm source to skin distance, for four fields of 5 cm × 5 cm, 10 cm × 10 cm, 15 cm × 15 cm and 20 cm × 20 cm. Compared to the open field, the maximum dose with mask was closer to the surface of the phantom by about 1.4 mm and 1.2 mm for 6 MV and 15 MV X-Rays, respectively. The surface dose increase from 10% to 42% for 6 MV and from 5% to 28% for 15 MV X-Rays.

  1. 6-MV photon beam modeling for the Varian Clinac iX by using the Geant4 virtual jaw

    NASA Astrophysics Data System (ADS)

    Kim, Byung Yong; Kim, Hyung Dong; Kim, Dong Ho; Baek, Jong Geun; Moon, Su Ho; Rho, Gwang Won; Kang, Jeong Ku; Kim, Sung Kyu

    2015-07-01

    Most virtual source models (VSMs), with the exception of the patient-dependent secondary collimator (jaw), use beam modeling. Unlike other components of the treatment head, the jaw absorbs many photons generated by bremsstrahlung, which decreases the efficiency of the simulation. In the present study, a new method of beam modeling using a virtual jaw was applied to improve the calculation efficiency of VSM. This new method of beam modeling was designed so that the interaction was not generated in the jaw. The results for the percentage depth dose and the profile of the virtual jaw VSM calculated in a homogeneous water phantom agreed with the measurement results for the CC13 cylinder-type ion chamber to within an error of 2%, and the 80-20% penumbra width agreed with the measurement results to within an error of 0.6 mm. Compared with the existing VSM, in which a great number of photons are absorbed, the calculation efficiency of the VSM using the virtual jaw is expected to be increased by approximately 67%.

  2. Using a photon phase-space source for convolution/superposition dose calculations in radiation therapy

    NASA Astrophysics Data System (ADS)

    Naqvi, Shahid A.; D'Souza, Warren D.; Earl, Matthew A.; Ye, Sung-Joon; Shih, Rompin; Li, X. Allen

    2005-09-01

    For a given linac design, the dosimetric characteristics of a photon beam are determined uniquely by the energy and radial distributions of the electron beam striking the x-ray target. However, in the usual commissioning of a beam from measured data, a large number of variables can be independently tuned, making it difficult to derive a unique and self-consistent beam model. For example, the measured dosimetric penumbra in water may be attributed in various proportions to the lateral secondary electron range, the focal spot size and the transmission through the tips of a non-divergent collimator; the head-scatter component in the tails of the transverse profiles may not be easy to resolve from phantom scatter and head leakage; and the head-scatter tails corresponding to a certain extra-focal source model may not agree self-consistently with in-air output factors measured on the central axis. To reduce the number of adjustable variables in beam modelling, we replace the focal and extra-focal sources with a single phase-space plane scored just above the highest adjustable collimator in a EGS/BEAM simulation of the linac. The phase-space plane is then used as photon source in a stochastic convolution/superposition dose engine. A photon sampled from the uncollimated phase-space plane is first propagated through an arbitrary collimator arrangement and then interacted in the simulation phantom. Energy deposition kernel rays are then randomly issued from the interaction points and dose is deposited along these rays. The electrons in the phase-space file are used to account for electron contamination. 6 MV and 18 MV photon beams from an Elekta SL linac are used as representative examples. Except for small corrections for monitor backscatter and collimator forward scatter for large field sizes (<0.5% with <20 × 20 cm2 field size), we found that the use of a single phase-space photon source provides accurate and self-consistent results for both relative and absolute dose

  3. Calculation of single-beam two-photon absorption rate of lanthanides: Effective operator method and perturbative expansion

    SciTech Connect

    Duan, C.-K.; Ruan Gang; Reid, Michael F.

    2004-11-01

    Perturbative contributions to single-beam two-photon transition rates may be divided into two types. The first, involving low-energy intermediate states, require a high-order perturbation treatment, or an exact diagonalization. The other, involving high-energy intermediate states, only require a low-order perturbation treatment. We show how to partition the effective transition operator into two terms, corresponding to these two types, in such a way that a many-body perturbation expansion may be generated that obeys the linked cluster theorem and has a simple diagrammatic representation.

  4. Design of high heat load white-beam slits for wiggler/undulator beamlines at the Advanced Photon Source

    SciTech Connect

    Shu, D.; Tcheskidov, V.; Nian, T.; Haeffner, D.R.; Alp, E.E.; Ryding, D.; Collins, J.; Li, Y.; Kuzay, T.M.

    1994-12-01

    A set of horizontal and vertical white-beam slits has been designed for the Advanced Photon Source wiggler/undulator beamlines at Argonne National Laboratory. While this slit set can handle the high heat flux from on e APS undulator source, it has large enough aperture to be compatible with a wiggler source also. A grazing-incidence, knife-edge configuration has been used in the design to eliminate downstream X-ray scattering. Enhanced heat transfer technology has been used in the water-cooling system. A unique stepping parallelogram driving structure provides precise vertical slit motion with large optical aperture. The full design detail is presented in this paper.

  5. Beaming photons with spin and orbital angular momentum via a dipole-coupled plasmonic spiral antenna.

    PubMed

    Rui, Guanghao; Nelson, Robert L; Zhan, Qiwen

    2012-08-13

    We analytically and numerically study the emission properties of an electric dipole coupled to a plasmonic spiral structure with different pitch. As a transmitting antenna, the spiral structure couples the radiation from the electric dipole into circularly polarized emitted photons in the far field. The spin carried by the emitted photons is determined by the handedness of the spiral antenna. By increasing the spiral pitch in the unit of surface plasmon wavelength, these circularly polarized photons also gain orbital angular momentum with different topological charges. This phenomenon is attributed to the presence of a geometric phase arising from the interaction of light from point source with the anisotropic spiral structure. The circularly polarized vortex emission from such optically coupled spiral antenna also has high directivity, which may find important applications in quantum optical information, single molecule sensing, and integrated photonic circuits. PMID:23038521

  6. Radiation hardness test of the Philips Digital Photon Counter with proton beam

    NASA Astrophysics Data System (ADS)

    Barnyakov, M. Yu.; Frach, T.; Kononov, S. A.; Kuyanov, I. A.; Prisekin, V. G.

    2016-07-01

    The Philips Digital Photon Counter (DPC) is a silicon photomultiplier combining Geiger-mode avalanche photodiodes (G-APD) and dedicated readout electronics in the same chip. The DPC is a promising photon sensor for future RICH detectors. A known issue of G-APD is its sensitivity to radiation damage. Two DPC sensors were tested using 800 MeV/c protons. An increase of dark counting rate with proton fluence up to 4 ·1011cm-2 has been measured.

  7. Two-photon excitation in scattering media by spatiotemporally shaped beams and their application in optogenetic stimulation

    PubMed Central

    Bègue, Aurélien; Papagiakoumou, Eirini; Leshem, Ben; Conti, Rossella; Enke, Leona; Oron, Dan; Emiliani, Valentina

    2013-01-01

    The use of wavefront shaping to generate extended optical excitation patterns which are confined to a predetermined volume has become commonplace on various microscopy applications. For multiphoton excitation, three-dimensional confinement can be achieved by combining the technique of temporal focusing of ultra-short pulses with different approaches for lateral light shaping, including computer generated holography or generalized phase contrast. Here we present a theoretical and experimental study on the effect of scattering on the propagation of holographic beams with and without temporal focusing. Results from fixed and acute cortical slices show that temporally focused spatial patterns are extremely robust against the effects of scattering and this permits their three-dimensionally confined excitation for depths more than 500 µm. Finally we prove the efficiency of using temporally focused holographic beams in two-photon stimulation of neurons expressing the red-shifted optogenetic channel C1V1. PMID:24409387

  8. Electrical conductivity of cluster-assembled carbon/titania nanocomposite films irradiated by highly focused vacuum ultraviolet photon beams

    SciTech Connect

    Amati, M.; Lenardi, C.; Agostino, R. G.; Caruso, T.; Ducati, C.; La Rosa, S.; Bongiorno, G.; Cassina, V.; Podesta, P.; Ravagnan, L.; Piseri, P.; Milani, P.

    2007-03-15

    We investigated the electrical transport properties of nanostructured carbon and carbon/titanium oxide nanocomposite films produced by supersonic cluster beam deposition and irradiated by highly focused vacuum UV photon beam. We have observed a relevant increase of the density of states at Fermi level, suggesting that the films acquire a 'metallic' character. This is confirmed by the increment of the conductivity of four orders of magnitude for pure nanostructured carbon films and at least eight orders of magnitude for films containing 9 at. % of titanium. A partial reversibility of the process is observed by exposing the modified films to molecular oxygen or directly to air. We demonstrate the capability of writing micrometric conductive strips (2-3 {mu}m width and 60 {mu}m length) and controlling the variation of the conductivity as a function of the titanium concentration.

  9. Beaming circularly polarized photons from quantum dots coupled with plasmonic spiral antenna.

    PubMed

    Rui, Guanghao; Chen, Weibin; Abeysinghe, Don C; Nelson, Robert L; Zhan, Qiwen

    2012-08-13

    Coupling nanoscale emitters via optical antennas enables comprehensive control of photon emission in terms of intensity, directivity and polarization. In this work we report highly directional emission of circularly polarized photons from quantum dots coupled to a spiral optical antenna. The structural chirality of the spiral antenna imprints spin state to the emitted photons. Experimental results reveal that a circular polarization extinction ratio of 10 is obtainable. Furthermore, increasing the number of turns of the spiral gives rise to higher antenna gain and directivity, leading to higher field intensity and narrower angular width of emission pattern in the far field. For a five-turn Archimedes' spiral antenna, field intensity increase up to 70-fold simultaneously with antenna directivity of 11.7 dB has been measured in the experiment. The highly directional circularly polarized photon emission from such optically coupled spiral antenna may find important applications in single molecule sensing, quantum optics information processing and integrated photonic circuits as a nanoscale spin photon source. PMID:23038571

  10. A possibility for using an APPLE undulator to generate a photon beam with transverse optical modes.

    SciTech Connect

    Sasaki, S.; McNulty, I.; Shimada, T.; JAEA

    2008-01-01

    We investigate use of an APPLE-type undulator for generating Laguerre-Gaussian (LG) and Hermite-Gaussian (HG) mode beams. We find that the second harmonic radiation in the circular mode corresponds to an LG beam with l=1, and the second harmonic in the linear mode corresponds to an HG beam with l=1. The combination of an APPLE undulator and conventional monochromator optics may provide an opportunity for a new type of experimental research in the synchrotron radiation community.

  11. Photon detection system for laser spectroscopy experiments with cooled/bunched beams at BECOLA facility at NSCL

    NASA Astrophysics Data System (ADS)

    Hughes, Maximilian; Minamisono, Kei; Mantica, Paul; Rossi, Dominic; Ryder, Caleb; Klose, Andrew; Tarazona, David; Strum, Ryan; Bollen, Georg; Ringle, Ryan; Barquest, Brad; Geppert, Christopher

    2013-10-01

    The BEam COoler and LAser spectroscopy (BECOLA) facility at NSCL is designed to determine fundamental properties of the atomic nucleus such as the charge radii, the spin and electromagnetic moments. Commissioning tests of BECOLA has been completed using a stable 39K beam produced from an offline ion source. The 39K beam was cooled and bunched and propagated collinearly with laser light. The resulting fluorescence was detected in a photomultiplier tube (PMT)sensitive to the wavelength of D1 transition of 39K The PMT was cooled to minimize background due to dark counts. The resulting fluorescence light was measured as a function of laser frequency and time relative to the 39K beam bunch. An EPICS-based Control Systems Studio (CSS) was used for data acquisition and the software package Root was used for data analysis. The performance characteristics of the photon detection system as well as the laser spectroscopy of bunched 39K will be discussed. Work was supported in part by the National Science Foundation, Grant PHY-11-02511.

  12. Insertion device and beam line plans for the Advanced Photon Source: A report and recommendations by the Insertion Device and Beam Line Planning Committee

    SciTech Connect

    Not Available

    1988-02-01

    In the 7-GeV Advanced Photon Source (APS) Conceptual Design Report (CDR), fifteen complete experimental beam lines were specified in order to establish a representative technical and cost base for the components involved. In order to optimize the composition of the insertion devices and the beam line, these funds are considered a ''Trust Fund.'' The present report evaluates the optimization for the distribution of these funds so that the short- and long-term research programs will be most productive, making the facility more attractive from the user's point of view. It is recommended that part of the ''Trust Fund'' be used for the construction of the insertion devices, the front-end components, and the first-optics, minimizing the cost to potential users of completing a beam line. In addition, the possibility of cost savings resulting from replication and standardization of high multiplicity components (such as IDs, front ends, and first-optics instrumentation) is addressed. 2 refs., 5 tabs.

  13. Simulation of the 6 MV Elekta Synergy Platform linac photon beam using Geant4 Application for Tomographic Emission.

    PubMed

    Didi, Samir; Moussa, Abdelilah; Yahya, Tayalati; Mustafa, Zerfaoui

    2015-01-01

    The present work validates the Geant4 Application for Tomographic Emission Monte Carlo software for the simulation of a 6 MV photon beam given by Elekta Synergy Platform medical linear accelerator treatment head. The simulation includes the major components of the linear accelerator (LINAC) with multi-leaf collimator and a homogeneous water phantom. Calculations were performed for the photon beam with several treatment field sizes ranging from 5 cm × 5 cm to 30 cm × 30 cm at 100 cm distance from the source. The simulation was successfully validated by comparison with experimental distributions. Good agreement between simulations and measurements was observed, with dose differences of about 0.02% and 2.5% for depth doses and lateral dose profiles, respectively. This agreement was also emphasized by the Kolmogorov-Smirnov goodness-of-fit test and by the gamma-index comparisons where more than 99% of the points for all simulations fulfill the quality assurance criteria of 2 mm/2%. PMID:26500399

  14. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams

    SciTech Connect

    McEwen, Malcolm; DeWerd, Larry; Ibbott, Geoffrey; Followill, David; Rogers, David W. O.; Seltzer, Stephen; Seuntjens, Jan

    2014-04-15

    An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new k{sub Q} data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of N{sub D,w} coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.

  15. A high-pressure polarized 3He gas target for nuclear-physics experiments using a polarized photon beam

    NASA Astrophysics Data System (ADS)

    Ye, Q.; Laskaris, G.; Chen, W.; Gao, H.; Zheng, W.; Zong, X.; Averett, T.; Cates, G. D.; Tobias, W. A.

    2010-04-01

    Following the first experiment on three-body photodisintegration of polarized 3He utilizing circularly polarized photons from High-Intensity Gamma Source (HI γ S) at Duke Free Electron Laser Laboratory (DFELL), a new high-pressure polarized 3He target cell made of pyrex glass coated with a thin layer of sol-gel doped with aluminum nitrate nonahydrate has been built in order to reduce the photon beam-induced background. The target is based on the technique of spin exchange optical pumping of hybrid rubidium and potassium and the highest polarization achieved is ˜ 62% determined from both NMR-AFP and EPR polarimetries. The phenomenological parameter that reflects the additional unknown spin relaxation processes, X , is estimated to be ˜ 0.10 and the performance of the target is in good agreement with theoretical predictions. We also present beam test results from this new target cell and the comparison with the GE180 3He target cell used previously at HI γ S. This is the first time that the sol-gel coating technique has been used in a polarized 3He target for nuclear-physics experiments.

  16. Improved Survival of Mice After Total Body Irradiation with 10 MV Photon, 2400 MU/min SRS Beam

    PubMed Central

    KALASH, RONNY; BERHANE, HEBIST; YANG, YONG; EPPERLY, MICHAEL W.; WANG, HONG; DIXON, TRACY; RHIEU, BYUNG; GREENBERGER, JOEL S.; HUQ, MOHAMMED SAIFUL

    2014-01-01

    Background/Aim We evaluated the radiobiological effects of stereotactic radiosurgery (SRS) photon beams on survival of C57BL/6NTac mice following total body irradiation. Materials and Methods Survival of Lewis lung carcinoma (3LL) cells was tested after irradiation using 6 MV: 300 MU/min or 1400 MU/min; or 10 MV: 300 MU/min or 2400 MU/min. Survival of C57BL/6NTac mice after a dose which is lethal to 50% of the mice in 30 days (LD50/30) (9.25 Gy) total body irradiation (TBI) and 21 Gy to orthotopic 3LL tumors was tested. We quantitated levels of organ-specific gene transcripts by Real Time Polymerase Chain Reaction (RT-PCR). Results While 3LL cell survival and inhibition of orthotopic tumor growth was uniform, 10 MV photons at 2400 MU/min TBI led to significantly greater survival (p=0.0218), with higher levels of intestinal (Sod2), (Gpx1), (Nrf2), and (NFκB) RNA transcripts. Conclusion Clinical 10 MV-2400 cGy/min SRS beams led to unexpected protection of mice on TBI and increased radioprotective gene transcripts. PMID:24425830

  17. Simulation of the 6 MV Elekta Synergy Platform linac photon beam using Geant4 Application for Tomographic Emission

    PubMed Central

    Didi, Samir; Moussa, Abdelilah; Yahya, Tayalati; Mustafa, Zerfaoui

    2015-01-01

    The present work validates the Geant4 Application for Tomographic Emission Monte Carlo software for the simulation of a 6 MV photon beam given by Elekta Synergy Platform medical linear accelerator treatment head. The simulation includes the major components of the linear accelerator (LINAC) with multi-leaf collimator and a homogeneous water phantom. Calculations were performed for the photon beam with several treatment field sizes ranging from 5 cm × 5 cm to 30 cm × 30 cm at 100 cm distance from the source. The simulation was successfully validated by comparison with experimental distributions. Good agreement between simulations and measurements was observed, with dose differences of about 0.02% and 2.5% for depth doses and lateral dose profiles, respectively. This agreement was also emphasized by the Kolmogorov–Smirnov goodness-of-fit test and by the gamma-index comparisons where more than 99% of the points for all simulations fulfill the quality assurance criteria of 2 mm/2%. PMID:26500399

  18. FEC coding for QKD at higher photon flux levels based on spatial entanglement of twin beams in PDC

    NASA Astrophysics Data System (ADS)

    Daneshgaran, Fred; Mondin, Marina; Bari, Inam

    2014-10-01

    A major problem with conventional QKD techniques is the raw key transmission rate which for acceptable level of security is generally low. One way to overcome this problem is to create either directly or indirectly a number of parallel QKD transmission channels thus achieving a rate multiplicity equal to the number of parallel channels. This paper explores how a number of parallel Discrete Memoryless Channels (DMCs) can be created from imaging twin beams from a Parametric Down Conversion (PDC) process and examines the performance of FEC coding for information reconciliation over the resulting parallel channels. Twin beams exhibit quantum correlations that has been effectively used as a tool for many applications including calibration of single photon detectors. By now, detection of multimode spatial correlations is a mature field and in principle, only depends on the transmission and detection efficiency of the devices and the channel. In,1-3 the authors utilized their know-how on almost perfect selection of modes of pairwise correlated entangled beams and the optimization of the noise reduction to below the shot-noise level, for absolute calibration of Charge Coupled Device (CCD) cameras. The same basic principle is currently being considered by the same authors for possible use in Quantum Key Distribution (QKD). The main advantage in such an approach would be the ability to work with much higher photon fluxes than that of a single photon regime that is theoretically required for discrete variable QKD applications (in practice, very weak laser pulses with mean photon count below one are used), and the fact that the QKD data rate is increased significantly since multiple equivalent parallel channels result from quantization of symmetric regions into super-pixels. The natural setup of quantization of CCD detection area and subsequent measurement of the correlation statistic needed to detect the presence of the eavesdropper Eve, leads to a number of parallel QKD

  19. Direct measurements of two photon exchange on lepton-proton elastic scattering using simultaneous electron-positron beams in CLAS

    NASA Astrophysics Data System (ADS)

    Adikaram, Dasuni Kalhari

    The electric (GE) and magnetic ( GM) form factors of the proton are fundamental observables which characterize its charge and magnetization distributions. There are two methods to measure the proton form factors: the Rosenbluth separation method and the polarization transfer technique. However, the ratio of the electric and magnetic form factors measured by those methods significantly disagree at momentum transfer Q2 > 1 GeV2. The most likely explanation of this discrepancy is the inclusion of two-photon exchange (TPE) amplitude contributions to the elastic electron-proton cross section which significantly changes the extraction of GE from the Rosenbluth separation measurement. The Jefferson Lab CLAS TPE experiment determined the TPE contribution by measuring the ratio of positron-proton to electron-proton elastic scattering cross sections. The primary electron beam was used to create an intense bremsstrahlung photon beam. Some of the photons were then converted to a mixed e+/ e- beam which then interacted with a liquid hydrogen target. The e+p and e-p events were detected by the CLAS (CEBAF Large Acceptance Spectrometer). The elastic cross section ratios ((sigma( e+p)/(sigma(e -p)) were measured over a wide range of virtual photon polarization epsilon and Q2. The cross section ratios displayed a strong epsilon dependence at Q2 = 1.45 GeV2. There is no significant Q2 dependence observed at epsilon = 0.45. The results are consistent with a recent measurement at the VEPP-3 lepton storage ring in Novosibirsk and with the hadronic calculation by Blunders, Melnitchouk and Tjon. The hadronic calculation resolves the disagreement between the Rosenbluth separation and polarization transfer extractions of GE/GM at Q2 up to 2 -- 3 GeV2. Applying the GLAS TPE correction to the Rosenbluth cross section measurements significantly decreases the extracted value of GE and brings it into good agreement with the polarization transfer measurement at Q2˜1.75 GeV2. Thus, these

  20. Monte Carlo simulations and benchmark measurements on the response of TE(TE) and Mg(Ar) ionization chambers in photon, electron and neutron beams

    NASA Astrophysics Data System (ADS)

    Lin, Yi-Chun; Huang, Tseng-Te; Liu, Yuan-Hao; Chen, Wei-Lin; Chen, Yen-Fu; Wu, Shu-Wei; Nievaart, Sander; Jiang, Shiang-Huei

    2015-06-01

    The paired ionization chambers (ICs) technique is commonly employed to determine neutron and photon doses in radiology or radiotherapy neutron beams, where neutron dose shows very strong dependence on the accuracy of accompanying high energy photon dose. During the dose derivation, it is an important issue to evaluate the photon and electron response functions of two commercially available ionization chambers, denoted as TE(TE) and Mg(Ar), used in our reactor based epithermal neutron beam. Nowadays, most perturbation corrections for accurate dose determination and many treatment planning systems are based on the Monte Carlo technique. We used general purposed Monte Carlo codes, MCNP5, EGSnrc, FLUKA or GEANT4 for benchmark verifications among them and carefully measured values for a precise estimation of chamber current from absorbed dose rate of cavity gas. Also, energy dependent response functions of two chambers were calculated in a parallel beam with mono-energies from 20 keV to 20 MeV photons and electrons by using the optimal simple spherical and detailed IC models. The measurements were performed in the well-defined (a) four primary M-80, M-100, M120 and M150 X-ray calibration fields, (b) primary 60Co calibration beam, (c) 6 MV and 10 MV photon, (d) 6 MeV and 18 MeV electron LINACs in hospital and (e) BNCT clinical trials neutron beam. For the TE(TE) chamber, all codes were almost identical over the whole photon energy range. In the Mg(Ar) chamber, MCNP5 showed lower response than other codes for photon energy region below 0.1 MeV and presented similar response above 0.2 MeV (agreed within 5% in the simple spherical model). With the increase of electron energy, the response difference between MCNP5 and other codes became larger in both chambers. Compared with the measured currents, MCNP5 had the difference from the measurement data within 5% for the 60Co, 6 MV, 10 MV, 6 MeV and 18 MeV LINACs beams. But for the Mg(Ar) chamber, the derivations reached 7

  1. Focused-ion-beam overlay-patterning of three-dimensional diamond structures for advanced single-photon properties

    SciTech Connect

    Jiang, Qianqing; Liu, Dongqi; Liu, Gangqin; Chang, Yanchun; Li, Wuxia E-mail: czgu@aphy.iphy.ac.cn; Pan, Xinyu; Gu, Changzhi E-mail: czgu@aphy.iphy.ac.cn

    2014-07-28

    Sources of single photons are of fundamental importance in many applications as to provide quantum states for quantum communication and quantum information processing. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, even at room temperature. However, the efficiency of photon collection of the color centers in bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, diamond structuring has been investigated by various methods. Among them, focused-ion-beam (FIB) direct patterning has been recognized as the most favorable technique. But it has been noted that diamond tends to present significant challenges in FIB milling, e.g., the susceptibility of forming charging related artifacts and topographical features. In this work, periodically-positioned-rings and overlay patterning with stagger-superimposed-rings were proposed to alleviate some problems encountered in FIB milling of diamond, for improved surface morphology and shape control. Cross-scale network and uniform nanostructure arrays have been achieved in single crystalline diamond substrates. High quality diamond solid immersion lens and nanopillars were sculptured with a nitrogen-vacancy center buried at the desired position. Compared with the film counterpart, an enhancement of about ten folds in single photon collection efficiency was achieved with greatly improved signal to noise ratio. All these results indicate that FIB milling through over-lay patterning could be an effective approach to fabricate diamond structures, potentially for quantum information studies.

  2. Focused-ion-beam overlay-patterning of three-dimensional diamond structures for advanced single-photon properties

    NASA Astrophysics Data System (ADS)

    Jiang, Qianqing; Liu, Dongqi; Liu, Gangqin; Chang, Yanchun; Li, Wuxia; Pan, Xinyu; Gu, Changzhi

    2014-07-01

    Sources of single photons are of fundamental importance in many applications as to provide quantum states for quantum communication and quantum information processing. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, even at room temperature. However, the efficiency of photon collection of the color centers in bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, diamond structuring has been investigated by various methods. Among them, focused-ion-beam (FIB) direct patterning has been recognized as the most favorable technique. But it has been noted that diamond tends to present significant challenges in FIB milling, e.g., the susceptibility of forming charging related artifacts and topographical features. In this work, periodically-positioned-rings and overlay patterning with stagger-superimposed-rings were proposed to alleviate some problems encountered in FIB milling of diamond, for improved surface morphology and shape control. Cross-scale network and uniform nanostructure arrays have been achieved in single crystalline diamond substrates. High quality diamond solid immersion lens and nanopillars were sculptured with a nitrogen-vacancy center buried at the desired position. Compared with the film counterpart, an enhancement of about ten folds in single photon collection efficiency was achieved with greatly improved signal to noise ratio. All these results indicate that FIB milling through over-lay patterning could be an effective approach to fabricate diamond structures, potentially for quantum information studies.

  3. SU-E-T-234: Modulated Photon Radiotherapy (XMRT):The Impact of Incorporating Energy Modulation Into Intensity Modulated Radiotherapy (IMRT) Optimization

    SciTech Connect

    McGeachy, P; Khan, R

    2014-06-01

    Purpose: To develop a new radiotherapy plan optimization technique that, for a given organ geometry, will find the optimal photon beam energies and fluences to produce a desirable dose distribution. This new modulated (both in energy and fluence) photon radiotherapy (XMRT) was compared with intensity modulated radiotherapy (IMRT) for a simple organ geometry. Methods: The XMRT optimization was formulated using a linear programming approach where the objective function is the mean dose to the healthy organs and dose-point constraints were assigned to each organ of interest. The organ geometry consisted of a target, two organs at risk (OARs), and normal tissue. A seven-equispaced-coplanar beam arrangement was used. For conventional IMRT, only 6 MV beams were available, while XMRT was optimized using 6 and 18 MV beams. A prescribed dose (PD) of 72 GY was assigned to the target, with upper and lower bounds of 110% and 95% of the PD, respectively. Both OARs were assigned a maximum dose of 64 Gy, while the normal tissue was assigned a maximum dose of 66 Gy. A numerical solver, Gurobi, generated solutions for the XMRT and IMRT problems. The dose-volume histograms from IMRT and XMRT solutions were compared. Results: The maximum, minimum, mean, and homogeneity of the dose to the target were comparable between IMRT and XMRT. Though IMRT had improved dose conformity relative to XMRT, XMRT reduced the mean dose to both OARs by more than 1 Gy. For normal tissue, an increase of 5 Gy in mean dose and 27 percent in integral dose was seen for IMRT relative to XMRT. Conclusion: This work demonstrates the benefits of simultaneously modulating photon beam energy and fluence using our XMRT approach in a given phantom geometry. While target coverage was comparable, dose to healthy structures was reduced using XMRT.

  4. A comparative dosimetric study on tangential photon beams, intensity-modulated radiation therapy (IMRT) and modulated electron radiotherapy (MERT) for breast cancer treatment

    NASA Astrophysics Data System (ADS)

    Ma, C.-M.; Ding, M.; Li, J. S.; Lee, M. C.; Pawlicki, T.; Deng, J.

    2003-04-01

    Recently, energy- and intensity-modulated electron radiotherapy (MERT) has garnered a growing interest for the treatment of superficial targets. In this work, we carried out a comparative dosimetry study to evaluate MERT, photon beam intensity-modulated radiation therapy (IMRT) and conventional tangential photon beams for the treatment of breast cancer. A Monte Carlo based treatment planning system has been investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. We have compared breast treatment plans generated using this home-grown treatment optimization and dose calculation software for these treatment techniques. The MERT plans were planned with up to two gantry angles and four nominal energies (6, 9, 12 and 16 MeV). The tangential photon treatment plans were planned with 6 MV wedged photon beams. The IMRT plans were planned using both multiple-gantry 6 MV photon beams or two 6 MV tangential beams. Our results show that tangential IMRT can reduce the dose to the lung, heart and contralateral breast compared to conventional tangential wedged beams (up to 50% reduction in high dose volume or 5 Gy in the maximum dose). MERT can reduce the maximum dose to the lung by up to 20 Gy and to the heart by up to 35 Gy compared to conventional tangential wedged beams. Multiple beam angle IMRT can significantly reduce the maximum dose to the lung and heart (up to 20 Gy) but it induces low and medium doses to a large volume of normal tissues including lung, heart and contralateral breast. It is concluded that MERT has superior capabilities to achieve dose conformity both laterally and in the depth direction, which will be well suited for treating superficial targets such as breast cancer.

  5. SU-E-T-220: Investigation of Intrafraction Changes to Photon Beam Profiles

    SciTech Connect

    Sterling, D; Ehler, E

    2014-06-01

    Purpose: Treatment Planning Systems model beam profiles to be static and independent of gantry angle. This work investigates how beam profiles change over time, with varying gantry angle. Methods: 200 cGy was delivered to ICProfiler (Sun Nuclear) on 2 Elekta Synergys and 1 Varian 21EX linacs at 8 gantry angles and 1 clockwise arc. Measurements were recorded 8 times per second. To investigate the initial portion of the beams, single-shot and multi-control-point beams were measured. The differences in beam profiles were analyzed as well as the length of time for the beam to stabilize. Symmetry was calculated 5cm from the central axis at 100cm SSD. Field sizes ranged from 30×30 cm{sup 2} to 40×40 cm{sup 2}. Results: The beam profiles changed over time and were dependent on gantry angle. The composite profile for each beam met 1% tolerance described in TG-142. It took up to 14.7, 3.7 and 11.3 cGy for the two Elektas and Varian respectively to satisfy the tolerance. All linacs had the most flat, symmetric, and stable beam profile with the gantry at 0 degrees, where the symmetry was 100.5%±0.55, 101.0%±0.52 and 101.1%±0.44 respectively. The symmetry was 100.7%±1.06, 101.1%±1.05 and 101.2%±0.64 at the gantry angle with the biggest discrepancy (90, 180 and 180 degrees respectively). Symmetry was better in the X direction for the Elektas and the Y for the Varian. Fluctuations in beam profiles corresponded to changes in dose rate. Conclusion: Flatness and symmetry changed over time and with gantry angle. Because Treatment Planning Systems do not account for these changes, it may be necessary to limit certain beams from clinical use, for example, beams with low MU. It may also be necessary to add additional QA procedures beyond those suggested in TG-142 to account for these changes.

  6. Characterization of the phantom material Virtual Water{sup TM} in high-energy photon and electron beams

    SciTech Connect

    McEwen, M.R.; Niven, D.

    2006-04-15

    The material Virtual Water{sup TM} has been characterized in photon and electron beams. Range-scaling factors and fluence correction factors were obtained, the latter with an uncertainty of around 0.2%. This level of uncertainty means that it may be possible to perform dosimetry in a solid phantom with an accuracy approaching that of measurements in water. Two formulations of Virtual Water{sup TM} were investigated with nominally the same elemental composition but differing densities. For photon beams neither formulation showed exact water equivalence--the water/Virtual Water{sup TM} dose ratio varied with the depth of measurement with a difference of over 1% at 10 cm depth. However, by using a density (range) scaling factor very good agreement (<0.2%) between water and Virtual Water{sup TM} at all depths was obtained. In the case of electron beams a range-scaling factor was also required to match the shapes of the depth dose curves in water and Virtual Wate{sup TM}. However, there remained a difference in the measured fluence in the two phantoms after this scaling factor had been applied. For measurements around the peak of the depth-dose curve and the reference depth this difference showed some small energy dependence but was in the range 0.1%-0.4%. Perturbation measurements have indicated that small slabs of material upstream of a detector have a small (<0.1% effect) on the chamber reading but material behind the detector can have a larger effect. This has consequences for the design of experiments and in the comparison of measurements and Monte Carlo-derived values.

  7. Design of an undulator white beam profiler and test results on the Advanced Photon Source beamline (abstract)

    NASA Astrophysics Data System (ADS)

    Shu, Deming; Ramanathan, Mohan; Singh, Om; Decker, Glenn

    2002-03-01

    At the Advanced Photon Source (APS), each insertion device (ID) beamline front end has two x-ray beam position monitors (XBPMs) to monitor the x-ray beam position for both the vertical and horizontal directions. The XBPMs measure photoelectrons generated by the chemical vapor deposited-diamond-based sensory blades and deduce the beam position by comparison of the relative signals from the blades [D. Shu, B. Rodricks, J. Barraza, T. Sanchez, and T. M. Kuzay, Nucl. Instrum. Methods. Phys. Res. A 319, 56 (1992)]. Performance challenges for an undulator XBPM during operation are contamination of the signal from the neighboring bending-magnet sources and the sensitivity of the XBPM to the ID gap variations. Problems are exacerbated because users change the ID gap during their operations, and hence the percentage level of the contamination in the front-end XBPM signals varies. The smart XBPM system partially solved these problems [D. Shu, H. Ding, J. Barraza, T. M. Kuzay, and M. Ramanathan, J. Synchrotron Radia. 5, 632 (1998)], but it is still very difficult to eliminate the contamination of the signal from the storage ring orbit-corrector magnets. A method was proposed by G. Decker and O. Singh [Phys. Rev. ST Accel. Beams 2, 112801 (1999)] that provides a solution to the long-standing problem of stray radiation-induced signals on photoemission-based XBPMs located on the ID beamline front end. The method involves the introduction of a chicane into the accelerator lattice that directs unwanted x rays away from the photosensitive XBPM blades. This technique has been implemented at the APS. In this paper, we present the design of an undulator white beam profiler that provides experimental confirmation of this technique.

  8. Perturbation correction for alanine dosimeters in different phantom materials in high-energy photon beams

    NASA Astrophysics Data System (ADS)

    von Voigts-Rhetz, P.; Anton, M.; Vorwerk, H.; Zink, K.

    2016-02-01

    In modern radiotherapy the verification of complex treatments plans is often performed in inhomogeneous or even anthropomorphic phantoms. For dose verification small detectors are necessary and therefore alanine detectors are most suitable. Though the response of alanine for a wide range of clinical photon energies in water is well know, the knowledge about the influence of the surrounding phantom material on the response of alanine is sparse. Therefore we investigated the influence of twenty different surrounding/phantom materials for alanine dosimeters in clinical photon fields via Monte Carlo simulations. The relative electron density of the used materials was in the range {{n}e}/{{n}e,\\text{w}}=0.20 up to 1.69, covering almost all materials appearing in inhomogeneous or anthropomorphic phantoms used in radiotherapy. The investigations were performed for three different clinical photon spectra ranging from 6 to 25 MV-X and Co-60 and as a result a perturbation correction {{k}\\text{env}} depending on the environmental material was established. The Monte Carlo simulation show, that there is only a small dependence of {{k}\\text{env}} on the phantom material and the photon energy, which is below  ±0.6%. The results confirm the good suitability of alanine detectors for in-vivo dosimetry.

  9. Perturbation correction for alanine dosimeters in different phantom materials in high-energy photon beams.

    PubMed

    von Voigts-Rhetz, P; Anton, M; Vorwerk, H; Zink, K

    2016-02-01

    In modern radiotherapy the verification of complex treatments plans is often performed in inhomogeneous or even anthropomorphic phantoms. For dose verification small detectors are necessary and therefore alanine detectors are most suitable. Though the response of alanine for a wide range of clinical photon energies in water is well know, the knowledge about the influence of the surrounding phantom material on the response of alanine is sparse. Therefore we investigated the influence of twenty different surrounding/phantom materials for alanine dosimeters in clinical photon fields via Monte Carlo simulations. The relative electron density of the used materials was in the range [Formula: see text] up to 1.69, covering almost all materials appearing in inhomogeneous or anthropomorphic phantoms used in radiotherapy. The investigations were performed for three different clinical photon spectra ranging from 6 to 25 MV-X and Co-60 and as a result a perturbation correction [Formula: see text] depending on the environmental material was established. The Monte Carlo simulation show, that there is only a small dependence of [Formula: see text] on the phantom material and the photon energy, which is below  ±0.6%. The results confirm the good suitability of alanine detectors for in-vivo dosimetry. PMID:26758810

  10. Evaluation of a photon and an electron beam of a 6-MV linear accelerator.

    PubMed

    Sharma, S C; Modur, P; Basavatia, R

    1988-01-01

    The first Mitsubishi medical linear accelerator in the United States was commissioned in April 1985. This unit EXL-8 (marketed by Mitsubishi International Corporation) produces 8-MeV electron beams in addition to 6-MV x rays. It is a 100-cm source-axis distance isocentric machine. Acceptance testing and performance evaluation of this accelerator were completed. Our measurements included beam characteristics and dosimetry parameters for both modalities. Central axis % depth dose (% DD), tissue-maximum ratio, field size output factors, wedge factors, etc., for this Linac 6-MV beam, are reported. Characteristics of the 8-MeV electron beam, namely % DD data, isodose curves, and cone ratios for various electron applicators are presented. PMID:3211045

  11. Can the Hypothesis 'Photon Interferes only with Itself' be Reconciled with Superposition of Light from Multiple Beams or Sources?

    NASA Technical Reports Server (NTRS)

    Roychoudhuri, Chandrasekhar; Prasad, Narasimha S.; Peng, Qing

    2007-01-01

    Any superposition effect as measured (SEM) by us is the summation of simultaneous stimulations experienced by a detector due to the presence of multiple copies of a detectee each carrying different values of the same parameter. We discus the cases with light beams carrying same frequency for both diffraction and multiple beam Fabry-Perot interferometer and also a case where the two superposed light beams carry different frequencies. Our key argument is that if light really consists of indivisible elementary particle, photon, then it cannot by itself create superposition effect since the state vector of an elementary particle cannot carry more than one values of any parameter at the same time. Fortunately, semiclassical model explains all light induced interactions using quantized atoms and classical EM wave packet. Classical physics, with its deeper commitment to Reality Ontology, was better prepared to nurture the emergence of Quantum Mechanics and still can provide guidance to explore nature deeper if we pay careful attention to successful classical formulations like Huygens-Fresnel diffraction integral.

  12. Determination of small field output factors in 6 and 10 MV flattening filter free photon beams using various detectors

    NASA Astrophysics Data System (ADS)

    Masanga, W.; Tangboonduangjit, P.; Khamfongkhruea, C.; Tannanonta, C.

    2016-03-01

    The study aimed to determine appropriate detectors for output factor measurement of small fields in 6 and 10 MV flattening filter free photon beams using five different detectors. Field sizes were varied between 0.6 × 0.6 and 4.0 × 4.0 cm2. An indirect method (daisy-chaining) was applied to normalize the output factors. For the smallest field size, the variations of output factors compared among the detectors were 13%. Exradin A16 had the lowest output factor and increasing in sequence with CC01, microDiamond, microLion and EDGE detectors, respectively, for both energies. The similarity between CC01 and microDiamond output factor values were within 1.6% and 1% for all field sizes of 6 and 10 MV FFF, respectively. EDGE and microLion presented the highest values while ExradinA16 gave lowest values. In conclusion, IBACC01, Exradin A16, microLion, microDiamond and EDGE detectors seem to be the detectors of choices for small field output factor measurement of FFF beams down to 1.6 × 1.6 cm2. However, we could not guarantee which detector is the most suitable for output factor measurement in small field less than 1.6 × 1.6 cm2 of FFF beams. Further studies are required to provide reference information for validation purposes.

  13. A standard Fricke dosimeter compared to an ionization chamber used for dosimetric characterization of 60Co photon beam

    NASA Astrophysics Data System (ADS)

    Moussous, Ouiza; Medjadj, Toufik

    2016-06-01

    The main objective of this study was to investigate the Fricke dosimeter water equivalent system for measurement of dosimetric parameters for photon beam. The parameters measured with the Fricke dosimeter were compared to those obtained with an ionization chamber. In this work characteristics for 60Co γ-rays of field sizes ranging from 5 × 5 cm2 to 20 × 20 cm2 are reported. The measurements were carried out in the secondary standard dosimetry laboratory using a collimated 60Co gamma source therapy unit. The 60Co beam output in terms of absorbed dose to water was obtained as per IAEA TRS 398 recommendations using cylindrical ionization chamber, whose ND,w has been supplied by the IAEA's reference laboratory. Specific quantities measured include: output factors, peak scatter factor, lateral beam profiles and percentage depth dose. The Fricke dosimeters were irradiated in a water phantom using the suitable poly (methyl methacrylate), PMMA stand. Our results demonstrate that Fricke dosimeter and ionization chamber agree with each other.

  14. A Pulsed X-Ray And Charged Particle Beam Generator Used In The Low Photon Energy Region

    NASA Astrophysics Data System (ADS)

    Sato, Eiichi; Isobe, Hiroshi; Tamakawa, Yoshiharu; Yanagisawa, Toru

    1989-06-01

    The construction and the fundamental studies for a pulsed x-ray and charged particle beam generator used in the low photon energy region are described. This generator consisted of the following components: a high-voltage power supply, a high-voltage coaxial oil condenser of 120kV-0.2pF, a gas gap switch, a low-impedance coaxial transmission line, a turbo molecular pump, and a pulsed x-ray and charged particle beam tube. The condenser was charged from -60 to -100kV and was connected to the radiation tube through a gas gap switch. The electric charge stored by the condenser was discharged to the radiation tube when the gas gap switch was closed. This radiation tube produced pulsed (flash) x-rays through copper foil anodes. The charged particle beam was produced by the ionized air outside of the anode window due to the production of a high dose rate of x-rays, and these charged particles were accelerated by the electric field between the anode and ground. Both kinds of radiation were produced simultaneously, and the migration time of the charged particles corresponded to the duration of the pulsed x-rays.

  15. Dosimetric characteristics of linear accelerator photon beams with small monitor unit settings.

    PubMed

    Kang, Sei-Kwon; Cheong, Kwang-Ho; Hwang, Taejin; Cho, Byung Chul; Kim, Su Ssan; Kim, Kyoung Ju; Oh, Do Hoon; Bae, Hoonsik; Suh, Tae-Suk

    2008-11-01

    Several studies on the effect of tumor cell killing by dose rate variation have implied that the use of a shorter treatment time is more favorable for intensity modulated radiation therapy (IMRT). Aiming at step-and-shoot IMRT with higher dose rates, the stabilities of beam output and profiles with small monitor unit (MU) settings were investigated for various dose rates. With the use of a Varian 21EX (Varian Medical Systems Inc., Palo Alto, CA), static and step-and-shoot IMRT beam output along with profiles were measured by use of an ion chamber and a two-dimensional diode array detector as a function of monitor units and dose rates. For a static case, as the MU approached 1, the beam output increased up to 2% for 300 MU/min and 4.5% for 600 MU/min, showing a larger overdose as the dose rate increased. Deterioration of the beam symmetry and flatness were also observed as the MU decreased to 1 monitor unit. For the step-and-shoot IMRT case, a large dosimetric error of more than 10% was also detected with the use of a small MU segment. However, no definite correlation with the dose rate was observed due to the combined beam start-up effects by the grid pulse and finite communication time between the machine console and multileaf collimator (MLC) controller. For step-and-shoot IMRT with higher dose rates, beam output and beam profile stability with small MU needs to be checked, and adequate MU limitation where segments are not allowed need to be reflected in the step-and-shoot IMRT planning. PMID:19070251

  16. Experimental investigation of the response of an a-Si EPID to an unflattened photon beam from an Elekta Precise linear accelerator

    SciTech Connect

    Tyner, Elaine; McClean, Brendan; McCavana, Patrick; Wetterstedt, Sacha af

    2009-04-15

    The characteristics of an Elekta amorphous silicon (a-Si) electronic portal imaging device (EPID) in response to a 6 MV photon beam generated without a flattening filter, an unflattened beam, have been determined. The characteristics were then compared to those for a conventional photon beam generated with a flattening filter in the beam, a flattened beam, in order to determine the suitability of an a-Si EPID for transit dosimetry. The response of the EPID to the unflattened beam increased by 7.3% compared to the flattened beam, and copper buildup of 3 mm reduces the variation in the EPID response over air gaps ranging from 60 to 40 cm to within 2.5%. The scattering properties of the EPID with changing field size for the unflattened beam agree with those measured for a flattened beam to within 2%. Due to the minimal variation in the energy spectrum of the unflattened beam with the distance from the central axis, it was expected and experimentally found that the profile shape of the unflattened beam changes minimally with increasing phantom thickness. For an unflattened beam, EPID measured profiles with and without a phantom in the beam agree to within 2% using confidence limits. The difference between EPID and ionization chamber profiles measured at a depth of 5 cm in water is reduced compared to a flattened beam and remains unchanged with increasing phantom thickness. A difference of 4% was found between EPID profiles and the corresponding profiles measured with an ionization chamber measured in water over a range of phantom thickness. A calibration procedure was developed to convert EPID images to the equivalent absolute dose in water, at the EPID plane. A gamma evaluation was performed comparing the calibrated EPID images to dose measured with an ionization chamber array for rectangular fields and an IMRT segment. The fields were situated on axis and at 5 cm off axis with and without a 25 cm thick phantom in the beam. The gamma evaluation criteria of 3% and 3 mm

  17. Deterministic photon kerma distribution based on the Boltzmann equation for external beam radiation therapy

    SciTech Connect

    Yuan Jiankui; Jette, David; Chen Weimin

    2008-09-15

    A photon transport algorithm for fully three-dimensional radiotherapy treatment planning has been developed based on the discrete ordinates (S{sub N}) solution of the Boltzmann equation. The algorithm is characterized by orthogonal adaptive meshes, which place additional points where large gradients occur and a procedure to evaluate the collided flux using the representation of spherical harmonic expansion instead of the summation of the volume-weighted contribution from discrete angles. The Boltzmann equation was solved in the form of S{sub N} spatial, energy, and angular discretization with mitigation of ray effects by the first-collision source method. Unlike existing S{sub N} codes, which were designed for general purpose for multiparticle transport in areas such as nuclear engineering, our code is optimized for medical radiation transport. To validate the algorithm, several examples were employed to calculate the photon flux distribution. Numerical results show good agreement with the Monte Carlo calculations using EGSnrc.

  18. Clinical implementation of the Peregrine Monte Carlo dose calculations system for photon beam therapy

    SciTech Connect

    Albright, N; Bergstrom, P M; Daly, T P; Descalle, M; Garrett, D; House, R K; Knapp, D K; May, S; Patterson, R W; Siantar, C L; Verhey, L; Walling, R S; Welczorek, D

    1999-07-01

    PEREGRINE is a 3D Monte Carlo dose calculation system designed to serve as a dose calculation engine for clinical radiation therapy treatment planning systems. Taking advantage of recent advances in low-cost computer hardware, modern multiprocessor architectures and optimized Monte Carlo transport algorithms, PEREGRINE performs mm-resolution Monte Carlo calculations in times that are reasonable for clinical use. PEREGRINE has been developed to simulate radiation therapy for several source types, including photons, electrons, neutrons and protons, for both teletherapy and brachytherapy. However the work described in this paper is limited to linear accelerator-based megavoltage photon therapy. Here we assess the accuracy, reliability, and added value of 3D Monte Carlo transport for photon therapy treatment planning. Comparisons with clinical measurements in homogeneous and heterogeneous phantoms demonstrate PEREGRINE's accuracy. Studies with variable tissue composition demonstrate the importance of material assignment on the overall dose distribution. Detailed analysis of Monte Carlo results provides new information for radiation research by expanding the set of observables.

  19. Effect of transverse magnetic fields on dose distribution and RBE of photon beams: comparing PENELOPE and EGS4 Monte Carlo codes

    NASA Astrophysics Data System (ADS)

    Nettelbeck, H.; Takacs, G. J.; Rosenfeld, A. B.

    2008-09-01

    The application of a strong transverse magnetic field to a volume undergoing irradiation by a photon beam can produce localized regions of dose enhancement and dose reduction. This study uses the PENELOPE Monte Carlo code to investigate the effect of a slice of uniform transverse magnetic field on a photon beam using different magnetic field strengths and photon beam energies. The maximum and minimum dose yields obtained in the regions of dose enhancement and dose reduction are compared to those obtained with the EGS4 Monte Carlo code in a study by Li et al (2001), who investigated the effect of a slice of uniform transverse magnetic field (1 to 20 Tesla) applied to high-energy photon beams. PENELOPE simulations yielded maximum dose enhancements and dose reductions as much as 111% and 77%, respectively, where most results were within 6% of the EGS4 result. Further PENELOPE simulations were performed with the Sheikh-Bagheri and Rogers (2002) input spectra for 6, 10 and 15 MV photon beams, yielding results within 4% of those obtained with the Mohan et al (1985) spectra. Small discrepancies between a few of the EGS4 and PENELOPE results prompted an investigation into the influence of the PENELOPE elastic scattering parameters C1 and C2 and low-energy electron and photon transport cut-offs. Repeating the simulations with smaller scoring bins improved the resolution of the regions of dose enhancement and dose reduction, especially near the magnetic field boundaries where the dose deposition can abruptly increase or decrease. This study also investigates the effect of a magnetic field on the low-energy electron spectrum that may correspond to a change in the radiobiological effectiveness (RBE). Simulations show that the increase in dose is achieved predominantly through the lower energy electron population.

  20. Poster — Thur Eve — 35: The impact of intensity- and energy-modulated photon radiotherapy (XMRT) optimization on a variety of organ geometries

    SciTech Connect

    McGeachy, P.; Villarreal-Barajas, J. E.; Khan, R.; Zinchenko, Y.

    2014-08-15

    We previously reported on a novel, modulated in both energy and intensity; photon radiotherapy (XMRT) optimization technique. The purpose of this investigation was to test this XMRT optimization against conventional intensity modulated radiotherapy (IMRT) optimization on four different organ test geometries. All geometries mimicked clinically relevant scenarios. Both IMRT and XMRT were based on a linear programming approach where the objective function was the mean dose to healthy organs and organ-specific linear dose-point constraints were used. For IMRT, the beam energy was fixed to 6 MV while XMRT optimized in terms of both 6 and 18 MV beams. All plans consisted of a seven beam coplanar arrangement. All organ geometries were contoured on a 25cm diameter cylindrical water phantom in open source radiotherapy research software known as CERR. Solutions for both IMRT and XMRT were obtained for each geometry using a numerical solver Gurobi. Analyzing the quality of the solutions was done by comparing dose distributions and dose volume histograms calculated using CERR. For all four geometries, IMRT and XMRT solutions were comparable in terms of target coverage. For two of the geometries, IMRT provided an advantage in terms of reduced dose to the healthy structures. XMRT showed improved dose reduction to healthy organs for one geometry and a comparable dose distribution to IMRT for the remaining geometry. The inability to exploit the benefits of using multiple energies may be attributed to limited water phantom diameter and having the majority of the organs in close proximity to the transverse axis.

  1. On the determination of reference levels for quality assurance of flattening filter free photon beams in radiation therapy

    SciTech Connect

    Clivio, Alessandro; Belosi, Maria Francesca; Cozzi, Luca; Nicolini, Giorgia; Vanetti, Eugenio; Fogliata, Antonella; Bolard, Grégory; Fenoglietto, Pascal; Krauss, Harald

    2014-02-15

    Purpose: New definitions for some dosimetric parameters for use in quality assurance of flattening filter free (FFF) beams generated by medical linear accelerators have been suggested. The present study aims to validate these suggestions and to propose possible reference levels. Methods: The main characteristics of FFF photon beams were described in terms of: field size, penumbra, unflatness, slope, and peak-position parameters. Data were collected for 6 and 10 MV-FFF beams from three different Varian TrueBeam Linacs. Measurements were performed with a 2D-array (Starcheck system from PTW-Freiburg) and with the portal dosimetry method GLAaS utilizing the build-in portal imager of TrueBeam. Data were also compared to ion chamber measurements. A cross check validation has been performed on a FFF beam of 6 MV generated by a Varian Clinac-iX upgraded to FFF capability. Results : All the parameters suggested to characterize the FFF beams resulted easily measurable and little variation was observed among different Linacs. Referring to two reference field sizes of 10 × 10 and 20 × 20 cm{sup 2}, at SDD = 100 cm and d = dmax, from the portal dosimetry data, the following results (averaging X and Y profiles) were obtained. Field size: 9.95 ± 0.02 and 19.98 ± 0.03 cm for 6 MV-FFF (9.94 ± 0.02 and 19.98 ± 0.03 cm for 10 MV-FFF). Penumbra: 2.7 ± 0.3 and 2.9 ± 0.3 mm for 6 MV-FFF (3.1 ± 0.2 and 3.3 ± 0.3 for 10 MV-FFF). Unflatness: 1.11 ± 0.01 and 1.25 ± 0.01 for 6 MV-FFF (1.21 ± 0.01 and 1.50 ± 0.01 for 10 MV-FFF). Slope: 0.320 ± 0.020%/mm and 0.43 ± 0.015%/mm for 6 MV-FFF (0.657 ± 0.023%/mm and 0.795 ± 0.017%/mm for 10 MV-FFF). Peak Position −0.2 ± 0.2 and −0.4 ± 0.2 mm for 6 MV-FFF (−0.3 ± 0.2 and 0.7 ± 0.3 mm for 10 MV-FFF). Results would depend upon measurement depth. With thresholds set to at least 95% confidence level from the measured data and to account for possible variations between detectors and methods and experimental settings, a

  2. Comparison of small photon beams measured using radiochromic and silver-halide films in solid water phantoms

    SciTech Connect

    Zeidan, Omar A.; Li, Jonathan G.; Low, Daniel A.; Dempsey, James F.

    2004-10-01

    In this study, we compared the dosimetric properties of four of the most commonly used films for megavoltage photon-beam dosimetry when irradiated under identical conditions by small multileaf-collimator (MLC) defined beamlets. Two silver-halide films (SHFs), Kodak XV2 and EDR2, and two radiochromic films (RCFs), Gafchromic HS and MD55-2, were irradiated by MLC-defined 1x1 cm{sup 2} beamlets from a Varian 2100 C/D linac equipped with a 120-leaf MLC. The beamlets were delivered with the accelerator gantry set laterally (90 deg. rotation) upon a solid-water compression film phantom at 100 cm source-to-surface distance which was positioned with the films parallel to the beam axis. Beamlets were delivered at central axis, 5.0 cm, and 10.5 cm off-axis for both leaf-end and leaf-side defined beamlets. The film dosimetry was performed using a quantitative optical density (OD) imaging system that was validated in a previous study. No significant differences between SHF and RCF measurements were observed in percentage depth doses, horizontal depth profiles, or two-dimension spatial isodose distributions in both the central axis and off-axis measurements. We found that regardless of the type of film used, RCF or SHF, a consistent data set for small beam dose modeling was generated. Previous validation studies based on the use of RCF and OD imaging system would indicate that all film produce an accurate result for small beam characterization.

  3. Excited state spectroscopy of para di-substituted benzenes in a supersonic beam using resonant two photon ionization

    NASA Astrophysics Data System (ADS)

    Tembreull, R.; Dunn, T. M.; Lubman, D. M.

    Excited state vibronic spectra of p-aminophenol, p-cresol, p-fluoroaniline, p-fluorophenol, hydroquinone and p-toluidine have been obtained using resonant two photon ionization supersonic beam mass spectrometry. Despite marked similarities in the spectra, notable differences exist and different para polyatomic substituents in the same molecule show vibronic evidence of their real molecular symmetry of C2ν. Expansion of the ring is also noted upon excitation in all cases. Further, it is now evident that the assignment of some vibronic bands historically interpreted as sequence structure must be reconsidered since molecules like hydroquinone are mixtures of cis and trans and others have a vibronic structure arising from the polyatomic nature of the substituents ( cƒ. CH 3).

  4. Use of the BIPM calorimetric and ionometric standards in megavoltage photon beams to determine Wair and Ic

    NASA Astrophysics Data System (ADS)

    Burns, D. T.; Picard, S.; Kessler, C.; Roger, P.

    2014-03-01

    The BIPM graphite calorimeter standard for absorbed dose to water has been used in conjunction with an ionization chamber of known volume and with Monte Carlo simulations of these arrangements to determine the value for Wair in 60Co radiation and in accelerator photon beams up to 25 MV. The results show no evidence for a variation in Wair at the 0.2% level over this energy range. Taking the constancy of Wair as established, the best estimate is Wair = 34.03 eV with a standard uncertainty of 0.21%. Consistent with this analysis, and assuming the use of the grain density in evaluating the stopping power of graphite, is the value Ic = 81.1 eV for the mean excitation energy for graphite, with standard uncertainty 1.8 eV.

  5. Precision white-beam slit design for high power density x-ray undulator beamlines at the Advanced Photon Source

    SciTech Connect

    Shu, D.; Brite, C.; Nian, T.

    1994-12-01

    A set of precision horizontal and vertical white-beam slits has been designed for the Advanced Photon Source (APS) X-ray undulator beamlines at Argonne National Laboratory. There are several new design concepts applied in this slit set, including: grazing-incidence knife-edge configuration to minimize the scattering of X-rays downstream, enhanced heat transfer tubing to provide water cooling, and a second slit to eliminate the thermal distortion on the slit knife edge. The novel aspect of this design is the use of two L-shaped knife-edge assemblies, which are manipulated by two precision X-Z stepping linear actuators. The principal and structural details of the design for this slit set are presented in this paper.

  6. Evaluation of the usefulness of a MOSFET detector in an anthropomorphic phantom for 6-MV photon beam.

    PubMed

    Kohno, Ryosuke; Hirano, Eriko; Kitou, Satoshi; Goka, Tomonori; Matsubara, Kana; Kameoka, Satoru; Matsuura, Taeko; Ariji, Takaki; Nishio, Teiji; Kawashima, Mitsuhiko; Ogino, Takashi

    2010-07-01

    In order to evaluate the usefulness of a metal oxide-silicon field-effect transistor (MOSFET) detector as a in vivo dosimeter, we performed in vivo dosimetry using the MOSFET detector with an anthropomorphic phantom. We used the RANDO phantom as an anthropomorphic phantom, and dose measurements were carried out in the abdominal, thoracic, and head and neck regions for simple square field sizes of 10 x 10, 5 x 5, and 3 x 3 cm(2) with a 6-MV photon beam. The dose measured by the MOSFET detector was verified by the dose calculations of the superposition (SP) algorithm in the XiO radiotherapy treatment-planning system. In most cases, the measured doses agreed with the results of the SP algorithm within +/-3%. Our results demonstrated the utility of the MOSFET detector for in vivo dosimetry even in the presence of clinical tissue inhomogeneities. PMID:20821083

  7. Accurate dosimetry with GafChromic EBT film of a 6 MV photon beam in water: What level is achievable?

    SciTech Connect

    Battum, L. J. van; Hoffmans, D.; Piersma, H.; Heukelom, S.

    2008-02-15

    This paper focuses on the accuracy, in absolute dose measurements, with GafChromic 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.

  8. Radiobiological effects of altering dose rate in filter-free photon beams.

    PubMed

    Karan, T; Moiseenko, V; Gill, B; Horwood, R; Kyle, A; Minchinton, A I

    2013-02-21

    To validate that altering radiotherapy dose rate through either changing pulse repetition frequency or instantaneous dose rate does not have an effect on cell survival, two human carcinoma and a hamster lung cell line were irradiated with various beam settings. Varian TrueBeam linac with a flattening filter free mode of operation was used for all experiments. The results obtained indicate that either method of changing dose rate has no effect on cell survival in the three cell lines studied. Filtered and filter free modes were also compared in treatments with protracted dose delivery which significantly increases overall treatment time. Cell survival indicated no difference between filter and filter free beam delivery in any of the protraction schemes. An increase in survival was seen in both modes upon protracting dose delivery to 15, 30 or 60 min rather than delivering acutely. Further, analysis of induced DNA double-strand breaks via the γH2AX assay showed no difference between filtered and unfiltered beams. The following study suggests that increasing dose rate is an acceptable manner of decreasing radiotherapy treatment time that does not have any detrimental effects on in vitro cell eradication. PMID:23363688

  9. Radiobiological effects of altering dose rate in filter-free photon beams

    NASA Astrophysics Data System (ADS)

    Karan, T.; Moiseenko, V.; Gill, B.; Horwood, R.; Kyle, A.; Minchinton, A. I.

    2013-02-01

    To validate that altering radiotherapy dose rate through either changing pulse repetition frequency or instantaneous dose rate does not have an effect on cell survival, two human carcinoma and a hamster lung cell line were irradiated with various beam settings. Varian TrueBeam linac with a flattening filter free mode of operation was used for all experiments. The results obtained indicate that either method of changing dose rate has no effect on cell survival in the three cell lines studied. Filtered and filter free modes were also compared in treatments with protracted dose delivery which significantly increases overall treatment time. Cell survival indicated no difference between filter and filter free beam delivery in any of the protraction schemes. An increase in survival was seen in both modes upon protracting dose delivery to 15, 30 or 60 min rather than delivering acutely. Further, analysis of induced DNA double-strand breaks via the γH2AX assay showed no difference between filtered and unfiltered beams. The following study suggests that increasing dose rate is an acceptable manner of decreasing radiotherapy treatment time that does not have any detrimental effects on in vitro cell eradication.

  10. Focus modulation of cylindrical vector beams by using 1D photonic crystal lens with negative refraction effect.

    PubMed

    Xu, Ji; Zhong, Yi; Wang, Shengming; Lu, Yunqing; Wan, Hongdan; Jiang, Jian; Wang, Jin

    2015-10-19

    Sub-wavelength focusing of cylindrical vector beams (CVBs) has attracted great attention due to the specific physical effects and the applications in many areas. More powerful, flexible and effective ways to modulate the focus transversally and also longitudinally are always being pursued. In this paper, cylindrically symmetric lens composed of negative-index one-dimensional photonic crystal is proposed to make a breakthrough. By revealing the relationship between focal length and the exit surface shape of the lens, a quite simple and effective principle of designing the lens structure is presented to realize specific focus modulation. Plano-concave lenses are parameterized to modulate the focal length and the number of focuses. An axicon constructed by one-dimensional photonic crystal is proposed for the first time to obtain a large depth of focus and an optical needle focal field with almost a theoretical minimum FWHM of 0.362λ is achieved under radially polarized incident light. Because of the almost identical negative refractive index for TE and TM polarization states, all the modulation methods can be applied for any arbitrary polarized CVBs. This work offers a promising methodology for designing negative-index lenses in related application areas. PMID:26480359

  11. A review of treatment planning for precision image-guided photon beam pre-clinical animal radiation studies.

    PubMed

    Verhaegen, Frank; van Hoof, Stefan; Granton, Patrick V; Trani, Daniela

    2014-12-01

    Recently, precision irradiators integrated with a high-resolution CT imaging device became available for pre-clinical studies. These research platforms offer significant advantages over older generations of animal irradiators in terms of precision and accuracy of image-guided radiation targeting. These platforms are expected to play a significant role in defining experiments that will allow translation of research findings to the human clinical setting. In the field of radiotherapy, but also others such as neurology, the platforms create unique opportunities to explore e.g. the synergy between radiation and drugs or other agents. To fully exploit the advantages of this new technology, accurate methods are needed to plan the irradiation and to calculate the three-dimensional radiation dose distribution in the specimen. To this end, dedicated treatment planning systems are needed. In this review we will discuss specific issues for precision irradiation of small animals, we will describe the workflow of animal treatment planning, and we will examine several dose calculation algorithms (factorization, superposition-convolution, Monte Carlo simulation) used for animal irradiation with kilovolt photon beams. Issues such as dose reporting methods, photon scatter, tissue segmentation and motion will also be discussed briefly. PMID:24629309

  12. Characterization of low-energy photon-emitting brachytherapy sources and kilovoltage x-ray beams using spectrometry

    NASA Astrophysics Data System (ADS)

    Moga, Jacqueline D.

    Low-energy photon sources are used in therapeutic radiation oncology for brachytherapy with low dose-rate (LDR) sources and for superficial and orthovoltage therapy with kilovolt-age x-ray beams. Current dosimetry methods for these sources utilize energy-integrating devices, such as thermoluminescent dosimeters and ionization chambers. This thesis work investigates the dosimetry of LDR brachytherapy sources and kilovoltage x-ray beams using spectrometry, which preserves the energy-specific source output. Several LDR brachytherapy source models were measured with a reverse-electrode germanium (REGe) detector. The measured spectra were corrected for MCNP5-calculated detector response using a deconvolution algorithm (Beach, 2005). The peak areas determined from the corrected spectra were used to calculate the dose-rate constant (Chen and Nath, 2001) and the air-kerma strength. Dose-rate constant results agreed well with the published values (Rivard et al., 2004; Chen and Nath, 2007). Air-kerma strength results were systematically 2%--5% low compared to calibration values and primary air-kerma strength measurements. The spectrometry methods for LDR brachytherapy sources offer a promising alternative to existing experimental techniques, but further work is necessary to improve agreement with the current air-kerma strength standard methodology. Spectra of 20kVp---250kVp x-ray beams were measured with a low-energy germanium detector (LEGe). The LEGe spectrometry system was modeled in MCNP5 to calculate a detector response function. Backward stripping, which showed less variability than deconvolution, was used for correcting the measured x-ray spectra. The corrected experimental spectra were compared to spectra from: (1) Monte Carlo simulations of the full x-ray tube with EGSnrc, (2) the SpekCalc program (Poludniowski et al., 2009), and (3) the Gesellschaft fur Strahlen-und Umweltforschung mbH Munchen (GSF) Report 560. Agreement was best for the UW60-M through UW150-M

  13. Optimal energy for cell radiosensitivity enhancement by gold nanoparticles using synchrotron-based monoenergetic photon beams

    PubMed Central

    Rahman, Wan Nordiana; Corde, Stéphanie; Yagi, Naoto; Abdul Aziz, Siti Aishah; Annabell, Nathan; Geso, Moshi

    2014-01-01

    Gold nanoparticles have been shown to enhance radiation doses delivered to biological targets due to the high absorption coefficient of gold atoms, stemming from their high atomic number (Z) and physical density. These properties significantly increase the likelihood of photoelectric effects and Compton scattering interactions. Gold nanoparticles are a novel radiosensitizing agent that can potentially be used to increase the effectiveness of current radiation therapy techniques and improve the diagnosis and treatment of cancer. However, the optimum radiosensitization effect of gold nanoparticles is strongly dependent on photon energy, which theoretically is predicted to occur in the kilovoltage range of energy. In this research, synchrotron-generated monoenergetic X-rays in the 30–100 keV range were used to investigate the energy dependence of radiosensitization by gold nanoparticles and also to determine the photon energy that produces optimum effects. This investigation was conducted using cells in culture to measure dose enhancement. Bovine aortic endothelial cells with and without gold nanoparticles were irradiated with X-rays at energies of 30, 40, 50, 60, 70, 81, and 100 keV. Trypan blue exclusion assays were performed after irradiation to determine cell viability. Cell radiosensitivity enhancement was indicated by the dose enhancement factor which was found to be maximum at 40 keV with a value of 3.47. The dose enhancement factor obtained at other energy levels followed the same direction as the theoretical calculations based on the ratio of the mass energy absorption coefficients of gold and water. This experimental evidence shows that the radiosensitization effect of gold nanoparticles varies with photon energy as predicted from theoretical calculations. However, prediction based on theoretical assumptions is sometimes difficult due to the complexity of biological systems, so further study at the cellular level is required to fully characterize the

  14. Optimal energy for cell radiosensitivity enhancement by gold nanoparticles using synchrotron-based monoenergetic photon beams.

    PubMed

    Rahman, Wan Nordiana; Corde, Stéphanie; Yagi, Naoto; Abdul Aziz, Siti Aishah; Annabell, Nathan; Geso, Moshi

    2014-01-01

    Gold nanoparticles have been shown to enhance radiation doses delivered to biological targets due to the high absorption coefficient of gold atoms, stemming from their high atomic number (Z) and physical density. These properties significantly increase the likelihood of photoelectric effects and Compton scattering interactions. Gold nanoparticles are a novel radiosensitizing agent that can potentially be used to increase the effectiveness of current radiation therapy techniques and improve the diagnosis and treatment of cancer. However, the optimum radiosensitization effect of gold nanoparticles is strongly dependent on photon energy, which theoretically is predicted to occur in the kilovoltage range of energy. In this research, synchrotron-generated monoenergetic X-rays in the 30-100 keV range were used to investigate the energy dependence of radiosensitization by gold nanoparticles and also to determine the photon energy that produces optimum effects. This investigation was conducted using cells in culture to measure dose enhancement. Bovine aortic endothelial cells with and without gold nanoparticles were irradiated with X-rays at energies of 30, 40, 50, 60, 70, 81, and 100 keV. Trypan blue exclusion assays were performed after irradiation to determine cell viability. Cell radiosensitivity enhancement was indicated by the dose enhancement factor which was found to be maximum at 40 keV with a value of 3.47. The dose enhancement factor obtained at other energy levels followed the same direction as the theoretical calculations based on the ratio of the mass energy absorption coefficients of gold and water. This experimental evidence shows that the radiosensitization effect of gold nanoparticles varies with photon energy as predicted from theoretical calculations. However, prediction based on theoretical assumptions is sometimes difficult due to the complexity of biological systems, so further study at the cellular level is required to fully characterize the effects

  15. An analytical method to calculate equivalent fields to irregular symmetric and asymmetric photon fields

    SciTech Connect

    Tahmasebi Birgani, Mohamad J.; Chegeni, Nahid; Zabihzadeh, Mansoor; Hamzian, Nima

    2014-04-01

    Equivalent field is frequently used for central axis depth-dose calculations of rectangular- and irregular-shaped photon beams. As most of the proposed models to calculate the equivalent square field are dosimetry based, a simple physical-based method to calculate the equivalent square field size was used as the basis of this study. The table of the sides of the equivalent square or rectangular fields was constructed and then compared with the well-known tables by BJR and Venselaar, et al. with the average relative error percentage of 2.5 ± 2.5% and 1.5 ± 1.5%, respectively. To evaluate the accuracy of this method, the percentage depth doses (PDDs) were measured for some special irregular symmetric and asymmetric treatment fields and their equivalent squares for Siemens Primus Plus linear accelerator for both energies, 6 and 18 MV. The mean relative differences of PDDs measurement for these fields and their equivalent square was approximately 1% or less. As a result, this method can be employed to calculate equivalent field not only for rectangular fields but also for any irregular symmetric or asymmetric field.

  16. Evaluation of the effect of tooth and dental restoration material on electron dose distribution and production of photon contamination in electron beam radiotherapy.

    PubMed

    Bahreyni Toossi, Mohammad Taghi; Ghorbani, Mahdi; Akbari, Fatemeh; Mehrpouyan, Mohammad; Sobhkhiz Sabet, Leila

    2016-03-01

    The aim of this study is to evaluate the effect of tooth and dental restoration materials on electron dose distribution and photon contamination production in electron beams of a medical linac. This evaluation was performed on 8, 12 and 14 MeV electron beams of a Siemens Primus linac. MCNPX Monte Carlo code was utilized and a 10 × 10 cm(2) applicator was simulated in the cases of tooth and combinations of tooth and Ceramco C3 ceramic veneer, tooth and Eclipse alloy and tooth and amalgam restoration materials in a soft tissue phantom. The relative electron and photon contamination doses were calculated for these materials. The presence of tooth and dental restoration material changed the electron dose distribution and photon contamination in phantom, depending on the type of the restoration material and electron beam's energy. The maximum relative electron dose was 1.07 in the presence of tooth including amalgam for 14 MeV electron beam. When 100.00 cGy was prescribed for the reference point, the maximum absolute electron dose was 105.10 cGy in the presence of amalgam for 12 MeV electron beam and the maximum absolute photon contamination dose was 376.67 μGy for tooth in 14 MeV electron beam. The change in electron dose distribution should be considered in treatment planning, when teeth are irradiated in electron beam radiotherapy. If treatment planning can be performed in such a way that the teeth are excluded from primary irradiation, the potential errors in dose delivery to the tumour and normal tissues can be avoided. PMID:26581762

  17. SU-F-19A-06: Experimental Investigation of the Energy Dependence of TLD Sensitivity in Low-Energy Photon Beams

    SciTech Connect

    Chen, Z; Nath, R

    2014-06-15

    Purpose: To measure the energy dependence of TLD sensitivity in lowenergy photon beams with equivalent mono-energetic energy matching those of 103Pd, 125I and 131Cs brachytherapy sources. Methods: A Pantek DXT 300 x-ray unit (Precision X-ray, Branford, CT), with stable digital voltage control down to 20 kV, was used to establish three lowenergy photon beams with narrow energy spread and equivalent monoenergetic energies matching those of 103Pd, 125I and 131Cs brachytherapy sources. The low-energy x-ray beams and a reference 6 MV photon beam were calibrated according to the AAPM TG-61 and TG-51 protocols, respectively, using a parallel-plate low-energy chamber and a Farmer cylindrical chamber with NIST traceable calibration factors. The dose response of model TLD-100 micro-cubes (1×1×1 mm{sup 3}) in each beam was measured for five different batches of TLDs (each contained approximately 100 TLDs) that have different histories of irradiation and usage. Relative absorbed dose sensitivity was determined as the quotient of the slope of dose response for a beam-of-interest to that of the reference beam. Results: Equivalent mono-energetic photon energies of the low-energy beams established for 103Pd, 125I and 131Cs sources were 20.5, 27.5, and 30.1 keV, respectively. Each beam exhibited narrow spectral spread with energyhomogeneity index close to 90%. The relative absorbed-dose sensitivity was found to vary between different batches of TLD with maximum differences of up to 8%. The mean and standard deviation determined from the five TLD batches was 1.453 ± 0.026, 1.541 ± 0.035 and 1.529 ± 0.051 for the simulated 103P, 125I and 131Cs beams, respectively. Conclusion: Our measured relative absorbed-dose sensitivities are greater than the historically measured value of 1.41. We find that the relative absorbed-dose sensitivity of TLD in the 103P beam is approximately 5% lower than that of 125I and 131Cs beams. Comparison of our results with other studies will be presented.

  18. Effects of computational phantoms on the effective dose and two-dosimeter algorithm for external photon beams.

    PubMed

    Karimi-Shahri, K; Rafat-Motavalli, L; Miri-Hakimabad, H; Liu, L; Li, J

    2016-09-01

    In this study, the effect of computational phantoms on the effective dose (E), dosimeter responses positioned on the front (chest) and back of phantom, and two-dosimeter algorithm was investigated for external photon beams. This study was performed using Korean Typical MAN-2 (KTMAN-2), Chinese Reference Adult Male (CRAM), ICRP male reference, and Male Adult meSH (MASH) reference phantoms. Calculations were performed for beam directions in different polar and azimuthal angles using the Monte Carlo code of MCNP at energies of 0.08, 0.3, and 1MeV. Results show that the body shape significantly affects E and two-dosimeter responses when the dosimeters are indirectly irradiated. The acquired two-dosimeter algorithms are almost the same for all the mentioned phantoms except for KTMAN-2. Comparisons between the obtained E and estimated E (Eest), acquired from two-dosimeter algorithm, illustrate that the Eest is overestimated in overhead (OH) and underfoot (UF) directions. The effect of using one algorithm for all phantoms was also investigated. Results show that application of one algorithm to all reference phantoms is possible. PMID:27389880

  19. Tailoring the Optical Properties of Silicon with Ion Beam Created Nanostructures for Advanced Photonics Applications

    NASA Astrophysics Data System (ADS)

    Akhter, Perveen

    In today's fast life, energy consumption has increased more than ever and with that the demand for a renewable and cleaner energy source as a substitute for the fossil fuels has also increased. Solar radiations are the ultimate source of energy but harvesting this energy in a cost effective way is a challenging task. Si is the dominating material for microelectronics and photovoltaics. But owing to its indirect band gap, Si is an inefficient light absorber, thus requiring a thickness of solar cells beyond tens of microns which increases the cost of solar energy. Therefore, techniques to increase light absorption in thin film Si solar cells are of great importance and have been the focus of research for a few decades now. Another big issue of technology in this fast-paced world is the computing rate or data transfer rate between components of a chip in ultra-fast processors. Existing electronic interconnects suffering from the signal delays and heat generation issues are unable to handle high data rates. A possible solution to this problem is in replacing the electronic interconnects with optical interconnects which have large data carrying capacity. However, optical components are limited in size by the fundamental laws of diffraction to about half a wavelength of light and cannot be combined with nanoscale electronic components. Tremendous research efforts have been directed in search of an advanced technology which can bridge the size gap between electronic and photonic worlds. An emerging technology of "plasmonics'' which exploits the extraordinary optical properties of metal nanostructures to tailor the light at nanoscale has been considered a potential solution to both of the above-mentioned problems. Research conducted for this dissertation has an overall goal to investigate the optical properties of silicon with metal nanostructures for photovoltaics and advanced silicon photonics applications. The first part of the research focuses on achieving enhanced

  20. Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom

    PubMed Central

    Ashokkumar, Sigamani; Nambiraj, Arunai; Sinha, Sujit Nath; Yadav, Girigesh; Raman, Kothanda; Bhushan, Manindra; Thiyagarajan, Rajesh

    2015-01-01

    Aim To measure and compare the head scatter factor for 7 MV unflattened and 6 MV flattened photon beam using a home-made designed mini phantom. Background The head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators. Materials and methods A columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10 cm and dmax dose water equivalent thickness. Results The Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6–2.2% (Primus), 0.2–1.4% (Artiste) and 0.6–3.7% (Clinac iX (2300CD))) for field sizes ranging from 10 cm × 10 cm to 40 cm × 40 cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF. Conclusions There were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10 cm × 10 cm to 40 cm × 04 cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms. PMID:25949220

  1. Enhanced Multi-MeV Photon Emission by a Laser-Driven Electron Beam in a Self-Generated Magnetic Field.

    PubMed

    Stark, D J; Toncian, T; Arefiev, A V

    2016-05-01

    We use numerical simulations to demonstrate that a source of collimated multi-MeV photons with high conversion efficiency can be achieved using an all-optical single beam setup at an intensity of 5×10^{22}  W/cm^{2} that is already within reach of existing laser facilities. In the studied setup, an unprecedented quasistatic magnetic field (0.4 MT) is driven in a significantly overdense plasma, coupling three key aspects of laser-plasma interactions at high intensities: relativistic transparency, direct laser acceleration, and synchrotron photon emission. The quasistatic magnetic field enhances the photon emission process, which has a profound impact on electron dynamics via radiation reaction and yields tens of TW of directed MeV photons for a PW-class laser. PMID:27203330

  2. Enhanced Multi-MeV Photon Emission by a Laser-Driven Electron Beam in a Self-Generated Magnetic Field

    NASA Astrophysics Data System (ADS)

    Stark, D. J.; Toncian, T.; Arefiev, A. V.

    2016-05-01

    We use numerical simulations to demonstrate that a source of collimated multi-MeV photons with high conversion efficiency can be achieved using an all-optical single beam setup at an intensity of 5 ×1022 W /cm2 that is already within reach of existing laser facilities. In the studied setup, an unprecedented quasistatic magnetic field (0.4 MT) is driven in a significantly overdense plasma, coupling three key aspects of laser-plasma interactions at high intensities: relativistic transparency, direct laser acceleration, and synchrotron photon emission. The quasistatic magnetic field enhances the photon emission process, which has a profound impact on electron dynamics via radiation reaction and yields tens of TW of directed MeV photons for a PW-class laser.

  3. The effect of low-energy electrons on the response of ion chambers to ionizing photon beams

    NASA Astrophysics Data System (ADS)

    La Russa, Daniel J.

    Cavity ionization chambers are one of the most popular and widely used devices for quantifying ionizing photon beams. This popularity originates from the precision of these devices and the relative ease with which ionization measurements are converted to quantities of interest in therapeutic radiology or radiation protection, collectively referred to as radiation dosimetry. The formalisms used for these conversions, known as cavity theory, make several assumptions about the electron spectrum in the low-energy range resulting from the incident photon beam. These electrons often account for a significant fraction of the ion chamber response. An inadequate treatment of low-energy electrons can therefore significantly effect calculated quantities of interest. This thesis sets out to investigate the effect of low-energy electrons on (1) the use of Spencer-Attix cavity theory with 60Co beams; and (2) the standard temperature-pressure correction factor, P TP, used to relate the measured ionization to a set of reference temperature and pressure conditions for vented ion chambers. Problems with the PTP correction are shown to arise when used with kilovoltage x rays, where ionization measurements are due primarily to electrons that do not have enough energy to cross the cavity. A combination of measurements and Monte Carlo calculations using the EGSnrc Monte Carlo code demonstrate the breakdown of PTP in these situations when used with non-air-equivalent chambers. The extent of the breakdown is shown to depend on cavity size, energy of the incident photons, and the composition of the chamber. In the worst case, the standard P TP factor overcorrects the response of an aluminum chamber by ≈12% at an air density typical of Mexico City. The response of a more common graphite-walled chamber with similar dimensions at the same air density is undercorrected by ≈ 2%. The EGSnrc Monte Carlo code is also used to investigate Spencer-Attix cavity theory as it is used in the

  4. Spectroscopic characterization of high-energy and high fluence rate photon beams

    NASA Astrophysics Data System (ADS)

    Bartol, Laura J.

    High-energy, high fluence rate photon sources are used in radiation oncology for the treatment of a variety of disease sites. Common dosimetry methods for characterizing these sources use energy-integrating devices; however, the most descriptive characterization of these sources are performed with devices that preserve the energy-specific information in the source output. This work used Monte-Carlo- (MC-) and measurement-based spectroscopic methods to characterize two therapeutic-level megavoltage photon sources. MC simulations were performed using the MCNP5 transport code and measurements were performed with a Compton-scattering (CS) technique. Because MC was used extensively in this work, some general MCNP5 investigations were performed to benchmark the techniques used. Limitations in the advanced variance reduction techniques, Doppler-broadening model, and use of phase space files were investigated. Based on the results of these investigations, recommendations were made for using each technique. The validity of the CS technique for use with megavoltage systems was demonstrated using MC simulations of a 6 MV linear accelerator field and measurements of a high dose rate 192Ir source. Following these initial demonstrations, the spectrum of a 60Co teletherapy unit was characterized. Simulations were performed to determine the spectrum's sensitivity to the source model. Multiple measurements were completed using a reverse-electrode germanium (REGe) detector with the CS spectrometry technique. The CS spectra were corrected for detector response and the CS geometry using a novel detector response function that was calculated using MCNP5. The detector response was unfolded using the Gold deconvolution method. Comparisons of the simulated and measured spectra showed agreement in terms of the peak positions, mean spectrum energy, and relative fluences under specific portions of the spectra. The spectrum of a 6 MV photon field from a Varian Clinac iX linear accelerator was

  5. Generation of photonic orbital angular momentum superposition states using vortex beam emitters with superimposed gratings.

    PubMed

    Xiao, Qingsheng; Klitis, Charalambos; Li, Shimao; Chen, Yueyang; Cai, Xinlun; Sorel, Marc; Yu, Siyuan

    2016-02-22

    An integrated approach to produce photonic orbital angular momentum (OAM) superposition states with arbitrary OAM spectrum has been demonstrated. Superposition states between two vector OAM modes have been achieved by integrating a superimposed angular grating in one silicon micro-ring resonator, with each mode having near equal weight. The topological charge difference between the two compositional OAM modes is determined by the difference between the numbers of elements in the two original gratings being superimposed, while the absolute values of the topological charge can be changed synchronously by switching WGM resonant wavelengths. This novel approach provides a scalable and flexible source for the OAM-based quantum information and optical manipulation applications. PMID:26906981

  6. ESR response of phenol compounds for dosimetry of gamma photon beams

    NASA Astrophysics Data System (ADS)

    Marrale, M.; Longo, A.; Panzeca, S.; Gallo, S.; Principato, F.; Tomarchio, E.; Parlato, A.; Buttafava, A.; Dondi, D.; Zeffiro, A.

    2014-11-01

    In the present paper we investigate the features of IRGANOX® 1076 phenols as a material for electron spin resonance (ESR) dosimetry. We experimentally analyzed the ESR response of pellets of IRGANOX® 1076 phenols irradiated with 60Co photons. The best experimental parameters (modulation amplitude and microwave power) for dosimetric applications have been obtained. The dependence of ESR signal as function of γ dose is found to be linear in the dose range studied (12-60 Gy) and the lowest measurable dose is found to be of the order of 1 Gy. The signal after irradiation is very stable in the first thirty days. From the point of view of the tissue equivalence, these materials have mass energy absorption coefficient values comparable with those of soft tissue.

  7. A water calorimeter for on-site absorbed dose to water calibrations in (60)Co and MV-photon beams including MRI incorporated treatment equipment.

    PubMed

    de Prez, Leon; de Pooter, Jacco; Jansen, Bartel; Aalbers, Tony

    2016-07-01

    In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for (60)Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL (60)Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous (60)Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k  =  1) for D w measurements in (60)Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%. PMID:27300589

  8. A water calorimeter for on-site absorbed dose to water calibrations in 60Co and MV-photon beams including MRI incorporated treatment equipment

    NASA Astrophysics Data System (ADS)

    de Prez, Leon; de Pooter, Jacco; Jansen, Bartel; Aalbers, Tony

    2016-07-01

    In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for 60Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL 60Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous 60Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k  =  1) for D w measurements in 60Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%.

  9. Correlative In Vivo 2 Photon and Focused Ion Beam Scanning Electron Microscopy of Cortical Neurons

    PubMed Central

    Maco, Bohumil; Holtmaat, Anthony; Cantoni, Marco; Kreshuk, Anna; Straehle, Christoph N.; Hamprecht, Fred A.; Knott, Graham W.

    2013-01-01

    Correlating in vivo imaging of neurons and their synaptic connections with electron microscopy combines dynamic and ultrastructural information. Here we describe a semi-automated technique whereby volumes of brain tissue containing axons and dendrites, previously studied in vivo, are subsequently imaged in three dimensions with focused ion beam scanning electron microcopy. These neurites are then identified and reconstructed automatically from the image series using the latest segmentation algorithms. The fast and reliable imaging and reconstruction technique avoids any specific labeling to identify the features of interest in the electron microscope, and optimises their preservation and staining for 3D analysis. PMID:23468982

  10. Potential of photon and particle beams for surface treatment of thin ceramic coatings

    NASA Astrophysics Data System (ADS)

    Celis, J. P.; Franck, M.; Roos, J. R.; Kreutz, E. W.; Gasser, A.; Wehner, M.; Wissenbach, K.; Pattyn, N.

    1992-01-01

    Laser irradiation and ion implantation have been investigated in order to modify in a two-step process the characteristics of TiN ceramic coatings obtained by physical vapour deposition (PVD) on steel surfaces. Depending on the beam properties and processing variables used, material modifications can be induced either in the coating itself, at the coating/substrate interface, or in the underlying substrate material. Laser irradiation and ion implantation offer possibilities of tailoring the functional surface properties of coated steels with respect to friction and wear resistance by the modification of surface roughness, by the alloying of ceramic coatings with either metallic or metalloid elements, and by inducing substrate hardening.

  11. The Use of Photon Beams of a Flattening Filter-free Linear Accelerator for Hypofractionated Volumetric Modulated Arc Therapy in Localized Prostate Cancer

    SciTech Connect

    Zwahlen, Daniel R.; Lang, Stephanie; Hrbacek, Jan; Glanzmann, Christoph; Kloeck, Stephan; Najafi, Yousef; Streller, Tino; Studer, Gabriela; Zaugg, Kathrin; Luetolf, Urs M.

    2012-08-01

    Purpose: To evaluate the potential usage of flattening filter-free (FFF) photon beams in the treatment of prostate cancer. Methods and Materials: Volumetric-modulated arc therapy (VMAT) treatment planning was performed for 7 patients using TrueBeam{sup Registered-Sign} linear accelerator and photon beams with (X6, X10) and without (X6FFF, X10FFF) flattening filter. Prescribed dose was 19 Multiplication-Sign 3 Gy = 57 Gy. One or two 360 Degree-Sign arcs with dose rate of 600 MU/min for flattened beams, and 1,200 MU/min for FFF beams were used. Results: No difference was detected between the four beams in PTV coverage, conformity, and homogeneity. Mean body dose and body volume receiving 50% of the prescribed dose decreased with increasing mean energy (r{sup 2} = 0.8275, p < 0.01). X6FFF delivered 3.6% more dose compared with the X6 (p < 0.01). X10FFF delivered 3.0% (p < 0.01), and the X10 5.8% (p < 0.01) less mean body dose compared with X6. There was a significant increase in the mean dose to the rectum for the X10 compared with X6 (2.6%, p < 0.01). Mean dose to the bladder increased by 1.3% for X6FFF and decreased by 2.3% for X10FFF. Using a single arc and FFF, treatment time was reduced by 35% (2 SD = 10%). Conclusion: FFF beams resulted in dose distributions similar to flattened beams. X10FFF beam provided the best solution, sparing rectum and bladder and minimizing whole-body dose. FFF beams lead to a time efficient treatment delivery, particularly when combined with hypofractionated VMAT.

  12. Modeling of energy transfer from the photon beam at an optical media

    NASA Astrophysics Data System (ADS)

    Isarie, Claudiu; Oprean, Constantin; Petrescu, Valentin; Herman, Richard

    2004-06-01

    Laser beam could be applied to act in optical media, to build different spatial images. The operation could be made direct by copying an image or through a C.D. The successive points could be realized with relatively high speed, like 103-105 points per second. Each point represents practically a machining operation done by the laser beam. In most cases, energy transfer is made not in a plane, but in a volume, and this requires moving the focal point in positions required by the image we want to create. This is a sequentially operation, made point by point following a definite order, but in the same time, because the image is spatially, we have to adapt also other parameters of the optical system, for each considered point. The energy required for each point of the image must be the same, because all the micro spheres representing a "point" of the image must have the same volume. In this way we could realize a coherent spatial image. From the experimental research we made, we have learnt that is important to build a model for the energy transfer to optical media, in order to have a good quality for the work we have to do.

  13. Beam perturbation characteristics of a 2D transmission silicon diode array, Magic Plate.

    PubMed

    Alrowaili, Ziyad A; Lerch, Michael L F; Petasecca, Marco; Carolan, Martin G; Metcalfe, Peter E; Rosenfeld, Anatoly B

    2016-01-01

    The main objective of this study is to demonstrate the performance characteristics of the Magic Plate (MP) system when operated upstream of the patient in trans-mission mode (MPTM). The MPTM is an essential component of a real-time QA system designed for operation during radiotherapy treatment. Of particular interest is a quantitative study into the influence of the MP on the radiation beam quality at several field sizes and linear accelerator potential differences. The impact is measured through beam perturbation effects such as changes in the skin dose and/or percentage depth dose (PDD) (both in and out of field). The MP was placed in the block tray of a Varian linac head operated at 6, 10 and 18 MV beam energy. To optimize the MPTM operational setup, two conditions were investigated and each setup was compared to the case where no MP is positioned in place (i.e., open field): (i) MPTM alone and (ii) MPTM with a thin passive contamination electron filter. The in-field and out-of-field surface doses of a solid water phantom were investigated for both setups using a Markus plane parallel (Model N23343) and Attix parallel-plate, MRI model 449 ionization chambers. In addition, the effect on the 2D dose distribution measured by the Delta4 QA system was also investi-gated. The transmission factor for both of these MPTM setups in the central axis was also investigated using a Farmer ionization chamber (Model 2571A) and an Attix ionization chamber. Measurements were performed for different irradiation field sizes of 5 × 5 cm2 and 10 × 10 cm2. The change in the surface dose relative to dmax was measured to be less than 0.5% for the 6 MV, 10 MV, and 18 MV energy beams. Transmission factors measured for both set ups (i & ii above) with 6 MV, 10 MV, and 18 MV at a depth of dmax and a depth of 10 cm were all within 1.6% of open field. The impact of both the bare MPTM and the MPTM with 1 mm buildup on 3D dose distribution in comparison to the open field investigated using

  14. SU-F-BRE-02: Characterization of a New Commercial Single Crystal Diamond Detector in Photon, Electron and Proton Beams

    SciTech Connect

    Akino, Y; Das, I

    2014-06-15

    Purpose: Diamond detectors even with superior characteristics have become obsolete due to poor design, selection of crystal and cost. Recently, microDiamond using synthetic single crystal diamond detector (SCDD) is commercially available which is characterized in various radiation beams in this study. Methods: The characteristics of a commercial SCDD model 60019 (PTW) to a 6- and 15-MV photon beams, 6- and 20-MeV electron beams, and 208 MeV proton beams were investigated and compared to the pre-characterized detectors: TN31010 (0.125 cm{sup 3}) and TN30006 (pinpoint) ionization chambers (PTW), EDGE detector (Sun Nuclear Corp), and SFD Stereotactic Dosimetry Diode Detector (IBA). The depth-dose and profiles data were collected for various field sizes and depths. The dose linearity and dose rate dependency were also evaluated. To evaluate the effects of the preirradiation, the diamond detector which had not been irradiated on the day was set up in the water tank and the response to 100 MU was measured every 20 s. The temperature dependency was tested for the range of 4–60 °C. Angular dependency was evaluated in water phantom by rotating the SCDD. Results: For all radiation types and field sizes, the depth-dose data of the diamond chamber showed identical curve to those of ionization chambers. The profile of the diamond detector was very similar to those of the Edge and SFD detectors, although the 0.125 cm{sup 3} and pinpoint chambers showed averaging effects in the penumbrae region. The temperature dependency was within 0.7% in the range of 4–41°C. A dose of 900 cGy and 1200 cGy were needed to stabilize the chamber to the level within 0.5% and 0.2%, respectively. Conclusion: The type 60019 SCDD detector showed suitable characteristics for depth-dose and profile measurements for wide range of field sizes. However, at least 1000 cGy of pre-irradiation is needed for accurate measurements.

  15. Development and characterization of a three-dimensional radiochromic film stack dosimeter for megavoltage photon beam dosimetry

    SciTech Connect

    McCaw, Travis J. Micka, John A.; DeWerd, Larry A.

    2014-05-15

    Purpose: Three-dimensional (3D) dosimeters are particularly useful for verifying the commissioning of treatment planning and delivery systems, especially with the ever-increasing implementation of complex and conformal radiotherapy techniques such as volumetric modulated arc therapy. However, currently available 3D dosimeters require extensive experience to prepare and analyze, and are subject to large measurement uncertainties. This work aims to provide a more readily implementable 3D dosimeter with the development and characterization of a radiochromic film stack dosimeter for megavoltage photon beam dosimetry. Methods: A film stack dosimeter was developed using Gafchromic{sup ®} EBT2 films. The dosimeter consists of 22 films separated by 1 mm-thick spacers. A Virtual Water™ phantom was created that maintains the radial film alignment within a maximum uncertainty of 0.3 mm. The film stack dosimeter was characterized using simulations and measurements of 6 MV fields. The absorbed-dose energy dependence and orientation dependence of the film stack dosimeter were investigated using Monte Carlo simulations. The water equivalence of the dosimeter was determined by comparing percentage-depth-dose (PDD) profiles measured with the film stack dosimeter and simulated using Monte Carlo methods. Film stack dosimeter measurements were verified with thermoluminescent dosimeter (TLD) microcube measurements. The film stack dosimeter was also used to verify the delivery of an intensity-modulated radiation therapy (IMRT) procedure. Results: The absorbed-dose energy response of EBT2 film differs less than 1.5% between the calibration and film stack dosimeter geometries for a 6 MV spectrum. Over a series of beam angles ranging from normal incidence to parallel incidence, the overall variation in the response of the film stack dosimeter is within a range of 2.5%. Relative to the response to a normally incident beam, the film stack dosimeter exhibits a 1% under-response when the

  16. Experimental determination of the effective point of measurement for various detectors used in photon and electron beam dosimetry

    NASA Astrophysics Data System (ADS)

    Khee Looe, Hui; Harder, Dietrich; Poppe, Björn

    2011-07-01

    The subject of this study is the 'shift of the effective point of measurement', Δz, well known as a method of correction compensating for the 'displacement effect' in photon and electron beam dosimetry. Radiochromic EBT 1 films have been used to measure the 'true' TPR curves of 6 and 15 MV photons and 6 and 9 MeV electrons in the solid water-equivalent material RW3. For the Roos and Markus chambers, the cylindrical 'PinPoint', 'Semiflex' and 'Rigid-Stem' chambers, the 2D-Array and the E-type silicon diode (all from PTW-Freiburg), the positions of the effective points of measurement have been determined by direct or indirect comparison between their TPR curves and those of the EBT 1 film. Both for the Roos and Markus chambers, we found Δz = (0.4 ± 0.1) mm, which confirms earlier experimental and Monte Carlo results, but means a shortcoming of the 'water-equivalent window thickness' formula. For the cylindrical chambers, the ratio Δz/r was observed to increase with r, confirming a recent Monte Carlo prediction by Tessier (2010 E2-CN-182, Paper no 147, IDOS, Vienna) as well as the experimental observations by Johansson et al (1978 IAEA Symp. Proc. (Vienna) IAEA-SM-222/35 pp 243-70). According to a theoretical consideration, the shift of the effective point of measurement from the reference point of the detector is caused by a gradient of the fluence of the ionizing particles. As the experiments have shown, the value of Δz depends on the construction of the detector, but remains invariant under changes of radiation quality and depth. Other disturbances, which do not belong to the class of 'gradient effects', are not corrected by shifting the effective point of measurement.

  17. Implementation and validation of a fluence pencil kernels model for GaN-based dosimetry in photon beam radiotherapy

    NASA Astrophysics Data System (ADS)

    Wang, Ruoxi; Pittet, Patrick; Ribouton, Julien; Lu, Guo-Neng; Chaikh, Abdulhamid; Ahnesjö, Anders

    2013-10-01

    Gallium nitride (GaN), a direct-gap semiconductor that is radioluminescent, can be used as a transducer yielding a high signal from a small detecting volume and thus potentially suitable for use in small fields and for high dose gradients. A common drawback of semiconductor dosimeters with effective atomic numbers higher than soft tissues is that their responses depend on the presence of low energy photons for which the photoelectric cross section varies strongly with atomic number, which may affect the accuracy of dosimetric measurements. To tackle this ‘over-response’ issue, we propose a model for GaN-based dosimetry with readout correction. The local photon spectrum is calculated by convolving fluence pencil kernel spectra with the beam aperture fluence distribution. The response of a GaN detector is modelled by combining large cavity theory and small cavity theory for the low and high energy components of the local spectrum. Monte Carlo simulations are employed for determination of specific correction factors for different GaN transducer sizes and irradiation conditions. Some model parameters such as the cut-off energy and partitioning energy are discussed. The accuracy of the GaN dosimetric response model has been evaluated for tissue phantom ratio experiments along the central axis. These experiments have shown that calculated and measured GaN responses stay within ±3% at all depths beyond the build-up depth. The calculated GaN response factor is also in good agreement with measured data (±2.5%). The validated model with response compensation improves significantly the accuracy of dosimetric measurements: below 2.5% deviation as compared to 13% without compensation, for a 10 × 10 cm2 field, at depth from 1.5 to 22 cm.

  18. Continuous all-optical deceleration and single-photon cooling of molecular beams

    NASA Astrophysics Data System (ADS)

    Jayich, A. M.; Vutha, A. C.; Hummon, M. T.; Porto, J. V.; Campbell, W. C.

    2014-02-01

    Ultracold molecular gases are promising as an avenue to rich many-body physics, quantum chemistry, quantum information, and precision measurements. This richness, which flows from the complex internal structure of molecules, makes the creation of ultracold molecular gases using traditional methods (laser plus evaporative cooling) a challenge, in particular due to the spontaneous decay of molecules into dark states. We propose a way to circumvent this key bottleneck using an all-optical method for decelerating molecules using stimulated absorption and emission with a single ultrafast laser. We further describe single-photon cooling of the decelerating molecules that exploits their high dark state pumping rates, turning the principal obstacle to molecular laser cooling into an advantage. Cooling and deceleration may be applied simultaneously and continuously to load molecules into a trap. We discuss implementation details including multilevel numerical simulations of strontium monohydride. These techniques are applicable to a large number of molecular species and atoms with the only requirement being an electric dipole transition that can be accessed with an ultrafast laser.

  19. Combined photon-electron beams in the treatment of the supraclavicular lymph nodes in breast cancer: A novel technique that achieves adequate coverage while reducing lung dose

    SciTech Connect

    Salem, Ahmed; Mohamad, Issa; Dayyat, Abdulmajeed; Kanaa’n, Haitham; Sarhan, Nasim; Roujob, Ibrahim; Salem, Abdel-Fattah; Afifi, Shatha; Jaradat, Imad; Mubiden, Rasmi; Almousa, Abdelateif

    2015-10-01

    Radiation pneumonitis is a well-documented side effect of radiation therapy for breast cancer. The purpose of this study was to compare combined photon-electron, photon-only, and electron-only plans in the radiation treatment of the supraclavicular lymph nodes. In total, 13 patients requiring chest wall and supraclavicular nodal irradiation were planned retrospectively using combined photon-electron, photon-only, and electron-only supraclavicular beams. A dose of 50 Gy over 25 fractions was prescribed. Chest wall irradiation parameters were fixed for all plans. The goal of this planning effort was to cover 95% of the supraclavicular clinical target volume (CTV) with 95% of the prescribed dose and to minimize the volume receiving ≥ 105% of the dose. Comparative end points were supraclavicular CTV coverage (volume covered by the 95% isodose line), hotspot volume, maximum radiation dose, contralateral breast dose, mean total lung dose, total lung volume percentage receiving at least 20 Gy (V{sub 20} {sub Gy}), heart volume percentage receiving at least 25 Gy (V{sub 25} {sub Gy}). Electron and photon energies ranged from 8 to 18 MeV and 4 to 6 MV, respectively. The ratio of photon-to-electron fractions in combined beams ranged from 5:20 to 15:10. Supraclavicular nodal coverage was highest in photon-only (mean = 96.2 ± 3.5%) followed closely by combined photon-electron (mean = 94.2 ± 2.5%) and lowest in electron-only plans (mean = 81.7 ± 14.8%, p < 0.001). The volume of tissue receiving ≥ 105% of the prescription dose was higher in the electron-only (mean = 69.7 ± 56.1 cm{sup 3}) as opposed to combined photon-electron (mean = 50.8 ± 40.9 cm{sup 3}) and photon-only beams (mean = 32.2 ± 28.1 cm{sup 3}, p = 0.114). Heart V{sub 25} {sub Gy} was not statistically different among the plans (p = 0.999). Total lung V{sub 20} {sub Gy} was lowest in electron-only (mean = 10.9 ± 2.3%) followed by combined photon-electron (mean = 13.8 ± 2.3%) and highest in photon

  20. Iodine enhanced focused-ion-beam etching of silicon for photonic applications

    SciTech Connect

    Schrauwen, Jonathan; Thourhout, Dries van; Baets, Roel

    2007-11-15

    Focused-ion-beam etching of silicon enables fast and versatile fabrication of micro- and nanophotonic devices. However, large optical losses due to crystal damage and ion implantation make the devices impractical when the optical mode is confined near the etched region. These losses are shown to be reduced by the local implantation and etching of silicon waveguides with iodine gas enhancement, followed by baking at 300 deg. C. The excess optical loss in the silicon waveguides drops from 3500 to 1700 dB/cm when iodine gas is used, and is further reduced to 200 dB/cm after baking at 300 deg. C. We present elemental and chemical surface analyses supporting that this is caused by the desorption of iodine from the silicon surface. Finally we present a model to extract the absorption coefficient from the measurements.

  1. Characterization of Scattered X-Ray Photons in Dental Cone-Beam Computed Tomography

    PubMed Central

    Yang, Ching-Ching

    2016-01-01

    Purpose Scatter is a very important artifact causing factor in dental cone-beam CT (CBCT), which has a major influence on the detectability of details within images. This work aimed to improve the image quality of dental CBCT through scatter correction. Methods Scatter was estimated in the projection domain from the low frequency component of the difference between the raw CBCT projection and the projection obtained by extrapolating the model fitted to the raw projections acquired with 2 different sizes of axial field-of-view (FOV). The function for curve fitting was optimized by using Monte Carlo simulation. To validate the proposed method, an anthropomorphic phantom and a water-filled cylindrical phantom with rod inserts simulating different tissue materials were scanned using 120 kVp, 5 mA and 9-second scanning time covering an axial FOV of 4 cm and 13 cm. The detectability of the CT image was evaluated by calculating the contrast-to-noise ratio (CNR). Results Beam hardening and cupping artifacts were observed in CBCT images without scatter correction, especially in those acquired with 13 cm FOV. These artifacts were reduced in CBCT images corrected by the proposed method, demonstrating its efficacy on scatter correction. After scatter correction, the image quality of CBCT was improved in terms of target detectability which was quantified as the CNR for rod inserts in the cylindrical phantom. Conclusions Hopefully the calculations performed in this work can provide a route to reach a high level of diagnostic image quality for CBCT imaging used in oral and maxillofacial structures whilst ensuring patient dose as low as reasonably achievable, which may ultimately make CBCT scan a reliable and safe tool in clinical practice. PMID:26950435

  2. Photon stimulated desorption measurements of extruded copper and of welded copper beam chambers for the PEP-II asymmetric B factory

    SciTech Connect

    Foerster, C.L.; Lanni, C.; Perkins, C.; Calderon, M.; Barletta, W.

    1995-05-01

    PEP II is being built as a higher luminosity electron--positron collider with asymmetric beams of 9 and 3.1 GeV, having maximum currents of 3.0 A. Based on our previous work on the National Synchrotron Light Source (NSLS) vacuum ultraviolet beamline U10B, a copper was selected for construction of ultrahigh vacuum beam chambers and absorbers to minimize the pressure rise from synchrotron radiation during operation. An extruded beam chamber and a welded beam chamber were fabricated from the selected copper for photon stimulated desorption measurements on the NSLS x-ray beamline X28A. The chambers were exposed to white light with a critical energy of 5 keV, both directly and through a 0.010-in.-thick beryllium filter. Each chamber was exposed to a dose of approximately 10{sup 23} photons per meter at an incidence angle of 25 mrad, after argon glow preconditioning and a 150 {degree}C vacuum bake. Desorption yields for H{sub 2} CO, CO{sub 2}, and CH{sub 4} are reported as a function of accumulated photon flux, critical energy, and chamber preparation. The results are compared with the previous work on the beamline U10B and with those of other published work on copper. {copyright} {ital 1995} {ital American} {ital Vacuum} {ital Society}

  3. Physics of the Brain: Interaction of the Optical-Fiber-Guided Multi-Ultraviolet-Photon Beams with the Epilepsy Topion, (the Seizure Onset Area)

    NASA Astrophysics Data System (ADS)

    Stefan, V. Alexander

    A novel method for the possible prevention of epileptic seizures is proposed, based on the multi-ultraviolet-photon beam interaction with the epilepsy topion, (nonlinear coupling of an ultra high frequency mode to the brain beta phonons). It is hypothesized that epilepsy is a chaotic-dynamics phenomenon: small electrical changes in the epilepsy-topion lead, (within the 10s of milliseconds), to the onset of chaos, (seizure--excessive electrical discharge), and subsequent cascading into adjacent areas. The ultraviolet photons may control the imbalance of sodium and potassium ions and, consequently, may prove to be efficient in the prevention of epileptic seizures. Supported by Nikola Tesla Labs, Stefan University.

  4. A new single crystal diamond dosimeter for small beam: comparison with different commercial active detectors

    NASA Astrophysics Data System (ADS)

    Marsolat, F.; Tromson, D.; Tranchant, N.; Pomorski, M.; Le Roy, M.; Donois, M.; Moignau, F.; Ostrowsky, A.; De Carlan, L.; Bassinet, C.; Huet, C.; Derreumaux, S.; Chea, M.; Cristina, K.; Boisserie, G.; Bergonzo, P.

    2013-11-01

    Recent developments of new therapy techniques using small photon beams, such as stereotactic radiotherapy, require suitable detectors to determine the delivered dose with a high accuracy. The dosimeter has to be as close as possible to tissue equivalence and to exhibit a small detection volume compared to the size of the irradiation field, because of the lack of lateral electronic equilibrium in small beam. Characteristics of single crystal diamond (tissue equivalent material Z = 6, high density) make it an ideal candidate to fulfil most of small beam dosimetry requirements. A commercially available Element Six electronic grade synthetic diamond was used to develop a single crystal diamond dosimeter (SCDDo) with a small detection volume (0.165 mm3). Long term stability was studied by irradiating the SCDDo in a 60Co beam over 14 h. A good stability (deviation less than ± 0.1%) was observed. Repeatability, dose linearity, dose rate dependence and energy dependence were studied in a 10 × 10 cm2 beam produced by a Varian Clinac 2100 C linear accelerator. SCDDo lateral dose profile, depth dose curve and output factor (OF) measurements were performed for small photon beams with a micro multileaf collimator m3 (BrainLab) attached to the linac. This study is focused on the comparison of SCDDo measurements to those obtained with different commercially available active detectors: an unshielded silicon diode (PTW 60017), a shielded silicon diode (Sun Nuclear EDGE), a PinPoint ionization chamber (PTW 31014) and two natural diamond detectors (PTW 60003). SCDDo presents an excellent spatial resolution for dose profile measurements, due to its small detection volume. Low energy dependence (variation of 1.2% between 6 and 18 MV photon beam) and low dose rate dependence of the SCDDo (variation of 1% between 0.53 and 2.64 Gy min-1) are obtained, explaining the good agreement between the SCDDo and the efficient unshielded diode (PTW 60017) in depth dose curve measurements. For

  5. Micro-metric electronic patterning of a topological band structure using a photon beam.

    PubMed

    Frantzeskakis, E; De Jong, N; Zwartsenberg, B; Huang, Y K; Bay, T V; Pronk, P; Van Heumen, E; Wu, D; Pan, Y; Radovic, M; Plumb, N C; Xu, N; Shi, M; De Visser, A; Golden, M S

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi(2-x)Sb(x)Te(3-y)Se(y) with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi(2-x)Sb(x)Te(3-y)Se(y) crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by 'writing' micron-sized letters in the Dirac point energy of the system. PMID:26543011

  6. Micro-metric electronic patterning of a topological band structure using a photon beam

    PubMed Central

    Frantzeskakis, E.; De Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; Van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; De Visser, A.; Golden, M. S.

    2015-01-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2−xSbxTe3−ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2−xSbxTe3−ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system. PMID:26543011

  7. Micro-metric electronic patterning of a topological band structure using a photon beam

    NASA Astrophysics Data System (ADS)

    Frantzeskakis, E.; de Jong, N.; Zwartsenberg, B.; Huang, Y. K.; Bay, T. V.; Pronk, P.; van Heumen, E.; Wu, D.; Pan, Y.; Radovic, M.; Plumb, N. C.; Xu, N.; Shi, M.; de Visser, A.; Golden, M. S.

    2015-11-01

    In an ideal 3D topological insulator (TI), the bulk is insulating and the surface conducting due to the existence of metallic states that are localized on the surface; these are the topological surface states. Quaternary Bi-based compounds of Bi2-xSbxTe3-ySey with finely-tuned bulk stoichiometries are good candidates for realizing ideal 3D TI behavior due to their bulk insulating character. However, despite its insulating bulk in transport experiments, the surface region of Bi2-xSbxTe3-ySey crystals cleaved in ultrahigh vacuum also exhibits occupied states originating from the bulk conduction band. This is due to adsorbate-induced downward band-bending, a phenomenon known from other Bi-based 3D TIs. Here we show, using angle-resolved photoemission, how an EUV light beam of moderate flux can be used to exclude these topologically trivial states from the Fermi level of Bi1.46Sb0.54Te1.7Se1.3 single crystals, thereby re-establishing the purely topological character of the low lying electronic states of the system. We furthermore prove that this process is highly local in nature in this bulk-insulating TI, and are thus able to imprint structures in the spatial energy landscape at the surface. We illustrate this by ‘writing’ micron-sized letters in the Dirac point energy of the system.

  8. The SPARC_LAB femtosecond synchronization for electron and photon pulsed beams

    NASA Astrophysics Data System (ADS)

    Bellaveglia, M.; Gallo, A.; Piersanti, L.; Pompili, R.; Gatti, G.; Anania, M. P.; Petrarca, M.; Villa, F.; Chiadroni, E.; Biagioni, A.; Mostacci, A.

    2015-05-01

    The SPARC LAB complex hosts a 150 MeV electron photo-injector equipped with an undulator for FEL production (SPARC) together with a high power TW laser (FLAME). Recently the synchronization system reached the performance of < 100 fsRMS relative jitter between lasers, electron beam and RF accelerating fields. This matches the requirements for next future experiments: (i) the production of X-rays by means of Thomson scattering (first collisions achieved in 2014) and (ii) the particle driven PWFA experiment by means of multiple electron bunches. We report about the measurements taken during the machine operation using BAMs (Bunch Arrival Monitors) and EOS (Electro-Optical Sampling) system. A new R and D activity concerning the LWFA using the external injection of electron bunches in a plasma generated by the FLAME laser pulse is under design. The upgrade of the synchronization system is under way to guarantee the < 30 fs RMS jitter required specification. It foresees the transition from electrical to optical architecture that mainly affects the reference signal distribution and the time of arrival detection performances. The new system architecture is presented together with the related experimental data.

  9. Photon-photon collisions

    SciTech Connect

    Brodsky, S.J.

    1985-01-01

    The study of photon-photon collisions has progressed enormously, stimulated by new data and new calculational tools for QCD. In the future we can expect precise determinations of ..cap alpha../sub s/ and ..lambda../sup ms/ from the ..gamma..*..gamma.. ..-->.. ..pi../sup 0/ form factor and the photon structure function, as well as detailed checks of QCD, determination of the shape of the hadron distribution amplitudes from ..gamma gamma.. ..-->.. H anti H, reconstruction of sigma/sub ..gamma gamma../ from exclusive channels at low W/sub ..gamma gamma../, definitive studies of high p/sub T/ hadron and jet production, and studies of threshold production of charmed systems. Photon-photon collisions, along with radiative decays of the psi and UPSILON, are ideal for the study of multiquark and gluonic resonances. We have emphasized the potential for resonance formation near threshold in virtually every hadronic exclusive channel, including heavy quark states c anti c c anti c, c anti c u anti u, etc. At higher energies SLC, LEP, ...) parity-violating electroweak effects and Higgs production due to equivalent Z/sup 0/ and W/sup + -/ beams from e ..-->.. eZ/sup 0/ and e ..-->.. nu W will become important. 44 references.

  10. Assessment of computerized treatment planning system accuracy in calculating wedge factors of physical wedged fields for 6 MV photon beams.

    PubMed

    Muhammad, Wazir; Maqbool, Muhammad; Shahid, Muhammad; Hussain, Amjad; Tahir, Sajjad; Matiullah; Rooh, Gul; Ahmad, Tanveer; Lee, Sang Hoon

    2011-07-01

    Wedge filters are commonly used in external beam radiotherapy to achieve a uniform dose distribution within the target volume. The main objective of this study was to investigate the accuracy of the beam modifier algorithm of Theraplan plus (TPP version 3.8) treatment planning system and to confirm that either the beam hardening, beam softening and attenuation coefficients along with wedge geometry and measured wedge factor at single depth and multiple fields sizes can be the replacement of wedged profile and wedged cross-sectional data or not. In this regard the effect of beam hardening and beam softening was studied with physical wedges for 6 MV photons. The Normalized Wedge Factors (NWFs) were measured experimentally as well as calculated with the Theraplan plus, as a function of depth and field size in a water phantom for 15°, 30°, 45°, and 60° wedge filters. The beam hardening and softening was determined experimentally by deriving the required coefficients for all wedge angles. The TPP version 3.8 requires wedge transmission factor at single depth and multiple field sizes. Without incorporating the hardening and softening coefficients the percent difference between measured and calculated NFWs was as high as 7%. After the introduction of these parameters into the algorithm, the agreement between measured and TPP (V 3.8) calculated NWFs were improved to within 2 percent for various depths. Similar improvement was observed in TPP version 3.8 while calculating NWFs for various field sizes when the required coefficients were adjusted. In conclusion, the dose calculation algorithm of TPP version 3.8 showed good accuracy for a 6 MV photon beam provided beam hardening and softening parameters are taken into account. From the results, it is also concluded that, the beam hardening, beam softening and attenuation coefficients along with wedge geometry and measured wedge factor at single depth and multiple fields sizes can be the replacement of wedged profile and

  11. Enhanced Etching, Surface Damage Recovery, and Submicron Patterning of Hybrid Perovskites using a Chemically Gas-Assisted Focused-Ion Beam for Subwavelength Grating Photonic Applications.

    PubMed

    Alias, Mohd S; Yang, Yang; Ng, Tien K; Dursun, Ibrahim; Shi, Dong; Saidaminov, Makhsud I; Priante, Davide; Bakr, Osman M; Ooi, Boon S

    2016-01-01

    The high optical gain and absorption of organic-inorganic hybrid perovskites have attracted attention for photonic device applications. However, owing to the sensitivity of organic moieties to solvents and temperature, device processing is challenging, particularly for patterning. Here, we report the direct patterning of perovskites using chemically gas-assisted focused-ion beam (GAFIB) etching with XeF2 and I2 precursors. We demonstrate etching enhancement in addition to controllability and marginal surface damage compared to focused-ion beam (FIB) etching without precursors. Utilizing the GAFIB etching, we fabricated a uniform and periodic submicron perovskite subwavelength grating (SWG) absorber with broadband absorption and nanoscale precision. Our results demonstrate the use of FIB as a submicron patterning tool and a means of providing surface treatment (after FIB patterning to minimize optical loss) for perovskite photonic nanostructures. The SWG absorber can be patterned on perovskite solar cells to enhance the device efficiency through increasing light trapping and absorption. PMID:26688008

  12. A finite element analysis of room temperature silicon crystals for the Advanced Photon Source bending-magnet and insertion-device beams

    SciTech Connect

    Assoufid, L.; Lee, W.K.; Mills, D.M.

    1994-08-01

    The third generation of synchrotron radiation sources, such as the Advanced Photon Source (APS), will provide users with a high brilliance x-ray beam with high power and power densities. In many cases, the first optical component to intercept the x-ray beam is a silicon-crystal monochromator. Due to extreme heat loading, the photon throughput and brilliance will be severely degraded if the monochromator is not properly designed (or cooled). This document describes a series of finite element analyses performed on room temperature silicon for the three standard APS sources, namely, the bending magnet, Wiggler A, and Undulator A. The modeling is performed with the silicon cooled directly with water or liquid gallium through rectangular channels. The temperature distributions and thermally induced deformations are presented.

  13. The FERMI@Elettra free-electron-laser source for coherent X-ray physics: photon properties, beam transport system, and applications

    SciTech Connect

    Allaria, Enrico; Callegari, Carlo; Cocco, Daniele; Fawley, William M.; Kiskinova, Maya; Masciovecchio, Claudio; Parmigiani, Fulvio

    2010-04-05

    FERMI@Elettra is comprised of two free electron lasers (FELs) that will generate short pulses (tau ~;; 25 to 200 fs) of highly coherent radiation in the XUV and soft X-ray region. The use of external laser seeding together with a harmonic upshift scheme to obtain short wavelengths will give FERMI@Elettra the capability to produce high quality, longitudinal coherent photon pulses. This capability together with the possibilities of temporal synchronization to external lasers and control of the output photon polarization will open new experimental opportunities not possible with currently available FELs. Here we report on the predicted radiation coherence properties and important configuration details of the photon beam transport system. We discuss the several experimental stations that will be available during initial operations in 2011, and we give a scientific perspective on possible experiments that can exploit the critical parameters of this new light source.

  14. Potential applications of a dual-sweep streak camera system for characterizing particle and photon beams of VUV, XUV, and x-ray FELS

    SciTech Connect

    Lumpkin, A.

    1995-12-31

    The success of time-resolved imaging techniques in the Characterization of particle beams and photon beams of the recent generation of L-band linac-driven or storage ring FELs in the infrared, visible, and ultraviolet wavelength regions can be extended to the VUV, XUV, and x-ray FELs. Tests and initial data have been obtained with the Hamamatsu C5680 dual-sweep streak camera system which includes a demountable photocathode (thin Au) assembly and a flange that allows windowless operation with the transport vacuum system. This system can be employed at wavelengths shorter than 100 nm and down to 1 {Angstrom}. First tests on such a system at 248-nm wavelengths have been performed oil the Argonne Wakefield Accelerator (AWA) drive laser source. A quartz window was used at the tube entrance aperture. A preliminary test using a Be window mounted on a different front flange of the streak tube to look at an x-ray bremsstrahlung source at the AWA was limited by photon statistics. This system`s limiting resolution of {sigma}{approximately}1.1 ps observed at 248 nm would increase with higher incoming photon energies to the photocathode. This effect is related to the fundamental spread in energies of the photoelectrons released from the photocathodes. Possible uses of the synchrotron radiation sources at the Advanced Photon Source and emerging short wavelength FELs to test the system will be presented.

  15. Breaking the diffraction-limited resolution barrier in fiber-optical two-photon fluorescence endoscopy by an azimuthally-polarized beam.

    PubMed

    Gu, Min; Kang, Hong; Li, Xiangping

    2014-01-01

    Although fiber-optical two-photon endoscopy has been recognized as a potential high-resolution diagnostic and therapeutic procedure in vivo, its resolution is limited by the optical diffraction nature to a few micrometers due to the low numerical aperture of an endoscopic objective. On the other hand, stimulated emission depletion (STED) achieved by a circularly-polarized vortex beam has been used to break the diffraction-limited resolution barrier in a bulky microscope. It has been a challenge to apply the STED principle to a fiber-optical two-photon endoscope as a circular polarization state cannot be maintained due to the birefringence of a fiber. Here, we demonstrate the first fiber-optical STED two-photon endoscope using an azimuthally-polarized beam directly generated from a double-clad fiber. As such, the diffraction-limited resolution barrier of fiber-optical two-photon endoscopy can be broken by a factor of three. Our new accomplishment has paved a robust way for high-resolution in vivo biomedical studies. PMID:24406685

  16. Breaking the diffraction-limited resolution barrier in fiber-optical two-photon fluorescence endoscopy by an azimuthally-polarized beam

    PubMed Central

    Gu, Min; Kang, Hong; Li, Xiangping

    2014-01-01

    Although fiber-optical two-photon endoscopy has been recognized as a potential high-resolution diagnostic and therapeutic procedure in vivo, its resolution is limited by the optical diffraction nature to a few micrometers due to the low numerical aperture of an endoscopic objective. On the other hand, stimulated emission depletion (STED) achieved by a circularly-polarized vortex beam has been used to break the diffraction-limited resolution barrier in a bulky microscope. It has been a challenge to apply the STED principle to a fiber-optical two-photon endoscope as a circular polarization state cannot be maintained due to the birefringence of a fiber. Here, we demonstrate the first fiber-optical STED two-photon endoscope using an azimuthally-polarized beam directly generated from a double-clad fiber. As such, the diffraction-limited resolution barrier of fiber-optical two-photon endoscopy can be broken by a factor of three. Our new accomplishment has paved a robust way for high-resolution in vivo biomedical studies. PMID:24406685

  17. Dose conversion and wall correction factors for Fricke dosimetry in high-energy photon beams: analytical model and Monte Carlo calculations.

    PubMed

    Ma, C M; Nahum, A E

    1993-01-01

    This paper presents the dose conversion and wall correction factors for Fricke dosimetry in high-energy photon beams calculated using both an analytical general cavity model and Monte Carlo techniques. The conversion factor is calculated as the ratio of the absorbed dose in water to that in the Fricke dosimeter solution with a water-walled vessel. The wall correction factor accounts for the change in the absorbed dose to the dosimeter solution caused by the inhomogeneous dosimeter wall material. A usercode based on the EGS4 Monte Carlo system, with the application of a correlated sampling variance reduction technique, has been employed in the calculations of these factors and the parameters used in the cavity model. Good agreement has been achieved between the predictions of the model and that obtained by direct Monte Carlo simulation and also with other workers' experiments. It is shown that Fricke dosimeters in common use cannot be considered to be 'large' detectors and therefore 'general cavity theory' should be applied in converting the dose to water. It is confirmed that plastic dosimeter vessels have a negligible wall effect. The wall correction factor for a 1 mm thick Pyrex-walled vessel varies with incident photon energy from 1.001 +/- 0.001 for a 60Co beam to 0.983 +/- 0.001 for a 24 MV (TPR(10)20 = 0.80) photon beam. This implies that previous Fricke measurements with glass-walled vessels should be re-evaluated. PMID:8426871

  18. Evaluation of the use of surrogate tissues for calculating radiation dose to lymphatic nodes from external photon beams

    PubMed Central

    Lamart, Stephanie; Moroz, Brian E.; Lee, Choonsik

    2013-01-01

    Lymphatic node chains of the human body are particularly difficult to realistically model in computational human phantoms. In the absence of a lymphatic node model, researchers have used the following surrogate tissues to calculate the radiation dose to the lymphatic nodes: blood vessels, muscle and the combination of the muscle and adipose tissues. In the present work, the authors investigated whether and in which extent the use of different surrogate tissues is appropriate to assess the lymph node dose, using a realistic model of lymphatic nodes that the authors recently reported. Using a Monte Carlo radiation transport method coupled with the adult male hybrid phantom that included the lymph node model, the air kerma-to-absorbed dose conversion coefficients (Gy Gy−1) to the lymph nodes and other tissues used as surrogates for external photon beams of 15 discrete energies (0.015–10 MeV) were computed using the following six idealised geometries: anterior–posterior (AP), posterior–anterior (PA), right lateral, left lateral, rotational and isotropic. To validate the results of this study, the lymph node dose calculated here was compared with the dose published by the International Commission on Radiological Protection for the adult male reference phantom. The lymph node dose conversion coefficients with the values calculated for the blood vessels, muscle, adipose tissue and the combination of muscle and adipose tissues were then compared. It was found that muscle was the best estimator for the lymph nodes, with a dose difference averaged across energies >0.08 MeV of <8 % in all irradiation geometries excluding the AP and PA geometries for which the blood vessels were found to be the best estimator. In conclusion, muscle and blood vessels may preferably be used as surrogate tissues in the absence of lymphatic nodes in a given voxel phantom. For energies <0.08 MeV, for which the authors observed a difference of up to 30-fold, an explicit lymph node model may

  19. Effusive molecular beam-sampled Knudsen flow reactor coupled to vacuum ultraviolet single photon ionization mass spectrometry using an external free radical source

    SciTech Connect

    Leplat, N.; Rossi, M. J.

    2013-11-15

    A new apparatus using vacuum ultraviolet single photon ionization mass spectrometry (VUV SPIMS) of an effusive molecular beam emanating from a Knudsen flow reactor is described. It was designed to study free radical-molecule kinetics over a significant temperature range (300–630 K). Its salient features are: (1) external free radical source, (2) counterpropagating molecular beam and diffuse VUV photon beam meeting in a crossed-beam ion source of a quadrupole mass spectrometer with perpendicular ion extraction, (3) analog detection of the photocurrent of the free radical molecular cation, and (4) possibility of detecting both free radicals and closed shell species in the same apparatus and under identical reaction conditions owing to the presence of photoelectrons generated by the photoelectric effect of the used VUV-photons. The measured thermal molecular beam-to-background ratio was 6.35 ± 0.39 for Ar and 10.86 ± 1.59 for i-C{sub 4}H{sub 10} at 300 K, a factor of 2.52 and 1.50 smaller, respectively, than predicted from basic gas-dynamic considerations. Operating parameters as well as the performance of key elements of the instrument are presented and discussed. Coupled to an external free radical source a steady-state specific exit flow of 1.6 × 10{sup 11} and 5.0 × 10{sup 11} molecule s{sup −1} cm{sup −3} of C{sub 2}H{sub 5}{sup •} (ethyl) and t-C{sub 4}H{sub 9}{sup •} (t-butyl) free radicals have been detected using VUV SPIMS at their molecular ion m/z 29 and 57, respectively, at 300 K.

  20. Effusive molecular beam-sampled Knudsen flow reactor coupled to vacuum ultraviolet single photon ionization mass spectrometry using an external free radical source.

    PubMed

    Leplat, N; Rossi, M J

    2013-11-01

    A new apparatus using vacuum ultraviolet single photon ionization mass spectrometry (VUV SPIMS) of an effusive molecular beam emanating from a Knudsen flow reactor is described. It was designed to study free radical-molecule kinetics over a significant temperature range (300-630 K). Its salient features are: (1) external free radical source, (2) counterpropagating molecular beam and diffuse VUV photon beam meeting in a crossed-beam ion source of a quadrupole mass spectrometer with perpendicular ion extraction, (3) analog detection of the photocurrent of the free radical molecular cation, and (4) possibility of detecting both free radicals and closed shell species in the same apparatus and under identical reaction conditions owing to the presence of photoelectrons generated by the photoelectric effect of the used VUV-photons. The measured thermal molecular beam-to-background ratio was 6.35 ± 0.39 for Ar and 10.86 ± 1.59 for i-C4H10 at 300 K, a factor of 2.52 and 1.50 smaller, respectively, than predicted from basic gas-dynamic considerations. Operating parameters as well as the performance of key elements of the instrument are presented and discussed. Coupled to an external free radical source a steady-state specific exit flow of 1.6 × 10(11) and 5.0 × 10(11) molecule s(-1) cm(-3) of C2H5(●) (ethyl) and t-C4H9(●) (t-butyl) free radicals have been detected using VUV SPIMS at their molecular ion m/z 29 and 57, respectively, at 300 K. PMID:24289411

  1. Vagus nerve stimulator stability and interference on radiation oncology x-ray beams.

    PubMed

    Gossman, Michael S; Ketkar, Amruta; Liu, Arthur K; Olin, Bryan

    2012-10-21

    Five different models of Cyberonics, Inc. vagus nerve stimulation (VNS) therapy pulse generators were investigated for their stability under radiation and their ability to change the absorbed dose from incident radiation. X-ray beams of 6 MV and 18 MV were used to quantify these results up to clinical doses of 68-78 Gy delivered in a single fraction. In the first part, the effect on electronic stimulation signaling of each pulse generator was monitored during and immediately afterwards with computer interrogation. In the second part, the effects of having the pulse generators scatter or attenuate the x-ray beam was also characterized from dose calculations on a treatment planning system as well as from actual radiation measurements. Some device models were found to be susceptible to radiation interference when placed directly in the beam of high energy therapeutic x-ray radiation. While some models exhibited no effect at all, others showed an apparent loss of stimulation output immediately after radiation was experienced. Still, other models were observed to have a cumulative dose effect with a reduced output signal, followed by battery depletion above 49 Gy. Absorbed dose changes on computer underestimated attenuation by nearly half for both energies amongst all pulse generators, although the computer did depict the proper shape of the changed distribution of dose around the device. Measured attenuation ranged from 7.0% to 11.0% at 6 MV and 4.2% to 5.2% at 18 MV for x-rays. Processes of back-scatter and side-scatter were deemed negligible although recorded. Identical results from 6 MV and 18 MV x-ray beams conclude no neutron effect was induced for the 18 MV beam. As there were documented effects identified in this research regarding pulse generation, it emphasizes the importance of caution when considering radiation therapy on patients with implanted VNS devices with observed malfunctions consequential. PMID:23032351

  2. Vagus nerve stimulator stability and interference on radiation oncology x-ray beams

    NASA Astrophysics Data System (ADS)

    Gossman, Michael S.; Ketkar, Amruta; Liu, Arthur K.; Olin, Bryan

    2012-10-01

    Five different models of Cyberonics, Inc. vagus nerve stimulation (VNS) therapy pulse generators were investigated for their stability under radiation and their ability to change the absorbed dose from incident radiation. X-ray beams of 6 MV and 18 MV were used to quantify these results up to clinical doses of 68-78 Gy delivered in a single fraction. In the first part, the effect on electronic stimulation signaling of each pulse generator was monitored during and immediately afterwards with computer interrogation. In the second part, the effects of having the pulse generators scatter or attenuate the x-ray beam was also characterized from dose calculations on a treatment planning system as well as from actual radiation measurements. Some device models were found to be susceptible to radiation interference when placed directly in the beam of high energy therapeutic x-ray radiation. While some models exhibited no effect at all, others showed an apparent loss of stimulation output immediately after radiation was experienced. Still, other models were observed to have a cumulative dose effect with a reduced output signal, followed by battery depletion above 49 Gy. Absorbed dose changes on computer underestimated attenuation by nearly half for both energies amongst all pulse generators, although the computer did depict the proper shape of the changed distribution of dose around the device. Measured attenuation ranged from 7.0% to 11.0% at 6 MV and 4.2% to 5.2% at 18 MV for x-rays. Processes of back-scatter and side-scatter were deemed negligible although recorded. Identical results from 6 MV and 18 MV x-ray beams conclude no neutron effect was induced for the 18 MV beam. As there were documented effects identified in this research regarding pulse generation, it emphasizes the importance of caution when considering radiation therapy on patients with implanted VNS devices with observed malfunctions consequential.

  3. Long-term Cosmetic Outcomes and Toxicities of Proton Beam Therapy Compared With Photon-Based 3-Dimensional Conformal Accelerated Partial-Breast Irradiation: A Phase 1 Trial

    SciTech Connect

    Galland-Girodet, Sigolène; Pashtan, Itai; MacDonald, Shannon M.; Ancukiewicz, Marek; Hirsch, Ariel E.; Kachnic, Lisa A.; Specht, Michelle; Gadd, Michele; Smith, Barbara L.; Powell, Simon N.; Recht, Abram; Taghian, Alphonse G.

    2014-11-01

    Purpose: To present long-term outcomes of a prospective feasibility trial using either protons or 3-dimensional conformal photon-based (accelerated partial-breast irradiation [APBI]) techniques. Methods and Materials: From October 2003 to April 2006, 98 evaluable patients with stage I breast cancer were treated with APBI (32 Gy in 8 fractions given twice daily) on a prospective clinical trial: 19 with proton beam therapy (PBT) and 79 with photons or mixed photons/electrons. Median follow-up was 82.5 months (range, 2-104 months). Toxicity and patient satisfaction evaluations were performed at each visit. Results: At 7 years, the physician rating of overall cosmesis was good or excellent for 62% of PBT patients, compared with 94% for photon patients (P=.03). Skin toxicities were more common for the PBT group: telangiectasia, 69% and 16% (P=.0013); pigmentation changes, 54% and 22% (P=.02); and other late skin toxicities, 62% and 18% (P=.029) for PBT and photons, respectively. There were no significant differences between the groups in the incidences of breast pain, edema, fibrosis, fat necrosis, skin desquamation, and rib pain or fracture. Patient-reported cosmetic outcomes at 7 years were good or excellent for 92% and 96% of PBT and photon patients, respectively (P=.95). Overall patient satisfaction was 93% for the entire cohort. The 7-year local failure rate for all patients was 6%, with 3 local recurrences in the PBT group (7-year rate, 11%) and 2 in photon-treated patients (4%) (P=.22). Conclusions: Local failure rates of 3-dimensional APBI and PBT were similar in this study. However, PBT, as delivered in this study, led to higher rates of long-term telangiectasia, skin color changes, and skin toxicities. We recommend the use of multiple fields and treatment of all fields per treatment session or the use of scanning techniques to minimize skin toxicity.

  4. Photon stimulated desorption (PSD) measurements of extruded copper and of welded copper beam chambers for the PEP II asymmetric B-factory

    SciTech Connect

    Foerster, C.L.; Lanni, C.; Perkins, C.; Calderon, M.; Barletta, W.

    1994-12-31

    PEP II is being built as a higher luminosity electron-positron collider, with asymmetric beams of 9 GeV and 3.1 GeV, having maximum currents of 3.0 A. Based on the previous work on the NSLS VUV beamline U10B, a copper was selected for construction of UHV beam chambers and absorbers to minimize the pressure rise from synchrotron radiation during operation. An extruded beam chamber and a welded beam chamber were fabricated from the selected copper for PSD measurements on NSLS X-ray beamline X28A. The chambers were exposed to white light with a critical energy of 5 KeV, both direct and through a 0.010 inch thick Beryllium filter. Each chamber was exposed to a dose of approximately 10{sup 23} photons per meter at an incidence angle of 25 mrad, after argon glow conditioning and a 150 C vacuum bake. Desorption yields for H{sub 2} CO, CO{sub 2}, and CH{sub 4} are reported as a function of accumulated photon flux, critical energy, and chamber preparation. The results are compared with the previous work on beamline U10B and with those of other published work for copper.

  5. Fast, accurate photon beam accelerator modeling using BEAMnrc: A systematic investigation of efficiency enhancing methods and cross-section data

    SciTech Connect

    Fragoso, Margarida; Kawrakow, Iwan; Faddegon, Bruce A.; Solberg, Timothy D.; Chetty, Indrin J.

    2009-12-15

    In this work, an investigation of efficiency enhancing methods and cross-section data in the BEAMnrc Monte Carlo (MC) code system is presented. Additionally, BEAMnrc was compared with VMC++, another special-purpose MC code system that has recently been enhanced for the simulation of the entire treatment head. BEAMnrc and VMC++ were used to simulate a 6 MV photon beam from a Siemens Primus linear accelerator (linac) and phase space (PHSP) files were generated at 100 cm source-to-surface distance for the 10x10 and 40x40 cm{sup 2} field sizes. The BEAMnrc parameters/techniques under investigation were grouped by (i) photon and bremsstrahlung cross sections, (ii) approximate efficiency improving techniques (AEITs), (iii) variance reduction techniques (VRTs), and (iv) a VRT (bremsstrahlung photon splitting) in combination with an AEIT (charged particle range rejection). The BEAMnrc PHSP file obtained without the efficiency enhancing techniques under study or, when not possible, with their default values (e.g., EXACT algorithm for the boundary crossing algorithm) and with the default cross-section data (PEGS4 and Bethe-Heitler) was used as the ''base line'' for accuracy verification of the PHSP files generated from the different groups described previously. Subsequently, a selection of the PHSP files was used as input for DOSXYZnrc-based water phantom dose calculations, which were verified against measurements. The performance of the different VRTs and AEITs available in BEAMnrc and of VMC++ was specified by the relative efficiency, i.e., by the efficiency of the MC simulation relative to that of the BEAMnrc base-line calculation. The highest relative efficiencies were {approx}935 ({approx}111 min on a single 2.6 GHz processor) and {approx}200 ({approx}45 min on a single processor) for the 10x10 field size with 50 million histories and 40x40 cm{sup 2} field size with 100 million histories, respectively, using the VRT directional bremsstrahlung splitting (DBS) with no

  6. Fast, accurate photon beam accelerator modeling using BEAMnrc: A systematic investigation of efficiency enhancing methods and cross-section data

    PubMed Central

    Fragoso, Margarida; Kawrakow, Iwan; Faddegon, Bruce A.; Solberg, Timothy D.; Chetty, Indrin J.

    2009-01-01

    In this work, an investigation of efficiency enhancing methods and cross-section data in the BEAMnrc Monte Carlo (MC) code sys