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1

Where does gel dosimetry fit in the clinic?  

Microsoft Academic Search

For over a decade our community has considered gel dosimetry a promising technique for the clinic, since it provides a unique methodology for three dimensionally dose measurement of the complex conformal dose distributions achieved by modern techniques such as Intensity Modulated Radiation Therapy. Even with improved gel dosimeters (such as normoxic polymer gel systems) and more accessible imaging for dose

L J Schreiner

2009-01-01

2

Applications of gel dosimetry  

Microsoft Academic Search

Gel dosimetry has been examined as a clinical dosimeter since the 1950s. During the last two decades, however, a rapid increase in the number of investigators has been seen, and the body of knowledge regarding gel dosimetry has expanded considerably. Gel dosimetry is still considered a research project, and the introduction of this tool into clinical use is proceeding slowly.

Geoffrey S Ibbott

2004-01-01

3

Polymer gel dosimetry.  

PubMed

Polymer gel dosimeters are fabricated from radiation sensitive chemicals which, upon irradiation, polymerize as a function of the absorbed radiation dose. These gel dosimeters, with the capacity to uniquely record the radiation dose distribution in three-dimensions (3D), have specific advantages when compared to one-dimensional dosimeters, such as ion chambers, and two-dimensional dosimeters, such as film. These advantages are particularly significant in dosimetry situations where steep dose gradients exist such as in intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery. Polymer gel dosimeters also have specific advantages for brachytherapy dosimetry. Potential dosimetry applications include those for low-energy x-rays, high-linear energy transfer (LET) and proton therapy, radionuclide and boron capture neutron therapy dosimetries. These 3D dosimeters are radiologically soft-tissue equivalent with properties that may be modified depending on the application. The 3D radiation dose distribution in polymer gel dosimeters may be imaged using magnetic resonance imaging (MRI), optical-computerized tomography (optical-CT), x-ray CT or ultrasound. The fundamental science underpinning polymer gel dosimetry is reviewed along with the various evaluation techniques. Clinical dosimetry applications of polymer gel dosimetry are also presented. PMID:20150687

Baldock, C; De Deene, Y; Doran, S; Ibbott, G; Jirasek, A; Lepage, M; McAuley, K B; Oldham, M; Schreiner, L J

2010-03-01

4

Polymer gel dosimetry technique  

SciTech Connect

Recent advances in radiation therapy techniques, including non-coplanar beams, dynamic wedge, multi-leaf collimator, sterotactic radiosurgery, high-dose-rate brachytherapy using remote afterloading and shielded applicators, and heavy-particle beams such as protons, have created a need for three-dimensional, tissue-equivalent dosimeters, capable of recording time-integrated dose distributions with high spatial resolution and accuracy, and independent of energy and dose rate. All these requirements are met by the recently developed polymer gel dosimetry technique, based on radiation induced formation of polymer microparticles in a tissue-equivalent gel. A permanent image of the dose distribution is encoded in the gel as the distribution of its optical turbidity and of the NMR relaxation rates of the water protons in the gel. Three dimensional dose distributions can be measured using magnetic resonance imaging or optical transmission tomography. The prototype gel, called BANG{trademark}, is now being tested at several hospital sites throughout the U.S. and Europe.

Maryanski, M.J.

1995-12-31

5

Topical Review: Polymer gel dosimetry  

PubMed Central

Polymer gel dosimeters are fabricated from radiation sensitive chemicals which, upon irradiation, polymerize as a function of the absorbed radiation dose. These gel dosimeters, with the capacity to uniquely record the radiation dose distribution in three-dimensions (3D), have specific advantages when compared to one-dimensional dosimeters, such as ion chambers, and two-dimensional dosimeters, such as film. These advantages are particularly significant in dosimetry situations where steep dose gradients exist such as in intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery. Polymer gel dosimeters also have specific advantages for brachytherapy dosimetry. Potential dosimetry applications include those for low-energy x-rays, high-linear energy transfer (LET) and proton therapy, radionuclide and boron capture neutron therapy dosimetries. These 3D dosimeters are radiologically soft-tissue equivalent with properties that may be modified depending on the application. The 3D radiation dose distribution in polymer gel dosimeters may be imaged using magnetic resonance imaging (MRI), optical-computerized tomography (optical-CT), x-ray CT or ultrasound. The fundamental science underpinning polymer gel dosimetry is reviewed along with the various evaluation techniques. Clinical dosimetry applications of polymer gel dosimetry are also presented.

Baldock, C; De Deene, Y; Doran, S; Ibbott, G; Jirasek, A; Lepage, M; McAuley, K B; Oldham, M; Schreiner, L J

2010-01-01

6

Research software for radiotherapy gel dosimetry.  

PubMed

Gel dosimetry using magnetic resonance imaging is a technique which allows measurement of three-dimensional absorbed dose distributions in radiation therapy. This paper presents details of a software tool written specifically to provide facilities to perform image processing required in research and development of gel dosimetry. Collections of magnetic resonance images can be converted into either longitudinal or transverse nuclear magnetic resonance relaxation images. The conversions are accomplished by means of a pixel-by-pixel non-linear least squares fitting algorithm. Adjustments can be made to the number of parameters used in the fitting algorithm. Fundamental image manipulation tools such as window width/level display adjustment, zooming, profile and region of interest tools are provided. The software has been developed using MATLAB (The MathWorks Inc., Natick, MA) running on Windows 95. User interaction is via a windows graphical user interface (GUI). Data such as statistics from regions of interest can be exported to other windows applications for further processing. Flexibility is incorporated in the GUI design by taking advantage of the developmental aspects of the MATLAB environment. Although originally designed for gel dosimetry, the software can be used in any application of MRI which requires production and manipulation of relaxation time images. PMID:10979593

Murry, P; Baldock, C

2000-06-01

7

Dose calibration optimization and error propagation in polymer gel dosimetry.  

PubMed

This study reports on the relative precision, relative error, and dose differences observed when using a new full-image calibration technique in NIPAM-based x-ray CT polymer gel dosimetry. The effects of calibration parameters (e.g. gradient thresholding, dose bin size, calibration fit function, and spatial remeshing) on subsequent errors in calibrated gel images are reported. It is found that gradient thresholding, dose bin size, and fit function all play a primary role in affecting errors in calibrated images. Spatial remeshing induces minimal reductions or increases in errors in calibrated images. This study also reports on a full error propagation throughout the CT gel image pre-processing and calibration procedure thus giving, for the first time, a realistic view of the errors incurred in calibrated CT polymer gel dosimetry. While the work is based on CT polymer gel dosimetry, the formalism is valid for and easily extended to MRI or optical CT dosimetry protocols. Hence, the procedures developed within the work are generally applicable to calibration of polymer gel dosimeters. PMID:24434649

Jirasek, A; Hilts, M

2014-02-01

8

Fundamentals of MRI measurements for gel dosimetry  

Microsoft Academic Search

In radiotherapy gel dosimetry a humanoid phantom is irradiated according to the planned treatment of a patient. This results in a three-dimensional dose distribution. In order to read-out the gel dosimeter phantom, magnetic resonance imaging (MRI) is often used. Due to specific disturbances both the spatial and the dose reliability can be compromised. It is essential that the measurement sequence

Y. DeDeene

2004-01-01

9

Evaluation of radiochromic gel dosimetry and polymer gel dosimetry in a clinical dose verification.  

PubMed

A quantitative comparison of two full three-dimensional (3D) gel dosimetry techniques was assessed in a clinical setting: radiochromic gel dosimetry with an in-house developed optical laser CT scanner and polymer gel dosimetry with magnetic resonance imaging (MRI). To benchmark both gel dosimeters, they were exposed to a 6 MV photon beam and the depth dose was compared against a diamond detector measurement that served as golden standard. Both gel dosimeters were found accurate within 4% accuracy. In the 3D dose matrix of the radiochromic gel, hotspot dose deviations up to 8% were observed which are attributed to the fabrication procedure. The polymer gel readout was shown to be sensitive to B0 field and B1 field non-uniformities as well as temperature variations during scanning. The performance of the two gel dosimeters was also evaluated for a brain tumour IMRT treatment. Both gel measured dose distributions were compared against treatment planning system predicted dose maps which were validated independently with ion chamber measurements and portal dosimetry. In the radiochromic gel measurement, two sources of deviations could be identified. Firstly, the dose in a cluster of voxels near the edge of the phantom deviated from the planned dose. Secondly, the presence of dose hotspots in the order of 10% related to inhomogeneities in the gel limit the clinical acceptance of this dosimetry technique. Based on the results of the micelle gel dosimeter prototype presented here, chemical optimization will be subject of future work. Polymer gel dosimetry is capable of measuring the absolute dose in the whole 3D volume within 5% accuracy. A temperature stabilization technique is incorporated to increase the accuracy during short measurements, however keeping the temperature stable during long measurement times in both calibration phantoms and the volumetric phantom is more challenging. The sensitivity of MRI readout to minimal temperature fluctuations is demonstrated which proves the need for adequate compensation strategies. PMID:23965800

Vandecasteele, Jan; De Deene, Yves

2013-09-21

10

A Practical Use for FXG Gel Dosimetry  

NASA Astrophysics Data System (ADS)

In-phantom Fricke-xylenol orange-gelatin (FXG) gel dosimetry yields three dimensional (3D) dose data for intensity modulated radiation therapy (IMRT) treatment plan verification within 18-24 hours from the point of request. The information obtained from a 3% dose difference, 3 mm distance-to-agreement gamma function comparison between treatment plan dose and gel-measured dose then provides a useful secondary 3D quality assurance check of the treatment plan prior to delivery.

Olding, T.; Salomons, G.; Darko, J.; Schreiner, L. J.

2010-11-01

11

Polymer gel dosimetry using computed tomography  

NASA Astrophysics Data System (ADS)

Polymer gel dosimeter (PGD) is a type of integrating chemical dosimeter that, with the use of a suitable phantom, can be used for evaluation of the absorbed dose (dose distribution) deposited into a polymer gel by various irradiation modalities. Using suitable compounds of gel and appropriate parameters affecting the quality of the final image, evaluation using computed tomography (CT) should become a more advantageous alternative to magnetic resonance (MR), which is the most frequently applied method for the purposes of polymer gel dosimetry so far. In our work, several compositions of polymer gels (PG) were tested; evaluation was made via CT and MR, and values of dose and relative dose resolution were calculated. The optimal protocol for CT imaging and comparison of results from CT and MR are discussed.

Ornová, D.; Šemnická, J.; Sp?vá?ek, V.; Kon?ek, O.

2011-10-01

12

TOPICAL REVIEW: Polymer gel dosimetry  

Microsoft Academic Search

Polymer gel dosimeters are fabricated from radiation sensitive chemicals which, upon irradiation, polymerize as a function of the absorbed radiation dose. These gel dosimeters, with the capacity to uniquely record the radiation dose distribution in three-dimensions (3D), have specific advantages when compared to one-dimensional dosimeters, such as ion chambers, and two-dimensional dosimeters, such as film. These advantages are particularly significant

C. Baldock; Y. De Deene; S. Doran; G. Ibbott; A. Jirasek; M. Lepage; K. B. McAuley; M. Oldham; L. J. Schreiner

2010-01-01

13

Image noise in X-ray CT polymer gel dosimetry  

Microsoft Academic Search

This work investigates factors which affect image noise in CT polymer gel dosimetry, discusses techniques that can be used to further improve image noise and provides overall recommendations for the CT imaging of polymer gels.

M. Hilts; C. Duzenli

2004-01-01

14

Quantitative ultrasonic elastography for gel dosimetry.  

PubMed

Advanced radiation techniques such as intensity-modulated radiotherapy (IMRT) for complex geometries in which targets are close to organs at risk have been introduced in radiation therapy, creating a need for procedures that allow easy three-dimensional (3-D) measurement of dose for verification purposes. Polymer gels that change their material properties when irradiated have been suggested for such use. For example, the change in their magnetic properties has been thoroughly investigated with magnetic resonance imaging (MRI). Also, we have previously shown that the mechanical stiffness, i.e., Young's modulus, of these gels changes with dose. This finding prompted us to assess whether we can image a radiation-induced stiffness distribution with quantitative ultrasound elastography and whether the stiffness distribution is correlated with the dose distribution. A methacrylic-acid-based gel was loaded with scatterers to create an ultrasound echoic signal. It was irradiated to create a rod-like region of increased stiffness with a 10 x 10 mm(2) cross-section. The gel block was compressed in a frame that restricted the movement of the gel to planes orthogonal to the long axis of the irradiated region and ultrasonic echo data were acquired in the central plane during compression. This simplified irradiation pattern and experimental set-up were designed to approximate plane-strain conditions and was chosen for proof of concept. The movement of the gel was tracked from ultrasound images of a different compressional state using cross-correlation, enabling a displacement map to be created. The shear modulus was reconstructed using an inverse algorithm. The role of the magnitude of the regularization parameter in the inverse problem and the boundary conditions in influencing the spatial distribution of stiffness and, thus, final dose contrast was investigated through parametric studies. These parameters were adjusted using prior knowledge about the stiffness in parts of the material, e.g., the background was not irradiated and therefore its stiffness was homogeneous. It was observed that a suitable choice for these reconstruction parameters was essential for a quantitative application of stiffness measurement such as dosimetry. The dose contrast and distribution found with the optimal parameters were close to those obtained with MRI. Initial results reported in this article are encouraging and indicate that with ongoing refinement of ultrasound elastography techniques and accompanying inverse algorithms, this approach could play an important role in gel dosimetry. PMID:19945211

Crescenti, Remo A; Bamber, Jeffrey C; Oberai, Assad A; Barbone, Paul E; Richter, Joseph P; Rivas, Carlos; Bush, Nigel L; Webb, Steve

2010-02-01

15

On the use of VIP gel dosimetry in HDR brachytherapy  

Microsoft Academic Search

An experimental procedure is discussed with regard to its potential in 192Ir HDR brachytherapy dosimetry. Two samples of VIP normoxic gel formulation are used; one for gel response calibration and the other for acquiring experimental data. Using the same irradiation method for both calibration and experimental purposes (an 192Ir HDR brachytherapy source) and treating the two samples identically (i.e. the

L. Petrokokkinos; A. Moutsatsos; P. Karaiskos; V. Kouridou; E. Pantelis; P. Papagiannis; I. Seimenis

2009-01-01

16

High-resolution gel dosimetry of a HDR brachytherapy source using normoxic polymer gel dosimeters: Preliminary study  

Microsoft Academic Search

Polymer gel dosimetry has been shown to be an effective tool in the analysis of radiotherapy treatments in cancer therapy, being used to map the dose distribution around an irradiation pattern of a polymer gel dosimeter. Combined with high-resolution magnetic resonance imaging (MRI), polymer gel dosimetry can be an effective dosimetry tool to map dose distributions with high spatial resolution

C. Hurley; C. McLucas; G. Pedrazzini; C. Baldock

2006-01-01

17

Initial experience with a commercial cone beam optical CT unit for polymer gel dosimetry I: Optical dosimetry issues  

Microsoft Academic Search

Treatment validation of conformal plans is becoming a very important part of radiation therapy. Soon after its inception, gel dosimetry was shown to have a great potential for 3D dosimetry, particularly after the development of more spatially stable polymer-based dosimeters. However, despite its promise, gel dosimetry has not come into widespread clinical use, in part because of limited access to

Paul DeJean; Rob Senden; Kim McAuley; Myron Rogers; L. John Schreiner

2006-01-01

18

Alternative imaging modalities for polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

This review summarizes recent work in the area of imaging polymer gel dosimeters using x-ray CT imaging, ultrasound, and radiation-induced changes in gel mechanical properties. In addition, recent work in the area of Raman tomographic imaging of canine bone, in conjunction with past efforts in Raman imaging of polymer gel dosimeters, raises new possibilities for new polymer gel imaging techniques.

Jirasek, Andrew

2010-11-01

19

Technical considerations for implementation of x-ray CT polymer gel dosimetry  

Microsoft Academic Search

Gel dosimetry is the most promising 3D dosimetry technique in current radiation therapy practice. X-ray CT has been shown to be a feasible method of reading out polymer gel dosimeters and, with the high accessibility of CT scanners to cancer hospitals, presents an exciting possibility for clinical implementation of gel dosimetry. In this study we report on technical considerations for

M. Hilts; A. Jirasek; C. Duzenli

2005-01-01

20

Optical-CT Gel-Dosimetry I: Basic Investigations  

PubMed Central

Comprehensive verification of the intricate dose distributions associated with advanced radiation treatments is now an immediate and substantial problem. The task is challenging using traditional dosimeters because of restrictions to point measurements (ion chambers, diodes, TLD, etc.) or planar measurements (film). In essence, rapid advances in the technology to deliver radiation treatments have not been paralleled by corresponding advances in the ability to verify these treatments. A potential solution has emerged in the form of water equivalent three dimensional (3D) gel-dosimetry. In this paper we present basic characterization and performance studies of a prototype optical-CT scanning system developed in our laboratory. An analysis of the potential role or scope of gel dosimetry, in relation to other dosimeters, and to verification across the spectrum of therapeutic techniques is also given. The characterization studies enabled the determination of nominal operating conditions for optical-CT scanning. “Finger” phantoms are introduced as a powerful and flexible tool for the investigation of optical-CT performance. The modulation-transfer function (MTF) of the system is determined to be better than 10% out to 1 mm-1, confirming sub-mm imaging ability. System performance is demonstrated by the acquisition of a 1×1×1 mm3 dataset through the dose distribution delivered by an x-ray lens that focuses x rays in the energy range 40-80 KeV. This 3D measurement would be extremely difficult to achieve with other dosimetry techniques and highlights some of the strengths of gel dosimetry. Finally, an optical Monte Carlo model is introduced and shown to have potential to model light transport through gel-dosimetry systems, and to provide a tool for the study and optimization of optical-CT gel dosimetry. The model utilizes Mie scattering theory and requires knowledge of the variation of the particle size distribution with dose. The latter was determined here using the technique of dynamic-light-scattering.

Oldham, Mark; Siewerdsen, Jeffrey H.; Kumar, Sai; Wong, John; Jaffray, David A.

2006-01-01

21

Improving calibration accuracy in gel dosimetry  

Microsoft Academic Search

A new method of calibrating gel dosimeters (applicable to both Fricke and polyacrylamide gels) is presented which has intrinsically higher accuracy than current methods, and requires less gel. Two test-tubes of gel (inner diameter 2.5 cm, length 20 cm) are irradiated separately with a field end-on in a water bath, such that the characteristic depth-dose curve is recorded in the

M. Oldham; M. McJury; I. B. Baustert; S. Webb; M. O. Leach

1998-01-01

22

Further developments and applications of layer gel dosimetry  

Microsoft Academic Search

The method used to perform dosimetry with Fricke-xylenol orange-infused gels in form of layers remains the most reliable method for in-phantom dose profiling and imaging in high fluxes of thermal and epithermal neutrons. Gel-dosimeters in form of layers really give the possibility not only of obtaining spatial dose distributions but also of achieving measurements of each dose contribution in neutron

G. Gambarini; M. Carrara; V. Colli; S. Gay; S. Tomatis

2004-01-01

23

[Investigation of polymer gel dosimetry for small circular irradiated fields].  

PubMed

Polymer gels can be used as tissue equivalent dosimeters, and polymer gel dosimetry can be employed without perturbation of the radiation field. In this study, polymer gel dosimetry was used for small circular irradiation fields 10-30 mm in diameter using a radiation planning system. The irradiated gels were compared with planned data for a 50% dose width of 6 Gy dose maximum, and for the dose difference between gels and planned data over an 80% dose maximum area. The present study investigated magnetic resonance imaging (MRI) conditions based on an optimal dose-R2 calibration curve. The average difference between the full width half maximum of the 50% dose width between gels and planned data was 11%. The average dose difference over 80% of the dose was 5.6%. Optimal dose-R2 calibration curves were acquired using images with echo times of 30 and 60 ms. For cases of larger thicknesses and an increasing number of averages, the coefficients of variance of the curves were smaller than under other conditions. Compared to other traditional dosimetric tools, polymer gels have the advantage of providing three-dimensional dosimetric data. An arbitrary profile from the gel's data can be compared with the profile of the planned data. In the future, new gel dosimeters will be needed that demonstrate improved dose evaluation under 1 Gy and stability in high dose areas. PMID:24064697

Kawamura, Hiraku; Shinoda, Kazuya; Miyamoto, Katsumi; Sakae, Takeji; Monma, Masahiko; Matsumura, Akira

2013-09-01

24

Further developments and applications of layer gel dosimetry  

NASA Astrophysics Data System (ADS)

The method used to perform dosimetry with Fricke-xylenol orange-infused gels in form of layers remains the most reliable method for in-phantom dose profiling and imaging in high fluxes of thermal and epithermal neutrons. Gel-dosimeters in form of layers really give the possibility not only of obtaining spatial dose distributions but also of achieving measurements of each dose contribution in neutron fields. These advantages arise from the layer-geometry thanks to which neutron transport is not sensibly altered, even if the elemental gel composition is changed adding particular isotopes (for example 10B), as necessary to perform the separation of dose contributions. The gel matrix composition and the experimental procedures, adopted for both dosimeter preparation and analysis, have been already described in previous works. In the present work, the improvements of the method employed for gel analysis, dose imaging and gel applications are illustrated.

Gambarini, G.; Carrara, M.; Colli, V.; Gay, S.; Tomatis, S.

2004-01-01

25

Magnetization transfer imaging for polymer gel dosimetry  

Microsoft Academic Search

Off-resonance RF pre-saturation was used to obtain contrast in MRI images of polymer gel dosimeters irradiated to doses up to 50 Gy. Two different polymer gel dosimeters composed of 2-hydroxyethyl-acrylate or methacrylic acid monomers mixed with N, N'-methylene-bisacrylamide (BIS), dispersed in an aqueous gelatin matrix were evaluated. Radiation-induced polymerization of the co-monomers generates a fast-relaxing insoluble polymer. Saturation of the

M. Lepage; K. McMahon; G. J. Galloway; Y. DeDeene; S. Å. J. Bäck; C. Baldock

2002-01-01

26

Investigations in x-ray computed tomography polyacrylamide gel dosimetry  

SciTech Connect

Polyacrylamide gels (PAGs) are radiosensitive materials currently under development for use as three-dimensional (3D) dosimeters in radiation therapy. Dose information is recorded in the gels and extracted through imaging. X-ray computed tomography (CT) has emerged as a promising gel imaging method due to a change in gel density that occurs upon irradiation. The accessibility of CT technology to cancer hospitals makes CT read out clinically attractive; however, the technique remains of limited clinical use due in part to poor dose resolution. This thesis investigates the use of CT for extracting dose information from PAGs with an overall goal of improving achievable dose resolution. Thesis results are divided into three studies: a gel-compositional study, a study of noise and dose resolution, and a digital filtering study. The first study investigates the effects of gel composition on PAG CT dose response and the underlying density change. Results indicate dramatic variation in CT dose response sensitivity and range with gel composition. A model is developed to describe gel density change with dose, revealing two fundamental properties of the density to dose response: the density change per unit polymer yield is highest for gels with low and high concentrations of crosslinking molecules, and dose response sensitivity is linearly dependent on the total concentration of monomers in the gel. The second study investigates strategies for minimizing noise in CT polymer gel dosimetry and assesses system performance. Specifically, the effects of phantom design, scanning technique, and voxel size on image noise are investigated and the effect of scanning protocol on imaging time is established. The dose resolution achievable with an optimized system is then calculated, given voxel size and imaging time constraints, and compared with published values for magnetic resonance imaging (MRI) and optical CT gel dosimetry. The third study investigates the potential of image filtering for improved dose resolution in CT gel dosimetry. CT image noise is characterized and appropriate filters are tested on a CT image of a PAG irradiated with a clinically relevant dose distribution. Filter performance is found to vary dramatically, with the best filters more than halving the dose resolution without significantly distorting the spatial distribution of dose. In summary, this thesis provides insight into the fundamental nature of PAG density to dose response, develops strategies for minimizing image noise, quantifies system performance, and demonstrates that digital image filtering is an effective tool to provide additional improvements to dose resolution.

Hilts, Michelle [Physics and Astronomy, University of British Columbia, British Columbia, Canada and Medical Physics, BC Cancer Agency, Vancouver Centre, British Columbia (Canada)]. E-mail: mhilts@bccancer.bc.ca

2005-09-15

27

Mathematical analysis and experimental investigation of noise in quantitative magnetic resonance imaging applied in polymer gel dosimetry  

Microsoft Academic Search

In polymer gel dosimetry, the spin–spin relaxation rate R2=1\\/T2, is related to the absorbed dose that is delivered to a gel phantom by high-energy radiation beams. In a two-points method, R2 is calculated from two differently T2-weighted images. In the many-points method, R2 is calculated by fitting the pixel intensities of a set of differently exponentially T2-weighted images. An analysis

Y. De Deene; R. Van de Walle; E. Achten; C. De Wagter

1998-01-01

28

Effective Management of FXG Gel Dosimetry  

NASA Astrophysics Data System (ADS)

The details of a calibration basis for the Fricke-xylenol orange-gelatin (FXG) gel dosimeter combined with the fast, easily accessible readout tool of cone beam optical computed tomography (CT) are described in this report. With proper controls in place, the results from a test intensity modulated radiation therapy (IMRT) treatment plan evaluation indicate that greater than 95% Low's gamma function agreement between plan and gel-measured dose using 3% dose and 3 mm distance-to-agreement criteria is achievable.

Olding, T.; Darko, J.; Schreiner, L. J.

2010-11-01

29

On the use of VIP gel dosimetry in HDR brachytherapy  

NASA Astrophysics Data System (ADS)

An experimental procedure is discussed with regard to its potential in 192Ir HDR brachytherapy dosimetry. Two samples of VIP normoxic gel formulation are used; one for gel response calibration and the other for acquiring experimental data. Using the same irradiation method for both calibration and experimental purposes (an 192Ir HDR brachytherapy source) and treating the two samples identically (i.e. the two samples are prepared, irradiated and scanned at the same time and stored together at all times) leads to total dose uncertainties comparable to those of other well established dosimetry methods over a significant dose range (~7Gy-40Gy). In this dose range, the described procedure can be used to either acquire absolute dosimetry results for the characterisation of new 192Ir HDR brachytherapy sources, or to facilitate the planning of relative dosimetry experiments for the verification of calculations by new generation treatment planning systems that are currently phasing in, in complex 3D dose distributions involving inhomogeneities and finite medium geometries.

Petrokokkinos, L.; Moutsatsos, A.; Karaiskos, P.; Kouridou, V.; Pantelis, E.; Papagiannis, P.; Seimenis, I.

2009-05-01

30

RapidArc™ treatment verification using polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

The aim of this study was to verify a novel volumetric arc therapy technique, RapidArc". Polymer gel dosimetry system was used to measure the advanced inhomogeneous 3D dose distribution produced using the technique RapidArc". A preclinical installation of the novel beam delivery approach was set up on a linear accelerator at Rigshospitalet in Copenhagen. A prostate treatment plan was delivered to a 1.3 l nPAG gel phantom using one single arc rotation from 200 to 160 degrees, and a target dose of 3.3 Gy. Magnetic resonance imaging of the gel was carried out using the 1.5 T scanner and MATLAB was used for image processing and 3D rendering. The difference in relative absorbed dose between the treatment planning system (TPS) and gel measurement was calculated voxel by voxel within the 80% and the 95% isodose volume, respectively. Measurements agreed well with the TPS within the treated volume. Within both isodose volumes 90% of the voxels showed a deviation less or equal to 5%. This study shows that the 3D gel dosimetry system is a useful tool for dose verification of advanced treatment delivery techniques.

Ceberg, Sofie; Gustavsson, Helen; Korreman, Stine; Medin, Joakim; Kjær-Kristoffersen, Flemming; Bäck, Sven ÅJ

2009-05-01

31

NOTE: Uncertainty analysis in polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

Verification of advanced radiotherapy treatment modalities requires measurement of three-dimensional absorbed dose distributions with high spatial resolution and precision. Polymer gel dosimeters combined with magnetic resonance imaging may be able to fulfil this requirement. However, verification requires that the uncertainty in the dosimeter is well known. One method of estimating the overall uncertainty in polymer gel dosimeters involves the propagation of the uncertainty in the R2 (nuclear magnetic resonance relaxation rate) map and the uncertainties in the calibration data. This work shows that using this method with current data suggests that the lowest uncertainty currently obtainable is about 3% at 8 Gy and 7% at 2 Gy. Furthermore, the most significant reductions in overall uncertainty will be achieved by reducing the noise in the R2 map.

Baldock, C.; Murry, P.; Kron, T.

1999-11-01

32

Uncertainty analysis in polymer gel dosimetry.  

PubMed

Verification of advanced radiotherapy treatment modalities requires measurement of three-dimensional absorbed dose distributions with high spatial resolution and precision. Polymer gel dosimeters combined with magnetic resonance imaging may be able to fulfil this requirement. However, verification requires that the uncertainty in the dosimeter is well known. One method of estimating the overall uncertainty in polymer gel dosimeters involves the propagation of the uncertainty in the R2 (nuclear magnetic resonance relaxation rate) map and the uncertainties in the calibration data. This work shows that using this method with current data suggests that the lowest uncertainty currently obtainable is about 3% at 8 Gy and 7% at 2 Gy. Furthermore, the most significant reductions in overall uncertainty will be achieved by reducing the noise in the R2 map. PMID:10588291

Baldock, C; Murry, P; Kron, T

1999-11-01

33

Dose resolution in radiotherapy polymer gel dosimetry: effect of echo spacing in MRI pulse sequence  

Microsoft Academic Search

In polymer gel dosimetry using magnetic resonance imaging, the uncertainty in absorbed dose is dependent on the experimental determination of T2. The concept of dose resolution (DDeltap) of polymer gel dosimeters is developed and applied to the uncertainty in dose related to the uncertainty in T2 from a range of T2 encountered in polymer gel dosimetry. DDeltap is defined as

C. Baldock; M. Lepage; S. Å. J. Bäck; P. J. Murry; P. M. Jayasekera; D. Porter; T. Kron

2001-01-01

34

Quantitative Ultrasonic Elastography for Gel Dosimetry  

Microsoft Academic Search

Advanced radiation techniques such as intensity-modulated radiotherapy (IMRT) for complex geometries in which targets are close to organs at risk have been introduced in radiation therapy, creating a need for procedures that allow easy three-dimensional (3-D) measurement of dose for verification purposes. Polymer gels that change their material properties when irradiated have been suggested for such use. For example, the

Remo A. Crescenti; Jeffrey C. Bamber; Assad A. Oberai; Paul E. Barbone; Joseph P. Richter; Carlos Rivas; Nigel L. Bush; Steve Webb

2010-01-01

35

Radiological properties of MAGIC normoxic polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

For a polymer gel dosimeter to be of use in radiation dosimetry, it should display water-equivalent radiological properties. In this study, the radiological properties of the MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) normoxic polymer gels were investigated. The mass density (?) was determined based on Archimedes' principle. The weight fraction of elemental composition and the effective atomic number (Zeff) were calculated. The electron density was also measured with 90° scattering angle at room temperature. The linear attenuation coefficient (?) of unirradiated gel, irradiated gel, and water were determined using Am-241 based on narrow beam geometry. Monte Carlo simulation was used to calculate the depth doses response of MAGIC gel and water for 6MV photon beam. The weight fractions of elements composition of MAGIC gel were close to that for water. The mass density was found to be 1027 ± 2 kg m-3, which is also very close to mass density of muscle tissue (1030 kg m-3) and 2.7% higher than that of water. The electron density (?e) and atomic number (Zeff) were found to be 3.43 × 1029 e m-3 and 7.105, respectively. The electron density measured was 2.6% greater than that for water. The atomic number was very close to that for water. The prepared MAGIC gel was found to be water equivalent based on the study of element composition, mass density, electron density and atomic number. The linear attenuation coefficient of unirradiated gel was very close to that of water. The ? of irradiated gel was found to be linear with dose 2-40 Gy. The depth dose response for MAGIC gel from a 6 MV photon beam had a percentage dose difference to water of less than 1%. Therefore it satisfies the criteria to be a good polymer gel dosimeter for radiotherapy.

Aljamal, M.; Zakaria, A.; Shamsuddin, S.

2013-04-01

36

Cone beam optical computed tomography-based gel dosimetry  

NASA Astrophysics Data System (ADS)

The complex dose distributions delivered by modern, conformal radiation therapy techniques present a considerable challenge in dose verification. Traditional measurement tools are difficult and laborious to use, since complete verification requires that the doses be determined in three dimensions (3D). The difficulty is further complicated by a required target accuracy of +/- 5% for the dose delivery. Gel dosimetry is an attractive option for realizing a tissue-equivalent, 3D dose verification tool with high resolution readout capabilities. However, much important work remains to be completed prior to its acceptance in the clinic. The careful development of easily accessible, fast optical readout tools such as cone beam optical computed tomography (CT) in combination with stable and reliable low-toxicity gel dosimeters is one key step in this process. In this thesis, the performance capabilities and limitations of the two main classes of cone beam optical CT-based absorbing and scattering gel dosimetry are characterized, and their measurement improved through careful matching of dosimeter and scanner performance. These systems are then applied to the evaluation of clinically relevant complex dose distributions. Three-dimensional quality assurance assessments of complex treatment plan dose distributions are shown to be feasible using an optically absorbing Fricke-xylenol-orange-gelatin-based gel dosimeter. Better than 95% voxel agreement is achieved between the plan and the delivery, using 3% dose difference and 3 mm spatial distance-to-agreement gamma function comparison criteria. Small field dose delivery evaluations are demonstrated to be viable using an optically scattering N-isopropylacrylamide (NIPAM)-based polymer gel, with the same comparison criteria. Full treatment process quality assurance is also possible using a NIPAM dosimeter in-phantom, but is limited in its accuracy due to the inherent difficulty of managing the effects of stray light pertubation in the optical attenuation-to-dose calibration.

Olding, Timothy Russell

37

Carbon beam dosimetry using VIP polymer gel and MRI  

NASA Astrophysics Data System (ADS)

VIP polymer gel dosimeter was used for Carbon ion beam dosimetry using a 150 MeV/n beam with 10 Gy plateau dose and a SOBP irradiation scheme with 5 Gy Bragg peak dose. The results show a decrease by 8 mm in the expected from Monte Carlo simulation range in water, suggesting that the dosimeter is non water equivalent. However VIP shows efficiency close to 1 in the plateau region and significantly reduced efficiency in the peak. On the other hand the SOBP results yield an efficiency close to 1 in the SOBP implying that the dose response of the VIP dosimeter may not be solely related to LET.

Kantemiris, I.; Petrokokkinos, L.; Angelopoulos, A.; Bassler, N.; Seimenis, I.; Karaiskos, P.

2009-05-01

38

Monte Carlo verification of gel dosimetry measurements for stereotactic radiotherapy  

NASA Astrophysics Data System (ADS)

The quality assurance of stereotactic radiotherapy and radiosurgery treatments requires the use of small-field dose measurements that can be experimentally challenging. This study used Monte Carlo simulations to establish that PAGAT dosimetry gel can be used to provide accurate, high-resolution, three-dimensional dose measurements of stereotactic radiotherapy fields. A small cylindrical container (4 cm height, 4.2 cm diameter) was filled with PAGAT gel, placed in the parietal region inside a CIRS head phantom and irradiated with a 12-field stereotactic radiotherapy plan. The resulting three-dimensional dose measurement was read out using an optical CT scanner and compared with the treatment planning prediction of the dose delivered to the gel during the treatment. A BEAMnrc/DOSXYZnrc simulation of this treatment was completed, to provide a standard against which the accuracy of the gel measurement could be gauged. The three-dimensional dose distributions obtained from Monte Carlo and from the gel measurement were found to be in better agreement with each other than with the dose distribution provided by the treatment planning system's pencil beam calculation. Both sets of data showed close agreement with the treatment planning system's dose distribution through the centre of the irradiated volume and substantial disagreement with the treatment planning system at the penumbrae. The Monte Carlo calculations and gel measurements both indicated that the treated volume was up to 3 mm narrower, with steeper penumbrae and more variable out-of-field dose, than predicted by the treatment planning system. The Monte Carlo simulations allowed the accuracy of the PAGAT gel dosimeter to be verified in this case, allowing PAGAT gel to be utilized in the measurement of dose from stereotactic and other radiotherapy treatments, with greater confidence in the future. Experimental aspects of this work were originally presented at the Engineering and Physical Sciences in Medicine Conference (EPSM-ABEC), Melbourne, 2010.

Kairn, T.; Taylor, M. L.; Crowe, S. B.; Dunn, L.; Franich, R. D.; Kenny, J.; Knight, R. T.; Trapp, J. V.

2012-06-01

39

Relative output factor measurements of a 5 mm diameter radiosurgical photon beam using polymer gel dosimetry  

Microsoft Academic Search

Besides the fine spatial resolution inherent in polymer gel-magnetic resonance imaging (MRI) dosimetry, the method also features the potential for multiple measurements of varying sensitive volume in a single experiment by integrating results in MRI voxels of finite dimensions (i.e., in plane resolution by slice thickness). This work exploits this feature of polymer gel dosimetry to propose an experimental technique

E. Pappas; L. Petrokokkinos; A. Angelopoulos; T. G. Maris; M. Kozicki; I. Dalezios; V. Kouloulias

2005-01-01

40

Dosimetry in HDR brachytherapy with Fricke-gel layers and Fricke-gel catheters  

NASA Astrophysics Data System (ADS)

Fricke-gel layer dosimeters (FGLD) and Fricke gel dosimetric catheters (FGDC) have been designed and tested with the aim of enquiring their suitability for HDR 192Ir brachytherapy source control and for in-vivo dose verification during treatment. Anisotropy function measurements have been carried out with FGLDs in which a thin plastic tube has been placed in for the 192Ir source insertion. FGDCs are constituted by plastic tubes (3 mm of external diameter and 13 cm of length) filled with the dosimeter-gel. Absorbed dose images and profiles were attained by means of optical analysis. Dedicated software has been developed both for achieving anisotropy function values and for obtaining reliable results in visible light absorbance measurements across the thin cylindrical dosimeters. Preparation and analysis procedures have been optimised. The results confirm that the proposed methods are very promising for HDR brachytherapy dosimetry.

Gambarini, G.; Carrara, M.; Negri, A.; Invernizzi, M.; Tenconi, C.; Scotti, A.; Pirola, L.; Borroni, M.; Tomatis, S.; Fallai, C.

2010-11-01

41

X-ray CT dose in normoxic polyacrylamide gel dosimetry  

SciTech Connect

This study reports on the effects of x-ray CT dose in CT imaged normoxic polyacrylamide (nPAG) gel dosimeters. The investigation is partitioned into three sections. First, the CT dose absorbed in nPAG is quantified under a range of typical gel CT imaging protocols. It is found that the maximum absorbed CT dose occurs for volumetric imaging and is in the range of 4.6{+-}0.2 cGy/image. This does scales linearly with image averaging. Second, using Raman spectroscopy, the response of nPAG to CT imaging photon energies (i.e., 120-140 kVp) is established and compared to the well known dose response of nPAG exposed to 6 MV photons. It is found that nPAG exhibits a weaker response (per unit dose) to 140-kVp incident photons as compared to 6 MV incident photons (slopes m{sub 6MV}=-0.0374{+-}0.0006 Gy{sup -1} and m{sub 140kVp}=-0.016{+-}0.001 Gy{sup -1}). Finally, using the above data, an induced change in CT number ({delta}N{sub CT}) is calculated for nPAG imaged using a range of gel imaging protocols. It is found that under typical imaging protocols (120-140 kVp, 200 mAs, {approx}16-32 image averages) a {delta}N{sub CT}<0.2 H is induced in active nPAG dosimeters. This {delta}N{sub CT} is below the current limit of detectability of CT nPAG polymer gel dosimetry. Under expanded imaging protocols (e.g., very high number of image averages) an induced {delta}N{sub CT} of {approx}0.5 H is possible. In these situations the additional polymerization occurring in nPAG due to the imaging process may need to be accounted for.

Baxter, P.; Jirasek, A.; Hilts, M. [Department of Physics and Astronomy, University of Victoria, Victoria BC V8W 3P6 (Canada); Medical Physics, BC Cancer Agency-Vancouver Island Centre, Victoria BC V8R 6V5 (Canada)

2007-06-15

42

An x-ray CT polymer gel dosimetry prototype: II. Gel characterization and clinical application  

NASA Astrophysics Data System (ADS)

This article reports on the dosimetric properties of a new N-isopropylacrylamide, high %T, polymer gel formulation (19.5%T, 23%C), optimized for x-ray computed tomography (CT) polymer gel dosimetry (PGD). In addition, a new gel calibration technique is introduced together with an intensity-modulated radiation therapy (IMRT) treatment validation as an example of a clinical application of the new gel dosimeter. The dosimetric properties investigated include the temporal stability, spatial stability, batch reproducibility and dose rate dependence. The polymerization reaction is found to stabilize after 15 h post-irradiation. Spatial stability investigations reveal a small overshoot in response for gels imaged later than 36 h post-irradiation. Based on these findings, it is recommended that the new gel formulation be imaged between 15-36 h after irradiation. Intra- and inter-batch reproducibility are found to be excellent over the entire range of doses studied (0-28 Gy). A significant dose rate dependence is found for gels irradiated between 100-600 MU?min-1. Overall, the new gel is shown to have promising characteristics for CT PGD, however the implication of the observed dose rate dependence for some clinical applications remains to be determined. The new gel calibration method, based on pixel-by-pixel matching of dose and measured CT numbers, is found to be robust and to agree with the previously used region of interest technique. Pixel-by-pixel calibration is the new recommended standard for CT PGD. The dose resolution for the system was excellent, ranging from 0.2-0.5 Gy for doses between 0-20 Gy and 0.3-0.6 Gy for doses beyond 20 Gy. Comparison of the IMRT irradiation with planned doses yields excellent results: gamma pass rate (3%, 3 mm) of 99.3% at the isocentre slice and 93.4% over the entire treated volume.

Johnston, H.; Hilts, M.; Carrick, J.; Jirasek, A.

2012-05-01

43

MAGAT gel dosimetry for its application in small field treatment techniques  

Microsoft Academic Search

Purpose of this work is to present the role of in-house manufactured MAGAT gel for treatment verification in small field dosimetric techniques such as Gammaknife (GK) and intensity-modulated radiation therapy (IMRT). Magnetic resonance imaging (MRI) is one of the most extensively used imaging technique for polymer gel dosimetry hence we used this method for gel evaluation. Different MR scanners and

N. Gopishankar; S. Vivekanandhan; S. S. Kale; G. K. Rath; S. Senthil Kumaran; Sanjay Thulkar; V. Subramani; M. A. Laviraj; R. K. Bisht; A. K. Mahapatra

2010-01-01

44

Initial experience with a commercial cone beam optical CT unit for polymer gel dosimetry II: Clinical potential  

Microsoft Academic Search

Gel dosimetry has been shown to have a great potential for 3D dosimetry for treatment delivery validation of conformal plans, particularly after the development of more spatially stable polymer-based dosimeters. However, despite its promise, gel dosimetry has not come into widespread clinical use, in part because of limited access to imaging modalities (particularly MRI) for dose readout. In this paper

Paul DeJean; Rob Senden; Kim McAuley; Myron Rogers; L John Schreiner

2006-01-01

45

Polymer gel dosimetry on a multislice computed tomography scanner: Effect of changing parameters on CTDI  

Microsoft Academic Search

Polymer gel dosimetry undertaken on a multislice CT scanner provides an alternative method to conventional dosimetry measurements. Polymer gel dosimeters were used to measure CT radiation doses and compared to TLD and ionization chamber measurements in different diameter phantoms. CTDI was investigated for each of these phantoms for a range of mAs (100–400mAs), tube voltage (100–135kV) and nominal slice width

B. Hill; A. J. Venning; C. Baldock

2008-01-01

46

A fast, high spatial resolution optical tomographic scanner for measurement of absorption in gel dosimetry  

Microsoft Academic Search

A fast tomographic optical density measurement system has been constructed and evaluated for application in Fricke 3D gel\\u000a dosimetry. Although the potential for full three-dimensional radiation dosimetry with Fricke gel dosimeters has been extensively\\u000a reported, its application has been limited due to a lack of fast optical density measurement systems. In this work, the emphasis\\u000a of the design has been

T. van Doorn; M. Bhat; T. P. Rutten; T. Tran; A. Costanzo

2005-01-01

47

P4F-2 Ultrasonic Elastography and Plane Strain Inverse Algorithms for Polymer Gel Dosimetry  

Microsoft Academic Search

In radiation therapy, 3D-dosimetry is needed for quality assurance of complicated irradiation geometries. Here, a preliminary evaluation of a combined system for dosimetry based on radiation sensitive gels, ultrasonic elastography and a plane strain inverse algorithm is presented. A block of gel was irradiated along one of its axes producing a stiff rod-like region. Good stiffness contrast between this region

Remo A Crescenti; Jeffrey C Bamber; Assad A Oberai; Paul E Barbone; Joseph P Richter; Nigel L Bush; Steve Webb

2007-01-01

48

An investigation into the dosimetry of a nine-field tomotherapy irradiation using BANG-gel dosimetry  

Microsoft Academic Search

BANG-gel dosimetry offers the potential for measuring the dose delivered by a radiotherapy treatment technique, in three dimensions, with high spatial resolution and good accuracy. The ability to measure comprehensively a 3D dose distribution is a major advantage of the gel dosimeter over conventional planar and point-based dosimeter devices, particularly when applied to the verification of complex dose distributions characteristic

M. Oldham; I. Baustert; C. Lord; T. A. D. Smith; M. McJury; A. P. Warrington; M. O. Leach; S. Webb

1998-01-01

49

Three-dimensional radiation dosimetry for gamma knife using a gel dosimeter  

NASA Astrophysics Data System (ADS)

The use of three-dimensional radiation dosimetry has been limited. With the use of water phantoms and ionization chambers, it has been possible to determine three dimensional dose distributions on a gross scale for cobalt 60 and linear accelerator sources. This method has been somewhat useful for traditional radiotherapy. There is, however, a need for more precise dosimetry, particularly with stereotactic radiosurgery. Most gamma knife facilities use either thermoluminescant dosimetry or film, neither of which provides three dimensional dose distributions. To overcome this limitation, we have developed a gel dosimetry system that relies on the production of a ferric ion-xylenol orange colored complex. This work demonstrates the use of laser light and a detector to quantify radiation-induced colorimetric changes in absorbance for the gel dosimeter. The absorbance has been reconstructed by the back projection technique to demonstrate the applicability of the gel dosimeter to gamma knife 3D-dose distributions.

Hussain, Kazi Muazzam

50

Adaptive mean filtering for noise reduction in CT polymer gel dosimetry  

Microsoft Academic Search

X-ray computed tomography (CT) as a method of extracting 3D dose information from irradiated polymer gel dosimeters is showing potential as a practical means to implement gel dosimetry in a radiation therapy clinic. However, the response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolutions with this method. Phantom design

Michelle Hilts; Andrew Jirasek

2008-01-01

51

Investigation of optimal scanning protocol for X-ray computed tomography polymer gel dosimetry  

Microsoft Academic Search

X-ray computed tomography is one of the potential tool used to evaluate the polymer gel dosimeters in three dimensions. The purpose of this study is to investigate the factors which affect the image noise for X-ray CT polymer gel dosimetry. A cylindrical water filled phantom was imaged with single slice Siemens Somatom Emotion CT scanner. The imaging parameters like tube

P. Sellakumar; E. James Jebaseelan Samuel; Sanjay S. Supe

2007-01-01

52

An investigation comparing optical CT with MR scanning for polymer gel dosimetry  

Microsoft Academic Search

Radiation sensitive gels, including BANG and Fricke-gels, are at the forefront of research into improved dosimetry techniques. Despite being the only dosimeter that offers true 3D information about the dose-distribution, radiation sensitive gels have to-date made little impact in most clinics. This is due to the fact that the field is still new and rapidly developing, but also due to

Mark Oldham; Jeffrey H Siewerdsen; A. Shetty; D. A. Jaffray

2000-01-01

53

Monte Carlo verification of polymer gel dosimetry applied to radionuclide therapy: a phantom study  

Microsoft Academic Search

This study evaluates the dosimetric performance of the polymer gel dosimeter 'Methacrylic and Ascorbic acid in Gelatin, initiated by Copper' and its suitability for quality assurance and analysis of I-131-targeted radionuclide therapy dosimetry. Four batches of gel were manufactured in-house and sets of calibration vials and phantoms were created containing different concentrations of I-131-doped gel. Multiple dose measurements were made

J. I. Gear; E. Charles-Edwards; M. Partridge; G. D. Flux

2011-01-01

54

Gamma Knife relative dosimetry using VIP polymer gel and EBT radiochromic films  

Microsoft Academic Search

The VIP polymer gel-MRI method and EBT Gafchromic films were employed to obtain relative dosimetry results for the Gamma Knife (GK) radiation fields of 4 mm and 18 mm nominal diameter. Results are compared to the corresponding calculations of GammaPlan Treatment Planning System (TPS) in the form of 1D profiles and 2D distributions. Measured and planned relative dosimetry datasets are

A. Moutsatsos; L. Petrokokkinos; K. Zourari; P. Papagiannis; P. Karaiskos; K. Dardoufas; J. Damilakis; I. Seimenis; E. Georgiou

2009-01-01

55

Fricke gel diffusion coefficient measurements for applications in radiotherapy level dosimetry  

NASA Astrophysics Data System (ADS)

In gel dosimetry applied to radiotherapy, the space-time corrections are necessary due to the diffusion of ions in the oxidized solution dosimetry. Consequently, methodologies are applied in order to determine diffusion coefficients corrected in space and time. Therefore, in this study the dosimetric solution Fricke Xylenol Gel (FXG) was modified and applied to two Gaussian and ISQR methodologies for comparison of the diffusion coefficients obtained. The results show that the FXG system can be modified for new applications in radiotherapy, and it may be corrected in space-time to the appropriate methodologies in the determination of diffusion coefficients.

de Oliveira, Lucas Nonato; de Almeida, Adelaide; Caldas, Linda V. E.

2014-05-01

56

PREFACE: The 5th International Conference on Radiotherapy Gel Dosimetry (DOSGEL 2008)  

NASA Astrophysics Data System (ADS)

The International Conference on Radiotherapy Gel Dosimetry (DOSGEL) is held every two years. Its purpose is to bring together basic science and clinical researchers, medical physicists and clinicians from around the world to discuss the state-of-the-art of the gel dosimetry technique and to set the directions and trends for its future improvements. Gel dosimetry can be broadly defined as using a gel that can react to the absorption of ionizing radiation, and that can retain this information which can subsequently be retrieved by an external imaging modality. Examples of radiation-sensitive gels include, but are not limited to, polymer gel dosimeters, Fricke gel dosimeters and others. Imaging modalities that are of general use in this field are (in alphabetical order) magnetic resonance imaging (MRI), optical light computed tomography and x-ray computed tomography. This volume comprises the proceedings of the 5th International Conference on Radiotherapy Gel Dosimetry (DOSGEL 2008). The conference, organised by the University of Crete, Medical Physics Department, took place in Hersonissos, Crete, Greece from 29 September to 3 October 2008. The meeting aimed to continue the series of biannual DOSGEL conferences and focused on the promotion of gel dosimetry techniques by setting the trends for their future improvements. The main scientific session topics of DOSGEL 2008 were the following: Chemistry and fundamental properties of polymer gel dosimeters Gel dosimetry with Optical Computed Tomography Gel dosimetry with Magnetic Resonance Imaging Gel dosimetry with other than Optical CT and MR scan Techniques Other 3D dosimeters Gel dosimetry applications Local Organizing Committee Thomas G Maris (University of Crete, Greece, Chairman DOSGEL 2008) John Damilakis (University of Crete, Greece) Evangelos Pappas (University of Crete, Greece) Antonios Papadakis (University of Crete, Greece) Fotini Zacharopoulou (University of Crete, Greece) John Stratakis (University of Crete, Greece) Pantelis Karaiskos (University of Athens, Greece) Panos Papagiannis (University of Athens, Greece) Scientific Committee President: Yves De Deene (Ghent University, Belgium) Sven Back (Lund University, Sweden) Clive Baldock (University of Sydney, Australia) David Bonnett (Kent Oncology Center, UK) Simon Doran (University of Surrey, UK) Cheryl Duzenli (University of British Columbia, Canada) Geoffrey Ibbott (Colorado State University, USA) Andrew Jirasek (University of Victoria, Canada) Kevin Jordan (University of Western Ontario, Canada) Martin Lepage (Universite de Sherbrooke, Canada) Mark Oldham (Duke University, USA) L John Schreiner (Kingston Regional Cancer Centre, Canada) Acknowledgements The local organising committee wishes to express its gratitude to all participants for their activities at DOSGEL 2008 and for creating such a friendly and inspiring environment. Special thanks are due to all the speakers, for preparing and presenting their talks, and for many valuable discussions. We also give thanks to all members of the scientific committee who, acting as referees, improved significantly the scientific quality of this proceedings volume. We would also like to thank all chairmen for their efficient leading of sessions. On Behalf of the local organizing committee of DOSGEL 2008 Thomas G Maris and Evangelos Pappas Editors Conference photograph

Maris, Thomas G.; Pappas, Evangelos

2009-07-01

57

MAGIC-f Gel in Nuclear Medicine Dosimetry: study in an external beam of Iodine-131  

NASA Astrophysics Data System (ADS)

MAGIC-f gel applicability in Nuclear Medicine dosimetry was investigated by exposure to a 131I source. Calibration was made to provide known absorbed doses in different positions around the source. The absorbed dose in gel was compared with a Monte Carlo Simulation using PENELOPE code and a thermoluminescent dosimetry (TLD). Using MRI analysis for the gel a R2-dose sensitivity of 0.23 s-1Gy-1was obtained. The agreement between dose-distance curves obtained with Monte Carlo simulation and TLD was better than 97% and for MAGIC-f and TLD was better than 98%. The results show the potential of polymer gel for application in nuclear medicine where three dimensional dose distribution is demanded.

Schwarcke, M.; Marques, T.; Garrido, C.; Nicolucci, P.; Baffa, O.

2010-11-01

58

Three-dimensional BANGTM gel dosimetry in conformal carbon ion radiotherapy  

Microsoft Academic Search

In this study we applied BANGTM polymer-gel dosimetry using magnetic resonance imaging (MRI) to densely ionizing radiation such as carbon ion beams. BANGTM polymer gels were irradiated with a quadratic field of monoenergetic 12C ions at different beam energies in the range of 135MeVu-1 to 410MeVu-1. They were irradiated at the radiotherapy facility of the GSI, Darmstadt, Germany. Our object

U Ramm; U Weber; M Bock; A Bankamp; M Damrau; C Thilmann; L R Schad; G Kraft

2000-01-01

59

Optimization of multiple spin-echo sequences for 3D polymer gel dosimetry  

Microsoft Academic Search

The overall performance of polymer gel dosimeters for three-dimensional radiation dosimetry is determined by the temporal and spatial stability of the gels, dose sensitivity and image quality with respect to both systematic and stochastic deviations. The dose resolution (Dp?) is determined by the dose sensitivity and the signal-to-noise ratio (SNR) in the dose images. The dose sensitivity can be altered

Y. DeDeene; C. Baldock

2002-01-01

60

The reproducibility of polyacrylamide gel dosimetry applied to stereotactic conformal radiotherapy  

Microsoft Academic Search

The reproducibility of polyacrylamide gel (PAG) dosimetry has been evaluated when used to verify two radiotherapy treatment plans of increasing complexity. The plans investigated were a three-field coplanar arrangement, using the linac jaws for field shaping, and a four-field, conformal, non-coplanar plan using precision-cast lead alloy shielding blocks. Each treatment was performed three times using phantoms and calibration gels manufactured

V. P. Cosgrove; P. S. Murphy; M. McJury; E. J. Adams; A. P. Warrington; M. O. Leach; S. Webb

2000-01-01

61

A procedure to mathematically amend possible thickness disuniformities in gel-layer dosimetry  

Microsoft Academic Search

The continuous development of conformal radiotherapies requires a corresponding improvement of dosimetric techniques. Fricke gel-layer dosimetry, coupled with a suitably developed software, has proven to be a reliable technique for 3D absorbed dose distribution verification. The method is based on the evaluation of the light transmitted by gel-layers due to the fact that th optical density difference between irradiated and

Mauro Carrara; Grazia Gambarini; Giacomo Bartesaghi; Carlo Fallai; Anna Negri

2009-01-01

62

Polymer gel dosimetry close to an 125I interstitial brachytherapy seed  

Microsoft Academic Search

Despite its advantages, the polymer gel-magnetic resonance imaging (MRI) method has not, as yet, been successfully employed in dosimetry of low energy\\/low dose rate photon-emitting brachytherapy sources such as 125I or 103Pd interstitial seeds. In the present work, two commercially available 125I seed sources, each of approximately 0.5 U, were positioned at two different locations of a polymer gel filled

E. Pantelis; G. Lymperopoulou; P. Papagiannis; L. Sakelliou; E. Stiliaris; P. Sandilos; I. Seimenis; M. Kozicki; J. M. Rosiak

2005-01-01

63

Comparison between polymer gel dosimetry and calculated dose with small field in stereotactic irradiation  

NASA Astrophysics Data System (ADS)

The purpose of this study is to investigate gel dosimetry for a small irradiation field in stereotactic radiotherapy. Treatment plans were generated by the Pinnacle3 treatment plan system (TPS) for three different circular irradiated fields: 10 mm, 15 mm, and 20 mm. The polymer gels were irradiated to 6 Gy with 10-, 15-, and 20-mm-diameter collimators in 4 MV photon beams for stereotactic irradiation following TPS. Irradiated gels were evaluated with MRI at 1.5 T with R2 images. Firstly, the line profile of the irradiated center between TPS plan and the R2 image was compared. In the center profile at a dose calculated from the treatment plan, the full width at half maximum (FWHM) of 10-mm, 15-mm, and 20-mm collimators, were 13 mm, 19 mm, and 25 mm, respectively. In the center profile at R2 from the gel dosimetry, the FWHM were 13 mm, 20 mm, and 23 mm, respectively. Secondly, R2 images were converted to dosimetric maps to apply the gamma evaluation method. Comparison using gamma evaluation in the center of the irradiated plane between TPS plan and the dose map from the R2 image was performed. In gamma evaluation, when 3% and 3 mm criteria were used for comparison of the center plane of dose image from TPS and gel dosimetry, the pass ratio of the gamma criterion between calculated dose from the TPS and the dose map of irradiated gels in stereotactic irradiation was 98.6%. In comparison of the center profile and center plane, results of gel dosimetry were shown to have good agreement with the generated treatment plan dosimetric map for stereotactic irradiation.

Kawamura, H.; Shinoda, K.; Fuse, H.; Terunuma, T.; Miyamoto, K.; Sakae, T.; Matsumura, A.

2013-06-01

64

High field magnetic resonance imaging-based gel dosimetry for small radiation fields  

NASA Astrophysics Data System (ADS)

Small megavoltage photon radiation fields (< 3cm diameter) are used in advanced radiation therapy techniques, such as intensity modulated radiotherapy, and stereotactic radiosurgery, as well as for cellular and preclinical radiobiology studies (very small fields, <1 mm diameter). Radiation dose characteristics for these small fields are difficult to determine in multiple dimensions because of steep dose gradients (30--40% per mm) and conditions of electronic disequilibrium. Conventional radiation dosimetry techniques have limitations for small fields because detector size may be large compared to radiation field size and/or dose acquisition may be restricted to one or two dimensions. Polymer gel dosimetry, is a three-dimensional (3D) dosimeter based on radiation-induced polymerization of tissue equivalent gelatin. Polymer gel dosimeters can be read using magnetic resonance imaging (MRI), which detects changes in relaxivity due to gel polymerization. Spatial resolution for dose readout is limited to 0.25--0.5mm pixel size because of available the magnetic field strengths (1.5T and 3T) and the stability of polymer gelatin at room temperature. A reliable glucose-based MAGIC (methacrylic and ascorbic acid in gelatine initiated by copper) gel dosimeter was formulated and evaluated for small field 3D dosimetry using 3T and 7T high field MRI for dose readout. The melting point of the original recipe MAGIC gel was increased by 4°C by adding 10% glucose to improve gel stability. Excellent spatial resolution of 79um (1.5 hr scan) and 39um (12 hr scan) was achieved using 7T MRI, proving gel stability for long scan times and high resolution 3D dosimetry.

Ding, Xuanfeng

65

Experimental properties of THPC based normoxic polyacrylamide gels for use in x-ray computed tomography gel dosimetry  

Microsoft Academic Search

The aim of the present study is to investigate the effects of tetrakis(hydroxymethyl)phosphonium chloride (THPC) on the experimental properties of normoxic polyacrylamide gels. Specifically we: (1) assess the use of THPC as an anti-oxidant for x-ray CT PAGAT dosimetry by investigating dose response reproducibility and stability, and optimal THPC concentration for maximum dose sensitivity while ensuring no O2 inhibition; (2)

A Jirasek; M Hilts; C Shaw; P Baxter

2006-01-01

66

Polymer gel dosimetry of an electron beam in the presence of a magnetic field  

NASA Astrophysics Data System (ADS)

The effect of a strong external magnetic field on 4 MeV electron beam was measured with polymer gel dosimetry. The measured entrance dose distribution was compared with a calculated fluence map. The magnetic field was created by use of two permanent Neodymium (NdFeB) magnets that were positioned perpendicular to the electron beam. The magnetic field between the magnets was measured with Hall sensors. Based on the magnetic field measurement and the law of Biot-Savart, the magnetic field distribution was extrapolated. Electron trajectories were calculated using a relativistic Lorentz force operator. Although the simplified computational model that was applied, the shape and position of the calculated entrance fluence map are found to be in good agreement with the measured dose distribution in the first layer of the phantom. In combination with the development of low density polymer gel dosimeters, these preliminary results show the potential of 3D gel dosimetry in MRI-linac applications.

Vandecasteele, J.; De Deene, Y.

2013-06-01

67

On the accuracy and precision of gel dosimetry  

Microsoft Academic Search

Gel dosimeters are radiation sensitive chemical dosimeters that aim at displaying the absorbed dose in three dimensions (3D) and integrated over time. Starting from the fundamental definitions of accuracy and precision this paper examines the unique meaurement challenges inherent to gel dosimetery.

Yves De Deene

2006-01-01

68

Application of MAGAT polymer gel dosimetry in breast balloon  

NASA Astrophysics Data System (ADS)

The purpose of this study is to characterize the response of MAGAT normoxic polymer gel for breast brachytherapy applications using two balloon applicators (MammoSite® and Contoura®) and verify the dose distribution with a commercial treatment planning system (BrachyVision® version 8.9.15). We present the fabrication, irradiation and readout of the gel used for the work described herein.

Govi, N.; Gueye, P.; Avery, S.

2013-06-01

69

Review of quantitative MRI principles for gel dosimetry  

Microsoft Academic Search

The radiation dose distribution absorbed by polymer gel dosimeters can be read out by several methods such as magnetic resonance imaging (MRI), optical CT, X-ray CT and ultrasound. MRI was the first method that was explored to read out polymer gel dosimeters. Although MRI was soon recognised as a promising technique, limited access to MRI scanners and the often (wrongly

Yves DeDeene

2009-01-01

70

In-phantom dosimetry for BNCT with Fricke and normoxic-polymer gels  

NASA Astrophysics Data System (ADS)

Measurements of in-phantom dose distributions and images are important for Boron Neutron Capture Therapy treatment planning. The method for spatial determination of absorbed doses in thermal or epithermal neutron fields, based on Fricke-xylenol-orange-infused gel dosimeters in form of layers, has revealed to be very reliable, as gel layer dosimeters give the possibility of obtaining spatial dose distributions and measurements of each dose contribution in neutron fields, by means of a properly studied procedure. Quite recently, BNCT has been applied to treat liver metastases; in this work the results of in-phantom dosimetry for explanted liver in BNCT treatments are described. Moreover, polyacrylamide gel (PAG) dosimeters in which a polymerization process appears as a consequence of absorbed dose, have been recently tested, because of their characteristic absence of diffusion. In fact, due to the diffusion of ferric ions, Fricke-gel dosimeters require prompt analysis after exposure to avoid spatial information loss. In this work the preliminary results of a study about the reliability of polymer gel in BNCT dosimetry are also discussed. Gel layers have been irradiated in a phantom exposed in the thermal column of the TRIGA MARK II reactor (Pavia). The results obtained with the two kinds of gel dosimeter have been compared.

Gambarini, G.; Agosteo, S.; Carrara, M.; Gay, S.; Mariani, M.; Pirola, L.; Vanossi, E.

2006-05-01

71

Evaluation of the potential for diacetylenes as reporter molecules in 3D micelle gel dosimetry.  

PubMed

Radiochromic micelle gel dosimeters are promising for three-dimensional (3D) radiation dosimetry because they can be read out by optical CT techniques and they have superior spatial stability compared to polymer and Fricke gel dosimeters. This study evaluates the use of diacetylenes as reporter molecules in micelle gel dosimeters. Several gels containing pentacosa-10,12-diynoic acid (PCDA) emulsified using sodium dodecyl sulfate (SDS) changed from colourless to blue upon irradiation. Unfortunately, all phantoms that experienced a colour change were turbid and would be unsuitable for 3D dosimetry. Two techniques (use of organic solvent and aqueous-phase additives) were successful in increasing colloidal stability to prevent the turbidity problem, but none of the resulting transparent gels changed colour in response to radiation. Transparent PCDA emulsions were prepared using NaOH solutions with no SDS or other emulsifier, but these transparent emulsions also did not change colour. Only turbid gels and emulsions with precipitated particles responded to radiation. These results indicate that the colour change was due to the oligomerization within precipitated PCDA crystals, and that liquid-phase emulsified PCDA did not undergo oligomerization. As a result, PCDA is not suitable for use in micelle gel dosimeters, and other radiochromic reporter molecules will need to be identified. PMID:23322115

Nasr, A T; Olding, T; Schreiner, L J; McAuley, K B

2013-02-21

72

Evaluation of the potential for diacetylenes as reporter molecules in 3D micelle gel dosimetry  

NASA Astrophysics Data System (ADS)

Radiochromic micelle gel dosimeters are promising for three-dimensional (3D) radiation dosimetry because they can be read out by optical CT techniques and they have superior spatial stability compared to polymer and Fricke gel dosimeters. This study evaluates the use of diacetylenes as reporter molecules in micelle gel dosimeters. Several gels containing pentacosa-10,12-diynoic acid (PCDA) emulsified using sodium dodecyl sulfate (SDS) changed from colourless to blue upon irradiation. Unfortunately, all phantoms that experienced a colour change were turbid and would be unsuitable for 3D dosimetry. Two techniques (use of organic solvent and aqueous-phase additives) were successful in increasing colloidal stability to prevent the turbidity problem, but none of the resulting transparent gels changed colour in response to radiation. Transparent PCDA emulsions were prepared using NaOH solutions with no SDS or other emulsifier, but these transparent emulsions also did not change colour. Only turbid gels and emulsions with precipitated particles responded to radiation. These results indicate that the colour change was due to the oligomerization within precipitated PCDA crystals, and that liquid-phase emulsified PCDA did not undergo oligomerization. As a result, PCDA is not suitable for use in micelle gel dosimeters, and other radiochromic reporter molecules will need to be identified.

Nasr, A. T.; Olding, T.; Schreiner, L. J.; McAuley, K. B.

2013-02-01

73

X-ray CT dose in normoxic polyacrylamide gel dosimetry  

Microsoft Academic Search

This study reports on the effects of x-ray CT dose in CT imaged normoxic polyacrylamide (nPAG) gel dosimeters. The investigation is partitioned into three sections. First, the CT dose absorbed in nPAG is quantified under a range of typical gel CT imaging protocols. It is found that the maximum absorbed CT dose occurs for volumetric imaging and is in the

P. Baxter; A. Jirasek; M. Hilts

2007-01-01

74

Adaptive mean filtering for noise reduction in CT polymer gel dosimetry  

SciTech Connect

X-ray computed tomography (CT) as a method of extracting 3D dose information from irradiated polymer gel dosimeters is showing potential as a practical means to implement gel dosimetry in a radiation therapy clinic. However, the response of CT contrast to dose is weak and noise reduction is critical in order to achieve adequate dose resolutions with this method. Phantom design and CT imaging technique have both been shown to decrease image noise. In addition, image postprocessing using noise reduction filtering techniques have been proposed. This work evaluates in detail the use of the adaptive mean filter for reducing noise in CT gel dosimetry. Filter performance is systematically tested using both synthetic patterns mimicking a range of clinical dose distribution features as well as actual clinical dose distributions. Both low and high signal-to-noise ratio (SNR) situations are examined. For all cases, the effects of filter kernel size and the number of iterations are investigated. Results indicate that adaptive mean filtering is a highly effective tool for noise reduction CT gel dosimetry. The optimum filtering strategy depends on characteristics of the dose distributions and image noise level. For low noise images (SNR {approx}20), the filtered results are excellent and use of adaptive mean filtering is recommended as a standard processing tool. For high noise images (SNR {approx}5) adaptive mean filtering can also produce excellent results, but filtering must be approached with more caution as spatial and dose distortions of the original dose distribution can occur.

Hilts, Michelle; Jirasek, Andrew [Medical Physics, BC Cancer Agency-Vancouver Island Centre, Victoria, British Columbia, V8R6V5 (Canada); Department of Physics and Astronomy, University of Victoria, Victoria, British Columbia, V8W2Y2 (Canada)

2008-01-15

75

Relative output factor measurements of a 5 mm diameter radiosurgical photon beam using polymer gel dosimetry  

SciTech Connect

Besides the fine spatial resolution inherent in polymer gel-magnetic resonance imaging (MRI) dosimetry, the method also features the potential for multiple measurements of varying sensitive volume in a single experiment by integrating results in MRI voxels of finite dimensions (i.e., in plane resolution by slice thickness). This work exploits this feature of polymer gel dosimetry to propose an experimental technique for relative output factor (OF) measurements of small radiosurgical beams. Two gel vials were irradiated with a 5 and 30 mm diameter 6 MV radiosurgery beam and MR scanned with the same slice thickness and three different in plane resolutions. Using this experimental data set, 5 mm OF measurements with the PinPoint ion chamber are simulated by integrating results over a sensitive volume equal to that of the chamber. Results are found in agreement within experimental uncertainties with actual PinPoint measurements verifying the validity of the proposed experimental procedure. The polymer gel data set is subsequently utilized for OF measurements of the 5 mm beam with varying sensitive volume to discuss the magnitude of detector volume averaging effects. Seeking to correct for volume averaging, results are extrapolated to zero sensitive volume yielding a 5 mm OF measurement of (0.66{+-}5%). This result compares reasonably with corresponding ionometric and radiographic film measurements of this work and corresponding, limited, data in the literature. Overall, results suggest that polymer gel dosimetry coupled with the proposed experimental procedure helps overcome not only tissue-equivalence and beam perturbation implications but also volume averaging and positioning uncertainties which constitute the main drawback in small radiosurgical beam dosimetry.

Pappas, E.; Petrokokkinos, L.; Angelopoulos, A.; Maris, T.G.; Kozicki, M.; Dalezios, I.; Kouloulias, V. [Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece); Radiology Section, Medical Physics Department, MRI Unit, University Hospital of Heraklion, 711 10 Stavrakia-Heraklion, Crete (Greece); Faculty of Textile Engineering, Technical University of Lodz, Zeromskiego St 116, 90-543 Lodz, Poland and Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego Street 15, 93-590 Lodz (Poland); Department of Biomedical Engineering, University General Hospital 'Attikon', 1 Rimini Street, 124 62, Chaidari, Athens (Greece); Department of Electrical Engineering and Computer Science, National Technical University of Athens, 9 Hroon Polytechniou Street, 157 73 Athens (Greece)

2005-06-15

76

Radiation dosimetry using magnetic resonance imaging. Development of a dosimeter gel for measurements of 3D dose distribution in radiotherapy.  

National Technical Information Service (NTIS)

A new dosimetry system for 3D dose distribution measurements based on the Fricke dosimeter and magnetic resonance imaging (MRI) has been developed. The dosimeter consists of a ferrous sulphate solution incorporated in an agarose gel, which together consti...

L. E. Olsson

1991-01-01

77

Design and Construction of an Optical Computed Tomography Scanner for Polymer Gel Dosimetry Application  

PubMed Central

Polymer gel dosimeter is the only accurate three dimensional (3D) dosimeter that can measure the absorbed dose distribution in a perfect 3D setting. Gel dosimetry by using optical computed tomography (OCT) has been promoted by several researches. In the current study, we designed and constructed a prototype OCT system for gel dosimetry. First, the electrical system for optical scanning of the gel container using a Helium-Neon laser and a photocell was designed and constructed. Then, the mechanical part for two rotational and translational motions was designed and step motors were assembled to it. The data coming from photocell was grabbed by the home-built interface and sent to a personal computer. Data processing was carried out using MATLAB software. To calibrate the system and tune up the functionality of it, different objects was designed and scanned. Furthermore, the spatial and contrast resolution of the system was determined. The system was able to scan the gel dosimeter container with a diameter up to 11 cm inside the water phantom. The standard deviation of the pixels within water flask image was considered as the criteria for image uniformity. The uniformity of the system was about ±0.05%. The spatial resolution of the system was approximately 1 mm and contrast resolution was about 0.2%. Our primary results showed that this system is able to obtain two-dimensional, cross-sectional images from polymer gel samples.

Zakariaee, Seyed Salman; Mesbahi, Asghar; Keshtkar, Ahmad; Azimirad, Vahid

2014-01-01

78

Design and construction of an optical computed tomography scanner for polymer gel dosimetry application.  

PubMed

Polymer gel dosimeter is the only accurate three dimensional (3D) dosimeter that can measure the absorbed dose distribution in a perfect 3D setting. Gel dosimetry by using optical computed tomography (OCT) has been promoted by several researches. In the current study, we designed and constructed a prototype OCT system for gel dosimetry. First, the electrical system for optical scanning of the gel container using a Helium-Neon laser and a photocell was designed and constructed. Then, the mechanical part for two rotational and translational motions was designed and step motors were assembled to it. The data coming from photocell was grabbed by the home-built interface and sent to a personal computer. Data processing was carried out using MATLAB software. To calibrate the system and tune up the functionality of it, different objects was designed and scanned. Furthermore, the spatial and contrast resolution of the system was determined. The system was able to scan the gel dosimeter container with a diameter up to 11 cm inside the water phantom. The standard deviation of the pixels within water flask image was considered as the criteria for image uniformity. The uniformity of the system was about ±0.05%. The spatial resolution of the system was approximately 1 mm and contrast resolution was about 0.2%. Our primary results showed that this system is able to obtain two-dimensional, cross-sectional images from polymer gel samples. PMID:24761377

Zakariaee, Seyed Salman; Mesbahi, Asghar; Keshtkar, Ahmad; Azimirad, Vahid

2014-04-01

79

Radiochromic gel dosemeter for three-dimensional dosimetry  

NASA Astrophysics Data System (ADS)

A gel dosemeter in which ionising radiation causes a colour change was produced by modifying an existing Fricke gel system. This allows a more convenient preparation procedure and gives a better quality dosimetric system for three-dimensional (3-D) dose measurements. The role of three active components of the Ferrous sulphate Xylenol orange Gelatin (FXG) gel dosemeter is quantified with special consideration of their effect on system sensitivity and stability. The optimal composition was found to be 0.5 mM ferrous sulphate, 0.1 mM xylenol orange and 25 mM sulphuric acid. The dose response is linear in the range 0.1-30 Gy. The FXG sensitivity, derived from the gradient of the dose response curve, was found to be ?A=0.084 cm -1 Gy -1, where A is the optical absorption coefficient at a wavelength of 585 nm, with reproducibility and 24 h stability of better than 5%.

Bero, M. A.; Gilboy, W. B.; Glover, P. M.

2001-06-01

80

MR Based Polymer Gel Dosimetry (MRPD) versus Film Dosimetry using Dose Modulation Transfer Function (DMTF)  

Microsoft Academic Search

Precise methods of modern radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods-ionization chambers, TLD arrangements or silicon detectors, for example-are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer

N. Riyahi Alam; A. Takavar; M. Moghadam; S. Haghgoo; K. Firooznia; P. Hadad; T. A. Pourfallah; E. Mohammadi; A. Nedaei

2007-01-01

81

Gel-layer dosimetry for dose verification in intensity-modulated radiation therapy  

NASA Astrophysics Data System (ADS)

Intensity-modulated radiotherapy (IMRT) is a technique in which the radiation fluence within each of the treatment beams is not uniformly distributed. This allows the patient dose to follow the boundaries even of a target volume of complex shape, and, virtually, to spare critical healthy organs at risk. The agreement between planned and delivered IMRT dose is verified by means of standard dosimetric methods such as film dosimetry or semiconductors array dosimetry. In this paper, we compare the output of a commercial device using an array of diodes for IMRT absolute dose verification with the output of a gel dosimeter, composed by a 10×8 cm 2 rectangular layer of a tissue-equivalent gel matrix in which a proper chemical dosimeter has been incorporated. The dose distribution is derived from the images of visible light transmittance, detected with a CCD camera before and after the gel exposure. The analysis was carried out on a single IMRT field chosen among those archived at the Istituto Nazionale Tumori of Milan. The radiation field was examined in an area common to both dosimeters. The agreement between the two detectors was good, as shown by analysis of dose profiles, especially for doses above 15-20 cGy. Gel dosimeter was in good agreement with the planned dose too, with a percentage of dosimeter points passing a dose to agreement test ranging between 90% and 93%. Although preliminary, our data suggest that gel dosimetry is a reliable method for IMRT dose verification. Due to the good spatial resolution and to the tissue equivalent properties of its composition, it would be suitable also for 3D IMRT dose reconstruction and verification in the form of multiple piled-up gel layers.

Tomatis, S.; Carrara, M.; Gambarini, G.; Marchesini, R.; Valente, M.

2007-09-01

82

Application of polymer-gel dosimetry in stereotactic radiosurgery  

Microsoft Academic Search

Stereotactic irradiation with the Leksell gamma knife (Elekta Instrument AB, Stockholm, Sweden) is one of the primary methods used for the stereotactic radiosurgery treatment of intracranial lesions. To assure the quality of the whole treatment procedure a proper dosimetric system is required. The polymer-gel dosimeter evaluated by nuclear magnetic resonance (NMR) is a promising tool to satisfy this requirement. The

J. Novotny Jr.; V. Spevacek; P. Dvorak; J. Hrbacek; D. Tlachacova; M. Schmitt; J. Vymazal; J. Tintera; T. Cechak

2004-01-01

83

Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry  

Microsoft Academic Search

The accuracy of the Leksell GammaPlan registered , the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near

Fatih Isbakan; Yekta Ülgen; Hatice Bilge; Zeynep Ozen; Onur Agus; Bora Buyuksarac

2007-01-01

84

NOTE: Dose resolution in gel dosimetry: effect of uncertainty in the calibration function  

Microsoft Academic Search

Dose resolution, DpDgr, is becoming a common method for characterizing the performance of a gel dosimeter. In this note we examine how the goodness of fit of the calibration function affects DpDgr and show that its inclusion in the calculation of DpDgr is essential to avoid overestimating the performance of the gel.

J. V. Trapp; G. Michael; P. M. Evans; C. Baldock; M. O. Leach; S. Webb

2004-01-01

85

NOTE: Dose resolution in gel dosimetry: effect of uncertainty in the calibration function  

NASA Astrophysics Data System (ADS)

Dose resolution, DpDgr, is becoming a common method for characterizing the performance of a gel dosimeter. In this note we examine how the goodness of fit of the calibration function affects DpDgr and show that its inclusion in the calculation of DpDgr is essential to avoid overestimating the performance of the gel.

Trapp, J. V.; Michael, G.; Evans, P. M.; Baldock, C.; Leach, M. O.; Webb, S.

2004-05-01

86

Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry.  

PubMed

The accuracy of the Leksell GammaPlan, the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near the paranosal sinuses cavities. The homogeneous phantom was a spherical glass balloon of 16 cm diameter, filled with MAGIC gel; i.e., the normoxic polymer gel. Two hollow PVC balls of 2 cm radius, filled with N2 gas, represented the air cavities inside the inhomogeneous phantom. For dose calibration purposes, 100 ml gel-containing vials were irradiated at predefined doses, and then scanned in a MR unit. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. Dose distributions are the results of a single shot of irradiation, obtained by collimating all 201 cobalt sources to a known target in the phantom. Both phantoms were irradiated at the same dose level at the same coordinates. Stereotactic frames and fiducial markers were attached to the phantoms prior to MR scanning. The dose distribution predicted by the Gamma Knife planning system was compared with that of the gel dosimetry. As expected, for the homogeneous phantom the isodose diameters measured by the gel dosimetry and the GammaPlan differed by 5% at most. However, with the inhomogeneous phantom, the dose maps in the axial, coronal and sagittal planes were spatially different. The diameters of the 50% isodose curves differed 43% in the X axis and 32% in the Y axis for the Z =90 mm axial plane; by 44% in the X axis and 24% in the Z axis for the Y=90 mm coronal plane; and by 32% in the Z axis and 42% in the Y axis for the X=92 mm sagittal plane. The lack of ability of the GammaPlan to predict the rapid dose fall off, due to the air cavities behind or near the lesion led to an overestimation of the dose that was actually delivered. Clinically, this can result in underdosing of lesions near tissue inhomogeneities in patients under treatment. PMID:17555244

Isbakan, Fatih; Ulgen, Yekta; Bilge, Hatice; Ozen, Zeynep; Agus, Onur; Buyuksarac, Bora

2007-05-01

87

Gamma Knife 3-D dose distribution near the area of tissue inhomogeneities by normoxic gel dosimetry  

SciTech Connect

The accuracy of the Leksell GammaPlan registered , the dose planning system of the Gamma Knife Model-B, was evaluated near tissue inhomogeneities, using the gel dosimetry method. The lack of electronic equilibrium around the small-diameter gamma beams can cause dose calculation errors in the neighborhood of an air-tissue interface. An experiment was designed to investigate the effects of inhomogeneity near the paranosal sinuses cavities. The homogeneous phantom was a spherical glass balloon of 16 cm diameter, filled with MAGIC gel; i.e., the normoxic polymer gel. Two hollow PVC balls of 2 cm radius, filled with N{sub 2} gas, represented the air cavities inside the inhomogeneous phantom. For dose calibration purposes, 100 ml gel-containing vials were irradiated at predefined doses, and then scanned in a MR unit. Linearity was observed between the delivered dose and the reciprocal of the T2 relaxation time constant of the gel. Dose distributions are the results of a single shot of irradiation, obtained by collimating all 201 cobalt sources to a known target in the phantom. Both phantoms were irradiated at the same dose level at the same coordinates. Stereotactic frames and fiducial markers were attached to the phantoms prior to MR scanning. The dose distribution predicted by the Gamma Knife planning system was compared with that of the gel dosimetry. As expected, for the homogeneous phantom the isodose diameters measured by the gel dosimetry and the GammaPlan registered differed by 5% at most. However, with the inhomogeneous phantom, the dose maps in the axial, coronal and sagittal planes were spatially different. The diameters of the 50% isodose curves differed 43% in the X axis and 32% in the Y axis for the Z=90 mm axial plane; by 44% in the X axis and 24% in the Z axis for the Y=90 mm coronal plane; and by 32% in the Z axis and 42% in the Y axis for the X=92 mm sagittal plane. The lack of ability of the GammaPlan registered to predict the rapid dose fall off, due to the air cavities behind or near the lesion led to an overestimation of the dose that was actually delivered. Clinically, this can result in underdosing of lesions near tissue inhomogeneities in patients under treatment.

Isbakan, Fatih; Uelgen, Yekta; Bilge, Hatice; Ozen, Zeynep; Agus, Onur; Buyuksarac, Bora [Institute of Biomedical Engineering, Bogazici University, Istanbul (Turkey); Institute of Radiation Oncology, Istanbul University, Istanbul (Turkey); Radiation Oncology Department, Marmara University Hospital, Istanbul (Turkey); Institute of Biomedical Engineering, Bogazici University, Istanbul (Turkey)

2007-05-15

88

Polymer gel - TPS radiotherapy dosimetry GeVero® software for ionizing radiation absorbed dose 3D distribution calculations  

Microsoft Academic Search

Implementation of polymer gel dosimetry in radiotherapy departments calls for: easily manufactured gel dosimeters of required physical-chemical properties, set-up procedures of irradiation, adaptation of three-dimensional scanning procedures and instruments as well as fast tool for calculation of 3D absorbed dose distribution in the polymer gel dosimeters and comparison with another treatment planning system calculated dose distribution. These challenges resulted in

Marek Kozicki; Piotr Maras; Jacek Jankowski; Andrzej C. Karwowski

2009-01-01

89

Three-dimensional dosimetry of small megavoltage radiation fields using radiochromic gels and optical CT scanning.  

PubMed

The dosimetry of small fields as used in stereotactic radiotherapy, radiosurgery and intensity-modulated radiation therapy can be challenging and inaccurate due to partial volume averaging effects and possible disruption of charged particle equilibrium. Consequently, there exists a need for an integrating, tissue equivalent dosimeter with high spatial resolution to avoid perturbing the radiation beam and artificially broadening the measured beam penumbra. In this work, radiochromic ferrous xylenol-orange (FX) and leuco crystal violet (LCV) micelle gels were used to measure relative dose factors (RDFs), percent depth dose profiles and relative lateral beam profiles of 6 MV x-ray pencil beams of diameter 28.1, 9.8 and 4.9 mm. The pencil beams were produced via stereotactic collimators mounted on a Varian 2100 EX linear accelerator. The gels were read using optical computed tomography (CT). Data sets were compared quantitatively with dosimetric measurements made with radiographic (Kodak EDR2) and radiochromic (GAFChromic EBT) film, respectively. Using a fast cone-beam optical CT scanner (Vista), corrections for diffusion in the FX gel data yielded RDFs that were comparable to those obtained by minimally diffusing LCV gels. Considering EBT film-measured RDF data as reference, cone-beam CT-scanned LCV gel data, corrected for scattered stray light, were found to be in agreement within 0.5% and -0.6% for the 9.8 and 4.9 mm diameter fields, respectively. The validity of the scattered stray light correction was confirmed by general agreement with RDF data obtained from the same LCV gel read out with a laser CT scanner that is less prone to the acceptance of scattered stray light. Percent depth dose profiles and lateral beam profiles were found to agree within experimental error for the FX gel (corrected for diffusion), LCV gel (corrected for scattered stray light), and EBT and EDR2 films. The results from this study reveal that a three-dimensional dosimetry method utilizing optical CT-scanned radiochromic gels allows for the acquisition of a self-consistent volumetric data set in a single exposure, with sufficient spatial resolution to accurately characterize small fields. PMID:19336848

Babic, Steven; McNiven, Andrea; Battista, Jerry; Jordan, Kevin

2009-04-21

90

Three-dimensional dosimetry of small megavoltage radiation fields using radiochromic gels and optical CT scanning  

NASA Astrophysics Data System (ADS)

The dosimetry of small fields as used in stereotactic radiotherapy, radiosurgery and intensity-modulated radiation therapy can be challenging and inaccurate due to partial volume averaging effects and possible disruption of charged particle equilibrium. Consequently, there exists a need for an integrating, tissue equivalent dosimeter with high spatial resolution to avoid perturbing the radiation beam and artificially broadening the measured beam penumbra. In this work, radiochromic ferrous xylenol-orange (FX) and leuco crystal violet (LCV) micelle gels were used to measure relative dose factors (RDFs), percent depth dose profiles and relative lateral beam profiles of 6 MV x-ray pencil beams of diameter 28.1, 9.8 and 4.9 mm. The pencil beams were produced via stereotactic collimators mounted on a Varian 2100 EX linear accelerator. The gels were read using optical computed tomography (CT). Data sets were compared quantitatively with dosimetric measurements made with radiographic (Kodak EDR2) and radiochromic (GAFChromic® EBT) film, respectively. Using a fast cone-beam optical CT scanner (Vista™), corrections for diffusion in the FX gel data yielded RDFs that were comparable to those obtained by minimally diffusing LCV gels. Considering EBT film-measured RDF data as reference, cone-beam CT-scanned LCV gel data, corrected for scattered stray light, were found to be in agreement within 0.5% and -0.6% for the 9.8 and 4.9 mm diameter fields, respectively. The validity of the scattered stray light correction was confirmed by general agreement with RDF data obtained from the same LCV gel read out with a laser CT scanner that is less prone to the acceptance of scattered stray light. Percent depth dose profiles and lateral beam profiles were found to agree within experimental error for the FX gel (corrected for diffusion), LCV gel (corrected for scattered stray light), and EBT and EDR2 films. The results from this study reveal that a three-dimensional dosimetry method utilizing optical CT-scanned radiochromic gels allows for the acquisition of a self-consistent volumetric data set in a single exposure, with sufficient spatial resolution to accurately characterize small fields.

Babic, Steven; McNiven, Andrea; Battista, Jerry; Jordan, Kevin

2009-04-01

91

Validation and application of polymer gel dosimetry for the dose verification of an intensity-modulated arc therapy (IMAT) treatment  

Microsoft Academic Search

Polymer gel dosimetry was used to assess an intensity-modulated arc therapy (IMAT) treatment for whole abdominopelvic radiotherapy. Prior to the actual dosimetry experiment, a uniformity study on an unirradiated anthropomorphic phantom was carried out. A correction was performed to minimize deviations in the R2 maps due to radiofrequency non-uniformities. In addition, compensation strategies were implemented to limit R2 deviations caused

K. Vergote; Y. DeDeene; W. Duthoy; W. DeGersem; W. DeNeve; E. Achten; C. DeWagter

2004-01-01

92

Deformable gel dosimetry I: application to external beam radiotherapy and brachytherapy  

NASA Astrophysics Data System (ADS)

Inter- and intra-fractional variation in anatomic structures is a significant challenge in contemporary radiotherapy (RT). In this study, we describe the implementation of a novel deformable gel dosimetry system (dubbed 'DEFGEL') for application to external beam RT and brachytherapy experimental measurements. Complex / redistributed dose distributions due to applied deformations were readily observed and the discrepancies relative to a control case with an absence of deformation could be quantified. This work has obvious extensions to validation of deformable image registration algorithms, deformable dose calculation algorithms, and quality assurance of motion compensation strategies in RT.

Yeo, U. J.; Taylor, M. L.; Supple, J. R.; Smith, R. L.; Kron, T.; Franich, R. D.

2013-06-01

93

The spatial resolution in dosimetry with normoxic polymer-gels investigated with the dose modulation transfer approach.  

PubMed

The verification of dose distributions with high dose gradients as appearing in brachytherapy or stereotactic radiotherapy for example, calls for dosimetric methods with sufficiently high spatial resolution. Polymer gels in combination with a MR or optical scanner as a readout device have the potential of performing the verification of a three-dimensional dose distribution within a single measurement. The purpose of this work is to investigate the spatial resolution achievable in MR-based polymer gel dosimetry. The authors show that dosimetry on a very small spatial scale (voxel size: 94 x 94 x 1000 microm3) can be performed with normoxic polymer gels using parameter selective T2 imaging. In order to prove the spatial resolution obtained we are relying on the dose-modulation transfer function (DMTF) concept based on very fine dose modulations at half periods of 200 microm. Very fine periodic dose modulations of a 60Co photon field were achieved by means of an absorption grid made of tungsten-carbide, specifically designed for quality control. The dose modulation in the polymer gel is compared with that of film dosimetry in one plane via the DMTF concept for general access to the spatial resolution of a dose imaging system. Additionally Monte Carlo simulations were performed and used for the calculation of the DMTF of both, the polymer gel and film dosimetry. The results obtained by film dosimetry agree well with those of Monte Carlo simulations, whereas polymer gel dosimetry overestimates the amplitude value of the fine dose modulations. The authors discuss possible reasons. The in-plane resolution achieved in this work competes with the spatial resolution of standard clinical film-scanner systems. PMID:18561650

Bayreder, Christian; Schön, Robert; Wieland, M; Georg, Dietmar; Moser, Ewald; Berg, Andreas

2008-05-01

94

The spatial resolution in dosimetry with normoxic polymer-gels investigated with the dose modulation transfer approach  

SciTech Connect

The verification of dose distributions with high dose gradients as appearing in brachytherapy or stereotactic radiotherapy for example, calls for dosimetric methods with sufficiently high spatial resolution. Polymer gels in combination with a MR or optical scanner as a readout device have the potential of performing the verification of a three-dimensional dose distribution within a single measurement. The purpose of this work is to investigate the spatial resolution achievable in MR-based polymer gel dosimetry. The authors show that dosimetry on a very small spatial scale (voxel size: 94x94x1000 {mu}m{sup 3}) can be performed with normoxic polymer gels using parameter selective T2 imaging. In order to prove the spatial resolution obtained we are relying on the dose-modulation transfer function (DMTF) concept based on very fine dose modulations at half periods of 200 {mu}m. Very fine periodic dose modulations of a {sup 60}Co photon field were achieved by means of an absorption grid made of tungsten-carbide, specifically designed for quality control. The dose modulation in the polymer gel is compared with that of film dosimetry in one plane via the DMTF concept for general access to the spatial resolution of a dose imaging system. Additionally Monte Carlo simulations were performed and used for the calculation of the DMTF of both, the polymer gel and film dosimetry. The results obtained by film dosimetry agree well with those of Monte Carlo simulations, whereas polymer gel dosimetry overestimates the amplitude value of the fine dose modulations. The authors discuss possible reasons. The in-plane resolution achieved in this work competes with the spatial resolution of standard clinical film-scanner systems.

Bayreder, Christian; Schoen, Robert; Wieland, M.; Georg, Dietmar; Moser, Ewald; Berg, Andreas [MR Centre of Excellence, Center for Biomedical Engineering and Physics, Medical University of Vienna, Vienna (Austria); Department of Nuclear Medicine, Medical University of Vienna, Vienna (Austria); MR Centre of Excellence, Center for Biomedical Engineering and Physics, Medical University of Vienna, Vienna (Austria); Division of Medical Radiation Physics, Medical University of Vienna/AKH, Vienna (Austria); MR Centre of Excellence, Center for Biomedical Engineering and Physics, Medical University of Vienna, Vienna (Austria)

2008-05-15

95

Effect of refraction on dose reconstruction in optical-CT gel dosimetry  

NASA Astrophysics Data System (ADS)

We address the problem of dose reconstruction based on limited experimentally accessible data due to the effect of refraction in optical-CT gel dosimetry. The refractive index mismatch between the components of the optical-CT scanner result in light scattering and ultimately in the inability to capture parts of the projection datasets. We determine the maximum loss of data and the corresponding refractive index mismatch for which accurate dose reconstruction in the central part of the phantom is still possible. Also, a mathematical formalism that indicates how exact reconstructions can be obtained using a priori knowledge of the optical attenuation coefficient of the gel is presented. This study establishes rigorous design principles for accurate 3D dose reconstruction.

Florescu, L.; Ambartsoumian, G.; Wuu, C.-S.

2013-06-01

96

Polymer gel dosimetry utilizing a 2D (SE) and a 2D (HASTE) multiple echo sequences  

NASA Astrophysics Data System (ADS)

Two pulse sequences were used for the estimation of dosimetric characteristics of VIPET polymer gels. The first one, multi- echo spin echo (MESE) is the well-established method for T2 measurements. The other method is a new multi-echo single shot turbo spin echo pulse sequence, MEHASTE that reduces the acquisition time significantly. Both techniques showed a linear R2-dose response. With MESE sequence, the dose sensitivity was slightly enhanced as compared to MEHASTE. The linear portion of the R2-dose curve was restricted using the MEHASTE sequence. For doses above 7 Gy both methods fulfill the 2% ICRU criterion limit for dose resolution estimations (95% confidence level). Finally, for a time period of one month the temporal stability of R2-dose response was maintained stable utilizing both MESE and MEHASTE pulse sequences. MEHASTE serves as an excellent means for fast 3D polymer gel dosimetry.

Papoutsaki, M.-V.; Pappas, E.; Papadakis, A. E.; Varveris, C.; Damilakis, J.; Maris, T. G.

2013-06-01

97

On the validity of 3D polymer gel dosimetry: II. physico-chemical effects.  

PubMed

This study quantifies some major physico-chemical factors that influence the validity of MRI (PAGAT) polymer gel dosimetry: temperature history (pre-, during and post-irradiation), oxygen exposure (post-irradiation) and volumetric effects (experiment with phantom in which a small test tube is inserted). Present results confirm the effects of thermal history prior to irradiation. By exposing a polymer gel sample to a linear temperature gradient of ?2.8 °C cm?¹ and following the dose deviation as a function of post-irradiation time new insights into temporal variations were added. A clear influence of the temperature treatment on the measured dose distribution is seen during the first hours post-irradiation (resulting in dose deviations up to 12%). This effect diminishes to 5% after 54 h post-irradiation. Imposing a temperature offset (maximum 6 °C for 3 h) during and following irradiation on a series of calibration phantoms results in only a small dose deviation of maximum 4%. Surprisingly, oxygen diffusing in a gel dosimeter up to 48 h post-irradiation was shown to have no effect. Volumetric effects were studied by comparing the dose distribution in a homogeneous phantom compared to the dose distribution in a phantom in which a small test tube was inserted. This study showed that the dose measured inside the test tube was closer to the ion chamber measurement in comparison to the reference phantom without test tube by almost 7%. It is demonstrated that physico-chemical effects are not the major causes for the dose discrepancies encountered in the reproducibility study discussed in the concurrent paper (Vandecasteele and De Deene 2013a Phys. Med. Biol. 58 19-42). However, it is concluded that these physico-chemical effects are important factors that should be addressed to further improve the dosimetric accuracy of 3D MRI polymer gel dosimetry. PMID:23221322

Vandecasteele, Jan; De Deene, Yves

2013-01-01

98

On the validity of 3D polymer gel dosimetry: II. Physico-chemical effects  

NASA Astrophysics Data System (ADS)

This study quantifies some major physico-chemical factors that influence the validity of MRI (PAGAT) polymer gel dosimetry: temperature history (pre-, during and post-irradiation), oxygen exposure (post-irradiation) and volumetric effects (experiment with phantom in which a small test tube is inserted). Present results confirm the effects of thermal history prior to irradiation. By exposing a polymer gel sample to a linear temperature gradient of ˜2.8 °C cm-1 and following the dose deviation as a function of post-irradiation time new insights into temporal variations were added. A clear influence of the temperature treatment on the measured dose distribution is seen during the first hours post-irradiation (resulting in dose deviations up to 12%). This effect diminishes to 5% after 54 h post-irradiation. Imposing a temperature offset (maximum 6 °C for 3 h) during and following irradiation on a series of calibration phantoms results in only a small dose deviation of maximum 4%. Surprisingly, oxygen diffusing in a gel dosimeter up to 48 h post-irradiation was shown to have no effect. Volumetric effects were studied by comparing the dose distribution in a homogeneous phantom compared to the dose distribution in a phantom in which a small test tube was inserted. This study showed that the dose measured inside the test tube was closer to the ion chamber measurement in comparison to the reference phantom without test tube by almost 7%. It is demonstrated that physico-chemical effects are not the major causes for the dose discrepancies encountered in the reproducibility study discussed in the concurrent paper (Vandecasteele and De Deene 2013a Phys. Med. Biol. 58 19-42). However, it is concluded that these physico-chemical effects are important factors that should be addressed to further improve the dosimetric accuracy of 3D MRI polymer gel dosimetry. Both authors contributed equally to this study.

Vandecasteele, Jan; De Deene, Yves

2013-01-01

99

Improved MAGIC gel for higher sensitivity and elemental tissue equivalent 3D dosimetry  

PubMed Central

Purpose: Polymer-based gel dosimeter (MAGIC type) is a preferable phantom material for PET range verification of proton beam therapy. However, improvement in elemental tissue equivalency (specifically O?C ratio) is very desirable to ensure realistic time-activity measurements. Methods: Glucose and urea was added to the original MAGIC formulation to adjust the O?C ratio. The dose responses of the new formulations were tested with MRI transverse relaxation rate (R2) measurements. Results: The new ingredients improved not only the elemental composition but also the sensitivity of the MAGIC gel. The O?C ratios of our new gels agree with that of soft tissue within 1%. The slopes of dose response curves were 1.6–2.7 times larger with glucose. The melting point also increased by 5 °C. Further addition of urea resulted in a similar slope but with an increased intercept and a decreased melting point. Conclusions: Our improved MAGIC gel formulations have higher sensitivity and better elemental tissue equivalency for 3D dosimetry applications involving nuclear reactions.

Zhu, Xuping; Reese, Timothy G.; Crowley, Elizabeth M.; El Fakhri, Georges

2010-01-01

100

Improved MAGIC gel for higher sensitivity and elemental tissue equivalent 3D dosimetry  

SciTech Connect

Purpose: Polymer-based gel dosimeter (MAGIC type) is a preferable phantom material for PET range verification of proton beam therapy. However, improvement in elemental tissue equivalency (specifically O/C ratio) is very desirable to ensure realistic time-activity measurements. Methods: Glucose and urea was added to the original MAGIC formulation to adjust the O/C ratio. The dose responses of the new formulations were tested with MRI transverse relaxation rate (R2) measurements. Results: The new ingredients improved not only the elemental composition but also the sensitivity of the MAGIC gel. The O/C ratios of our new gels agree with that of soft tissue within 1%. The slopes of dose response curves were 1.6-2.7 times larger with glucose. The melting point also increased by 5 deg. C. Further addition of urea resulted in a similar slope but with an increased intercept and a decreased melting point. Conclusions: Our improved MAGIC gel formulations have higher sensitivity and better elemental tissue equivalency for 3D dosimetry applications involving nuclear reactions.

Zhu Xuping; Reese, Timothy G.; Crowley, Elizabeth M.; El Fakhri, Georges [Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, Massachusetts 02114 (United States); Department of Radiology, Massachusetts General Hospital, Athinoula A. Martinos Center for Biomedical Imaging, 149 Thirteenth Street, Charlestown, Massachusetts 02129 (United States); Department of Radiation Oncology, Massachusetts General Hospital, 100 Blossom Street, Boston, Massachusetts 02114 (United States); Department of Radiology, Massachusetts General Hospital, 55 Fruit Street, Boston, Massachusetts 02114 (United States)

2010-01-15

101

An x-ray CT polymer gel dosimetry prototype: I. Remnant artefact removal  

NASA Astrophysics Data System (ADS)

In this study a new x-ray CT polymer gel dosimetry (PGD) filtering technique is presented for the removal of (i) remnant ring and streak artefacts, and (ii) ‘structured’ noise in the form of minute, intrinsic gel density fluctuations. It is shown that the noise present within x-ray CT PGD images is not purely stochastic (pixel by pixel) in nature, but rather is ‘structured’, and hence purely stochastic-based noise-removal filters fail in removing this significant, unwanted noise component. The remnant artefact removal (RAR) technique is based on a class of signal stripping (i.e. baseline-estimation) algorithms typically used in the estimation of unwanted non-uniform baselines underlying spectral data. Here the traditional signal removal algorithm is recast, whereby the ‘signal’ that is removed is the structured noise and remnant artefacts, leaving the desired polymer gel dose distribution. The algorithm is extended to 2D and input parameters are optimized for PGD images. RAR filter results are tested on (i) synthetic images with measured gel background images added, in order to accurately represent actual noise present in PGD images, and (ii) PGD images of a three-field gel irradiation. RAR results are compared to a top-performing noise filter (adaptive mean, AM), used in previous x-ray CT PGD studies. It is shown that, in all cases, the RAR filter outperforms the AM filter, particularly in cases where either (i) a low-dose gel image has been acquired or (ii) the signal-to-noise ratio of the PG image is low, as in the case when a low number of image averages are acquired within a given experiment. Guidelines for the implementation of the RAR filter are given.

Jirasek, A.; Carrick, J.; Hilts, M.

2012-05-01

102

Fourier transform Raman spectroscopy of polyacrylamide gels (PAGs) for radiation dosimetry  

NASA Astrophysics Data System (ADS)

Polyacrylamide gels (PAGs) are used for magnetic resonance imaging radiation dosimetry. Fourier transform (FT) Raman spectroscopy studies were undertaken to investigate cross-linking changes during the copolymerization of polyacrylamide gels in the spectral range of 200-3500 . Vibrational bands of 1285 and 1256 were assigned to acrylamide and bis-acrylamide single binding modes. Bands were found to decrease in amplitude with increasing absorbed radiation dose as a result of copolymerization. Principal component regression was performed on FT-Raman spectra of PAG samples irradiated to 50 Gy. Two components were found to be sufficient to account for 98.7% of the variance in the data. Cross validation was used to establish the absorbed radiation dose of an unknown PAG sample from the FT-Raman spectra. The calculated correlation coefficient between measured and predictive samples was 0.997 with a standard error of estimate of 0.976 and a standard error of prediction of 1.140. Results demonstrate the potential of FT-Raman spectroscopy for ionizing radiation dosimetry using polyacrylamide gels.

Baldock, C.; Rintoul, L.; Keevil, S. F.; Pope, J. M.; George, G. A.

1998-12-01

103

Three-dimensional dosimetry using polymer gel and magnetic resonance imaging applied to the verification of conformal radiation therapy in head-and-neck cancer  

Microsoft Academic Search

Background and purpose: It was our aim to investigate NMR-based BANG gel dosimetry as a three-dimensional dosimetry technique in conformal radiotherapy.Materials and methods: The BANG gel consisting of gelatin, water and co-monomers was first validated in a cylindrical glass flask for a single standard beam. Next, the gel contained in a human neck-shaped cast was used to verify a treatment

Y De Deene; C De Wagter; B Van Duyse; S Derycke; W De Neve; E Achten

1998-01-01

104

The effect of water molecular self-diffusion on quantitative high-resolution MRI polymer gel dosimetry  

Microsoft Academic Search

In polymer gel dosimetry, magnetic resonance imaging (MRI) is used to determine the spin-spin relaxation rate (R2) which in turn can be correlated with absorbed dose to provide a map of the spatial distribution of the absorbed dose in the irradiated dosimeter. High accuracy, precision and reproducibility of these dose maps are essential. Moreover, for dose verification around brachytherapy sources

C. Hurley; Y. DeDeene; R. Meder; J. M. Pope; C. Baldock

2003-01-01

105

On the validity of 3D polymer gel dosimetry: III. MRI-related error sources  

NASA Astrophysics Data System (ADS)

In MRI (PAGAT) polymer gel dosimetry, there exists some controversy on the validity of 3D dose verifications of clinical treatments. The relative contribution of important sources of uncertainty in MR scanning to the overall accuracy and precision of 3D MRI polymer gel dosimetry is quantified in this study. The performance in terms of signal-to-noise and imaging artefacts was evaluated on three different MR scanners (two 1.5 T and a 3 T scanner). These include: (1) B0-field inhomogeneity, (2) B1-field inhomogeneity, (3) dielectric effects (losses and standing waves) and (4) temperature inhomogeneity during scanning. B0-field inhomogeneities that amount to maximum 5 ppm result in dose deviations of up to 4.3% and deformations of up to 5 pixels. Compensation methods are proposed. B1-field inhomogeneities were found to induce R2 variations in large anthropomorphic phantoms both at 1.5 and 3 T. At 1.5 T these effects are mainly caused by the coil geometry resulting in dose deviations of up to 25%. After the correction of the R2 maps using a heuristic flip angle-R2 relation, these dose deviations are reduced to 2.4%. At 3 T, the dielectric properties of the gel phantoms are shown to strongly influence B1-field homogeneity, hence R2 homogeneity, especially of large anthropomorphic phantoms. The low electrical conductivity of polymer gel dosimeters induces standing wave patterns resulting in dose deviations up to 50%. Increasing the conductivity of the gel by adding NaCl reduces the dose deviation to 25% after which the post-processing is successful in reducing the remaining inhomogeneities caused by the coil geometry to within 2.4%. The measurements are supported by computational modelling of the B1-field. Finally, temperature fluctuations of 1 °C frequently encountered in clinical MRI scanners result in dose deviations up to 15%. It is illustrated that with adequate temperature stabilization, the dose uncertainty is reduced to within 2.58%. Both authors contributed equally to this study.

Vandecasteele, Jan; De Deene, Yves

2013-01-01

106

On the validity of 3D polymer gel dosimetry: III. MRI-related error sources.  

PubMed

In MRI (PAGAT) polymer gel dosimetry, there exists some controversy on the validity of 3D dose verifications of clinical treatments. The relative contribution of important sources of uncertainty in MR scanning to the overall accuracy and precision of 3D MRI polymer gel dosimetry is quantified in this study. The performance in terms of signal-to-noise and imaging artefacts was evaluated on three different MR scanners (two 1.5 T and a 3 T scanner). These include: (1) B?-field inhomogeneity, (2) B?-field inhomogeneity, (3) dielectric effects (losses and standing waves) and (4) temperature inhomogeneity during scanning. B?-field inhomogeneities that amount to maximum 5 ppm result in dose deviations of up to 4.3% and deformations of up to 5 pixels. Compensation methods are proposed. B?-field inhomogeneities were found to induce R? variations in large anthropomorphic phantoms both at 1.5 and 3 T. At 1.5 T these effects are mainly caused by the coil geometry resulting in dose deviations of up to 25%. After the correction of the R? maps using a heuristic flip angle-R? relation, these dose deviations are reduced to 2.4%. At 3 T, the dielectric properties of the gel phantoms are shown to strongly influence B?-field homogeneity, hence R? homogeneity, especially of large anthropomorphic phantoms. The low electrical conductivity of polymer gel dosimeters induces standing wave patterns resulting in dose deviations up to 50%. Increasing the conductivity of the gel by adding NaCl reduces the dose deviation to 25% after which the post-processing is successful in reducing the remaining inhomogeneities caused by the coil geometry to within 2.4%. The measurements are supported by computational modelling of the B?-field. Finally, temperature fluctuations of 1 °C frequently encountered in clinical MRI scanners result in dose deviations up to 15%. It is illustrated that with adequate temperature stabilization, the dose uncertainty is reduced to within 2.58%. PMID:23221352

Vandecasteele, Jan; De Deene, Yves

2013-01-01

107

Introducing gel dosimetry in a clinical environment: Customization of polymer gel composition and magnetic resonance imaging parameters used for 3D dose verifications in radiosurgery and intensity modulated radiotherapy  

Microsoft Academic Search

Radiation sensitive gels have been used as dosimeters for clinical dose verification of different radiation therapy modalities. However, the use of gels is not widespread, because careful techniques are required to achieve the dose precision and accuracy aimed for in clinical dose verification. Here, the introduction of gel dosimetry in a clinical environment is described, including the whole chain of

Stefano Gianolini; Uwe Schneider; Stefan G. Scheib; Remo A. Crescenti

2007-01-01

108

Gel dosimetry measurements and Monte Carlo modeling for external radiotherapy photon beams: Comparison with a treatment planning system dose distribution  

NASA Astrophysics Data System (ADS)

Gel dosimetry has proved to be useful to determine absorbed dose distributions in radiotherapy, as well as to validate treatment plans. Gel dosimetry allows dose imaging and is particularly helpful for non-uniform dose distribution measurements, as may occur when multiple-field irradiation techniques are employed. In this work, we report gel-dosimetry measurements and Monte Carlo (PENELOPE ®) calculations for the dose distribution inside a tissue-equivalent phantom exposed to a typical multiple-field irradiation. Irradiations were performed with a 10 MV photon beam from a Varian ® Clinac 18 accelerator. The employed dosimeters consisted of layers of Fricke Xylenol Orange radiochromic gel. The method for absorbed dose imaging was based on analysis of visible light transmittance, usually detected by means of a CCD camera. With the aim of finding a simple method for light transmittance image acquisition, a commercial flatbed-like scanner was employed. The experimental and simulated dose distributions have been compared with those calculated with a commercially available treatment planning system, showing a reasonable agreement.

Valente, M.; Aon, E.; Brunetto, M.; Castellano, G.; Gallivanone, F.; Gambarini, G.

2007-09-01

109

Image filtering for improved dose resolution in CT polymer gel dosimetry.  

PubMed

X-ray computed tomography (CT) has been established as a feasible method of performing dosimetry using polyacrylamide gels (PAGs). A small density change occurs in PAG upon irradiation that provides contrast in PAG CT images. However, low dose resolution limits the clinical usefulness of the technique. This work investigates the potential of using image filtering techniques on PAG CT images in order to reduce image noise and improve dose resolution. CT image noise for the scanner and protocol used for the gel images is analyzed and found to be Gaussian distributed and independent of the contrast level in the images. As a result, several filters for reducing spatially invariant noise are investigated: mean, median, midpoint, adaptive mean, alpha-trimmed mean, sigma mean, and a relatively new filter called SUSAN (smallest univalue segment assimilating nucleus). All filters are applied, using 3x3, 5x5, and 7x7 pixel masks, to a CT image of a PAG irradiated with a stereotactic radiosurgery dose distribution. The dose resolution within 95% confidence (D(delta)95%) is calculated and compared for each filtered image, as well the unfiltered image. In addition, the ability of the filters to maintain the spatial integrity of the dose distribution is evaluated and compared. Results clearly indicate that the filters are not equal in their ability to improve D(delta)95% or in their effect on the spatial integrity of the dose distribution. In general, increasing mask size improves D(delta)95% but simultaneously degrades spatial dose information. The mean filter provides the greatest improvement in D(delta)95%, but also the greatest loss of spatial dose information. The SUSAN, mean adaptive, and alpha-trimmed mean filters all provide comparable, but slightly poorer dose resolution. In addition, the SUSAN and adaptive filters both excel at maintaining the spatial distribution of dose and overall are the best performing filters for this application. The midpoint filter, normally useful for Gaussian noise, is poor all-round, dramatically distorting the dose distribution for masks greater than 3x3. The median filter, a common edge preserving noise reduction filter, performs moderately well, but artificially increases high dose gradients. The sigma filter preserves the spatial distribution of dose very well but is least effective at improving dose resolution. In summary, dose resolution can be significantly improved in CT PAG dosimetry through postprocessing of CT images using spatial noise reduction filters. However, such filters are not equal in their ability to improve dose resolution or to maintain the spatial integrity of the dose distribution and an appropriate filter must be chosen depending on clinical demands of the application. PMID:14761019

Hilts, Michelle; Duzenli, Cheryl

2004-01-01

110

Three-dimensional dose verification for intensity modulated radiation therapy using optical CT based polymer gel dosimetry  

SciTech Connect

Dose distributions generated from intensity-modulated-radiation-therapy (IMRT) treatment planning present high dose gradient regions in the boundaries between the target and the surrounding critical organs. Dose accuracy in these areas can be critical, and may affect the treatment. With the increasing use of IMRT in radiotherapy, there is an increased need for a dosimeter that allows for accurate determination of three-dimensional (3D) dose distributions with high spatial resolution. In this study, polymer gel dosimetry and an optical CT scanner have been employed to implement 3D dose verification for IMRT. A plastic cylinder of 17 cm diameter and 12 cm height, filled with BANG registered 3 polymer gels (MGS Research, Inc., Madison, CT) and modified to optimal dose-response characteristics, was used for IMRT dose verification. The cylindrical gel phantom was immersed in a 24x24x20 cm water tank for an IMRT irradiation. The irradiated gel sample was then scanned with an optical CT scanner (MGS Research Inc., Madison, CT) utilizing a single He-Ne laser beam and a single photodiode detector. Similar to the x-ray CT process, filtered back-projection was used to reconstruct the 3D dose distribution. The dose distributions measured from the gel were compared with those from the IMRT treatment planning system. For comparative dosimetry, a solid water phantom of 24x24x20 cm, having the same geometry as the water tank for the gel phantom, was used for EDR2 film and ion chamber measurements. Root mean square (rms) deviations for both dose difference and distance-to-agreement (DTA) were used in three-dimensional analysis of the dose distribution comparison between treatment planning calculations and the gel measurement. Comparison of planar dose distributions among gel dosimeter, film, and the treatment planning system showed that the isodose lines were in good agreement on selected planes in axial, coronal, and sagittal orientations. Absolute point-dose verification was performed with ion chamber measurements at four different points, varying from 48% to 110% of the prescribed dose. The measured and calculated doses were found to agree to within 4.2% at all measurement points. For the comparison between the gel measurement and treatment planning calculations, rms deviations were 2%-6% for dose difference and 1-3 mm for DTA, at 60%-110% doses levels. The results from this study show that optical CT based polymer gel dosimetry has the potential to provide a high resolution, accurate, three-dimensional tool for IMRT dose distribution verification.

Wuu Chengshie; Xu, Y. [Department of Radiation Oncology, Columbia University, New York, New York 10032 (United States)

2006-05-15

111

The use of gel dosimetry for verification of electron and photon treatment plans in carcinoma of the scalp  

NASA Astrophysics Data System (ADS)

In recent years there has been a large amount of research into the potential use of radiation sensitive gels for three-dimensional verification of clinical radiotherapy doses. In this paper we report the use of a MAGIC gel dosimeter (Fong et al 2001 Phys. Med. Biol. 46 3105) for the verification of a specific patient's radiation therapy dose distribution. A 69-year-old male patient presented with a squamous cell carcinoma extending approximately 180° across the top of the scalp (anterior to posterior) and from just over midline to 90° left of the skull. The patient's treatment was commenced using two electron fields. For gel dosimetry, phantoms were produced in which the outer surface spatially corresponded to the outer contours of the patient's anatomy in the region of irradiation. The phantoms were treated with either electrons or intensity modulated radiation therapy (IMRT) with photons. The results identified a hot spot between the matched electron fields and confirmed the more homogeneous dose distribution produced by the IMRT planning system. The IMRT plan was then clinically implemented. The application of a clinical dose to a phantom shaped to a specific patient as well as the ability to select a slice at will during phantom imaging means that gel dosimetry can no longer be considered to simply have potential alone, but is now in fact a useful dosimetric tool.

Trapp, J. V.; Partridge, M.; Hansen, V. N.; Childs, P.; Bedford, J.; Warrington, A. P.; Leach, M. O.; Webb, S.

2004-05-01

112

Evaluation of three-dimensional polymer gel dosimetry using X-ray CT and R2 MRI.  

PubMed

It is difficult to obtain images of thin slices from measurement of spin-spin relaxation (R2) with magnetic resonance imaging (MRI) using the traditional dose reading method of polymer gel dosimetry. In this study, the dose reading method was performed using X-ray computed tomography (CT) for proton beam measurements in order to enable collection of thin slices. In addition, three-dimensional (3D) images of polymer gels were constructed using volume rendering. As a result of acquisition of thin slices, more detailed 3D data consisting of smaller voxel sizes compared to R2 were acquired. However, it was found that with thin slice thicknesses and small voxels, the signal-to-noise ratio around the voxels deteriorated. In addition, the coefficient of variation of non-irradiated gels with CT was smaller than that with R2 MRI. PMID:23542121

Kawamura, H; Sakae, T; Terunuma, T; Ishida, M; Shibata, Y; Matsumura, A

2013-07-01

113

Initial investigation of a novel light-scattering gel phantom for evaluation of optical CT scanners for radiotherapy gel dosimetry  

Microsoft Academic Search

There is a need for stable gel materials for phantoms used to validate optical computerized tomography (CT) scanners used in conjunction with radiation-induced polymerizing gel dosimeters. Phantoms based on addition of light-absorbing dyes to gelatine to simulate gel dosimeters have been employed. However, to more accurately simulate polymerizing gels one requires phantoms that employ light-scattering colloidal suspensions added to the

Stephen Bosi; Pourandokht Naseri; Alicia Puran; Justin Davies; Clive Baldock

2007-01-01

114

Optical CT scanner for in-air readout of gels for external radiation beam 3D dosimetry  

NASA Astrophysics Data System (ADS)

Optical CT scanners for a 3D readout of externally irradiated radiosensitive hydrogels currently require the use of a refractive index (RI) matching liquid bath to obtain suitable optical ray paths through the gel sample to the detector. The requirement for a RI matching liquid bath has been negated by the design of a plastic cylindrical gel container that provides parallel beam geometry through the gel sample for the majority of the projection. The design method can be used for various hydrogels. Preliminary test results for the prototype laser beam scanner with ferrous xylenol-orange gel show geometric distortion of 0.2 mm maximum, spatial resolution limited to beam spot size of about 0.4 mm and 0.8% noise (1 SD) for a uniform irradiation. Reconstruction of a star pattern irradiated through the cylinder walls demonstrates the suitability for external beam applications. The extremely simple and cost-effective construction of this optical CT scanner, together with the simplicity of scanning gel samples without RI matching fluid increases the feasibility of using 3D gel dosimetry for clinical external beam dose verifications.

Ramm, Daniel; Rutten, Thomas P.; Shepherd, Justin; Bezak, Eva

2012-06-01

115

Optical CT scanner for in-air readout of gels for external radiation beam 3D dosimetry.  

PubMed

Optical CT scanners for a 3D readout of externally irradiated radiosensitive hydrogels currently require the use of a refractive index (RI) matching liquid bath to obtain suitable optical ray paths through the gel sample to the detector. The requirement for a RI matching liquid bath has been negated by the design of a plastic cylindrical gel container that provides parallel beam geometry through the gel sample for the majority of the projection. The design method can be used for various hydrogels. Preliminary test results for the prototype laser beam scanner with ferrous xylenol-orange gel show geometric distortion of 0.2 mm maximum, spatial resolution limited to beam spot size of about 0.4 mm and 0.8% noise (1 SD) for a uniform irradiation. Reconstruction of a star pattern irradiated through the cylinder walls demonstrates the suitability for external beam applications. The extremely simple and cost-effective construction of this optical CT scanner, together with the simplicity of scanning gel samples without RI matching fluid increases the feasibility of using 3D gel dosimetry for clinical external beam dose verifications. PMID:22644104

Ramm, Daniel; Rutten, Thomas P; Shepherd, Justin; Bezak, Eva

2012-06-21

116

Validation and application of polymer gel dosimetry for the dose verification of an intensity-modulated arc therapy (IMAT) treatment  

NASA Astrophysics Data System (ADS)

Polymer gel dosimetry was used to assess an intensity-modulated arc therapy (IMAT) treatment for whole abdominopelvic radiotherapy. Prior to the actual dosimetry experiment, a uniformity study on an unirradiated anthropomorphic phantom was carried out. A correction was performed to minimize deviations in the R2 maps due to radiofrequency non-uniformities. In addition, compensation strategies were implemented to limit R2 deviations caused by temperature drift during scanning. Inter- and intra-slice R2 deviations in the phantom were thereby significantly reduced. This was verified in an investigative study where the same phantom was irradiated with two rectangular superimposed beams: structural deviations between gel measurements and computational results remained below 3% outside high dose gradient regions; the spatial shift in those regions was within 2.5 mm. When comparing gel measurements with computational results for the IMAT treatment, dose deviations were noted in the liver and right kidney, but the dose-volume constraints were met. Root-mean-square differences between both dose distributions were within 5% with spatial deviations not more than 2.5 mm. Dose fluctuations due to gantry angle discretization in the dose computation algorithm were particularly noticeable in the low-dose region.

Vergote, K.; DeDeene, Y.; Duthoy, W.; DeGersem, W.; DeNeve, W.; Achten, E.; DeWagter, C.

2004-01-01

117

The role of dose distribution gradient in the observed ferric ion diffusion time scale in MRI-Fricke-infused gel dosimetry  

Microsoft Academic Search

Ferric ion diffusion is a detrimental factor in MRI-Fricke-infused gel dosimetry. In this study, a novel approach involving MR image subtraction and a fast image-based dosimetry technique to study ferric ion diffusion effects is presented. The fast image-based approach allows studying dose profile degradation within minutes post-irradiation. The relationship between the rate of dose profile deterioration and dose distribution gradients

Y. J. Tseng; W. C. Chu; W. Y. Chung; W. Y. Guo; Y.-H. Kao; J. Wang; Sung-Cheng Huang

2002-01-01

118

High-resolution gel dosimetry using flat-panel detector cone-beam computed tomography: preliminary study.  

PubMed

This study compares the dose response of irradiated polymer gel with acrylic and styrofoam housing while applying multi-detector CT (MDCT) and cone-beam CT (CBCT). The dose response for MDCT and CBCT, while using an acrylic phantom is 1.34 and 0.67 DeltaHU Gy(-1), respectively, and becomes 1.54 and 0.84 DeltaHU Gy(-1) while using styrofoam, suggesting styrofoam is the better housing material. While the dose response of MDCT is better than that of CBCT, CBCT is yet a promising 3D dosimetry technique, given its potentially better spatial resolution and sensitive dose interpretation capability. PMID:19914082

Huang, Kuo-Ming; Huang, Tzung-Chi; Tsai, Chia-Jung; Lu, Kun-Mu; Chen, Liang-Kuang; Wu, Tung-Hsin

2010-01-01

119

Polyvinyl alcohol-Fricke hydrogel and cryogel: two new gel dosimetry systems with low Fe3+ diffusion  

NASA Astrophysics Data System (ADS)

Two new Fricke dosimeter gel systems with low diffusion rates have been developed for 3D radiation dosimetry purposes. Both systems consist of a solution of 20% (by weight) polyvinyl alcohol (PVA) in a 50 mM H2 SO4 solution with 0.4 mM ferrous ammonium sulphate and xylenol orange (FX). The difference in the two gels is the way that the gelation process was initiated: either by bringing the temperature to (a) +5 °C or (b) -20 °C before returning them to room temperature. These gels are termed `hydrogel' and `cryogel', respectively. The hydrogel is optically transparent, and can be used with either optical or MRI detection methods for dosimetric imaging. The cryogel is rubbery in texture but opaque, so its internal Fe3+ concentration can only be measured with MRI. The hydrogel's optical attenuation coefficient is linear (r 2 = 0.99) with dose from 0 to 20 Gy with a sensitivity of 0.106 cm-1 Gy-1 (at 543 nm). In terms of MR relaxation rate, the dose response for both the hydrogel and cryogel was linear (r 2 = 0.99) with a sensitivity of 0.020 s-1 Gy-1 (at 1.5 T). The Fe3+ diffusion coefficient (at 20 °C) was measured to be 0.14 mm2 h-1 , which is significantly lower than similar preparations reported for porcine gelatin or agarose. The PVA-FX gels can be stored for long periods of time before exposure to radiation, since the auto-oxidation rate was 10 times less than that of gelatin-Fricke recipes. The new gels developed in this work are a significant improvement on previous Fricke gel systems.

Chu, K. C.; Jordan, K. J.; Battista, J. J.; Van Dyk, J.; Rutt, B. K.

2000-04-01

120

High resolution gel-dosimetry by optical-CT and MR scanning  

Microsoft Academic Search

aging time, accurate to within 3%, and within <1% precision. The RTAP criteria is applied to an in-house laser-based optical-CT scanning system presented here, and evaluated using gel-flasks containing BANG3™ gel. The same gel flasks were subsequently imaged using the MR imaging protocol recommended by the gel manufacturer, but modified to match as closely as possible the RTAP. The resulting

Mark Oldham; Jeffrey H. Siewerdsen; Anil Shetty; David A. Jaffray

2001-01-01

121

Preliminary dosimetry investigation of Tc-99m diagnostic radionuclide by NIPAM gel dosimeter  

NASA Astrophysics Data System (ADS)

The N-isopropylacrylamide (NIPAM) gel dosimeter was investigated as a suitable material for measuring absorbed doses from radionuclide sources. In this study, NIPAM gel dosimeter was used to evaluate the dose distributions of the Tc-99m radionuclide in NIPAM gel. The accumulated radioactivity range of the Tc-99m NIPAM gel is from approximately 0 MBq to 13.6 MBq (about 0.37 mCi). The NIPAM gel dosimeter with high stability and high-dose linear and non-energy dependent properties can provide various radiopharmaceutical activity intensities in the conduct of dose assessment in nuclear medicine, thereby producing the most promising dose verification tools.

Huang, You-Ruei; Chang, Yuan-Jen; Hsieh, Ling-Ling; Yu, Bi-Wei; Chu, Chien-Hau; Hsieh, Bor-Tsung

2013-06-01

122

An evaluation of the TSE MR sequence for time efficient data acquisition in polymer gel dosimetry of applications involving high doses and steep dose gradients  

Microsoft Academic Search

The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to

P. Baras; I. Seimenis; P. Sandilos; L. Vlahos; T. Bieganski; E. Georgiou; E. Pantelis; P. Papagiannis; L. Sakelliou

2005-01-01

123

Comparison of Monte Carlo calculations around a Fletcher Suit Delclos ovoid with radiochromic film and normoxic polymer gel dosimetry  

SciTech Connect

The Fletcher Suit Delclos (FSD) ovoids employed in intracavitary brachytherapy (ICB) for cervical cancer contain shields to reduce dose to the bladder and rectum. Many treatment planning systems (TPS) do not include the shields and other ovoid structures in the dose calculation. Instead, TPSs calculate dose by summing the dose contributions from the individual sources and ignoring ovoid structures such as the shields. The goal of this work was to calculate the dose distribution with Monte Carlo around a Selectron FSD ovoid and compare these calculations with radiochromic film (RCF) and normoxic polymer gel dosimetry. Monte Carlo calculations were performed with MCNPX 2.5.c for a single Selectron FSD ovoid with and without shields. RCF measurements were performed in a plane parallel to and displaced laterally 1.25 cm from the long axis of the ovoid. MAGIC gel measurements were performed in a polymethylmethacrylate phantom. RCF and MAGIC gel were irradiated with four 33 {mu}Gy m{sup 2} h{sup -1} Cs-137 pellets for a period of 24 h. Results indicated that MCNPX calculated dose to within {+-}2% or 2 mm for 98% of points compared with RCF measurements and to within {+-}3% or 3 mm for 98% of points compared with MAGIC gel measurements. It is concluded that MCNPX 2.5.c can calculate dose accurately in the presence of the ovoid shields, that RCF and MAGIC gel can demonstrate the effect of ovoid shields on the dose distribution and the ovoid shields reduce the dose by as much as 50%.

Gifford, Kent A.; Horton, John L. Jr.; Jackson, Edward F.; Steger, Theodore R. III; Heard, Malcolm P.; Mourtada, Firas; Lawyer, Ann A.; Ibbott, Geoffrey S. [Department of Radiation Physics, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 (United States); Department of Imaging Physics, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 (United States); Department of Radiation Physics, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 (United States)

2005-07-15

124

Dose integration characteristics in normoxic polymer gel dosimetry investigated using sequential beam irradiation  

Microsoft Academic Search

Dose integration properties were investigated for normoxic polymer gels based on methacrylic acid (nMAG) and acrylamide\\/N, N'-methylenebisacrylamide (nPAG). The effect of sequential irradiation was studied for different fractionation schemes and varying amounts of methacrylic acid for the nMAG gels. Magnetic resonance imaging (MRI) was used for read out of the absorbed dose response. The investigated gels exhibited a dependence on

A. Karlsson; H. Gustavsson; S. Månsson; K. B. McAuley; S. Å. J. Bäck

2007-01-01

125

Feasibility of radiochromic gels for 3D dosimetry of brachytherapy sources  

NASA Astrophysics Data System (ADS)

Two radiochromic gel dosimeters, Fricke-xylenol orange (FXO) gel and Turnbull Blue (TB) gel, were studied in the scope of the iMERA+ project ‘Increasing cancer treatment efficacy using 3D brachytherapy’ for their feasibility for the determination of relative 3D dose distribution of brachytherapy (BT) sources. Initially, the dose, dose rate and energy dependence of the gels were investigated. Subsequently, the gels were irradiated by a point low-dose-rate source IsoSeed I25.S16 (125I) and a high-dose-rate source GammaMed+ (192Ir) and scanned using optical computed tomography. Optical transmission images of irradiated gels were processed to obtain detailed 3D optical density maps inside the gels with voxel dimensions of 0.25 × 0.25 × 0.25 mm3. The radial dose function between 1.5 mm and 35 mm from the source and the anisotropy function at 10 mm radius were determined and compared with Monte Carlo calculations and TG-43 data, showing agreement mostly within the measurement uncertainty. Results revealed that the TB gel is feasible for measurements of the relative 3D dose distributions very close to the point BT source because it conserves sharp dose gradients as this gel does not suffer diffusion of dye created upon irradiation. On the other hand, FXO gel underestimates doses closer than 5 mm from the source due to diffusion effects, but it has a significantly higher sensitivity which enables convenient measurement of relative doses up to 35 mm from the source. Further development, especially on gel composition and corrections to optical CT images, is desirable.

Šolc, Jaroslav; Sochor, Vladimír

2012-10-01

126

A self consistent normalized calibration protocol for three dimensional magnetic resonance gel dosimetry  

Microsoft Academic Search

In a clinical setting, mixed and inconsistent results have been reported using Magnetic Resonance Relaxation imaging of irradiated aqueous polymeric gels as a three-dimensional dosimeter, for dose verification of conformal radiation therapy. The problems are attributed to the difficulty of identifying an accurate dose calibration protocol for each delivered gel at the radiation site in a clinical setting. While careful

Richard L Cardenas; Kwan Hon Cheng; Lynn J Verhey; Ping Xia; Lorne Davis; Brian Cannon

2002-01-01

127

Effect of container size on the accuracy of polymer gel dosimetry  

Microsoft Academic Search

The radiation-induced polymerization reaction in polymer gel dosimeters is exothermic. The rate of polymerization for vinyl groups depends on the temperature. In this paper we show that the size of the container filled with gel being irradiated affects the values of T2 determined by magnetic resonance imaging (MRI), and consequently leads to modulations in the determination of the absorbed dose.

Eve-Marie Dumas; Ghyslain Leclerc; Martin Lepage

2006-01-01

128

Focusing optics of a parallel beam CCD optical tomography apparatus for 3D radiation gel dosimetry  

Microsoft Academic Search

Optical tomography of gel dosimeters is a promising and cost-effective avenue for quality control of radiotherapy treatments such as intensity-modulated radiotherapy (IMRT). Systems based on a laser coupled to a photodiode have so far shown the best results within the context of optical scanning of radiosensitive gels, but are very slow (~9 min per slice) and poorly suited to measurements

Nikola Krstajic; Simon J. Doran

2006-01-01

129

NIPAM polymer gel dosimetry for IMRT four-field box irradiation using optical-CT scanner  

NASA Astrophysics Data System (ADS)

The study assessed the dosimetric characteristics of the N-isopropylacrylamide (NIPAM) polymer gel dosimeter. Experiments on the intra-dosimeter consistency and reproducibility of NIPAM polymer gels were performed. A cylindrical NIPAM gel phantom measuring 10 cm (diameter) by 10 cm (height) by 3 mm (thickness) was irradiated using the four-field box treatment with a field size of 3 cm × 3 cm. A fast, optical computerized tomography scanner was used to scan the gel phantoms. The results showed that the dose profiles were consistent at various depths. The isodose lines agreed quantitatively with the calculated TPS dose and the measured NIPAM polymer gel dose within the 30 to 90 percentage isodose lines. In addition, the Gamma pass rates were determined to be 94.9%, 95.2%, and 95.7% at depths of 40 mm, 45 mm, and 50 mm, respectively, using 5% dose difference and 5 mm distance-to-agreement criteria. Using the same Gamma criteria, the Gamma pass rates were 95.1%, 95.3%, and 95.7% for the three replicated. The results indicated that the NIPAM polymer gel dosimeter was stable and reliable. The dosimetric characteristics highlighted the potential of NIPAM polymer gel dosimeter in radiotherapy.

Yao, C. H.; Hsu, W. T.; Hsu, S. M.; Ma, P. Y. L.; Hsieh, B. T.; Chang, Y. J.

2013-06-01

130

Effects of ambient temperature on the FXG radiochromic gels used for 3-D dosimetry  

NASA Astrophysics Data System (ADS)

Environmental effects on the optical properties of a sensitive radiochromic gel dosemeter; in particular storage, irradiation and measurements temperature were studied. Knowledge of light temperature and other ambient effects help to optimise working conditions and minimize errors. A ferrous-sulphate dosemeter with xylenol orange ion indicator incorporated in a gelatin gel matrix (FXG) was prepared under normal working conditions, and the samples were then kept in closed storage area at different temperature ranging from 5°C up to the gel melting temperature about 35°C. The samples optical absorbance was then measured quantitatively using double beam spectrophotometry. There is a small and steady increase in the absorbance 0.3×10-3 /°C with increasing temperature until about 30°C when we observe a big jump in the gel absorbance. Finally, additional important behaviour of FXG material was noticed, that is the changes occurred under the influence of rising temperature are reversible which is different from the permanent radiation caused changes.

Bero, M. A.; Kharita, M. H.

2004-01-01

131

Three-dimensional polymer gel dosimetry: basic physical properties of the dosimeter  

Microsoft Academic Search

This study concentrated on assessment of the basic physical properties of a polymer gel dosimeter evaluated by NMR. For this, BANG-2 type polymer gel was prepared. The dosimeters were irradiated by 60Co gamma photons and by 4, 6 and 18MV X-ray photons for doses in the range 0–50Gy. The multi-echo CPMG sequence was used for the evaluation of T2-relaxation times

J. Novotný; V. Sp?vá?ek; P. Dvorák; T. ?echák

2001-01-01

132

Quality control of the stereotactic radiosurgery procedure with the polymer-gel dosimetry  

Microsoft Academic Search

Purpose: To assess the entire geometric and dosimetric (relative) uncertainties of the radiosurgery procedure with the Leksell gamma knife.Materials and methods: The entire Leksell gamma knife stereotactic radiosurgery treatment procedure was simulated with the use of a special water filled head phantom and polymer-gel dosimeter evaluated by nuclear magnetic resonance (NMR). A test vessel filled with the polymer-gel dosimeter was

Josef Novotný; Pavel Dvo?ák; Václav Sp?vá?ek; Jaroslav Tint?ra; Tomᚠ?echák; Roman Liš?ák

2002-01-01

133

Fricke gel-layer dosimetry in high dose-rate brachytherapy  

Microsoft Academic Search

The aim of this study was to evaluate the reliability of Fricke gel-layer dosimeters for the measurement of in-phantom dose distributions produced by a 192Ir brachytherapy source. The doses obtained were compared to measurements performed with thermoluminescent dosimeters and treatment planning calculations. Fricke gel-layer dosimeters have proven to be a promising tool to measure three-dimensional dose distributions in high dose-rate

M. Carrara; C. Fallai; G. Gambarini; A. Negri

2010-01-01

134

New radiochromic gel for 3D dosimetry based on Turnbull blue: basic properties  

NASA Astrophysics Data System (ADS)

The recently developed new radiochromic gel dosimeter based on Turnbull blue dye formed by irradiation (the TBG dosimeter) does not exhibit dose pattern degradation due to diffusion effects as observed in the Fricke-gel dosimeter with xylenol orange incorporated into the gel matrix (the FXG dosimeter). The TBG dosimeter can be easily prepared and its optical properties enable evaluation of the gel's response using the cone-beam optical computed tomography technique. The preparation procedure is described in the paper along with the basic characteristics of the gel, including dose response, dose sensitivity, ageing under different storage conditions, diffusion rates of Turnbull blue and gel density. The measurement of diffusion is described in more detail. The same method was applied to the FXG dosimeter for direct comparison. It was found that the diffusion coefficient of the TBG dosimeter stored at 24 °C is less than 4 × 10-3 mm2 h-1 (1? confidence level), compared to the value of 7.3 × 10-1 mm2 h-1 (1?) of the FXG dosimeter measured at the same temperature. Although the TBG dosimeter is less sensitive than the FXG dosimeter, its diffusion coefficient is practically negligible and, therefore, it offers large potential as a three-dimensional dosimeter for applications encompassing sharp dose gradients such as high-dose-rate brachytherapy.

Šolc, Jaroslav; Sp?vá?ek, Václav

2009-09-01

135

New radiochromic gel for 3D dosimetry based on Turnbull blue: basic properties.  

PubMed

The recently developed new radiochromic gel dosimeter based on Turnbull blue dye formed by irradiation (the TBG dosimeter) does not exhibit dose pattern degradation due to diffusion effects as observed in the Fricke-gel dosimeter with xylenol orange incorporated into the gel matrix (the FXG dosimeter). The TBG dosimeter can be easily prepared and its optical properties enable evaluation of the gel's response using the cone-beam optical computed tomography technique. The preparation procedure is described in the paper along with the basic characteristics of the gel, including dose response, dose sensitivity, ageing under different storage conditions, diffusion rates of Turnbull blue and gel density. The measurement of diffusion is described in more detail. The same method was applied to the FXG dosimeter for direct comparison. It was found that the diffusion coefficient of the TBG dosimeter stored at 24 degrees C is less than 4 x 10(-3) mm(2) h(-1) (1sigma confidence level), compared to the value of 7.3 x 10(-1) mm(2) h(-1) (1sigma) of the FXG dosimeter measured at the same temperature. Although the TBG dosimeter is less sensitive than the FXG dosimeter, its diffusion coefficient is practically negligible and, therefore, it offers large potential as a three-dimensional dosimeter for applications encompassing sharp dose gradients such as high-dose-rate brachytherapy. PMID:19652291

Solc, Jaroslav; Spevácek, Václav

2009-09-01

136

High resolution dosimetry in monoenergetic proton beam therapy on a normoxic polymer gel: the importance of high spatial resolution for reduced Bragg-Peak-quenching  

NASA Astrophysics Data System (ADS)

Proton ion beam therapy demands for high resolution dosimetry due to the high dose gradients present in lateral confinement and final Bragg-peak. In polymer gels the reduction of the linear dose response in the area of the Bragg-peak is reported (Bragg-peak quenching), which is assumed to be mainly due to the high linear energy transfer (LET). We here investigate the impact of the spatial resolution in T2-mapping for accurate Magnetic Resonance Imaging (MRI)-based polymer gel dosimetry in the Bragg-peak for monoenergetic ion beams. We implemented MR-protocols for T2-mapping at microscopic resolution on a High-Field 7T human MR-scanner using an insert gradient system and sensitive rf-coils. The best results are obtained for an optimzed polymer gel based on THPC with an optimized MR-protocol for reduced measurement time and sufficient SNR at 0,547 mm pixel size. The dose in the fine Bragg-peak could be measured correctly for a monoenergetic proton beam as confirmed by Monte Carlo dose simulations. Such high spatial resolutions at minimum are necessary for an accurate measurement of the dose in the sharp Bragg-peak for monoenergetic ion beams. We demonstrate that at higher pixel size the dose levels may be underestimated due to spatial averaging in MRI-based polymer gel dosimetry.

Berg, A.; Wieland, M.; Naumann, J.; Jaekel, O.

2013-06-01

137

Tomotherapy dose distribution verification using MAGIC-f polymer gel dosimetry  

SciTech Connect

Purpose: This paper presents the application of MAGIC-f gel in a three-dimensional dose distribution measurement and its ability to accurately measure the dose distribution from a tomotherapy unit. Methods: A prostate intensity-modulated radiation therapy (IMRT) irradiation was simulated in the gel phantom and the treatment was delivered by a TomoTherapy equipment. Dose distribution was evaluated by the R2 distribution measured in magnetic resonance imaging. Results: A high similarity was found by overlapping of isodoses of the dose distribution measured with the gel and expected by the treatment planning system (TPS). Another analysis was done by comparing the relative absorbed dose profiles in the measured and in the expected dose distributions extracted along indicated lines of the volume and the results were also in agreement. The gamma index analysis was also applied to the data and a high pass rate was achieved (88.4% for analysis using 3%/3 mm and of 96.5% using 4%/4 mm). The real three-dimensional analysis compared the dose-volume histograms measured for the planning volumes and expected by the treatment planning, being the results also in good agreement by the overlapping of the curves. Conclusions: These results show that MAGIC-f gel is a promise for tridimensional dose distribution measurements.

Pavoni, J. F.; Pike, T. L.; Snow, J.; DeWerd, L.; Baffa, O. [Departamento de Fisica, Faculdade de Filosofia Ciencias e Letras de Ribeirao Preto-Universidade de Sao Paulo, Av. Bandeirantes, 3900 - CEP 14040-901 - Bairro Monte Alegre - Ribeirao Preto, SP (Brazil); Medical Radiation Research Center, Department of Medical Physics, University of Wisconsin, 1111 Highland Avenue, B1002 WIMR, Madison, Wisconsin 53705-2275 (United States); Departamento de Fisica, Faculdade de Filosofia Ciencias e Letras de Ribeirao Preto-Universidade de Sao Paulo, Av. Bandeirantes, 3900 - CEP 14040-901 - Bairro Monte Alegre - Ribeirao Preto, SP (Brazil)

2012-05-15

138

Comparison of TSE, TGSE, and CPMG measurement techniques for MR polymer gel dosimetry  

Microsoft Academic Search

A radiation dose distribution that optimally conforms to the target volume is of major interest for stereotactic radiotherapy. For this purpose treatment plans have to be verified experimentally before transferring to the patient. The requirements regarding dose accuracy and spatial resolution can be fulfilled with tissue equivalent polymer gel dosimeters which offer the possibility to visualize 3D dose distributions. Herewith,

A Bankamp; L. R Schad

2003-01-01

139

The application of polymer gel dosimeters to dosimetry for targeted radionuclide therapy  

Microsoft Academic Search

There is a lack of standardized methodology to perform dose calculations for targeted radionuclide therapy and at present no method exists to objectively evaluate the various approaches employed. The aim of the work described here was to investigate the practicality and accuracy of calibrating polymer gel dosimeters such that dose measurements resulting from complex activity distributions can be verified. Twelve

J. I. Gear; G. D. Flux; E. Charles-Edwards; M. Partridge; G. Cook; R. J. Ott

2006-01-01

140

Application of monomer\\/polymer gel dosimetry to study the effects of tissue inhomogeneities on intensity-modulated radiation therapy (IMRT) dose distributions  

Microsoft Academic Search

Background and purpose: When planning an intensity-modulated radiation therapy (IMRT) treatment in a heterogeneous region (e.g. the thorax), the dose computation algorithm of a treatment planning system may need to account for these inhomogeneities in order to obtain a reliable prediction of the dose distribution. An accurate dose verification technique such as monomer\\/polymer gel dosimetry is suggested to verify the

Koen Vergote; Yves De Deene; Filip Claus; Werner De Gersem; Bart Van Duyse; Leen Paelinck; Eric Achten; Wilfried De Neve; Carlos De Wagter

2003-01-01

141

The use of gel dosimetry to measure the 3D dose distribution of a 90Sr\\/90Y intravascular brachytherapy seed  

Microsoft Academic Search

Absorbed dose distributions in 3D imparted by a single 90Sr\\/90Y beta particle seed source of the type used for intravascular brachytherapy were investigated. A polymer gel dosimetry medium was used as a dosemeter and phantom, while a special high-resolution laser CT scanner with a spatial resolution of 100 µm in all dimensions was used to quantify the data. We have

G Massillon-JL; R Minniti; M G Mitch; M J Maryanski; C G Soares

2009-01-01

142

On the validity of 3D polymer gel dosimetry: I. reproducibility study.  

PubMed

The intra- and inter-batch accuracy and precision of MRI (polyacrylamide gelatin gel fabricated at atmospheric conditions) polymer gel dosimeters are assessed in full 3D. In the intra-batch study, eight spherical flasks were filled with the same polymer gel along with a set of test tubes that served as calibration phantoms. In the inter-batch study, the eight spherical flasks were filled with different batches of gel. For each spherical phantom, a separate set of calibration phantoms was used. The spherical phantoms were irradiated using a three-field coplanar beam configuration in a very reproducible manner. The calibration phantoms were irradiated to known doses to obtain a dose-R? calibration plot which was applied on the corresponding R? maps of all spherical phantoms on an individual basis. The intra-batch study showed high dosimetric precision (3.1%) notwithstanding poor accuracy (mean dose discrepancies up to 13.0%). In the inter-batch study, a similar dosimetric precision (4.3%) and accuracy (mean dose discrepancies up to 13.7%) were found. The poor dosimetric accuracy was attributed to a systematic fault that was related to the calibration method. Therefore, the dose maps were renormalized using an independent ion chamber dose measurement. It is illustrated that with this renormalization, excellent agreement between the gel measured and TPS calculated 3D dose maps is achievable: 97% and 99% of the pixels meet the 3%/3 mm criteria for the intra- and inter-batch experiments, respectively. However renormalization will result in significant dose deviations inside a realistically sized anthropomorphic phantom as will be shown in a concurrent paper. PMID:23221300

Vandecasteele, Jan; De Deene, Yves

2013-01-01

143

On the validity of 3D polymer gel dosimetry: I. Reproducibility study  

NASA Astrophysics Data System (ADS)

The intra- and inter-batch accuracy and precision of MRI (polyacrylamide gelatin gel fabricated at atmospheric conditions) polymer gel dosimeters are assessed in full 3D. In the intra-batch study, eight spherical flasks were filled with the same polymer gel along with a set of test tubes that served as calibration phantoms. In the inter-batch study, the eight spherical flasks were filled with different batches of gel. For each spherical phantom, a separate set of calibration phantoms was used. The spherical phantoms were irradiated using a three-field coplanar beam configuration in a very reproducible manner. The calibration phantoms were irradiated to known doses to obtain a dose-R2 calibration plot which was applied on the corresponding R2 maps of all spherical phantoms on an individual basis. The intra-batch study showed high dosimetric precision (3.1%) notwithstanding poor accuracy (mean dose discrepancies up to 13.0%). In the inter-batch study, a similar dosimetric precision (4.3%) and accuracy (mean dose discrepancies up to 13.7%) were found. The poor dosimetric accuracy was attributed to a systematic fault that was related to the calibration method. Therefore, the dose maps were renormalized using an independent ion chamber dose measurement. It is illustrated that with this renormalization, excellent agreement between the gel measured and TPS calculated 3D dose maps is achievable: 97% and 99% of the pixels meet the 3%/3 mm criteria for the intra- and inter-batch experiments, respectively. However renormalization will result in significant dose deviations inside a realistically sized anthropomorphic phantom as will be shown in a concurrent paper. Both authors contributed equally to this study.

Vandecasteele, Jan; De Deene, Yves

2013-01-01

144

Indigenously developed multipurpose acrylic head phantom for verification of IMRT using film and gel dosimetry.  

PubMed

The purpose of this study was to validate the newly designed acrylic phantom for routine dosimetric purpose in radiotherapy. The phantom can be used to evaluate and compare the calculated dose and measured dose using film and gel dosimetric methods. In this study, a doughnut-shaped planning target volume (8.54 cm3) and inner organ at risk (0.353 cm3) were delineated for an IMRT test plan using the X-ray CT image of the phantom. The phantom consists of acrylic slabs which are integrated to form a human head with a hole in the middle where several dosimetric inserts can be positioned for measurement. An inverse planning with nine coplanar intensity-modulated fields was created using Pinnacle TPS. For the film analysis, EBT2 film, flatbed scanner, in-house developed MATLAB codes and ImageJ software were used. The 3D dose distribution recorded in the MAGAT gel dosimeter was read using a 1.5 T MRI scanner. Scanning parameters were CPMG pulse sequence with 8 equidistant echoes, TR = 5600, echo step = 22 ms, pixel size = 0.5 × 0.5, slice thickness = 2 mm. Using a calibration relationship between absorbed dose and spin-spin relaxation rate (R2), R2 images were converted to dose images. The dose comparison was accomplished using in-house MATLAB-based graphical user interface named "IMRT3DCMP". For gel measurement dose grid from the TPS was extracted and compared with the measured dose grid of the gel. Gamma index analysis of film measurement for the tolerance criteria of 2%/2mm, 1%/1 mm showed more than 90% voxels pass rate. Gamma index analysis of 3D gel measurement data showed more than 90% voxels pass rate for different tolerance criteria of 2%/2 mm and 1%/1 mm. Overall both 2D and 3D measurement were in close agreement with the Pinnacle TPS calculated dose. The phantom designed is cost-effective and the results are promising, but further investigation is required to validate the phantom with other 3D conformal techniques for dosimetric purpose. PMID:23470932

Gopishankar, N; Vivekanandhan, S; Rath, G K; Laviraj, M A; Senthilkumaran, S; Kale, S S; Thulkar, S; Bisht, R K; Subramani, V

2013-01-01

145

Clinical Applications of Gel Dosimeters  

NASA Astrophysics Data System (ADS)

This paper reviews the characteristics of gel dosimetry that make it desirable for clinical use, the postulated and demonstrated applications of gel dosimetry, and some complications, setbacks, and failures that have contributed to the slow introduction into routine clinical use.

Ibbott, Geoffrey S.

2006-12-01

146

Introducing gel dosimetry in a clinical environment: Customization of polymer gel composition and magnetic resonance imaging parameters used for 3D dose verifications in radiosurgery and intensity modulated radiotherapy  

SciTech Connect

Radiation sensitive gels have been used as dosimeters for clinical dose verification of different radiation therapy modalities. However, the use of gels is not widespread, because careful techniques are required to achieve the dose precision and accuracy aimed for in clinical dose verification. Here, the introduction of gel dosimetry in a clinical environment is described, including the whole chain of customizations and preparations required to introduce magnetic resonance (MR) based gel dosimetry into clinical routine. In order to standardize gel dosimetry in dose verifications for radiosurgery and intensity modulated radiotherapy (IMRT), we focused on both the customization of the gel composition and of the MR imaging parameters to increase its precision. The relative amount of the components of the normoxic, methacrylic acid based gel (MAGIC) was changed to obtain linear and steep dose response relationships. MR imaging parameters were customized for the different dose ranges used in order to lower the relative standard deviation of the measured transversal relaxation rate (R{sub 2}). An optimization parameter was introduced to quantify the change in the relative standard deviation of R{sub 2} ({sigma}{sub R2,rel}) taking the increase in MR time into account. A 9% methacrylic acid gel customized for radiosurgery was found to give a linear dose response up to 40 Gy with a slope of 0.94 Gy{sup -1} s{sup -1}, while a 6% methacrylic acid gel customized for IMRT had a linear range up to 3 Gy with a slope of 1.86 Gy{sup -1} s{sup -1}. With the help of an introduced optimization parameter, the mean {sigma}{sub R2,rel} was improved by 13% for high doses and by 55% for low doses, without increasing MR time to unacceptable values. A mean dose resolution of less than 0.13 Gy has been achieved with the gel and imaging parameters customized for IMRT and a dose resolution from 0.97 Gy (at 5 Gy) to 2.15 Gy (at 40 Gy) for the radiosurgery dose range. The comparisons of calculated and measured relative 3D dose distributions performed for radiosurgery and IMRT showed an acceptable overall correlation. The gamma criterion for the radiosurgery verification with a voxel size of 1.5x1.5x1.5 mm{sup 3} was passed by 96.8% of the voxels (1.5 mm distance, 8% in dose). For the IMRT verification using a voxel size of 1.25x1.25x5 mm{sup 3} the gamma criterion was passed by 50.3% of the voxels (3 mm distance, 3% dose uncertainty). Using dedicated data analysis and visualization software, MR based normoxic gel dosimetry was found to be a valuable tool for clinically based dose verification, provided that customized gel compositions and MR imaging parameters are used. While high dose precision was achieved, further work is required to achieve clinically acceptable dose accuracy.

Crescenti, Remo A.; Scheib, Stefan G.; Schneider, Uwe; Gianolini, Stefano [Department of Information Technology and Electrical Engineering, ETH, Zurich (Switzerland); Department of Medical Radiation Physics, Klinik Im Park, Zurich (Switzerland); Department of Radiation Oncology and Nuclear Medicine, City Hospital Triemli, Zurich (Switzerland); Department of Medical Radiation Physics, Klinik Im Park, Zurich (Switzerland)

2007-04-15

147

Mycosis Fungoides electron beam absorbed dose distribution using Fricke xylenol gel dosimetry  

NASA Astrophysics Data System (ADS)

Radiotherapy uses ionizing radiation to destroy tumor cells. The absorbed dose control in the target volume is realized through radiation sensors, such as Fricke dosimeters and radiochromic film, which permit to realize bi-dimensional evaluations at once and because of that, they will be used in this study as well. Among the several types of cancer suitable for ionizing radiation treatment, the Mycosis Fungoides, a lymphoma that spreads on the skin surface and depth, requires for its treatment total body irradiation by high-energy electrons. In this work the Fricke xylenol gel (FXG) was used in order to obtain information about the absorbed dose distribution induced by the electron interactions with the irradiated tissues and to control this type of treatment. FXG can be considered as an alternative dosimeter, since up to now only films have been used. FXG sample cuvettes, simulating two selected tomos (cranium and abdomen) of the Rando anthropomorphic phantom, were positioned along with radiochromic films for comparison. The phantom was subjected to Stanford total body irradiation using 6 MeV electrons. Tomographic images were acquired for both dosimeters and evaluated through horizontal and vertical profiles along the tomographic centers. These profiles were obtained through a Matlab routine developed for this purpose. From the obtained results, one could infer that, for a superficial and internal patient irradiation, the FXG dosimeter showed an absorbed dose distribution similar to the one of the film. These results can validate the FXG dosimeter as an alternative dosimeter for the Mycosis Fungoides treatment planning.

da Silveira, Michely C.; Sampaio, Francisco G. A.; Petchevist, Paulo C. D.; de Oliveira, André L.; Almeida, Adelaide de

2011-12-01

148

Cone-beam optical computed tomography for gel dosimetry II: imaging protocols.  

PubMed

This work develops imaging protocols for improved dose readout of a Fricke-xylenol orange-gelatin (FXG) gel-filled 1 L polyethylene terephthalate (PETE) jar dosimeter using a commercial Vista(TM) cone-beam optical computed tomography (CT) scanner from Modus Medical Devices Inc. (London, ON, Canada). To ensure good management of light source-detector stability, it was determined that (a) a minimum of 2 h warm-up time is necessary prior to dosimeter scanning, (b) the light source should be kept on until the completion of the last data scan except for the minimum amount of time required to acquire dark field images, and (c) the optional Vista software projection image normalization routine should be used in image reconstruction. The institution of dosimeter scan time and temperature control was strongly indicated from the experiments. A standard post-irradiation wait time of 30 min measured to within ±30 s was established to minimize the measurement uncertainties due to dosimeter development and diffusion. To alleviate thermochromic behavior leading to inaccurate dose readout, holding bath warm up and pre-scan temperature adjustment procedures were developed to control dosimeter temperature to within ±0.2 °C. The possibility of stray light minimizing protocols was also investigated and deemed to be unnecessary. The largest significant sources of stray light in the system were identified as being due to angled scatter from the dosimeter gelatin matrix and refraction from the jar wall interfaces. It was concluded that these phenomena would be better addressed through dosimeter modification and an inter-jar dose-to-attenuation calibration methodology, rather than by setting additional imaging protocols. PMID:21285484

Olding, Tim; Schreiner, L John

2011-03-01

149

An evaluation of the TSE MR sequence for time efficient data acquisition in polymer gel dosimetry of applications involving high doses and steep dose gradients  

SciTech Connect

The use of magnetic resonance imaging as a readout method for polymer gel dosimetry commonly involves long imaging sessions, particularly when high spatial resolution is required in all three dimensions, for the investigation of dose distributions with steep dose gradients and stringent dose delivery specifications. In this work, a volume selective turbo spin echo (TSE) pulse sequence is compared to the established Carr-Purcell-Meiboom-Gill (CPMG) multiecho acquisition with regard to providing accurate dosimetric results in significantly reduced imaging times. Polyethylene glycol diacrylate based (PABIG) gels were irradiated and subsequently scanned to obtain R2 relaxation rate measurements, using a CPMG multiecho sequence and a dual echo TSE utilizing an acceleration (turbo) factor of 64. R2 values, plotted against corresponding Monte Carlo dose calculations, provided calibration data of PABIG gels dose response over a wide dose range. A linear R2 versus dose relationship was demonstrated for both sequences with TSE results presenting reduced dose sensitivity. Although TSE data were found to deviate from linearity at lower doses compared to CPMG data, a relatively wide dynamic dose range of response extending up to approximately 100 Gy was observed for both sequences. The TSE and CPMG sequences were evaluated with a brachytherapy irradiation using a high dose rate {sup 192}Ir source and a gamma knife stereotactic radiosurgery irradiation with a single 4 mm collimator helmet shot. Dosimetric results obtained with the TSE and CPMG are shown to compare equally well with the expected dose distributions for these irradiations. The 60-fold scan time reduction achieved with TSE implies that this sequence could prove to be a useful tool for the introduction of polymer gel dosimetry in clinical radiation therapy applications involving high doses and steep dose gradients.

Baras, P.; Seimenis, I.; Sandilos, P.; Vlahos, L.; Bieganski, T.; Georgiou, E.; Pantelis, E.; Papagiannis, P.; Sakelliou, L. [Philips Hellas Medical Systems, 44 Kifissias Ave., Maroussi 151 25, Athens (Greece); Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece) and Medical Physics Department, Hygeia Hospital, Kiffisias Avenue, 24 Erythrou Stavrou, Marousi, 151 23, Athens (Greece); Department of Radiology, Mother's Memorial Hospital, Rzgowska 281/289, 93-388, Lodz (Poland); Medical Physics Department, University of Athens, 75 Mikras Asias, 115 27 Athens (Greece); Nuclear and Particle Physics Section, Physics Department, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece)

2005-11-15

150

Characterization of the essential dosimetric properties of cosolvent-free polymer gel dosimeters: Recent progress in x-ray CT based normoxic polymer gel dosimetry  

NASA Astrophysics Data System (ADS)

This work evaluates the temporal stability, spatial stability, batch reproducibility and dose rate dependence of a new cosolvent-free polymer gel dosimeter optimized for use with x-ray computed tomography readout. Temporal and spatial stability investigations reveal the new gel formulation should be imaged between 15-36 hours after irradiation. Intra- and inter-batch reproducibility were found to be excellent over the entire range of doses examined. A dose rate dependence was found for gels irradiated with machine dose rates between 100-600MU/min. An intensity-modulated radiation therapy treatment validation is also presented to illustrate an example clinical application using the new gel formulation.

Johnston, H.; Hilts, M.; Carrick, J.; Jirasek, A.

2013-06-01

151

Investigation of tetrakis hydroxymethyl phosphonium chloride as an antioxidant for use in x-ray computed tomography polyacrylamide gel dosimetry  

Microsoft Academic Search

Of the antioxidants used to scavenge oxygen in polymer gel dosimeters, tetrakis (hydroxymethyl) phosphonium chloride (THPC) has been shown to hold great promise due to its rapid oxygen scavenging abilities. In this study we (a) investigate the use of THPC as an antioxidant for polyacrylamide gel (PAGAT) dosimeters used in conjunction with x-ray computed tomography (CT) and (b) work to

A. Jirasek; M. Hilts; C. Shaw; P. Baxter

2006-01-01

152

High resolution polymer gel dosimetry for small beam irradiation using a 7T micro-MRI scanner  

Microsoft Academic Search

The use of small field radiation beams has greatly increased with advanced radiation therapy techniques such as IMRT, rotational IMRT, and stereotactic body radiotherapy. In this work small field 3D dose distributions have been measured with high spatial resolution using polymer gels and 7T micro-MR imaging. A MAGIC (Methacrylic and Ascorbic acid in Gelatin Initiated by Copper) polymer gel [1

Xuanfeng Ding; John Olsen; Ryan Best; Marcus Bennett; Inna McGowin; Jennifer Dorand; Kerry Link; J. Daniel Bourland

2010-01-01

153

3D verification of a prostate IMRT treatment by polymer gel-dosimetry and optical-CT scanning  

Microsoft Academic Search

A laser-based optical-CT scanning system has been developed in our laboratory with the capability for high resolution 3D dosimetry. Basic characterization of the performance of the scanner, presented in previous work showed that relative 3D dose mapping with accuracy >=96% at a spatial resolution of 1 mm3 was a feasible goal. Here we present initial clinical application of the system

M. Oldham; G. Gluckman; L. Kim

2004-01-01

154

Investigation of tetrakis hydroxymethyl phosphonium chloride as an antioxidant for use in x-ray computed tomography polyacrylamide gel dosimetry  

NASA Astrophysics Data System (ADS)

Of the antioxidants used to scavenge oxygen in polymer gel dosimeters, tetrakis (hydroxymethyl) phosphonium chloride (THPC) has been shown to hold great promise due to its rapid oxygen scavenging abilities. In this study we (a) investigate the use of THPC as an antioxidant for polyacrylamide gel (PAGAT) dosimeters used in conjunction with x-ray computed tomography (CT) and (b) work to establish the reaction mechanisms of THPC with the polymer gel constituents. We establish the dose response reproducibility of PAGAT dosimeters when imaged with CT and show that PAGAT dosimeters exhibit highly reproducible dose responses for a range of irradiation times post gel manufacture (2-6 h) and CT imaging times post gel irradiation (1-5 days). The THPC concentration within the gel leading to a maximized dose response and minimized O2 inhibition of polymerization is found to be ~4.5 mM. We further assess the stability of PAGAT dosimeters by investigating the reactions of THPC with the individual gel constituents. The importance of utilizing deionized water in polymer gel manufacture is noted. We show that, while THPC remains unreactive with acrylamide and bis-acrylamide under unirradiated conditions, THPC can react with gelatin to increase the cross-linking of the gelatin matrix in unirradiated dosimeters. THPC reactions with gelatin can lead to the lower observed dose sensitivity of PAGAT (~0.36 ± 0.04 H Gy-1) as compared to polyacrylamide gels manufactured under anoxic conditions (~0.83 ± 0.03 H Gy-1). The reactions of THPC which lead to O2 scavenging, and potential reactions of THPC with other gel constituents, are proposed.

Jirasek, A.; Hilts, M.; Shaw, C.; Baxter, P.

2006-04-01

155

A simple modification of TG-43 based brachytherapy dosimetry with improved fitting functions: application to the selectSeed source.  

PubMed

A variation of TG-43 protocol for seeds with cylindrical symmetry aiming at a better description of the radial and anisotropy functions is proposed. The TG-43 two dimensional formalism is modified by introducing a new anisotropy function. Also new fitting functions that permit a more robust description of the radial and anisotropy functions than usual polynomials are studied. The relationship between the new anisotropy function and the anisotropy factor included in the one-dimensional TG-43 formalism is analyzed. The new formalism is tested for the (125)I Nucletron selectSeed brachytherapy source, using Monte Carlo simulations performed with PENELOPE. The goodness of the new parameterizations is discussed. The results obtained indicate that precise fits can be achieved, with a better description than that provided by previous parameterizations. Special care has been taken in the description and fitting of the anisotropy factor near the source. The modified formalism shows advantages with respect to the usual one in the description of the anisotropy functions. The new parameterizations obtained can be easily implemented in the clinical planning calculation systems, provided that the ratio between geometry factors is also modified according to the new dose rate expression. PMID:22698855

Juan-Senabre, Xavier J; Porras, Ignacio; Lallena, Antonio M

2013-06-01

156

Low-density polymer gel dosimeters for 3D radiation dosimetry in the thoracic region: A preliminary study  

NASA Astrophysics Data System (ADS)

Different low-density polymer gel dosimeters have been constructed that can be used to acquire the radiation dose distribution of IMRT treatments in the thoracic region. A heterogeneous phantom consisting of a low density polymer gel dosimeter sandwiched between two layers of soft tissue equivalent gel has been constructed. As a proof-of-principle, the phantom has been irradiated with a square 4 cm × 4 cm beam. The dose distribution is read out by use of both quantitative NMR spin-spin (R2) and magnetization transfer (MT) imaging. Sources of error in the dose readout have been assessed and are discussed.

De Deene, Yves; Vandecasteele, Jan; Vercauteren, Tom

2013-06-01

157

The use of gel dosimetry for verification of electron and photon treatment plans in carcinoma of the scalp  

Microsoft Academic Search

In recent years there has been a large amount of research into the potential use of radiation sensitive gels for three-dimensional verification of clinical radiotherapy doses. In this paper we report the use of a MAGIC gel dosimeter (Fong et al 2001 Phys. Med. Biol. 46 3105) for the verification of a specific patient's radiation therapy dose distribution. A 69-year-old

J. V. Trapp; M. Partridge; V. N. Hansen; P. Childs; J. Bedford; A. P. Warrington; M. O. Leach; S. Webb

2004-01-01

158

Polymer gel dosimetry for the TG43 dosimetric characterization of a new 125I interstitial brachytherapy seed  

Microsoft Academic Search

In this work, a polymer gel-magnetic resonance (MR) imaging method is employed for the dosimetric characterization of a new 125I low dose rate seed (IsoSeed® model I25.S17). Two vials filled with PABIG gel were prepared in-house and one new seed as well as one commercially available 125I seed of similar dose rate and well-known dosimetric parameters (IsoSeed® model I25.S06) were

P. Papagiannis; E. Pantelis; E. Georgiou; P. Karaiskos; A. Angelopoulos; L. Sakelliou; S. Stiliaris; D. Baltas; I. Seimenis

2006-01-01

159

Polymer gel water equivalence and relative energy response with emphasis on low photon energy dosimetry in brachytherapy  

Microsoft Academic Search

The water equivalence and stable relative energy response of polymer gel dosimeters are usually taken for granted in the relatively high x-ray energy range of external beam radiotherapy based on qualitative indices such as mass and electron density and effective atomic number. However, these favourable dosimetric characteristics are questionable in the energy range of interest to brachytherapy especially in the

E. Pantelis; A. K. Karlis; M. Kozicki; P. Papagiannis; L. Sakelliou; J. M. Rosiak

2004-01-01

160

A method for determining the diffusion coefficient in Fe(II/III) radiation dosimetry gels using finite elements  

NASA Astrophysics Data System (ADS)

Magnetic resonance imaging (MRI) may be used to image three-dimensional dose distributions of ionizing radiation in tissue equivalent gels infused with ferrous sulphate solutions, commonly known as Fricke gels. In this technique, ferrous ions are oxidized to ferric ions by free radicals produced by ionizing radiation. A limitation on this technique is the diffussion of ferric ions in the gel. A method is presented for evaluating the diffusion coefficient in Fricke gels. Finite elements are used to model variations of the concentration in space, coupled with an analytical scheme to integrate the resulting system of equations through time. This method may be used for problems with one, two or three space dimensions and with arbitrary initial and boundary conditions. Results are presented for one- and two-dimensional data.

Harris, P. J.; Piercy, A.; Baldock, C.

1996-09-01

161

The spatial resolution in dosimetry with normoxic polymer-gels investigated with the dose modulation transfer approach  

Microsoft Academic Search

The verification of dose distributions with high dose gradients as appearing in brachytherapy or stereotactic radiotherapy for example, calls for dosimetric methods with sufficiently high spatial resolution. Polymer gels in combination with a MR or optical scanner as a readout device have the potential of performing the verification of a three-dimensional dose distribution within a single measurement. The purpose of

Christian Bayreder; Robert Schoen; M. Wieland; Dietmar Georg; Ewald Moser; Andreas Berg

2008-01-01

162

Investigation of dose characteristics in three-dimensional MAGAT-type polymer gel dosimetry with MSE MR imaging  

NASA Astrophysics Data System (ADS)

A new type of normoxic polymer gel dosimeter, named MAGAT responses well to absorbed dose even when manufacturing in the presence of normal levels of oxygen. The aim of this study was to evaluate dose response, diffusion effect and cumulated dose response under multiple fractional irradiations of the MAGAT gel dosimeter using Multiple Spin-Echo (MSE) Magnetic Resonance (MR) sequence. Dose response was performed by irradiating MAGAT-gel-filled testing vials with a 6 MV linear accelerator and a linear relationship was present with doses from 0 to 6 Gy, but gradually, a bi-exponential function result was obtained with given doses up to 20 Gy. No significant difference in dose response was present between single and cumulated doses ( p > 0.05). For study of diffusion effect, edge sharpness of the R2 map imaging between two split doses was smaller than 1 cm of dose profile penumbra between 20% and 80%. In conclusion, the MAGAT polymer gel dosimeter with MSE MR imaging is a promising method for dose verification in clinical radiation therapy practice.

Lee, Jason J. S.; Tsai, Chia-Jung; Lo, Man-Kuok; Huang, Yung-Hui; Chen, Chien-Chuan; Wu, Jay; Tyan, Yeu-Sheng; Wu, Tung-Hsin

2008-05-01

163

Spot quantification in two dimensional gel electrophoresis image analysis: comparison of different approaches and presentation of a novel compound fitting algorithm  

PubMed Central

Background Various computer-based methods exist for the detection and quantification of protein spots in two dimensional gel electrophoresis images. Area-based methods are commonly used for spot quantification: an area is assigned to each spot and the sum of the pixel intensities in that area, the so-called volume, is used a measure for spot signal. Other methods use the optical density, i.e. the intensity of the most intense pixel of a spot, or calculate the volume from the parameters of a fitted function. Results In this study we compare the performance of different spot quantification methods using synthetic and real data. We propose a ready-to-use algorithm for spot detection and quantification that uses fitting of two dimensional Gaussian function curves for the extraction of data from two dimensional gel electrophoresis (2-DE) images. The algorithm implements fitting using logical compounds and is computationally efficient. The applicability of the compound fitting algorithm was evaluated for various simulated data and compared with other quantification approaches. We provide evidence that even if an incorrect bell-shaped function is used, the fitting method is superior to other approaches, especially when spots overlap. Finally, we validated the method with experimental data of urea-based 2-DE of A? peptides andre-analyzed published data sets. Our methods showed higher precision and accuracy than other approaches when applied to exposure time series and standard gels. Conclusion Compound fitting as a quantification method for 2-DE spots shows several advantages over other approaches and could be combined with various spot detection methods. The algorithm was scripted in MATLAB (Mathworks) and is available as a supplemental file.

2014-01-01

164

Measurement of the absorbed dose distribution near an 192Ir intravascular brachytherapy seed using a high-spatial-resolution gel dosimetry system  

NASA Astrophysics Data System (ADS)

The absorbed dose distribution at sub-millimeter distances from the Best single 192Ir intravascular brachytherapy seed was measured using a high-spatial-resolution gel dosimetry system. Two gel phantoms from the same batch were used; one for the seed irradiation and one for calibration. Since the response of this gel is energy independent for photons between 20 and 1250 keV, the gel was calibrated using a narrowly collimated 60Co gamma-ray beam (cross-sectional area ˜1 cm2). A small format laser computed tomography scanner was used to acquire the data. The measurements were carried out with a spatial resolution of 100 µm in all dimensions. The seed was calibrated at NIST in terms of air-kerma strength. The absorbed dose rate as well as the radial dose function, gL(r), was measured for radial distances between 0.6 and 12.6 mm from the seed center. The dose rate constant was measured, yielding a value of ? = (1.122 ± 0.032) cGy h-1 U-1, which agrees with published data within the measurement uncertainty. For distances between 0.6 and 1.5 mm, gL(r) decreases from a maximum value of 1.06 down to 1.00; between 1.5 and 6.7 mm, an enhancement is clearly observed with a maximum value around 1.24 and beyond 6.7 mm, gL(r) has an approximately constant value around 1.0, which suggests that this seed can be considered as a point source only at distances larger than 6.7 mm. This latter observation agrees with data for the same seed reported previously using Gafchromic film MD-55-2. Additionally, published Monte Carlo (MC) calculations have predicted the observed behavior of the radial dose function resulting from the absorbed dose contributions of beta particles and electrons emitted by the 192Ir seed. Nonetheless, in the enhancement region, MC underestimates the dose by approximately 20%. This work suggests that beta particles and electrons emitted from the seed make a significant contribution to the total absorbed dose delivered at distances near the seed center (less than 6 mm) and therefore cannot be neglected, given the dimensions of blood vessel walls.

Massillon-JL, G.; Minniti, R.; Mitch, M. G.; Soares, C. G.

2012-06-01

165

Fundamentals of gel dosimeters  

NASA Astrophysics Data System (ADS)

Fundamental chemical and physical phenomena that occur in Fricke gel dosimeters, polymer gel dosimeters, micelle gel dosimeters and genipin gel dosimeters are discussed. Fricke gel dosimeters are effective even though their radiation sensitivity depends on oxygen concentration. Oxygen contamination can cause severe problems in polymer gel dosimeters, even when THPC is used. Oxygen leakage must be prevented between manufacturing and irradiation of polymer gels, and internal calibration methods should be used so that contamination problems can be detected. Micelle gel dosimeters are promising due to their favourable diffusion properties. The introduction of micelles to gel dosimetry may open up new areas of dosimetry research wherein a range of water-insoluble radiochromic materials can be explored as reporter molecules.

McAuley, K. B.; Nasr, A. T.

2013-06-01

166

Evaluation of the dosimetric performance of BANG3? polymer gel  

Microsoft Academic Search

New radiotherapy techniques call for three-dimensional dosimetric methods with high spatial resolution. Radiation sensitive gels read out using MRI T2 mapping provide an extremely promising option, and commercially available BANG polymer gels provide a convenient route into gel dosimetry. Gel dosimetry is dependent on the ability to calibrate gel response against radiation dose. This in turn is dependent on the

N D MacDougall; M E Miquel; D J Wilson; S F Keevil; M A Smith

2005-01-01

167

Computational dosimetry  

SciTech Connect

The paper presents a definition of the term ``Computational Dosimetry`` that is interpreted as the sub-discipline of computational physics which is devoted to radiation metrology. It is shown that computational dosimetry is more than a mere collection of computational methods. Computational simulations directed at basic understanding and modelling are important tools provided by computational dosimetry, while another very important application is the support that it can give to the design, optimization and analysis of experiments. However, the primary task of computational dosimetry is to reduce the variance in the determination of absorbed dose (and its related quantities), for example in the disciplines of radiological protection and radiation therapy. In this paper emphasis is given to the discussion of potential pitfalls in the applications of computational dosimetry and recommendations are given for their avoidance. The need for comparison of calculated and experimental data whenever possible is strongly stressed.

Siebert, B.R.L.; Thomas, R.H.

1996-01-01

168

Monte Carlo simulation and polymer gel dosimetry of 60 MeV clinical proton beams for the treatment of ocular tumours  

Microsoft Academic Search

Monte Carlo (MCNPX) simulations of a clinical proton beam-line under a range of beam conditions have been compared with MR analysis of irradiated polymer gel (BANG-1©). Gel results were found to under-estimate the height of the full energy Bragg peak relative to simulation by the order of 30%, due to increased LET in this region, which has been reported elsewhere.

C. R. Baker; T. E. Quine; J. N. H. Brunt; A. Kacperek

2009-01-01

169

Improved image quality for x-ray CT imaging of gel dosimeters  

SciTech Connect

Purpose: This study provides a simple method for improving precision of x-ray computed tomography (CT) scans of irradiated polymer gel dosimetry. The noise affecting CT scans of irradiated gels has been an impediment to the use of clinical CT scanners for gel dosimetry studies. Methods: In this study, it is shown that multiple scans of a single PAGAT gel dosimeter can be used to extrapolate a ''zero-scan'' image which displays a similar level of precision to an image obtained by averaging multiple CT images, without the compromised dose measurement resulting from the exposure of the gel to radiation from the CT scanner. Results: When extrapolating the zero-scan image, it is shown that exponential and simple linear fits to the relationship between Hounsfield unit and scan number, for each pixel in the image, provide an accurate indication of gel density. Conclusions: It is expected that this work will be utilized in the analysis of three-dimensional gel volumes irradiated using complex radiotherapy treatments.

Kakakhel, M. B.; Kairn, T.; Kenny, J.; Trapp, J. V. [Faculty of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Queesland 4001, Australia and Department of Physics and Applied Mathematics, DPAM, Pakistan Institute of Engineering and Applied Sciences, PO Nilore, Islamabad 45450 (Pakistan); Premion, The Wesley Medical Centre, Suite 1, 40 Chasely St, Auchenflower, Queensland 4066 (Australia); Premion, The Wesley Medical Centre, Suite 1, 40 Chasely St, Auchenflower, Queensland 4066, Australia and Australian Clinical Dosimetry Service, ARPANSA, Yallambie, Vic 3085 (Australia); Faculty of Science and Technology, Queensland University of Technology, GPO Box 2434, Brisbane, Ql d 4001 (Australia)

2011-09-15

170

A systematic review of the precision and accuracy of dose measurements in photon radiotherapy using polymer and Fricke MRI gel dosimetry  

Microsoft Academic Search

The purpose of this work is to undertake a critical appraisal of the evidence in the published literature concerning the basic parameters of accuracy and precision associated with the use of Fricke and polymer gels (in conjunction with MR imaging) as radiation dosimeters in photon radiotherapy, condensing and analysing the body of published information (to the end of April 2002).A

N D MacDougall; W G Pitchford; M A Smith

2002-01-01

171

Epid Dosimetry  

NASA Astrophysics Data System (ADS)

Electronic portal imaging devices (EPIDs) were introduced originally for patient position verification. The idea of using EPIDs for dosimetry was realised in the 1980s. Little was published on the topic until the mid 1990's, when the interest in EPIDs for dosimetry increased rapidly and continues to grow. The increasing research on EPID dosimetry coincided with the introduction of intensity modulated radiation therapy (IMRT). EPIDs are well suited to IMRT dosimetry because they are high resolution, two-dimensional (2D) digital detectors. They are also pre-existing on almost all modern linear accelerators. They generally show a linear response to increasing dose. Different types of EPIDs have been clinically implemented, and these have been described in several review papers. The current generation of commercially available EPIDs are indirect detection active matrix flat panel imagers, also known as amorphous silicon (a-Si) EPIDs. Disadvantages of a-Si EPIDs for dosimetry include non-water equivalent construction materials, and the energy sensitivity and optical scatter of the phosphor scintillators used to create optical signal from the megavoltage beam. This report discusses current knowledge regarding a-Si EPIDs for dosimetry.

Greer, Peter B.; Vial, Philip

2011-05-01

172

Differential dose volume histograms of Gamma Knife in the presence of inhomogeneities using MRI-polymer gel dosimetry and MC simulation  

SciTech Connect

Polymer gel dosimeters offer a practical solution to 3D dose verification for conventional radiotherapy as well as intensity-modulated and stereotactic radiotherapy. In this study, EGSnrc calculated and PAGAT polymer gel dosimeter measured dose volume histograms (DVHs) for single-shot irradiations of the Gamma Knife (GK) unit were used to investigate the effects of the presence of inhomogeneities on 3D dose distribution. The head phantom was a custom-built 16 cm diameter Plexiglas sphere. Inside the phantom, there is a cubic cutout for inserting the gel vials and another cutout for inserting the inhomogeneities. Following irradiation with the GK unit, the polymer gel phantoms were scanned with a 1.5 T MRI scanner. Comparing the results of measurement in homogeneous and heterogeneous phantoms revealed that inserting inhomogeneities inside the homogeneous phantom did not cause considerable disturbances on dose distribution in irradiation with 8 mm collimator within low isodose levels (<50%), which is essential for the dose sparing of sensitive structures. The results of simulation for homogeneous and inhomogeneous phantoms in irradiation with 18 mm collimator of the GK unit showed 23.24% difference in DVH within 90%-100% relative isodose level and also revealed that a significant part of the target (28.56%) received relative doses higher than the maximum dose, which exceeds the acceptance criterion (5%). Based on these results it is concluded that the presence of inhomogeneities inside the phantom can cause considerable errors in dose calculation within high isodose levels with respect to LGP prediction which assumes that the target is a homogeneous material. Moreover, it is demonstrated that the applied MC code is an accurate and stand-alone tool for 3D evaluation of dose distribution in irradiation with the GK unit, which can provide important, 3D plan evaluation criteria used in clinical practice.

Allahverdi Pourfallah, Tayyeb; Allahverdi, Mahmoud; Riahi Alam, Nader; Ay, Mohammad-Reza; Zahmatkesh, Mohammad-Hasan [Department of Biochemistry and Biophysics, Faculty of Medicine, Mazandaran University of Medical Sciences, 48175-1665 Sari (Iran, Islamic Republic of) and Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, 14155-7661 Tehran (Iran, Islamic Republic of); Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, 14155-7661 Tehran (Iran, Islamic Republic of); Novin Medical Radiation Center, 14665-599 Tehran (Iran, Islamic Republic of)

2009-07-15

173

(Biological dosimetry)  

SciTech Connect

The traveler attended the 1st International Conference on Biological Dosimetry in Madrid, Spain. This conference was organized to provide information to a general audience of biologists, physicists, radiotherapists, industrial hygiene personnel and individuals from related fields on the current ability of cytogenetic analysis to provide estimates of radiation dose in cases of occupational or environmental exposure. There is a growing interest in Spain in biological dosimetry because of the increased use of radiation sources for medical and occupational uses, and with this the anticipated and actual increase in numbers of overexposure. The traveler delivered the introductory lecture on Biological Dosimetry: Mechanistic Concepts'' that was intended to provide a framework by which the more applied lectures could be interpreted in a mechanistic way. A second component of the trip was to provide advice with regard to several recent cases of overexposure that had been or were being assessed by the Radiopathology and Radiotherapy Department of the Hospital General Gregorio Maranon'' in Madrid. The traveler had provided information on several of these, and had analyzed cells from some exposed or purportedly exposed individuals. The members of the biological dosimetry group were referred to individuals at REACTS at Oak Ridge Associated Universities for advice on follow-up treatment.

Preston, R.J.

1990-12-17

174

Radiation dosimetry.  

PubMed Central

This article summarizes the basic facts about the measurement of ionizing radiation, usually referred to as radiation dosimetry. The article defines the common radiation quantities and units; gives typical levels of natural radiation and medical exposures; and describes the most important biological effects of radiation and the methods used to measure radiation. Finally, a proposal is made for a new radiation risk unit to make radiation risks more understandable to nonspecialists.

Cameron, J

1991-01-01

175

Biological Dosimetry  

Microsoft Academic Search

Chromosome analysis is the method of choice in case of biological dosimetry, used for the quantification of exposures to ionising\\u000a radiation. The advantages and disadvantages of dicentric chromosomes and symmetrical translocations are described. In general,\\u000a confounding factors on the lower detectable dose limit and scoring criteria for symmetrical translocations are discussed.\\u000a In the case of acute exposures, scoring of dicentric

Günter Stephan; Ursula Oestreicher; Horst Romm

176

Fun Fitness  

MedlinePLUS

Printer Friendly F un Fitness Fitness is fun! It's a great way to experience health and wellness. Enjoying fitness is the key to keeping exercise a part of your life. Fun Fitness will teach you all about the right way ...

177

Internal calibration of gel dosimeters: A feasibility study  

NASA Astrophysics Data System (ADS)

In this work we test the feasibility of a new calibration method for gel dosimetry. We examine, through Monte Carlo modelling, whether the inclusion of an organic plastic scintillator system at key points within the gel phantom would perturb the dose map. Such a system would remove the requirement for a separate calibration gel, removing many sources of uncertainty.

Trapp, J. V.; Kairn, T.; Crowe, S.; Fielding, A.

2009-05-01

178

Reconstructing 3D x-ray CT images of polymer gel dosimeters using the zero-scan method  

NASA Astrophysics Data System (ADS)

In this study x-ray CT has been used to produce a 3D image of an irradiated PAGAT gel sample, with noise-reduction achieved using the 'zero-scan' method. The gel was repeatedly CT scanned and a linear fit to the varying Hounsfield unit of each pixel in the 3D volume was evaluated across the repeated scans, allowing a zero-scan extrapolation of the image to be obtained. To minimise heating of the CT scanner's x-ray tube, this study used a large slice thickness (1 cm), to provide image slices across the irradiated region of the gel, and a relatively small number of CT scans (63), to extrapolate the zero-scan image. The resulting set of transverse images shows reduced noise compared to images from the initial CT scan of the gel, without being degraded by the additional radiation dose delivered to the gel during the repeated scanning. The full, 3D image of the gel has a low spatial resolution in the longitudinal direction, due to the selected scan parameters. Nonetheless, important features of the dose distribution are apparent in the 3D x-ray CT scan of the gel. The results of this study demonstrate that the zero-scan extrapolation method can be applied to the reconstruction of multiple x-ray CT slices, to provide useful 2D and 3D images of irradiated dosimetry gels.

Kakakhel, M. B.; Kairn, T.; Kenny, J.; Trapp, J. V.

2013-06-01

179

Dosimetry of space radiations  

NASA Technical Reports Server (NTRS)

Harmful effects of space radiation are discussed. Radiation dosimetry methods are given. Dosimetry monitoring is investigated. Methods for measuring space radiation by ionization, thermoluminescence, and nuclear photographic emulsions are described.

Arkhangelskiy, V. V.; Markelov, V. V.; Skvortsov, S. S.; Smirennyy, L. N.; Turkin, V. N.; Chernykh, I. V.

1973-01-01

180

Individual Neutron Dosimetry.  

National Technical Information Service (NTIS)

The most important concepts and development in individual neutron dosimetry are presented, especially the dosimetric properties of the albedo technique. The main problem in albedo dosimetry is to calibrate the dosemeter in the environs of each neutron sou...

C. L. P. Mauricio

1987-01-01

181

Ion storage dosimetry  

Microsoft Academic Search

The availability of a reliable, accurate and cost-effective real-time personnel dosimetry system is fascinating to radiation workers. Electronic dosimeters are contemplated to meet this demand of active dosimetry. The development of direct ion storage (DIS) dosimeters, a member of the electronic dosimeter family, for personnel dosimetry is also an attempt in this direction. DIS dosimeter is a hybrid of the

V. K Mathur

2001-01-01

182

Software for 3D radiotherapy dosimetry. Validation.  

PubMed

The subject of this work is polyGeVero(®) software (GeVero Co., Poland), which has been developed to fill the requirements of fast calculations of 3D dosimetry data with the emphasis on polymer gel dosimetry for radiotherapy. This software comprises four workspaces that have been prepared for: (i) calculating calibration curves and calibration equations, (ii) storing the calibration characteristics of the 3D dosimeters, (iii) calculating 3D dose distributions in irradiated 3D dosimeters, and (iv) comparing 3D dose distributions obtained from measurements with the aid of 3D dosimeters and calculated with the aid of treatment planning systems (TPSs). The main features and functions of the software are described in this work. Moreover, the core algorithms were validated and the results are presented. The validation was performed using the data of the new PABIG(nx) polymer gel dosimeter. The polyGeVero(®) software simplifies and greatly accelerates the calculations of raw 3D dosimetry data. It is an effective tool for fast verification of TPS-generated plans for tumor irradiation when combined with a 3D dosimeter. Consequently, the software may facilitate calculations by the 3D dosimetry community. In this work, the calibration characteristics of the PABIG(nx) obtained through four calibration methods: multi vial, cross beam, depth dose, and brachytherapy, are discussed as well. PMID:25003788

Kozicki, Marek; Maras, Piotr; Karwowski, Andrzej C

2014-08-01

183

Determination of 3D dose distribution from intracavitary brachytherapy of cervical cancer by MRI of irradiated ferrous sulphate gel  

Microsoft Academic Search

Background and purpose: MRI ferrous sulphate gel dosimetry has proven to be a valuable method for assessment of dose delivered in teletherapy. The intention of this study was to investigate ferrous sulphate gel as a possible dosimeter for intracavitary brachytherapy applications.Materials and methods: A plastic duplicate of a cervix ring applicator set was submerged in Fe2+-infused gelatin gel. The gel

Bjørn H. Knutsen; Arne Skretting; Taran P. Hellebust; Dag R. Olsen

1997-01-01

184

Effects of gel composition on the radiation induced density change in PAG polymer gel dosimeters: a model and experimental investigations  

Microsoft Academic Search

Due to a density change that occurs in irradiated polyacrylamide gel (PAG), x-ray computed tomography (CT) has emerged as a feasible method of performing polymer gel dosimetry. However, applicability of the technique is currently limited by low sensitivity of the density change to dose. This work investigates the effect of PAG composition on the radiation induced density change and provides

M. Hilts; A. Jirasek; C. Duzenli

2004-01-01

185

Gel Electrophoresis  

NSDL National Science Digital Library

This interactive activity from the Dolan DNA Learning Center illustrates the process of gel electrophoresis, in which DNA fragments are separated by size as they migrate at different rates through a gel matrix.

Foundation, Wgbh E.

2007-04-19

186

Thermoluminescence in medical dosimetry.  

PubMed

Thermoluminescence dosimetry (TLD) is applied worldwide for personal and medical dosimetry. TLD method has resulted in many interesting findings in medicine as TL dosimeters have many relevant advantages such as high sensitivity, small physical size, tissue equivalence, etc. The main characteristics of various TL materials used in radiation measurements and their practical consequences are overviewed: well defined TL glow curve, batch homogeneity, signal stability after irradiation, precision and accuracy, response with dose, and influence of energy. In this paper a brief summary of the advances in the application of thermally stimulated luminescence (TSL) to dosimetry in radiation therapy application is presented. PMID:22633888

Rivera, T

2012-12-01

187

Internal dosimetry - a review.  

SciTech Connect

The field history and current status of internal dosimetry is reviewed in this article. Elements of the field that are reviewed include standards and models, derivation of dose coefficients and intake retention fractions, bioassay measurements, and intake and dose calculations. In addition, guidance is developed and provided as to the necessity of internal dosimetry for a particular facility or operation and methodology for implementing a program. A discussion of the purposes of internal dosimetry is included as well as recommendations for future development and direction.

Potter, Charles Augustus

2004-06-01

188

Study of density and stability of a lung-equivalent gel  

NASA Astrophysics Data System (ADS)

Gel dosimetry is a useful tool for the verification of radiation treatments in water-equivalent tissues. In order to extend the application of gel dosimetry to the lung, the density of the dosimeter should be reduced. Some methods have been proposed for the fabrication of low-density gels. Major challenges in the fabrication of these gel dosimeters are to achieve a density that equals the electron-density of lung tissue and to obtain an acceptable homogeneity. Both polymer and Fricke gel formulations have been used as basic chemical compositions for low-density gel dosimeters. To reduce the density, two approaches have been suggested: (1) Styrofoam beads can be added to the gel or (2) the gel can be beaten until a foam is obtained. In this study we followed the latter method and added sodium-dodecyl-sulphate (SDS) as a surfactant to increase the surface tension of the gel.

Claeys, Carolien; de Deene, Yves; Truyens, Bart; de Wagter, Carlos

2006-12-01

189

Fitness Factor  

NSDL National Science Digital Library

In this online activity, learners partner up to complete several physical exercises and assess their starting fitness level. Over the course of 6 weeks, learners practice the activities and record their improvement. This is a simple way to get young learners interested in practicing fitness. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. They can also keep track of their progress in all of the Kinetic City activities, and compare their progress to other participants worldwide.

Science, American A.

2009-01-01

190

Fitness landscapes  

NASA Astrophysics Data System (ADS)

Fitness landscapes are a valuable concept in evolutionary biology, combinatorial optimization, and the physics of disordered systems. A fitness landscape is a mapping from a configuration space that is equipped with some notion of adjacency, nearness, distance or accessibility, into the real numbers. Landscape theory has emerged as an attempt to devise suitable mathematical structures for describing the "static" properties of landscapes as well as their influence on the dyn amics of adaptation. This chapter gives a brief overview on recent developments in this area, focusing on "geometrical" properties of landscapes.

Stadler, Peter F.

191

Optically stimulated luminescence dosimetry  

Microsoft Academic Search

Models and the conceptual framework necessary for an understanding of optically stimulated luminescence (OSL) are described. Examples of various OSL readout schemes are described, along with examples of the use of OSL in radiation dosimetry.

Stephen W. S. McKeever

2001-01-01

192

Dose verification of single shot gamma knife applications using VIPAR polymer gel and MRI  

Microsoft Academic Search

This work describes an experimental procedure with potential to assess the overall accuracy associated with gamma knife clinical applications, from patient imaging and dosimetry planning to patient positioning and dose delivery using the automated positioning system of a Leksell Gamma Knife model C. The VIPAR polymer gel-MRI dosimetry method is employed due to its inherent three-dimensional feature and linear dose

P. Karaiskos; L. Petrokokkinos; E. Tatsis; A. Angelopoulos; P. Baras; M. Kozicki; P. Papagiannis; J. M. Rosiak; L. Sakelliou; P. Sandilos; L. Vlachos

2005-01-01

193

Characterisation of the ferrous-xylenol orange-gelatin (FXG) gel dosimeter  

NASA Astrophysics Data System (ADS)

Recent studies have used the ferrous-xylenol orange-gelatin (FXG) gel dosimeter for 3D radiation field mapping using the optical computed tomography technique. However the characterisation of the dosimetry performance of the FXG gel has not been detailed, such as the variation in dose-response of the FXG gel with changes in preparation techniques, constituent concentrations, pre-irradiation storage time, and concentrations of additives such as oxygen and saccharides. In this paper these issues are addressed with the aim of developing a standard FXG gel for future use in radiation dosimetry applications.

Healy, B.; Brindha, S.; Zahmatkesh, M.; Baldock, C.

2004-01-01

194

Flash X-Ray Dosimetry.  

National Technical Information Service (NTIS)

A Methodology Investigation of dosimetry techniques has been developed and calibrated to provide radiation monitors in a combined fast burst reactor/flash X ray environment. These techniques include improved neutron fluence dosimetry, development of suita...

C. R. Heimbach

1986-01-01

195

Gel Electrophoresis  

NSDL National Science Digital Library

In the early days of DNA manipulation, DNA fragments were laboriously separated by gravity. In the 1970s, the powerful tool of DNA gel electrophoresis was developed. This process uses electricity to separate DNA fragments by size as they migrate through a gel matrix. This animation from Cold Spring Harbor Laboratory's Dolan DNA Learning Center presents Gel Electrophoresis through a series of illustrations of the processes involved.

2012-01-20

196

Men's Fitness  

NSDL National Science Digital Library

It seems that people in the United States are going through a new and renewed commitment to getting back in shape, and there are a variety of helpful online resources to make this a viable possibility for millions of Americans. This particular site (sponsored by a number of fitness-related publications) brings together information on a host of timely topics, including weight loss, healthy eating, building muscle mass, and seasonal training suggestions. The homepage contains links on such topics as diminishing cellulite and eating organic, and also contains a number of online calculators. These calculators can help individuals determine their body mass index, their weight loss potential, and their ideal weight. The site also has an area where visitors can sign up to receive any number of free electronic newsletters from some of the magazines that sponsor the site.

197

Ion storage dosimetry  

NASA Astrophysics Data System (ADS)

The availability of a reliable, accurate and cost-effective real-time personnel dosimetry system is fascinating to radiation workers. Electronic dosimeters are contemplated to meet this demand of active dosimetry. The development of direct ion storage (DIS) dosimeters, a member of the electronic dosimeter family, for personnel dosimetry is also an attempt in this direction. DIS dosimeter is a hybrid of the well-established technology of ion chambers and the latest advances in data storage using metal oxide semiconductor field effect transistor (MOSFET) analog memory device. This dosimeter is capable of monitoring legal occupational radiation doses of gamma, X-rays, beta and neutron radiation. Similar to an ion chamber, the performance of the dosimeter for a particular application can be optimized through the selection of appropriate wall materials. The use of the floating gate of a MOSFET as one of the electrodes of the ion chamber allows the miniaturization of the device to the size of a dosimetry badge and avoids the use of power supplies during dose accumulation. The concept of the device, underlying physics and the design of the DIS dosimeter are discussed. The results of preliminary testing of the device are also provided.

Mathur, V. K.

2001-09-01

198

Dosimetry considerations in phototherapy  

Microsoft Academic Search

Dosimetry in phototherapy involves a determination of the energy absorbed per unit mass of tissue, corrected for the quantum yield in a photochemical reaction. The dose rate in photochemotherapy of cancer with hematoporphyrin derivative and visible light is related to the extinction coefficient, quantum yield for singlet oxygen production, concentration of sensitizer and energy flux density at depth. Data or

A. Edward Profio; D. R. Doiron

1981-01-01

199

Ion-kill dosimetry  

NASA Technical Reports Server (NTRS)

Unanticipated late effects in neutron and heavy ion therapy, not attributable to overdose, imply a qualitative difference between low and high LET therapy. We identify that difference as 'ion kill', associated with the spectrum of z/beta in the radiation field, whose measurement we label 'ion-kill dosimetry'.

Katz, R.; Cucinotta, F. A.; Fromm, M.; Chambaudet, A.

2001-01-01

200

Radiation dose imaging with ultrasound shear-wave elastography and radiation sensitive gels  

Microsoft Academic Search

Radiation sensitive gels have been investigated for use in radiation dosimetry for a number of years. Previously we have determined the applied dose distribution by measuring the radiation induced stiffness distribution with quantitative quasistatic ultrasound elastography. Here, a preliminary assessment of shear-wave elastography for radiation dose measurement is presented. A block of radiation sensitive gel was irradiated along one of

Remo A Crescenti; Jeffrey C Bamber; Nigel L Bush; Steve Webb

2009-01-01

201

In vivo dosimetry for IMRT  

SciTech Connect

In vivo dosimetry has a well established role in the quality assurance of 2D radiotherapy and 3D conformal radiotherapy. The role of in vivo dosimetry for IMRT is not as well established. IMRT introduces a range of technical issues that complicate in vivo dosimetry. The first decade or so of IMRT implementation has largely relied upon pre-treatment phantom based dose verification. During that time, several new devices and techniques for in vivo dosimetry have emerged with the promise of providing the ultimate form of IMRT dose verification. Solid state dosimeters continue to dominate the field of in vivo dosimetry in the IMRT era. In this report we review the literature on in vivo dosimetry for IMRT, with an emphasis on clinical evidence for different detector types. We describe the pros and cons of different detectors and techniques in the IMRT setting and the roles that they are likely to play in the future.

Vial, Philip [Department of Medical Physics, Liverpool Cancer Therapy Centre (Australia); Institute of Medical Physics, School of Physics, University of Sydney (Australia)

2011-05-05

202

Sensitivity and stability of the Fricke gelatin xylenol orange gel dosimeter  

NASA Astrophysics Data System (ADS)

Spectrophotometric measurements of the Fricke-gelatin-xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25 Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy dosimetry measurements contains 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3.0% by weight gelatin.

Davies, J. B.; Baldock, C.

2008-06-01

203

Neutron Exposure Parameters for the Dosimetry Capsule in the Heavy-Section Steel Irradiation Program Tenth Irradiation Series  

SciTech Connect

This report describes the computational methodology for the least-squares adjustment of the dosimetry data from the HSSI 10.OD dosimetry capsule with neutronics calculations. It presents exposure rates at each dosimetry location for the neutron fluence greater than 1.0 MeV, fluence greater than 0.1 MeV, and displacements per atom. Exposure parameter distributions are also described in terms of three- dimensional fitting functions. When fitting functions are used it is suggested that an uncertainty of 6% (1 o) should be associated with the exposure rate values. The specific activity of each dosimeter at the end of irradiation is listed in the Appendix.

C.A. Baldwin; F.B.K. Kam; I. Remec

1998-10-01

204

Electron Paramagnetic Resonance Retrospective Dosimetry  

SciTech Connect

Necessity for, principles of, and general concepts of the electron paramagnetic resonance (EPR) retrospective dosimetry are presented. Also presented and given in details are examples of EPR retrospective dosimetry applications in tooth enamel, bone, and fingernails with focus on general approaches for solving technical and methodological problems. Advantages, drawbacks, and possible future developments are discussed and an extensive bibliography on EPR retrospective dosimetry is provided.

Romanyukha, Alex [Naval Dosimetry Center, 8901 Wisconsin Ave., Bethesda, MD, 20889 (United States); Trompier, Francois [Institute for Radiological Protection and Nuclear Safety, Fontenay-aux-Roses, France 92262 (France)

2011-05-05

205

Hanford External Dosimetry Program  

SciTech Connect

This document describes the Hanford External Dosimetry Program as it is administered by Pacific Northwest Laboratory (PNL) in support of the US Department of Energy (DOE) and its Hanford contractors. Program services include administrating the Hanford personnel dosimeter processing program and ensuring that the related dosimeter data accurately reflect occupational dose received by Hanford personnel or visitors. Specific chapters of this report deal with the following subjects: personnel dosimetry organizations at Hanford and the associated DOE and contractor exposure guidelines; types, characteristics, and procurement of personnel dosimeters used at Hanford; personnel dosimeter identification, acceptance testing, accountability, and exchange; dosimeter processing and data recording practices; standard sources, calibration factors, and calibration processes (including algorithms) used for calibrating Hanford personnel dosimeters; system operating parameters required for assurance of dosimeter processing quality control; special dose evaluation methods applied for individuals under abnormal circumstances (i.e., lost results, etc.); and methods for evaluating personnel doses from nuclear accidents. 1 ref., 14 figs., 5 tabs.

Fix, J.J.

1990-10-01

206

Thorium metabolism and dosimetry  

SciTech Connect

Thorium occurs widely in nature, and has been used in medicine, industry, and advanced nuclear fuel cycles. Despite many studies, there still remains uncertainty in the dosimetry of Th, particularly that associated with the Th-232 decay chain. This presentation reviews past and current uses of thorium, and describes the residual difficulties involved with monitoring methods and calculations used in both environmental and occupational exposure evaluations.

Johnson, J.R.; Hill, R.L. [Pacific Northwest Lab., Richland, WA (United States); Birchall, A.; Jarvis, N.S. [National Radiological Protection Board, Chilton (United Kingdom)

1994-07-01

207

Cosmic Ray Dosimetry  

NASA Astrophysics Data System (ADS)

Radiation levels at aircraft cruising altitudes are twenty times higher than at sea level. Thus, on average, a typical airline pilot receives a larger annual radiation dose than some one working in nuclear industry. The main source of this radiation is from galactic cosmic radiation, high energy particles generated by exploding stars within our own galaxy. In this work we study cosmic rays dosimetry at various aviation altitudes using the PARMA model.

Si Belkhir, F.; Attallah, R.

2010-10-01

208

Gel Electrophoresis  

NSDL National Science Digital Library

In this activity, learners simulate the process of DNA fingerprinting by using electricity to separate colored dyes. Learners use simple materials to assemble a comb (electrophoresis chamber) to hold the samples, make a 0.2% sodium bicarbonate buffer and 1% gel solution, connect a high voltage power supply, and prepare 5 different samples. Then learners test their model and observe each sample.

Yu, Julie

2007-01-01

209

Sensitivity and stability of the Fricke–gelatin–xylenol orange gel dosimeter  

Microsoft Academic Search

Spectrophotometric measurements of the Fricke–gelatin–xylenol orange (FGX) gel dosimeter demonstrated reproducible linear dose response up to 25Gy. However, oxidation processes continue post-irradiation, affecting the response of this dosimetry system. Additional oxygenation during preparation increases the sensitivity of the gel but does not improve the auto-oxidation stability of the dosimeter post-irradiation. A suitably stable gel composition that is recommended for radiotherapy

J. B. Davies; C. Baldock

2008-01-01

210

PyFITS: Python FITS Module  

NASA Astrophysics Data System (ADS)

PyFITS provides an interface to FITS formatted files in the Python scripting language and PyRAF, the Python-based interface to IRAF. It is useful both for interactive data analysis and for writing analysis scripts in Python using FITS files as either input or output. PyFITS is a development project of the Science Software Branch at the Space Telescope Science Institute.

Barrett, Paul; Hsu, J. C.; Hanley, Chris; Taylor, James; Droettboom, Michael; Bray, Erik M.; Hack, Warren; Greenfield, Perry; Wyckoff, Eric; Jedrzejewski, Robert; De La Pena, Michele; Hodge, Phil

2012-07-01

211

Aerosol gels  

NASA Technical Reports Server (NTRS)

An improved process for the production of ultralow density, high specific surface area gel products is provided which comprises providing, in an enclosed chamber, a mixture made up of small particles of material suspended in gas; the particles are then caused to aggregate in the chamber to form ramified fractal aggregate gels. The particles should have a radius (a) of up to about 50 nm and the aerosol should have a volume fraction (f.sub.v) of at least 10.sup.-4. In preferred practice, the mixture is created by a spark-induced explosion of a precursor material (e.g., a hydrocarbon) and oxygen within the chamber. New compositions of matter are disclosed having densities below 3.0 mg/cc.

Sorensen, Christopher M. (Inventor); Chakrabarti, Amitabha (Inventor); Dhaubhadel, Rajan (Inventor); Gerving, Corey (Inventor)

2010-01-01

212

Fast neutron dosimetry  

SciTech Connect

This progress report concentrates on two major areas of dosimetry research: measurement of fast neutron kerma factors for several elements for monochromatic and white spectrum neutron fields and determination of the response of thermoluminescent phosphors to various ultra-soft X-ray energies and beta-rays. Dr. Zhixin Zhou from the Shanghai Institute of Radiation Medicine, People's Republic of China brought with him special expertise in the fabrication and use of ultra-thin TLD materials. Such materials are not available in the USA. The rather unique properties of these materials were investigated during this grant period.

DeLuca, P.M. Jr.; Pearson, D.W.

1992-01-01

213

Heavy-ion dosimetry  

SciTech Connect

This lecture deals with some of the more important physical characteristics of relativistic heavy ions and their measurement, with beam delivery and beam monitoring, and with conventional radiation dosimetry as used in the operation of the BEVALAC biomedical facility for high energy heavy ions (Lyman and Howard, 1977; BEVALAC, 1977). Even so, many fundamental aspects of the interaction of relativistic heavy ions with matter, including important atomic physics and radiation chemical considerations, are not discussed beyond the reminder that such additional understanding is required before an adequte perspective of the problem can be attained.

Schimmerling, W.

1980-03-01

214

Liquid radiochromic dosimetry  

NASA Astrophysics Data System (ADS)

By strategic combination of weak acid, mild oxidizing agent, and polar organic solvents containing millimolar concentrations of leucocyanides of certain triphenylmethane dyes, fairly broad ranges of absorbed doses of ionizing radiation can be determined. The yield of dye ions as determined by spectrophotometry can be made essentially constant with dose (i.e. linear response) from 0.01 to 30 kGy and it does not vary with dose rate upto 10 11 Gy·s -1. The radiation-induced color is stable and offers fast-retrieval dosimetry if N-vinyl-2-pyrrolidone is used as solvent. Other possible polar solvents are 2-propanol, 2-methoxy ethanol, N, N-dimethyl formamide, dimethyl sulfoxide, and triethyl phosphate. Dimethyl sulfoxide is found to give the widest and most linear response. Suitable dye precursors are leucocyanides of pararosaniline, new fuchsin, hexa (hydroxyethyl) pararosaniline, crystal violet, malachite green, setoglaucine, ethyl violet, helvetia green, basic violet-14, and formyl violet. Low concentrations of carboxylic acids contribute stability to the system. Typical mild oxidizing agents are nitrobenzene, and atmospheric oxygen, or oxygen released radiolytically from the solvents. The dosimetry systems do not require high-purity of ingredients or ultracleanliness of containers, although, for reproducibility of dye yields (G-values), thoroughly purified and uniform dye derivates are recommended.

Rativanich, N.; Radak, B. B.; Miller, A.; Uribe, R. M.; McLaughlin, W. L.

215

Reaching Your Fitness Goals  

MedlinePLUS

Everyday Fitness Ideas from the National Institute on Aging at NIH www.nia.nih.gov/Go4Life Reaching Your Fitness ... longer, and more easily. As you increase your fitness level, you also might find that you need ...

216

Fricke Gel Dosimeter Tissue-Equivalence a Monte Carlo Study  

NASA Astrophysics Data System (ADS)

Gel dosimetry has proved to be a valuable technique for absorbed dose distribution measurements in radiotherapy. FriXy-gel dosimeters consist of Fricke (ferrous sulphate) solution infused with xylenol orange. The solution is incorporated to a gel matrix in order to fix it to a solid structure allowing good spatial resolution and is imaged with a transportable optical system, measuring visible light transmittance before and after irradiation. This paper presents an evaluation of total photon mass attenuation coefficients at energies in the range of 50 keV-10MeV for the radiochromic FriXy gel dosimeter sensitive material. Mass attenuation coefficient estimations have been performed by means of Monte Carlo (PENELOPE) simulations. These calculations have been carried out for the FriXy gel sensitive material as well as for soft tissue (ICRU) and pure liquid water; a comparison of the obtained data shows good agreement between the different materials.

Valente, M.; Bartesaghi, G.; Gambarini, G.; Brusa, D.; Castellano, G.; Carrara, M.

2008-06-01

217

FITS Foreign File Encapsulation  

NASA Astrophysics Data System (ADS)

FITS FOREIGN is a new FITS extension type that has been submitted to the FITS Registry {http://fits.gsfc.nasa.gov/fits_registry.html} as a standard way to wrap an arbitrary file, allowing a file or tree of files to be wrapped up in FITS and later restored to disk. Certain of the file attribute keywords can be included in the header of any FITS file or extension to support such things as storing a directory tree containing images, tables, and other non-FITS types of files in a multi-extension FITS (MEF) file, and later restoring the whole tree to disk. The motivation for this extension was to allow an implementation that is based on the FITS multi-extension mechanism to encapsulate and pass non-FITS data.

Zárate, N.; Seaman, R.; Tody, D.

2007-10-01

218

Internal dosimetry technical basis manual.  

National Technical Information Service (NTIS)

The internal dosimetry program at the Savannah River Site (SRS) consists of radiation protection programs and activities used to detect and evaluate intakes of radioactive material by radiation workers. Examples of such programs are: air monitoring; surfa...

1990-01-01

219

Internal dosimetry technical basis manual  

SciTech Connect

The internal dosimetry program at the Savannah River Site (SRS) consists of radiation protection programs and activities used to detect and evaluate intakes of radioactive material by radiation workers. Examples of such programs are: air monitoring; surface contamination monitoring; personal contamination surveys; radiobioassay; and dose assessment. The objectives of the internal dosimetry program are to demonstrate that the workplace is under control and that workers are not being exposed to radioactive material, and to detect and assess inadvertent intakes in the workplace. The Savannah River Site Internal Dosimetry Technical Basis Manual (TBM) is intended to provide a technical and philosophical discussion of the radiobioassay and dose assessment aspects of the internal dosimetry program. Detailed information on air, surface, and personal contamination surveillance programs is not given in this manual except for how these programs interface with routine and special bioassay programs.

Not Available

1990-12-20

220

Surveillance Dosimetry: Achievements and Disappointments.  

National Technical Information Service (NTIS)

A methodology has been developed for reducing the uncertainties in estimates of neutron fluence spectra within the pressure vessel of a PWR from dosimetry measurements performed at a surveillance location. This new procedure, named the LEPRICON methodolog...

J. J. Wagschal R. E. Maerker B. L. Broadhead

1982-01-01

221

Dosimetry studies in Zaborie village  

Microsoft Academic Search

Dosimetry studies in Zaborie, a territory in Russia highly contaminated by the Chernobyl accident, were carried out in July, 1997. Studies on dosimetry for people are important not only for epidemiology but also for recovery of local social activity. The local contamination of the soil was measured to be 1.5–6.3 MBq\\/m2 of Cs-137 with 0.7–4 ?Sv\\/h of dose rate. A

J. Takada; M. Hoshi; S. Endo; V. F. Stepanenko; A. E. Kondrashov; D. Petin; V. Skvortsov; A. Ivannikov; D. Tikounov; Y. Gavrilin; V. P. Snykov

2000-01-01

222

Fifth international radiopharmaceutical dosimetry symposium  

SciTech Connect

This meeting was held to exchange information on how to get better estimates of the radiation absorbed dose. There seems to be a high interest of late in patient dosimetry; discussions were held in the light of revised risk estimates for radiation. Topics included: Strategies of Dose Assessment; Dose Estimation for Radioimmunotherapy; Dose Calculation Techniques and Models; Dose Estimation for Positron Emission Tomography (PET); Kinetics for Dose Estimation; and Small Scale Dosimetry and Microdosimetry. (VC)

Watson, E.E.; Schlafke-Stelson, A.T. (eds.)

1992-05-01

223

Hanford internal dosimetry program manual  

SciTech Connect

This document describes the Hanford Internal Dosimetry program. Program Services include administrating the bioassay monitoring program, evaluating and documenting assessments of internal exposure and dose, ensuring that analytical laboratories conform to requirements, selecting and applying appropriate models and procedures for evaluating internal radionuclide deposition and the resulting dose, and technically guiding and supporting Hanford contractors in matters regarding internal dosimetry. 13 refs., 16 figs., 42 tabs.

Carbaugh, E.H.; Sula, M.J.; Bihl, D.E.; Aldridge, T.L.

1989-10-01

224

Dosimetry in molecular nuclear therapy.  

PubMed

Advanced personalized dosimetry for molecular nuclear therapy has been shown to be feasible in clinical practice. At the same time instrumentation and dosimetric software are still evolving at a high pace. Procedures developed so far differ in approach and sophistication, and standard operating procedures necessary for accurate patient specific dosimetry do not yet exist. For this reason we restricted ourselves to reviewing the literature and highlighting relevant developments. PMID:21958989

Wierts, Roel; de Pont, Cécile D J M; Brans, Boudewijn; Mottaghy, Felix M; Kemerink, Gerrit J

2011-11-01

225

Dosimetry during space missions  

NASA Technical Reports Server (NTRS)

Comparative radiation hazards due to various sources of radiation in several prominent manned space missions are surveyed, along with techniques for coping with the hazards. Cosmic radiation of solar and galactic origin, and Van Allen belt radiation, are the major hazards outside the earth's geomagnetic shield, and were a major problem in the Apollo missions. The Skylab missions, while within the geomagnetic field, were subject to extensive exposure to the trapped radiation belts (Van Allen belts), while the Soyuz-Apollo test project involved orbiting at a lower altitude, with lower exposure. No solar particle bursts affected Apollo missions, and the Solar Particle Alert Network devised to help cope with the problem is described. Dosimetry practices and devices are described. Radiation experience and dose readings logged with the various missions are reported.

Bailey, J. V.

1976-01-01

226

Medical dosimetry in Hungary  

NASA Astrophysics Data System (ADS)

Radiation exposure of medical staff during cardiological and radiological procedures was investigated. The exposure of medical staff is directly connected to patient exposure. The aim of this study was to determine the distribution of doses on uncovered part of body of medical staff using LiF thermoluminescent (TL) dosimeters in seven locations. Individual Kodak film dosimeters (as authorized dosimetry system) were used for the assessment of medical staff's effective dose. Results achieved on dose distribution measurements confirm that wearing only one film badge under the lead apron does not provide enough information on the personal dose. The value of estimated annual doses on eye lens and extremities (fingers) were in good correlation with international publications.

Turák, O.; Osvay, M.; Ballay, L.

2012-09-01

227

Fundamentals of Radiation Dosimetry  

SciTech Connect

The basic concepts of radiation dosimetry are reviewed on basis of ICRU reports and text books. The radiation field is described with, among others, the particle fluence. Cross sections for indirectly ionizing radiation are defined and indicated is how they are related to the mass energy transfer and mass energy absorption coefficients. Definitions of total and restricted mass stopping powers of directly ionizing radiation are given. The dosimetric quantities, kerma, absorbed dose and exposure together with the relations between them are discussed in depth. Finally it is indicated how the absorbed dose can be measured with a calorimeter by measuring the temperature increase and with an ionisation chamber measuring the charge produced by the ionizing radiation and making use of the Bragg-Gray relation.

Bos, Adrie J. J. [Delft University of Technology, Faculty of Applied Sciences, Mekelweg 15, 2629JB Delft (Netherlands)

2011-05-05

228

A Pretty Good Fit  

ERIC Educational Resources Information Center

We often look for a best-fit function to a set of data. This article describes how a "pretty good" fit might be better than a "best" fit when it comes to promoting conceptual understanding of functions. In a pretty good fit, students design the function themselves rather than choosing it from a menu; they use appropriate variable names; and they…

Erickson, Tim

2008-01-01

229

Internal dosimetry, past and future  

SciTech Connect

This paper is a review of the progress in the dosimetry of internally deposited radionuclides (internal dosimetry) since World War II. Previous to that, only naturally occurring radionuclides were available and only a limited number of studies of biokinetics and dosimetry were done. The main radionuclides studied were /sup 226/Ra, /sup 228/Ra, and /sup 224/Ra but natural uranium was also studied mainly because of its toxic effect as a heavy metal, and not because it was radioactive. The effects of /sup 226/Ra in bone, mainly from the radium dial painters, also formed the only bases for the radiotoxicity of radionuclides in bone for many years, and it is still, along with /sup 224/Ra, the main source of information on the effects of alpha emitters in bone. The publications of the International Commission on Radiological Protection that have an impact on internal dosimetry are used as mileposts for this review. These series of publications, more than any other, represent a broad consensus of opinion within the radiation protection community at the time of their publication, and have formed the bases for radiation protection practice throughout the world. This review is not meant to be exhaustive; it is meant to be a personnel view of the evolution of internal dosimetry, and to present the author's opinion of what the future directions in internal dosimetry will be. 39 refs., 2 tabs.

Johnson, J.R.

1989-03-01

230

Characterization of dose-dependent Young's modulus for a radiation-sensitive polymer gel  

NASA Astrophysics Data System (ADS)

Radiation-sensitive polymer gels for clinical dosimetry have been intensively investigated with magnetic resonance imaging (MRI) because the transversal magnetic relaxation time is dependent on irradiation dose. MRI is expensive and not easily available in most clinics. For this reason, low-cost, quick and easy-to-use potential alternatives such as optical computed tomography (CT), x-ray CT or ultrasound attenuation CT have also been studied by others. Here, we instead evaluate the dose dependence of the elastic material property, Young's modulus and the dose response of the viscous relaxation of radiation-sensitive gels to discuss their potential for dose imaging. Three batches of a radiation-sensitive polymer gel (MAGIC gel) samples were homogeneously irradiated to doses from 0 Gy to 45.5 Gy. Young's modulus was computed from the measured stress on the sample surface and the strain applied to the sample when compressing it axially, and the viscous relaxation was determined from the stress decay under sustained compression. The viscous relaxation was found not to change significantly with dose. However, Young's modulus was dose dependent; it approximately doubled in the gels between 0 Gy and 20 Gy. By fitting a second-order polynomial to the Young's modulus-versus-dose data, 99.4% of the variance in Young's modulus was shown to be associated with the change in dose. The precision of the gel production, irradiation and Young's modulus measurement combined was found to be 4% at 2 Gy and 3% at 20 Gy. Potential sources of measurement error, such as those associated with the boundary conditions in the compression measurement, inhomogeneous polymerization, temperature (up to 1% error) and the evaporation of water from the sample (up to 1% error), were estimated and discussed. It was concluded that Young's modulus could be used for dose determination. Imaging techniques such as elastography may help to achieve this if they can provide a local measurement of Young's modulus, which may eliminate problems associated with the boundaries (e.g. variation in coefficient of friction) and inhomogeneous polymerization. Elastography combined with a calibration should also be capable of mapping dose in three dimensions.

Crescenti, Remo A.; Bamber, Jeffrey C.; Bush, Nigel L.; Webb, Steve

2009-02-01

231

Fit for purpose: Australia's National Fitness Campaign.  

PubMed

During a time of war, the federal government passed the National Fitness Act 1941 to improve the fitness of the youth of Australia and better prepare them for roles in the armed services and industry. Implementation of the National Fitness Act made federal funds available at a local level through state-based national fitness councils, which coordinated promotional campaigns, programs, education and infrastructure for physical fitness, with volunteers undertaking most of the work. Specifically focused on children and youth, national fitness councils supported the provision of children's playgrounds, youth clubs and school camping programs, as well as the development of physical education in schools and its teaching and research in universities. By the time the Act was repealed in 1994, fitness had become associated with leisure and recreation rather than being seen as equipping people for everyday life and work. The emergence of the Australian National Preventive Health Agency Act 2010 offers the opportunity to reflect on synergies with its historic precedent. PMID:22171877

Collins, Julie A; Lekkas, Peter

2011-12-19

232

Hanford External Dosimetry Technical Basis Manual.  

National Technical Information Service (NTIS)

The Hanford External Dosimetry Technical Basis Manual PNL-MA-842 documents the design and implementation of the external dosimetry system used at Hanford. The manual describes the dosimeter design, processing protocols, dose calculation methodology, radia...

B. A. Rathbone

2010-01-01

233

Initial radiation dosimetry at Hiroshima and Nagasaki  

SciTech Connect

The dosimetry of A-bomb survivors at Hiroshima and Nagasaki is discussed in light of the new dosimetry developed in 1980 by the author. The important changes resulting from the new dosimetry are the ratios of neutron to gamma doses, particularly at Hiroshima. The implications of these changes in terms of epidemiology and radiation protection standards are discussed. (ACR)

Loewe, W.E.

1983-09-01

234

10 CFR 35.630 - Dosimetry equipment.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 2009-01-01 false Dosimetry equipment. 35.630 Section 35...Stereotactic Radiosurgery Units § 35.630 Dosimetry equipment. (a) Except for low...manufacturer, a licensee shall have a calibrated dosimetry system available for use. To...

2009-01-01

235

4.2 Methods for Internal Dosimetry  

NASA Astrophysics Data System (ADS)

This document is part of Subvolume A 'Fundamentals and Data in Radiobiology, Radiation Biophysics, Dosimetry and Medical Radiological Protection' of Volume 7 'Medical Radiological Physics' of Landolt-Börnstein - Group VIII 'Advanced Materials and Technologies'. It contains the Section '4.2 Methods for Internal Dosimetry' of the Chapter '4 Dosimetry in Nuclear Medicine Diagnosis and Therapy' with the contents:

Noßke, D.; Mattsson, S.; Johansson, L.

236

Family Activities for Fitness  

ERIC Educational Resources Information Center

This article discusses how families can increase family togetherness and improve physical fitness. The author provides easy ways to implement family friendly activities for improving and maintaining physical health. These activities include: walking, backyard games, and fitness challenges.

Grosse, Susan J.

2009-01-01

237

Taurine for EPR dosimetry.  

PubMed

EPR dosimetry is characterized by its non-destructive read-out and the possibility of dose archival. Here, taurine is proposed as a radiation dosimeter using EPR spectroscopy. The EPR spectrum of taurine was studied and assigned, and changes in the taurine EPR spectrum as a result of the change in both modulation amplitude and microwave power were quantified. For gamma radiation, the energy absorption coefficient and the collision mass stopping power of taurine were compared to the corresponding values of soft tissue and alanine, in addition to calculation of effective atomic numbers. The response of taurine to gamma radiation doses in the range from 0.1 to 50 kGy was investigated, as well as that in the range from 1.0 to 20.0 Gy using numerically enhanced EPR taurine spectra. Both response curves showed a linear behavior. In addition, the time dependence of radiation-induced radicals was studied for short (during the first 6 h after irradiation) and long (during about 3 months after irradiation) time periods, and a reasonable degree of stability of the taurine radicals was observed. It is concluded that taurine is a promising dosimeter, which is characterized by its simple spectrum, radical stability, and wide range of linear response to gamma radiation. PMID:22526915

Maghraby, A; Mansour, A; Tarek, E

2012-08-01

238

Kids and Fitness.  

ERIC Educational Resources Information Center

Too many U.S. children are out of shape. Parents must help them learn to improve their fitness by exercising with them. The U.S. Conference of Mayors recently made physical fitness of the nation's children a primary emphasis. A sidebar presents information on how to contact local mayors to start up programs to help children improve their fitness

Corradini, Deedee

1999-01-01

239

Value From Regulatory Fit  

Microsoft Academic Search

Where does value come from? I propose a new answer to this classic question. People experience regulatory fit when the manner of their engagement in an activity sustains their goal orientation or interests regarding that activity. When there is fit, people engage more strongly in what they are doing and “feel right” about it. Fit influences the strength of value

E. Tory Higgins

2005-01-01

240

Fourth Personnel Dosimetry Intercomparison Study  

SciTech Connect

The fourth Personnel Dosimetry Intercomparison Study was held at the Oak Ridge National Laboratory's Dosimetry Applications Research Facility during March 15-23, 1978. The Health Physics Research Reactor (HPRR) used unshielded, with a 12-cm-thick Lucite shield, a 20-cm-thick concrete shield, or a 5-cm-thick steel and 15-cm-thick concrete shield, and provided four neutron and gamma-ray spectra. Then the dose was calculated based on the HPRR neutron spectra and dose conversion factors which had been determined previously for the four spectra. The results of these personnel dosimetry intercomparison studies reveal that estimates of dose equivalent vary over a wide range. The standard deviation of the mean of participants data for gamma measurements was in the range of 29 to 43%; for neutrons it was 57 to 188%. (PCS)

Dickson, H.W.

1980-02-01

241

ELECTROPHORESIS GEL BUFFER RECIRCULATOR FOR UNDER 20 DOLLARS  

EPA Science Inventory

Procedures requiring extended periods of electrophoresis frequently require recirculation of the get buffer in order to reduce gel artifacts. ere we describe a recirculation device which can be built inexpensively and will fit many different model get boxes....

242

The radiation dosimetry of Re-186 HEDP  

SciTech Connect

Patients suffering from metastatic bone cancer may be offered some relief of bone pain by several palliative agents currently under study. One such agent is Re-186 HEDP (etidronate). We gathered biodistribution data from 27 patients receiving this agent for palliation of bone pain. Skeletal activity was estimated as that portion of administered activity not recovered in urine or measured in kidneys or extracellular fluid (ECF) space. Activity in kidneys was estimated through scintigraphic imaging. Activity in urine and blood were estimated by direct counting of samples; activity in ECF was approximated as blood activity divided by the plasmacrit, multiplied by 0.2 times body weight. All retention data were fit to a sum of exponentials for estimation of residence times. Activity in the urinary bladder contents was estimated from the urinary excretion data using the dynamic bladder model of Cloutier et al. Estimated residence times were kidneys 0.538 hr, bone 33.3 hr (divided evenly between cortical and trabecular bone for dosimetry purposes), urinary bladder contents 1.18 hr, and remainder of body 6.52hr. Radiation dose estimates were developed, using the MIRDOSE 3 software. Radiation dose estimates for bone surfaces and red marrow are 1.9 and 0.82 mGy/MBq, respectively. The estimate for the urinary bladder wall is 0.57 mGy/MBq. Most other organs` estimates were around 0.02 mGy/MBq. The new marrow dose model presented in MIRDOSE 3 was used to look at the distribution of marrow dose in different bones, and to develop a dose-volume histogram. These data should be used as the basis for the radiation dosimetry of this agent.

Stabin, M.G. [Oak Ridge Inst. for Science and Education, TN (United States); Graham, M.C.; Scher, H.J. [Memorial Sloan-Kettering Cancer Center, NY (United States)

1995-05-01

243

Dosimetry models for radioimmunotherapy  

SciTech Connect

Tumor therapy using radiolabeled antibodies presents a challenging problem in absorbed dose determination. The purpose of this study is to evaluate the effect of tumor size on the absorbed dose distribution from beta-emitters when the radiolabeled antibody is not uniformly distributed throughout the tumor. Two theoretical dosimetry models are constructed, one for nonvascularized micrometastases and the other for vascularized tumors. All calculations assume no penetration of radionuclide into the tumor. These are compared to an even distribution of radionuclide throughout the tumor. In micrometastases of 1-mm diameter or less, emitters of low energy such as /sup 131/I give higher dose rates than emitters of higher energy because less energy is lost outside the target volume. However, even with /sup 131/I, a significant proportion of the energy is not absorbed in the tumor and, as a result, the concentration of radionuclide necessary for a therapeutic radiation dose becomes higher as the tumor diameter gets smaller. Because it may be impossible to achieve these concentrations in very small tumors (<0.5-mm diameter), alpha-emitters may be useful in combination with beta-emitters for therapy of micrometastatic disease. In vascularized tumors, higher energy emitters such as /sup 90/Y yield higher doses because of overlapping dose distributions from multiple vascular sources. This also produces a more even dose distribution across a tumor, even when there is poor penetration of the radiolabeled antibody. Thus tumor size, antibody penetration, and tumor vascularity all influence the choice of radionuclide and, depending on the circumstances, alpha-emitters, low-energy beta-emitters, high-energy beta-emitters, or some combination of the three may be most efficacious.

Langmuir, V.K.; Sutherland, R.M.

1988-11-01

244

Monte Carlo portal dosimetry  

SciTech Connect

This project developed a solution for verifying external photon beam radiotherapy. The solution is based on a calibration chain for deriving portal dose maps from acquired portal images, and a calculation framework for predicting portal dose maps. Quantitative comparison between acquired and predicted portal dose maps accomplishes both geometric (patient positioning with respect to the beam) and dosimetric (two-dimensional fluence distribution of the beam) verifications. A disagreement would indicate that beam delivery had not been according to plan. The solution addresses the clinical need for verifying radiotherapy both pretreatment (without the patient in the beam) and on treatment (with the patient in the beam). Medical linear accelerators mounted with electronic portal imaging devices (EPIDs) were used to acquire portal images. Two types of EPIDs were investigated: the amorphous silicon (a-Si) and the scanning liquid ion chamber (SLIC). The EGSnrc family of Monte Carlo codes were used to predict portal dose maps by computer simulation of radiation transport in the beam-phantom-EPID configuration. Monte Carlo simulations have been implemented on several levels of high throughput computing (HTC), including the grid, to reduce computation time. The solution has been tested across the entire clinical range of gantry angle, beam size (5 cmx5 cm to 20 cmx20 cm), and beam-patient and patient-EPID separations (4 to 38 cm). In these tests of known beam-phantom-EPID configurations, agreement between acquired and predicted portal dose profiles was consistently within 2% of the central axis value. This Monte Carlo portal dosimetry solution therefore achieved combined versatility, accuracy, and speed not readily achievable by other techniques.

Chin, P.W. [Department of Medical Physics, Velindre Cancer Centre, Velindre Road, Cardiff CF14 2TL (United Kingdom)]. E-mail: mary.chin@physics.org

2005-10-15

245

Dosimetry and physical treatment planning for iodine eye plaque therapy  

SciTech Connect

The dosimetry of eye plaques loaded with iodine-125 seeds (type 6702) was performed by means of computer calculations and measurements with thermoluminescent dosimeters (TLD). Measurements of the depth dose distribution (2-25.5 mm) along the transverse axis of a single seed were performed in water equivalent phantom material. The transverse axis attenuation and geometry factor F(r) was obtained by applying a least squares fit to the measured data. Based on the resulting radial dose function, a computer program was developed which calculates dose distributions within the eye for arbitrary loading and placement of the eye plaque. The computational results were verified by TLD measurements in an eye phantom.

Alberti, W.; Pothmann, B.; Tabor, P.; Muskalla, K.; Hermann, K.P.; Harder, D. (Alfried Krupp Krankenhaus, Essen, (F.R.Germany))

1991-05-01

246

Practical neutron dosimetry with superheated drops  

SciTech Connect

The Superheated Drop Detector (SDD) is a new kind of neutron detector based on the same principle as that of the bubble chamber, except the superheated material is in drop form suspended by a gel or polymer as first described by Apfel. Previously, we have developed a theoretical model for the prediction of the threshold neutron energy to nucleate bubbles in our superheated materials and a model for the calculation of the energy dependent response function of SDD. The results of the theoretical calculations agree with the experimental measurements reasonably well. We found the measured response curve of one of our SDDs follows the same trend as the ideal ICRP dose equivalent response curve within 40% for neutrons of energy above 100 keV and within a factor of 10 below 100 keV. Therefore, it is possible to make a rem-response Superheated Drop Detector. We have further calibrated our SDD with /sup 252/Cf neutron sources (both bare and D/sub 2/O moderated). The results are in reasonable agreement with our theoretical predictions, which proves that our model is valid not only for monoenergetic neutrons but also for neutrons from a radioactive source. The principles of operation of our detector, which can be used in neutron dosimetry, area monitoring, and neutron spectrometry, are discussed.

Apfel, R.E.; Lo, Y.C.

1989-01-01

247

DOSIMETRY BY SOLID STATE DEVICES  

Microsoft Academic Search

Any material which has a conveniently measurable parameter that varies ; as a function of the absorbed dose (or absorbed dose rate) deposited by ionizing ; radiation in the material can serve as the basis for a dosimetry system. A ; number of solid materials were investigated as dosimeters and found to be useful ; in various applications. The principal

Attix

1962-01-01

248

Breast dosimetry in clinical mammography  

Microsoft Academic Search

The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetric breast phantom series based on population anthropometric measurements can reliably predict the average glandular dose (AGD) imparted to the patient during a routine screening mammogram. In the study, AGD was calculated using entrance skin exposure and dose conversion factors based on fibroglandular content, compressed

Luis Alberto Do Rego Benevides

2005-01-01

249

Leak test fitting  

DOEpatents

A hollow fitting for use in gas spectrometry leak testing of conduit joints is divided into two generally symmetrical halves along the axis of the conduit. A clip may quickly and easily fasten and unfasten the halves around the conduit joint under test. Each end of the fitting is sealable with a yieldable material, such as a piece of foam rubber. An orifice is provided in a wall of the fitting for the insertion or detection of helium during testing. One half of the fitting also may be employed to test joints mounted against a surface.

Pickett, Patrick T. (Kettering, OH)

1981-01-01

250

An alternative method using microwave power saturate in fingernail/electron paramagnetic resonance dosimetry.  

PubMed

An alternative method for fingernail/electron paramagnetic resonance (EPR) dosimetry valid at low doses (0-3 Gy) is suggested in this paper. The method consisted of two steps. The first step involved dehydrating fingernail clippings to remove their water content by heating them at 70 °C for 72 h. As the water content in the fingernails decreased, the variability of the EPR signals improved. The second step involved measuring and fitting the EPR signals at successive microwave power levels. A newly derived value known as 'curvature', which was based on the conventional peak-to-peak amplitudes of the EPR signals, was applied for the dosimetry. This method could be used as an alternative method in cases of low-radiation exposure doses (<3 Gy) or where use of the conventional dosimetry method is not proper for a fingernail sample. PMID:24876339

Choi, Hoon; Park, Byeongryong; Choi, Muhyun; Lee, Byungil; Lee, Cheol Eui

2014-06-01

251

10 CFR 835.1304 - Nuclear accident dosimetry.  

Code of Federal Regulations, 2010 CFR

...2009-01-01 false Nuclear accident dosimetry. 835.1304 Section 835.1304...Situations § 835.1304 Nuclear accident dosimetry. (a) Installations possessing...possible, shall provide nuclear accident dosimetry for those individuals. (b)...

2009-01-01

252

Isopropanol-based polymer gel dosimeters for use with x-ray CT imaging  

NASA Astrophysics Data System (ADS)

We report on investigations aimed at increasing the dose response sensitivity and resolution in x-ray CT imaging of polymer gel dosimeters (PGD). We incorporate isopropanol as co-solvent into the gel formulation and show that this incorporation increases dose sensitivity and dose resolution of x-ray CT imaged gel dosimeters. These gels are reproducible in response and stable post-irradiation. We apply the system to a simple 1L gel test case where 2 separate irradiations are used to generate a dose response calibration curve. A third irradiation (3-field) is then calibrated and compared to treatment planning predictions. Results indicate that isopropanol-based PGDs are promising formulations for x-ray CT gel dosimetry and that this current system outperforms previous attempts at dose reconstruction using x-ray CT imaging of PGDs.

Jirasek, A.; Hilts, M.; McAuley, K.

2010-11-01

253

Fitness: A Lifestyle Value.  

ERIC Educational Resources Information Center

Factors contributing to the evolution of fitness are discussed, and some of the challenges these hold for those in the fields of food and nutrition are identified. This includes a discussion of basic concepts of nutrition and exercise, misconceptions of nutrition and exercise, and fitness instructors as nutrition educators. (Author/CT)

Hennyey, Donna J.

1985-01-01

254

Equality of Fitness Centers  

ERIC Educational Resources Information Center

The author, who has been a personal trainer for the past ten years, recently realized that all fitness centers are not equal. In February, he was able to participate in the grand opening of the Center for Independent Living of Central PA (CILCP), a fitness center that is designed to accommodate persons with disabilities living in the Central…

Swoyer, Jesse O.

2008-01-01

255

Fitness in Disguise  

ERIC Educational Resources Information Center

Physical fitness activities are often viewed as monotonous and tedious, so they fail to motivate students to become more physically active. This tedium could be relieved by using a "learning as play" strategy, widely used in other academic disciplines. This article describes how to incorporate fitness into a variety of games so that students do…

Williams, Neil F.; Germain, Jenna

2008-01-01

256

Fun & Fitness with Balloons  

ERIC Educational Resources Information Center

The urgency to improve fitness levels and decrease the rate of childhood obesity has been at the forefront of physical education philosophy and praxis. Few would dispute that school-age youth need to participate regularly in physical activities that enhance and maintain both skill- and health-related physical fitness. Regular physical activity…

Farrell, Anne; Faigenbaum, Avery; Radler, Tracy

2010-01-01

257

Fitness and Americans.  

ERIC Educational Resources Information Center

This document makes a number of observations about physical fitness in America. Among them are: (1) the symptoms of aging (fat accumulation, lowered basal metabolic rate, loss of muscular strength, reduction in motor fitness, reduction in work capacity, etc.) are not the result of disease but disuse; (2) society conditions the individual to…

Nordholm, Catherine R.

258

Facing Up To Fitness  

PubMed Central

Becoming fit means preparing ourselves to cope more effectively with environmental stresses. Exercise programs represent one approach to the fitness struggle. There are alternatives for those who find regular exercise unappealing - Yoga, biofeedback training or self hypnosis. At the moment these techniques appear unscientific and spooky - but they work.

Schatz, Douglas

1974-01-01

259

Ames Fitness Program.  

National Technical Information Service (NTIS)

The Ames Fitness Program services 5,000 civil servants and contractors working at Ames Research Center. A 3,000 square foot fitness center, equipped with cardiovascular machines, weight training machines, and free weight equipment is on site. Thirty exerc...

R. Pratt

1993-01-01

260

Uncertainty propagation: Curve fitting  

NSDL National Science Digital Library

Students will learn a sample-variance curve fitting method that can be used to determine whether a set of experimental data appears to have been generated by a model. This method is based on minimizing the reduced chi-squared value. This video includes a reminder to inspect normalized residuals before reporting fitted parameters.

Liao, David

261

Fit for Life.  

ERIC Educational Resources Information Center

Although the 1980's fitness craze is wearing off and adults are again becoming "couch potatoes," this trend does not justify expansion of high school compulsory physical education requirements. To encourage commitment to lifetime physical fitness, the Phoenix (Arizona) Union High School District offers students private showers, relaxed uniform…

Klahr, Gary Peter

1992-01-01

262

Results from 2010 Caliban Criticality Dosimetry Intercomparison  

SciTech Connect

The external dosimetry program participated in a criticality dosimetry intercomparison conducted at the Caliban facility in Valduc, France in 2010. Representatives from the dosimetry and instrumentation groups were present during testing which included irradiations of whole-body beta/gamma (HBGT) and neutron thermoluminescent dosimeters (TLDs), a fixed nuclear accident dosimeter (FNAD), electronic alarming dosimeters, and a humanoid phantom filled with reference man concentrations of sodium. This report reviews the testing procedures, preparations, irradiations, and presents results of the tests.

Veinot, K. G.

2011-10-12

263

Verification of a non-diffusing gel dosimeter  

NASA Astrophysics Data System (ADS)

An evaluation of the diffusion coefficient of a genipin-gelatin gel dosimeter was carried out by fitting an inverse square root function to image profile data. A comparison was made with a Fricke-gelatin-xylenol orange (FGX) gel dosimeter, in which the ions are known to diffuse. The diffusion coefficient for this FGX gel, consisting of 0.5 mM ferrous ammonium sulphate, 50 mM sulphuric acid, 0.15 mM xylenol orange and 3 % by weight gelatin was 0.70 ± 0.05 mm2 h-1 at 5 Gy. The genipin-gelatin gel consisted of 50 ?M genipin, 4 % by weight gelatin and 100 mM sulphuric acid. The fitted parameter that is proportional to the diffusion coefficient did not significantly change over time, demonstrating that this genipin-gelatin gel is a non-diffusing dosimeter.

Davies, J. B.; Bosi, S. G.; Baldock, C.

2013-06-01

264

Explicit dosimetry for photodynamic therapy: macroscopic singlet oxygen modeling  

PubMed Central

Singlet oxygen (1O2) is the major cytotoxic agent responsible for cell killing for type-II photodynamic therapy (PDT). An empirical four-parameter macroscopic model is proposed to calculate the “apparent reacted 1O2 concentration”, [1O2]rx, as a clinical PDT dosimetry quantity. This model incorporates light diffusion equation and a set of PDT kinetics equations, which can be applied in any clinical treatment geometry. We demonstrate that by introducing a fitting quantity “apparent singlet oxygen threshold concentration” [1O2]rx,sd, it is feasible to determine the model parameters by fitting the computed [1O2]rx to the Photofrin-mediated PDT-induced necrotic distance using interstitially-measured Photofrin concentration and optical properties within each mouse. After determining the model parameters and the [1O2]rx,sd, we expect to use this model as an explicit dosimetry to assess PDT treatment outcome for a specific photosensitizer in an in vivo environment. The results also provide evidence that the [1O2]rx, because it takes into account the oxygen consumption (or light fluence rate) effect, can be a better predictor of PDT outcome than the PDT dose defined as the energy absorbed by the photosensitizer, which is proportional to the product of photosensitizer concentration and light fluence.

Wang, Ken Kang-Hsin; Finlay, Jarod C.; Busch, Theresa M.; Hahn, Stephen M.; Zhu, Timothy C.

2011-01-01

265

GENII - The Hanford Environmental Dosimetry software package  

SciTech Connect

At the direction of the US Department of Energy, the Hanford Environmental Dosimetry Upgrade Project was undertaken by Pacific Northwest Laboratory to incorporate the internal dosimetry models recommended by the International Commission on Radiological Protection in updated versions of the environmental pathway analysis models used at Hanford. The resulting second generation of Hanford environmental dosimetry computer codes is compiled in the Hanford environmental dosimetry system (Generation II or GENII). The GENII system provides a state-of-the-art, technically peer-reviewed, documented set of programs for calculating radiation doses from radionuclides released to the environment.

Napier, B.A.; Peloquin, R.A.; Strenge, D.L.; Ramsdell, J.V. (Pacific Northwest Lab., Richland, WA (United States))

1990-01-01

266

Non-diffusing photochromic gel for optical computed tomography phantoms  

NASA Astrophysics Data System (ADS)

This study examines photochromic response in radiation sensitive hydrogels. Genipin, crosslinked, gelatin gel can support high resolution images because the chromophores do not diffuse. A low power, 633 nm He-Ne laser was used to write lines into the gels by a photobleaching reaction. Optical cone-beam computed tomography (CBCT) scans mapped the high resolution images in 3D with 0.25 mm voxel resolution. A straight line was written into a deformed gel and then readout in its relaxed, initial shape. The curved, photo-bleached line demonstrated deformable 3D dosimetry is possible with this system to the balloon edge. High resolution, photochromic images provide key information for characterizing optical CT scanners and 3D dosimeters. Many, ionizing radiation, dosimeter materials demonstrate either a photochromic or photothermal response, allowing this approach to be widely used in quantitative 3D scanning.

Jordan, K.

2013-06-01

267

Reactor dosimetry and RPV life management  

SciTech Connect

Reactor dosimetry (RD) is a tool that provides data for neutron fluence accumulated over the reactor pressure vessel (RPV) during the reactor operation. This information, however, is not sufficient for RPV lifetime assessment. The life management of RPV is a multidisciplinary task. To assess whether the RPV steel properties at the current stage (for actual accumulated neutron fluence) of reactor operation are still 'safe enough,' the dependence of material properties on the fluence must be known; this is a task for material science (MS). Moreover, the mechanical loading over the RPV during normal operation and accidence have to be known, as well, for evaluation, if the RPV material integrity in this loading condition and existing cracks is provided. The crack loading path in terms of stress intensity factor is carried out by structural analyses (SA). Pressure and temperature distribution over RPV used in these analyses are obtained from a thermal hydraulic (TH) calculation. The conjunction of RD and other disciplines in RPV integrity assessment is analyzed in accordance with the FFP (fitness for purpose) approach. It could help to improve the efficiency in multi-disciplinary tasks solutions. (authors)

Belousov, S.; Ilieva, K.; Mitev, M. [Inst. for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Tsarigradsko 72, 1784 Sofia (Bulgaria)

2011-07-01

268

Imaging technologies for radionuclide dosimetry  

NASA Astrophysics Data System (ADS)

Targeted radionuclide therapy is becoming an increasingly popular treatment modality as an alternative or as an adjunct to external beam radiotherapy and chemotherapy. The present method of dosimetry based on the MIRD system requires measurements of the concentration of the radionuclide in the target and risk tissues and the effective half-life of the radionuclide in these tissues. Radionuclide imaging techniques including planar scintigraphy, rectilinear scanning, single-photon emission computed tomography and positron emission tomography have all been used to provide data from which this information can be obtained. Additionally anatomical imaging has been used to aid these estimates. This paper reviews the application of imaging technology and methodology to radionuclide dosimetry.

Ott, R. J.

1996-10-01

269

A FITS Library Package  

NASA Astrophysics Data System (ADS)

The Flexible Image Transport System (FITS) Library Package for Linux, and Mac OS X consists of a collection of high and low level routines to carry out various useful functions associated with FITS image files. Besides the source code for the library, a demonstration program, "testfits", which illustrates the library's capabilities and shows how to code the subroutines into your own customized applications, is included. Source code of subroutines from the MIIPS Plot Package and subroutines to display images on Enhanced SAOimage are included as well. The source code and executables can be downloaded from www.chara.gsu.edu/ gudehus/fits_library_package.html.

Gudehus, Donald H.

2009-12-01

270

Luminescent radio frequency radiation dosimetry.  

PubMed

Thermoluminescent dosimetry has been the industry standard for ionizing radiation dosimetry because it is inexpensive, sensitive, and accurate. No such system exists for radio frequency radiation. This paper describes the state of the art of efforts toward developing such a system. Thermochemiluminescent (TCL) dosimetry, first reported in 1991, is a first step toward achieving this goal. However, it has had problems in the production of TCL materials and in conversion of the luminescent signal into specific absorption rate (SAR). The former problem has been solved by the development of a genetically engineered Escherichia coli bacterium (JM 109/plC20RNR1.1), described herein, that produces the TCL material in a fermentation process. The latter problem stems from the difficulty in determining the structure of the currently best TCL material diazoluminomelanin. A theoretical approach for the solution of this problem has been achieved by combining equations for delayed fluorescence, temperature determination by TCL, and the free energy equation for equilibrium reactions. It has led to an explanation for the stable display of steady-state energy disposition, illustrated by TCL, in phantoms without the expected disruption by thermal conduction or convection, at frequencies ranging from 2.06 GHz to 35 GHz. PMID:10334714

Kiel, J L; Alls, J L; Mason, P A; Erwin, D N

1999-01-01

271

Unified Theory for Gel Electrophoresis and Gel Filtration  

Microsoft Academic Search

Unified theory for gel electrophoresis and gel filtration: The behavior of macromolecules in gel filtration and gel electrophoresis may be predicted from Ogston's model for a random meshwork of fibers. This model has been generalized to apply to nonspherical molecules and to several gel types. The model provides equations for inter-relationships between mobility, partition coefficient, gel concentration, and molecular radius;

David Rodbard; Andreas Chrambach

1970-01-01

272

Integrating the Levels of Person-Environment Fit: The Roles of Vocational Fit and Group Fit  

ERIC Educational Resources Information Center

Previous research on fit has largely focused on person-organization (P-O) fit and person-job (P-J) fit. However, little research has examined the interplay of person-vocation (P-V) fit and person-group (P-G) fit with P-O fit and P-J fit in the same study. This article advances the fit literature by examining these relationships with data collected…

Vogel, Ryan M.; Feldman, Daniel C.

2009-01-01

273

The universal Higgs fit  

NASA Astrophysics Data System (ADS)

We perform a state-of-the-art global fit to all Higgs data. We synthesise them into a `universal' form, which allows to easily test any desired model. We apply the proposed methodology to extract from data the Higgs branching ratios, production cross sections, couplings and to analyse composite Higgs models, models with extra Higgs doublets, supersymmetry, extra particles in the loops, anomalous top couplings, and invisible Higgs decays into Dark Matter. Best fit regions lie around the Standard Model predictions and are well approximated by our `universal' fit. Latest data exclude the dilaton as an alternative to the Higgs, and disfavour fits with negative Yukawa couplings. We derive for the first time the SM Higgs boson mass from the measured rates, rather than from the peak positions, obtaining M h = 124 .4 ± 1 .6 GeV.

Giardino, Pier Paolo; Kannike, Kristjan; Masina, Isabella; Raidal, Martti; Strumia, Alessandro

2014-05-01

274

Exercise and Physical Fitness  

MedlinePLUS

... Increase your chances of living longer Fitting regular exercise into your daily schedule may seem difficult at ... fine. The key is to find the right exercise for you. It should be fun and should ...

275

Proper fitting shoes (image)  

MedlinePLUS

Shoes should be comfortable and fit well when you buy them. Never buy shoes that are tight, hoping they will stretch as ... damage, people with diabetes may not feel a shoe rubbing against the skin of their foot. Blisters ...

276

Glasses Fitting for Children  

MedlinePLUS

... and continued good fit for your child. What frame should be chosen? Size is very important. (Figure ... wear spectacles. Children should not be given adult frames to grow into. Some children wear straps to ...

277

Modelling of the inhomogeneous interior of polymer gels  

NASA Astrophysics Data System (ADS)

A simple model has been investigated to elucidate the mean squared displacement (MSD) of probe molecules in cross-linked polymer gels. In the model, we assume that numerous cavities distribute in the inhomogeneous interior of a gel, and probe molecules are confined within these cavities. The individual probe molecules trapped in a gel are treated as Brownian particles confined to a spherical harmonic potential. The harmonic potential is chosen to model the effective potential experienced by the probe particle in the cavity of a gel. Each field strength is corresponding to the characteristic of one type of effective cavity. Since the statistical distribution of different effective cavity sizes is unknown, several distribution functions are examined. Meanwhile, the calculated averaged MSDs are compared to the experimental data by Nisato et al (2000 Phys. Rev. E 61 2879). We find that the theoretical results of the MSD are sensitive to the shape of the distribution function. For low cross-linked gels, the best fit is obtained when the interior cavities of a gel follow a bimodal distribution. Such a result may be attributed to the presence of at least two distinct classes of cavity in gels. For high cross-linked gels, the cavities in the gel can be depicted by a single-modal uniform distribution function, suggesting that the range of cavity sizes becomes smaller. These results manifest the voids inside a gel, and the shape of distribution functions may provide the insight into the inhomogeneous interior of a gel.

Shew, Chwen-Yang; Iwaki, Takafumi

2006-04-01

278

The Langley Fitness Center  

NASA Technical Reports Server (NTRS)

NASA Langley recognizes the importance of healthy employees by committing itself to offering a complete fitness program. The scope of the program focuses on promoting overall health and wellness in an effort to reduce the risks of illness and disease and to increase productivity. This is accomplished through a comprehensive Health and Fitness Program offered to all NASA employees. Various aspects of the program are discussed.

1993-01-01

279

Fitting Galaxies on GPUs  

NASA Astrophysics Data System (ADS)

Structural parameters are normally extracted from observed galaxies by fitting analytic light profiles to the observations. Obtaining accurate fits to high-resolution images is a computationally expensive task, requiring many model evaluations and convolutions with the imaging point spread function. While these algorithms contain high degrees of parallelism, current implementations do not exploit this property. With ever-growing volumes of observational data, an inability to make use of advances in computing power can act as a constraint on scientific outcomes. This is the motivation behind our work, which aims to implement the model-fitting procedure on a graphics processing unit (GPU). We begin by analysing the algorithms involved in model evaluation with respect to their suitability for modern many-core computing architectures like GPUs, finding them to be well-placed to take advantage of the high memory bandwidth offered by this hardware. Following our analysis, we briefly describe a preliminary implementation of the model fitting procedure using freely-available GPU libraries. Early results suggest a speed-up of around 10× over a CPU implementation. We discuss the opportunities such a speed-up could provide, including the ability to use more computationally expensive but better-performing fitting routines to increase the quality and robustness of fits.

Barsdell, B. R.; Barnes, D. G.; Fluke, C. J.

2011-07-01

280

Rules, culture, and fitness  

PubMed Central

Behavior analysis risks intellectual isolation unless it integrates its explanations with evolutionary theory. Rule-governed behavior is an example of a topic that requires an evolutionary perspective for a full understanding. A rule may be defined as a verbal discriminative stimulus produced by the behavior of a speaker under the stimulus control of a long-term contingency between the behavior and fitness. As a discriminative stimulus, the rule strengthens listener behavior that is reinforced in the short run by socially mediated contingencies, but which also enters into the long-term contingency that enhances the listener's fitness. The long-term contingency constitutes the global context for the speaker's giving the rule. When a rule is said to be “internalized,” the listener's behavior has switched from short- to long-term control. The fitness-enhancing consequences of long-term contingencies are health, resources, relationships, or reproduction. This view ties rules both to evolutionary theory and to culture. Stating a rule is a cultural practice. The practice strengthens, with short-term reinforcement, behavior that usually enhances fitness in the long run. The practice evolves because of its effect on fitness. The standard definition of a rule as a verbal statement that points to a contingency fails to distinguish between a rule and a bargain (“If you'll do X, then I'll do Y”), which signifies only a single short-term contingency that provides mutual reinforcement for speaker and listener. In contrast, the giving and following of a rule (“Dress warmly; it's cold outside”) can be understood only by reference also to a contingency providing long-term enhancement of the listener's fitness or the fitness of the listener's genes. Such a perspective may change the way both behavior analysts and evolutionary biologists think about rule-governed behavior. ImagesFigure 1

Baum, William M.

1995-01-01

281

Optimization of inclusive fitness.  

PubMed

The first fully explicit argument is given that broadly supports a widespread belief among whole-organism biologists that natural selection tends to lead to organisms acting as if maximizing their inclusive fitness. The use of optimization programs permits a clear statement of what this belief should be understood to mean, in contradistinction to the common mathematical presumption that it should be formalized as some kind of Lyapunov or even potential function. The argument reveals new details and uncovers latent assumptions. A very general genetic architecture is allowed, and there is arbitrary uncertainty. However, frequency dependence of fitnesses is not permitted. The logic of inclusive fitness immediately draws together various kinds of intra-genomic conflict, and the concept of 'p-family' is introduced. Inclusive fitness is thus incorporated into the formal Darwinism project, which aims to link the mathematics of motion (difference and differential equations) used to describe gene frequency trajectories with the mathematics of optimization used to describe purpose and design. Important questions remain to be answered in the fundamental theory of inclusive fitness. PMID:16046225

Grafen, Alan

2006-02-01

282

Ames Fitness Program  

NASA Technical Reports Server (NTRS)

The Ames Fitness Program services 5,000 civil servants and contractors working at Ames Research Center. A 3,000 square foot fitness center, equipped with cardiovascular machines, weight training machines, and free weight equipment is on site. Thirty exercise classes are held each week at the Center. A weight loss program is offered, including individual exercise prescriptions, fitness testing, and organized monthly runs. The Fitness Center is staffed by one full-time program coordinator and 15 hours per week of part-time help. Membership is available to all employees at Ames at no charge, and there are no fees for participation in any of the program activities. Prior to using the Center, employees must obtain a physical examination and complete a membership package. Funding for the Ames Fitness Program was in jeopardy in December 1992; however, the employees circulated a petition in support of the program and collected more than 1500 signatures in only three days. Funding has been approved through October 1993.

Pratt, Randy

1993-01-01

283

Status of neutron dosimetry cross sections  

SciTech Connect

Several new cross section libraries, such as ENDF/B-VI(release 2), IRDF-90,JEF-2.2, and JENDL-3 Dosimetry, have recently been made available to the dosimetry community. the Sandia National Laboratories (SNL) Radiation Metrology Laboratory (RML) has worked with these libraries since pre-release versions were available. this paper summarizes the results of the intercomparison and testing of dosimetry cross sections. As a result of this analysis, a compendium of the best dosimetry cross sections was assembled from the available libraries for use within the SNL RML. this library, referred to as the SNLRML Library, contains 66 general dosimetry sensors and 3 special dosimeters unique to the RML sensor inventory. The SNLRML cross sections have been put into a format compatible with commonly used spectrum determination codes.

Griffin, P.J.; Kelly, J.G.

1992-12-31

284

Film dosimetry of megavoltage photon beams: a practical method of isodensity-to-isodose curve conversion  

Microsoft Academic Search

The central problems of photon beam film dosimetry are the dependence of film response upon photon energy, processing conditions, and film plane orientation. Researchers have overcome these problems by accurately fitting the depth-dependent sensitometric curve of Kodak XV-2 film to the equation OD(D,d) = OHs(1 - exp (- ..cap alpha.. 0(1 + ..beta..(d-dm))D)) where OD(D,d) is the optical density for

Jeffrey F. Williamson; F. M. Khan; S. C. Sharma

1981-01-01

285

Monte Carlo Simulation of MAGIC-f gel for Radiotherapy using PENELOPE  

NASA Astrophysics Data System (ADS)

MAGIC-f gel has been shown as a suitable dosimeter for different techniques in radiotherapy due to its characteristics of water equivalence (effective atomic number of 7.41) and a spatial resolution better than 1mm. One way to predict the gel results is the use of simulations through PENELOPE Monte Carlo code. This simulation code was used to simulate the MAGIC-f gel and its use for dosimetry in conventional and conformal radiotherapy. The results obtained from the simulation were compared with experimental values. Comparisons from simulation and experimental values show mean differences of 2.88 % and 3.75% for conventional and conformal, respectively. This study shows that PENELOPE code can be simulate the components of the MAGIC- f gel to study and predict the gel response.

Alva, M.; Pianoschi, T.; Marques, T.; Santanna M, M.; Baffa, O.; Nicolucci, P.

2010-11-01

286

Water equivalence of NIPAM based polymer gel dosimeters with enhanced sensitivity for x-ray CT  

NASA Astrophysics Data System (ADS)

Two new formulations of N-isopropylacrylamide (NIPAM) based three dimensional (3D) gel dosimeters have recently been developed with improved sensitivity to x-ray CT readout, one without any co-solvent and the other one with isopropanol co-solvent. The water equivalence of the NIPAM gel dosimeters was investigated using different methods to calculate their radiological properties including: density, electron density, number of electrons per grams, effective atomic number, photon interaction probabilities, mass attenuation and energy absorption coefficients, electron collisional, radiative and total mass stopping powers and electron mass scattering power. Monte Carlo modelling was also used to compare the dose response of these gel dosimeters with water for kilovoltage and megavoltage x-ray beams and for megavoltage electron beams. We found that the density and electron density of the co-solvent free gel dosimeter are more water equivalent with less than a 2.6% difference compared to a 5.7% difference for the isopropanol gel dosimeter. Both the co-solvent free and isopropanol solvent gel dosimeters have lower effective atomic numbers than water, differing by 2.2% and 6.5%, respectively. As a result, their photoelectric absorption interaction probabilities are up to 6% and 19% different from water, respectively. Compton scattering and pair production interaction probabilities of NIPAM gel with isopropanol differ by up to 10% from water while for the co-solvent free gel, the differences are 3%. Mass attenuation and energy absorption coefficients of the co-solvent free gel dosimeter and the isopropanol gel dosimeter are up to 7% and 19% lower than water, respectively. Collisional and total mass stopping powers of both gel dosimeters differ by less than 2% from those of water. The dose response of the co-solvent free gel dosimeter is water equivalent (with <1% discrepancy) for dosimetry of x-rays with energies <100 keV while the discrepancy increases (up to 5%) for the isopropanol gel dosimeter over the same energy range. For x-ray beams over the energy range 180 keV-18 MV, both gel dosimeters have less than 2% discrepancy with water. For megavoltage electron beams, the dose differences with water reach 7% and 14% for the co-solvent free gel dosimeter and the isopropanol gel dosimeter, respectively. Our results demonstrate that for x-ray beam dosimetry with photon energies higher than 100 keV and megavoltage electron beams, correction factors are needed for both NIPAM gels to be used as water equivalent dosimeters.

Gorjiara, Tina; Hill, Robin; Bosi, Stephen; Kuncic, Zdenka; Baldock, Clive

2013-10-01

287

Quantum Data Fitting  

NASA Astrophysics Data System (ADS)

We provide a new quantum algorithm that efficiently determines the quality of a least-squares fit over an exponentially large data set by building upon an algorithm for solving systems of linear equations efficiently (Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)). In many cases, our algorithm can also efficiently find a concise function that approximates the data to be fitted and bound the approximation error. In cases where the input data is a pure quantum state, the algorithm can be used to provide an efficient parametric estimation of the quantum state and therefore can be applied as an alternative to full quantum state tomography given a fault tolerant quantum computer.

Wiebe, Nathan

2013-03-01

288

Personal Fitness Plan  

NSDL National Science Digital Library

This activity will help you create a personal fitness plan that is right for you. Maintaining a physically active lifestyle can help you feel your best and prevent the onset of certain diseases. At the conclusion of this activity, you will: Understand the health benefits of physical activity. Be able to describe three types of exercise. Create a custom plan based on your own preferences. The first step in creating your personal fitness plan is to understand why one is important to have and to maintain. Read ...

Cross, Mrs.

2005-11-26

289

Line of Best Fit  

NSDL National Science Digital Library

When data is displayed with a scatter plot, it is often useful to attempt to represent that data with the equation of a straight line for purposes of predicting values that may not be displayed on the plot. Such a straight line is called the "line of best fit." In this activity, students discover the relationship between the fat grams and the total calories in fast food by graphing the given data, estimate the line of best fit using a strand of spaghetti, calculate the slope of that line, and translate it into an equation. Then, they use that equation to predict information not originally included in the scatter plot.

Roberts, Donna

290

Solid-State Personal Dosimetry  

NASA Technical Reports Server (NTRS)

This document is a web site page, and a data sheet about Personal protection (i.e., space suits) presented to the Radiation and Micrometeoroid Mitigation Technology Focus Group meeting. The website describes the work of the PI to improve solid state personal radiation dosimetry. The data sheet presents work on the active personal radiation detection system that is to provide real-time local radiation exposure information during EVA. Should undue exposure occur, knowledge of the dynamic intensity conditions during the exposure will allow more precise diagnostic assessment of the potential health risk to the exposed individual.

Wrbanek, John D.; Fralick, Gustave C.; Wrbanek, Susan Y.

2005-01-01

291

Water Fit to Drink.  

ERIC Educational Resources Information Center

The major objective of this module is to help students understand how water from a source such as a lake is treated to make it fit to drink. The module, consisting of five major activities and a test, is patterned after Individualized Science Instructional System (ISIS) modules. The first activity (Planning) consists of a brief introduction and a…

Donovan, Edward P.

292

Teaching Aerobic Fitness Concepts.  

ERIC Educational Resources Information Center

Discusses how to teach aerobic fitness concepts to elementary students. Some of the K-2 activities include location, size, and purpose of the heart and lungs; the exercise pulse; respiration rate; and activities to measure aerobic endurance. Some of the 3-6 activities include: definition of aerobic endurance; heart disease risk factors;…

Sander, Allan N.; Ratliffe, Tom

2002-01-01

293

Wheel of Fitness  

NSDL National Science Digital Library

In this fun activity for any size group, early elementary learners complete physical challenges while playing a game. Learners add new challenges to the "wheel of fitness" that they want to try. During this activity, learners practice their counting skills and discover new ways to get moving. This lesson plan includes extensions, questions to ask learners, and a sample wheel.

Houston, Children'S M.

2007-01-01

294

Talking Sport and Fitness  

ERIC Educational Resources Information Center

For some time the Association for Science Education (ASE) has been aware that it would be useful to have some resources available to get children talking and thinking about issues related to health, sport and fitness. Some of the questions about pulse, breathing rate and so on are pretty obvious to everyone, and there is a risk of these being…

Dixon-Watmough, Rebecca; Keogh, Brenda; Naylor, Stuart

2012-01-01

295

Manual for physical fitness  

NASA Technical Reports Server (NTRS)

Training manual used for preflight conditioning of NASA astronauts is written for audience with diverse backgrounds and interests. It suggests programs for various levels of fitness, including sample starter programs, safe progression schedules, and stretching exercises. Related information on equipment needs, environmental coonsiderations, and precautions can help readers design safe and effective running programs.

Coleman, A. E.

1981-01-01

296

Directory of Fitness Certifications.  

ERIC Educational Resources Information Center

This article discusses the need for certification of fitness instructors in the aerobic dance/dance-exercise industry and presents results of a survey of 18 agencies that certify instructors. Survey data has been compiled and published. An excerpt is included which lists organizations, training, certification and renewal procedures, publications,…

Parks, Janet B.

1990-01-01

297

Measuring Your Fitness Progress  

MedlinePLUS

... you’re becoming more fit, such as increased energy, greater ability to perform daily tasks, or even an improved outlook on life. VISIT www.nia.nih.gov/Go4Life l Read more about increasing your activity level. l Print useful tools. l Order a free exercise guide or DVD. l Share your exercise ...

298

ACSM Fit Society Page  

MedlinePLUS

... Aging 2010 -- Weight Loss & Weight Management 2010 -- Fitness Assessment & Injury Prevention 2009 -- Strength Training 2009 -- Menopause 2009 -- Preparing for Fall Sports 2009 -- Cancer and Exercise 2008 -- Group Exercise 2008 -- Alternative Medicine & Mind/Body Exercise 2008 -- The Heart 2008 -- Managing Chronic Disease ...

299

Curve Fit Challenge  

ERIC Educational Resources Information Center

Graphic tips for using the Geometer's Sketchpad (GSP) are described. The methods to import an image into GSP, define a coordinate system, plot points and curve fit the function using a graphical calculator are demonstrated where the graphic features of GSP allow teachers to expand the use of the technology application beyond the classroom.

Harper, Suzanne R.; Driskell, Shannon

2005-01-01

300

Fit for Play?  

ERIC Educational Resources Information Center

This article reports on the findings of a small-scale investigation into the views of children on potential changes to the playground in a large primary school. As a parent, midday supervisor and member of the school Grounds Development Committee I was interested in how views gathered to underpin change to the playground of one school might fit…

Smith, Angela

2007-01-01

301

The Right Fit  

NSDL National Science Digital Library

In this math activity, learners trace their hands and estimate the number of beans that can fit into their hand tracings. Then, learners glue the beans to the tracing to test out their estimations. This activity guide contains a material list, sample questions to ask, literary connections, extensions, and alignment to local and national standards.

Houston, Children'S M.

2014-04-07

302

Quenching correction for volumetric scintillation dosimetry of proton beams  

PubMed Central

Purpose Volumetric scintillation dosimetry has the potential to provide fast, high-resolution, three-dimensional radiation dosimetry. However, scintillators exhibit a nonlinear response at the high linear energy transfer (LET) values characteristic of proton Bragg peaks. The purpose of this study was to develop a quenching correction method for volumetric scintillation dosimetry of proton beams. Methods Scintillation light from a miniature liquid scintillator detector was measured along the central axis of a 161.6-MeV proton pencil beam. Three-dimensional dose and LET distributions were calculated for 85.6-, 100.9-, 144.9-, and 161.6-MeV beams using a validated Monte Carlo model. LET values were also calculated using an analytical formula. A least-squares fit to the data established the empirical parameters of a quenching correction model. The light distribution in a tank of liquid scintillator was measured with a CCD camera at all four beam energies. The quenching model and LET data were used to correct the measured light distribution. Results The calculated and measured Bragg peak heights agreed within ±3% for all energies except 85.6 MeV, where the agreement was within ±10%. The quality of the quenching correction was poorer for sharp low-energy Bragg peaks because of blurring and detector size effects. The corrections performed using analytical LET values resulted in doses within 1% of those obtained using Monte Carlo LET values. Conclusion The proposed method can correct for quenching with sufficient accuracy for dosimetric purposes. The required LET values may be computed effectively using Monte Carlo or analytical methods. Future detectors should improve blurring correction methods and optimize the pixel size to improve accuracy for low-energy Bragg peaks.

Robertson, Daniel; Mirkovic, Dragan; Sahoo, Narayan; Beddar, Sam

2013-01-01

303

Quenching correction for volumetric scintillation dosimetry of proton beams.  

PubMed

Volumetric scintillation dosimetry has the potential to provide fast, high-resolution, three-dimensional radiation dosimetry. However, scintillators exhibit a nonlinear response at the high linear energy transfer (LET) values characteristic of proton Bragg peaks. The purpose of this study was to develop a quenching correction method for volumetric scintillation dosimetry of proton beams. Scintillation light from a miniature liquid scintillator detector was measured along the central axis of a 161.6 MeV proton pencil beam. Three-dimensional dose and LET distributions were calculated for 85.6, 100.9, 144.9 and 161.6 MeV beams using a validated Monte Carlo model. LET values were also calculated using an analytical formula. A least-squares fit to the data established the empirical parameters of a quenching correction model. The light distribution in a tank of liquid scintillator was measured with a CCD camera at all four beam energies. The quenching model and LET data were used to correct the measured light distribution. The calculated and measured Bragg peak heights agreed within ±3% for all energies except 85.6 MeV, where the agreement was within ±10%. The quality of the quenching correction was poorer for sharp low-energy Bragg peaks because of blurring and detector size effects. The corrections performed using analytical LET values resulted in doses within 1% of those obtained using Monte Carlo LET values. The proposed method can correct for quenching with sufficient accuracy for dosimetric purposes. The required LET values may be computed effectively using Monte Carlo or analytical methods. Future detectors should improve blurring correction methods and optimize the pixel size to improve accuracy for low-energy Bragg peaks. PMID:23257200

Robertson, Daniel; Mirkovic, Dragan; Sahoo, Narayan; Beddar, Sam

2013-01-21

304

Measurement of particle size in polymer gel dosimeters using spectrophotometry  

NASA Astrophysics Data System (ADS)

Polymer gel dosimeters have proven to be useful for three-dimensional radiation dosimetry in clinical radiation therapy. However, more study and development work is needed to quantify and further understand the dose response mechanism, with the goal of improving the dosimeters. In this work we seek to determine the diameter of the polymer particles formed upon irradiation, for a range of irradiation dose rates. It is expected that this information will be used to further understand the actual formation of polymer in the gelatin matrix, and how it affects the relaxation of water in the dosimeter as measured with magnetic resonance imaging or optical methods.

Whitney, Heather M.; Gore, John C.

2006-12-01

305

In vitro dosimetry of agglomerates  

NASA Astrophysics Data System (ADS)

Agglomeration of nanoparticles in biological fluids is a pervasive phenomenon that leads to difficulty in the interpretation of results from in vitro exposure, primarily due to differing particokinetics of agglomerates to nanoparticles. Therefore, well-defined small agglomerates were designed that possessed different particokinetic profiles, and their cellular uptake was compared to a computational model of dosimetry. The approach used here paves the way for a better understanding of the impact of agglomeration on the nanoparticle-cell interaction.Agglomeration of nanoparticles in biological fluids is a pervasive phenomenon that leads to difficulty in the interpretation of results from in vitro exposure, primarily due to differing particokinetics of agglomerates to nanoparticles. Therefore, well-defined small agglomerates were designed that possessed different particokinetic profiles, and their cellular uptake was compared to a computational model of dosimetry. The approach used here paves the way for a better understanding of the impact of agglomeration on the nanoparticle-cell interaction. Electronic supplementary information (ESI) available: ITC data for tiopronin/Au-NP interactions, agglomeration kinetics at different pHs for tiopronin-coated Au-NPs, UV-Vis spectra in water, PBS and DMEM and temporal correlation functions for single Au-NPs and corresponding agglomerates, calculation of diffusion and sedimentation parameters, modelling of relative cell uptake based on the ISDD model and cytotoxicity of single Au-NPs and their agglomerates, and synthesis and cell uptake of large spherical Au-NPs. See DOI: 10.1039/c4nr00460d

Hirsch, V.; Kinnear, C.; Rodriguez-Lorenzo, L.; Monnier, C. A.; Rothen-Rutishauser, B.; Balog, S.; Petri-Fink, A.

2014-06-01

306

Path forward for dosimetry cross sections  

SciTech Connect

In the 1980's the dosimetry community embraced the need for a high fidelity quantification of uncertainty in nuclear data used for dosimetry applications. This led to the adoption of energy-dependent covariance matrices as the accepted manner of quantifying the uncertainty data. The trend for the dosimetry community to require high fidelity treatment of uncertainty estimates has continued to the current time where requirements on nuclear data are codified in standards such as ASTM E 1018. This paper surveys the current state of the dosimetry cross sections and investigates the quality of the current dosimetry cross section evaluations by examining calculated-to-experimental ratios in neutron benchmark fields. In recent years more nuclear-related technical areas are placing an emphasis on uncertainty quantification. With the availability of model-based cross sections and covariance matrices produced by nuclear data codes, some nuclear-related communities are considering the role these covariance matrices should play. While funding within the dosimetry community for cross section evaluations has been very meager, other areas, such as the solar-related astrophysics community and the US Nuclear Criticality Safety Program, have been supporting research in the area of neutron cross sections. The Cross Section Evaluation Working Group (CSEWG) is responsible for the creation and maintenance of the ENDF/B library which has been the mainstay for the reactor dosimetry community. Given the new trends in cross section evaluations, this paper explores the path forward for the US nuclear reactor dosimetry community and its use of the ENDF/B cross-sections. The major concern is maintenance of the sufficiency and accuracy of the uncertainty estimate when used for dosimetry applications. The two major areas of deficiency in the proposed ENDF/B approach are: 1) the use of unrelated covariance matrices in ENDF/B evaluations and 2) the lack of 'due consideration' of experimental data in the evaluation. (authors)

Griffin, P.J. [Sandia National Laboratories, Albuquerque, NM 87185-1146 (United States); Peters, C.D. [Sandia Staffing Alliance, Albuquerque, NM 87110 (United States)

2011-07-01

307

Fitting PAC spectra with stochastic models: PolyPacFit  

NASA Astrophysics Data System (ADS)

PolyPacFit is an advanced fitting program for time-differential perturbed angular correlation (PAC) spectroscopy. It incorporates stochastic models and provides robust options for customization of fits. Notable features of the program include platform independence and support for (1) fits to stochastic models of hyperfine interactions, (2) user-defined constraints among model parameters, (3) fits to multiple spectra simultaneously, and (4) any spin nuclear probe.

Zacate, M. O.; Evenson, W. E.; Newhouse, R.; Collins, G. S.

2010-04-01

308

FIT testing: an overview.  

PubMed

Colorectal cancer (CRC) is a common, but preventable, disease and is the second most common cause of cancer-related deaths in the U.S. CRC screening has proven effective at reducing both the incidence and mortality of this disease, using any of a number of screening tests available. The test options range from the least invasive and least expensive to more invasive and costly options. Fecal occult blood testing is the oldest, least expensive, and least invasive of these options and has evolved from the poorly sensitive standard guaiac test to the newer and diagnostically superior fecal immunochemical test (FIT) for hemoglobin. This article explores the evolutionary history of fecal occult blood testing, examines test performance characteristics among different FOBTs, and evaluates the role of the FIT in programmatic CRC screening. PMID:24218070

Day, Lukejohn W; Bhuket, Taft; Allison, James

2013-11-01

309

Global Fits for PDFs  

SciTech Connect

Constraining the d PDF at large values of x has traditionally relied, in part, on the use of deeply inelastic lepton deuterium scattering data. In order to utilize such data, one must include nuclear corrections which account for Fermi motion, binding, and off-shell effects. The impact of these corrections in the context of a global fit are examined. The uncertainties due to these nuclear effects are large.

Owens, J. F. [Florida State University, Tallahassee, Florida 32306-4350 (United States); Accardi, A.; Keppel, C. E. [Hampton University, Hampton, Virginia 23668 (United States); Christy, E.; Melnitchouk, W. [Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606 (United States); Morfin, J. G. [Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States)

2011-09-21

310

QCD FITS to Diffraction  

NASA Astrophysics Data System (ADS)

The most recent H1 and ZEUS data for diffractive structure functions are analyzed under three different theoretical approaches. This includes the Pomeron Structure Function (PSF) framework, Bartels-Ellis-Kowalski-Wüsthoff (BEKW) color dipole approach and the Golec-Biernat-Wüsthoff (GBW) saturation model. The models are shown to successfully fit the set of combined data. Conceptual differences between the models are discussed and, as an example, the prediction for the longitudinal diffractive structure function is presented.

Sapeta, S.

2007-11-01

311

Fitting the correlation function.  

PubMed

The whole correlation function of the intensity of scattered light is usually determined from a single realization of the photocurrent. As a result, the values of the correlation function at different delay times are not statistically independent. A standard least-squares fitting procedure is not optimal for an analysis of such data. However, the benefits of mathematically rigorous but highly nonlinear and less stable methods are not known. We consider the test case of a Gaussian signal with a single-exponential correlation function without shot noise. In this case the fitting procedure, which is based on the maximum-likelihood principle for the observed signal, permits an analytical solution. We demonstrate that such a rigorous statistical analysis produces an approximately two times more-accurate result for the relaxation time than does the standard least-squares fit. This gain, however, is greatly reduced by the presence of shot noise, which introduces additional uncorrelated errors into the values of the correlation function. PMID:18360444

Lomakin, A

2001-08-20

312

Fitting the Correlation Function  

NASA Astrophysics Data System (ADS)

The whole correlation function of the intensity of scattered light is usually determined from a single realization of the photocurrent. As a result, the values of the correlation function at different delay times are not statistically independent. A standard least-squares fitting procedure is not optimal for an analysis of such data. However, the benefits of mathematically rigorous but highly nonlinear and less stable methods are not known. We consider the test case of a Gaussian signal with a single-exponential correlation function without shot noise. In this case the fitting procedure, which is based on the maximum-likelihood principle for the observed signal, permits an analytical solution. We demonstrate that such a rigorous statistical analysis produces an approximately two times more-accurate result for the relaxation time than does the standard least-squares fit. This gain, however, is greatly reduced by the presence of shot noise, which introduces additional uncorrelated errors into the values of the correlation function.

Lomakin, Aleksey

2001-08-01

313

Fitting the phenomenological MSSM  

SciTech Connect

We perform a global Bayesian fit of the phenomenological minimal supersymmetric standard model (pMSSM) to current indirect collider and dark matter data. The pMSSM contains the most relevant 25 weak-scale MSSM parameters, which are simultaneously fit using 'nested sampling' Monte Carlo techniques in more than 15 years of CPU time. We calculate the Bayesian evidence for the pMSSM and constrain its parameters and observables in the context of two widely different, but reasonable, priors to determine which inferences are robust. We make inferences about sparticle masses, the sign of the {mu} parameter, the amount of fine-tuning, dark matter properties, and the prospects for direct dark matter detection without assuming a restrictive high-scale supersymmetry breaking model. We find the inferred lightest CP-even Higgs boson mass as an example of an approximately prior-independent observable. This analysis constitutes the first statistically convergent pMSSM global fit to all current data.

AbdusSalam, Shehu S.; Allanach, Benjamin C. [DAMTP, Center for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Quevedo, Fernando [DAMTP, Center for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); CERN, PH-TH, CH-1211, Geneva 23 (Switzerland); Feroz, Farhan; Hobson, Mike [Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

2010-05-01

314

International intercomparison for criticality dosimetry: the case of biological dosimetry.  

PubMed

The Institute of Radiation Protection and Nuclear Safety (IRSN) organized a biological dosimetry international intercomparison with the purpose of comparing (i) dicentrics yield produced in human lymphocytes; (ii) the gamma and neutron dose estimate according to the corresponding laboratory calibration curve. The experimental reactor SILENE was used with different configurations: bare source 4 Gy, lead shield 1 and 2 Gy and a 60Co source 2 Gy. An increasing variation of dicentric yield per cell was observed between participants when there were more damages in the samples. Doses were derived from the observed dicentric rates according to the dose-effect relationship provided by each laboratory. Differences in dicentric rate values are more important than those in the corresponding dose values. The doses obtained by the participants were found to be in agreement with the given physical dose within 20%. The evaluation of the respective gamma and neutron dose was achieved only by four laboratories, with some small variations among them. PMID:15353693

Roy, L; Buard, V; Delbos, M; Durand, V; Paillole, N; Grégoire, E; Voisin, P

2004-01-01

315

Three-Dimensional Dose Verification for Intensity-Modulated Radiation Therapy in the Radiological Physics Centre Head-and-Neck Phantom Using Optical Computed Tomography Scans of Ferrous Xylenol–Orange Gel Dosimeters  

Microsoft Academic Search

Purpose: To extend the Radiological Physics Centre (RPC) intensity-modulated radiation therapy dose verification protocol to three dimensions using optical computed tomography (CT) scans of ferrous xylenol-orange (FX) gels. Methods and Materials: The dosimetry insert in the RPC head-and-neck phantom was replaced with an FX cylindrical gel dosimeter. Two gels were calibrated, independently irradiated with 6-MV X-ray beams and scanned using

Steven Babic; Jerry Battista; Kevin Jordan

2008-01-01

316

Health/Fitness Instructor's Handbook.  

ERIC Educational Resources Information Center

This book identifies the components of physical fitness that are related to positive health as distinct from the simple performance of specific motor tasks. The positive health concept is expanded to further clarify the relationship of physical fitness to total fitness. The disciplinary knowledge base that is essential for fitness professionals is…

Howley, Edward T.; Franks, B. Don

317

Computational methods in radionuclide dosimetry  

NASA Astrophysics Data System (ADS)

The various approaches in radionuclide dosimetry depend on the size and spatial relation of the sources and targets considered in conjunction with the emission range of the radionuclide used. We present some of the frequently reported computational techniques on the basis of the source/target size. For whole organs, or for sources or targets bigger than some centimetres, the acknowledged standard was introduced 30 years ago by the MIRD committee and is still being updated. That approach, based on the absorbed fraction concept, is mainly used for radioprotection purposes but has been updated to take into account the dosimetric challenge raised by therapeutic use of vectored radiopharmaceuticals. At this level, the most important computational effort is in the field of photon dosimetry. On the millimetre scale, photons can often be disregarded, and or electron dosimetry is generally reported. Heterogeneities at this level are mainly above the cell level, involving groups of cell or a part of an organ. The dose distribution pattern is often calculated by generalizing a point source dose distribution, but direct calculation by Monte Carlo techniques is also frequently reported because it allows media of inhomogeneous density to be considered. At the cell level, and electron (low-range or Auger) are the predominant emissions examined. Heterogeneities in the dose distribution are taken into account, mainly to determine the mean dose at the nucleus. At the DNA level, Auger electrons or -particles are considered from a microdosimetric point of view. These studies are often connected with radiobiological experiments on radionuclide toxicity.

Bardiès, M.; Myers, M. J.

1996-10-01

318

Technical Basis for Internal Dosimetry at Hanford.  

National Technical Information Service (NTIS)

The Hanford Internal Dosimetry Program, administered by Pacific Northwest Laboratory for the US Department of Energy, provides routine bioassay monitoring for employees who are potentially exposed to radionuclides in the workplace. This report presents th...

M. J. Sula E. H. Carbaugh D. E. Bihl

1989-01-01

319

Radon Progeny Dosimetry in the Rat Lung.  

National Technical Information Service (NTIS)

Deposition, mucociliary clearance, and dosimetry for the inhalation of radon progeny in the rat lung have been simulated for a variety of inhalation conditions. Computations indicate that the exposure-dose conversion factor for the rat lung is approximate...

W. Hofmann M. G. Menache R. C. Graham

1993-01-01

320

VVER-440 dosimetry and neutron spectrum benchmark.  

National Technical Information Service (NTIS)

Light Water Reactor (LWR) benchmark experiments performed in the United States under the Surveillance Dosimetry Improvement Program (SDIP), in general, reported measured reaction rates and not neutron flux spectrum. The VVER-440 benchmark experiments, usi...

E. Sajot F. B. K. Kam

1993-01-01

321

A genipin-gelatin gel dosimeter for radiation processing  

NASA Astrophysics Data System (ADS)

Genipin, a fruit extract from Gardenia jasminoides Ellis, forms cross-links in solutions of gelatin, to form a blue hydrogel that bleaches quantitatively upon irradiation and the colour change can be measured with a spectrophotometer. With the addition of sulphuric acid this dosimeter is sufficiently sensitive for quality assurance of radiotherapy level dosimetry. Without sulphuric acid the gel has a reduced sensitivity and responds linearly with dose between 100 and 1000 Gy, making it potentially useful as a dosimeter for radiation processing applications such as the phytosanitary irradiation treatment of food. We investigated the dose response characteristics of this new formulation and found that the darker gels are more sensitive to dose and have a reduced uncertainty.

Davies, J. B.; Bosi, S. G.; Baldock, C.

2012-08-01

322

The Radiofrequency Radiation Dosimetry Handbook: reminiscences.  

PubMed

This paper traces the history of the development of the Radiofrequency Radiation Dosimetry Handbook and its subsequent impact on radio frequency radiation exposure standards. The author's recollections are used to illustrate the behind the scenes efforts of the individuals involved in this project. The development of models at the University of Utah and confirmation of these results by various experimenters led to the publication of four editions of the Radiofrequency Radiation Dosimetry Handbook, i.e., "The RFR Experimenters Bible." PMID:10334710

Allen, S J

1999-01-01

323

Dosimetric evaluation of a novel polymer gel dosimeter for proton therapy  

SciTech Connect

Purpose: The aim of this study is to evaluate the dosimetric performance of a newly developed proton-sensitive polymer gel formulation for proton therapy dosimetry. Methods: Using passive scattered modulated and nonmodulated proton beams, the dose response of the gel was assessed. A next-generation optical CT scanner is used as the readout mechanism of the radiation-induced absorbance in the gel medium. Comparison of relative dose profiles in the gel to ion chamber profiles in water is performed. A simple and easily reproducible calibration protocol is established for routine gel batch calibrations. Relative stopping power ratio measurement of the gel medium was performed to ensure accurate water-equivalent depth dose scaling. Measured dose distributions in the gel were compared to treatment planning system for benchmark irradiations and quality of agreement is assessed using clinically relevant gamma index criteria. Results: The dosimetric response of the gel was mapped up to 600 cGy using an electron-based calibration technique. Excellent dosimetric agreement is observed between ion chamber data and gel. The most notable result of this work is the fact that this gel has no observed dose quenching in the Bragg peak region. Quantitative dose distribution comparisons to treatment planning system calculations show that most (>97%) of the gel dose maps pass the 3%/3 mm gamma criterion. Conclusions: This study shows that the new proton-sensitive gel dosimeter is capable of reproducing ion chamber dose data for modulated and nonmodulated Bragg peak beams with different clinical beam energies. The findings suggest that the gel dosimeter can be used as QA tool for millimeter range verification of proton beam deliveries in the dosimeter medium.

Zeidan, O. A.; Sriprisan, S. I.; Lopatiuk-Tirpak, O.; Kupelian, P. A.; Meeks, S. L.; Hsi, W. C.; Li, Z.; Palta, J. R.; Maryanski, M. J. [M. D. Anderson Cancer Center Orlando, Orlando, Florida 32806 (United States); University of Florida Proton Therapy Institute, Jacksonville, Florida 32206 (United States); MGS Research, Inc., Madison, Connecticut 06443 (United States)

2010-05-15

324

New materials for ESR dosimetry  

NASA Astrophysics Data System (ADS)

New materials for electron spin resonance (ESR) dosimetry have been investigated with the aim to find systems more sensitive than L-alanine accepted as a standard for high dose determinations. Among the investigated systems ammonium tartrate, 2-methylalanine, salts of formic acids and dithionates have been found to be more sensitive than alanine by a factor 2-10. The lower limit applies to tissue equivalent materials, while much higher sensitivities were obtained with formates and dithionates containing heavier atoms. The increased sensitivity was mainly attributed to suitable ESR properties of the room temperature stable radicals as regards spectral shape (narrow lines, little or no hyperfine structure) and microwave saturation properties (short relaxation times). The radical structures have when necessary been clarified by ENDOR spectroscopy, while the saturation properties have been screened by pulsed ESR measurements.

Lund, A.; Olsson, S.; Bonora, M.; Lund, E.; Gustafsson, H.

2002-04-01

325

In vivo dosimetry in brachytherapy  

SciTech Connect

In vivo dosimetry (IVD) has been used in brachytherapy (BT) for decades with a number of different detectors and measurement technologies. However, IVD in BT has been subject to certain difficulties and complexities, in particular due to challenges of the high-gradient BT dose distribution and the large range of dose and dose rate. Due to these challenges, the sensitivity and specificity toward error detection has been limited, and IVD has mainly been restricted to detection of gross errors. Given these factors, routine use of IVD is currently limited in many departments. Although the impact of potential errors may be detrimental since treatments are typically administered in large fractions and with high-gradient-dose-distributions, BT is usually delivered without independent verification of the treatment delivery. This Vision 20/20 paper encourages improvements within BT safety by developments of IVD into an effective method of independent treatment verification.

Tanderup, Kari [Department of Oncology, Aarhus University Hospital, Aarhus 8000 (Denmark); Department of Clinical Medicine, Aarhus University, Aarhus 8000 (Denmark); Beddar, Sam [Department of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States); Andersen, Claus E.; Kertzscher, Gustavo [Center of Nuclear Technologies, Technical University of Denmark, Roskilde 4000 (Denmark); Cygler, Joanna E. [Department of Physics, Ottawa Hospital Cancer Centre, Ottawa, Ontario K1H 8L6 (Canada)

2013-07-15

326

Fill tube fitted spheres  

SciTech Connect

The high temperature diffusion technique for fuel filling of some future direct drive cryogenic ICF targets may be unacceptable. The following describes a technique of fitting a 1 mm diameter x 6 ..mu..m thick glass microsphere with an approx. 50 ..mu..m O.D. glass fill tube. The process of laser drilling a 50 ..mu..m diameter hole in the microsphere wall, technique for making the epoxy joint between the sphere and fill tube, as well as the assembly procedure are also discussed.

Ives, B.H.

1981-07-13

327

Evaluation of dose delivery accuracy of gamma knife using MRI polymer gel dosimeter in an inhomogeneous phantom  

NASA Astrophysics Data System (ADS)

Polymer gel dosimetry is still the only dosimetry method for directly measuring three-dimensional dose distributions. MRI Polymer gel dosimeters are tissue equivalent and can act as a phantom material. Because of high dose response sensitivity, the MRI was chosen as readout device. In this study dose profiles calculated with treatment-planning software (LGP) and measurements with the MR polymer gel dosimeter for single-shot irradiations were compared. A custom-built 16 cm diameter spherical plexiglas head phantom was used in this study. Inside the phantom, there is a cubic cutout for insertion of gel phantoms and another cutout for inserting the inhomogeneities. The phantoms were scanned with a 1.5T MRI (Siemens syngo MR 2004A 4VA25A) scanner. The multiple spin-echo sequence with 32 echoes was used for the MRI scans. Calibration relations between the spin-spin relaxation rate and the absorbed dose were obtained by using small cylindrical vials, which were filled with the PAGAT polymer gel from the same batch as for the spherical phantom. 1D and 2D data obtained using gel dosimeter for homogeneous and inhomogeneous phantoms were compared with dose obtained using LGP calculation. The distance between relative isodose curves obtained for homogeneous phantom and heterogeneous phantoms exceed the accepted total positioning error (>±2mm). The findings of this study indicate that dose measurement using PAGAT gel dosimeter can be used for verifying dose delivering accuracy in GK unit in presence of inhomogeneities.

Pourfallah T, A.; Alam N, Riahi; M, Allahverdi; M, Ay; M, Zahmatkesh

2009-05-01

328

Gel dosimeters as useful dose and thermal-fluence detectors in boron neutron capture therapy  

NASA Astrophysics Data System (ADS)

The dosimetry method based on Fricke-Xylenol-Orange-infused gels in form of layers has shown noticeable potentiality for in-phantom or in-free-beam dose and thermal flux profiling and imaging in the high fluxes of thermal or epithermal neutrons utilised for boron neutron capture therapy (BNCT). Gel-dosimeters in form of layers give the possibility not only of obtaining spatial dose distributions but also of achieving measurements of each dose contribution in neutron fields. The discrimination of the various dose components is achieved by means of pixel-to-pixel manipulations of pairs of images obtained with gel-dosimeters having different isotopic composition. It is possible to place large dosimeters, detecting in such a way large dose images, because the layer geometry of dosimeters avoids sensitive variation of neutron transport due to the gel isotopic composition. Some results obtained after the last improvements of the method are reported.

Gambarini, G.; Moss, R. L.; Mariani, M.; Carrara, M.; Daquino, G. G.; Nievaart, V. A.; Valente, M.; Vanossi, E.

329

TelFit: Fitting the telluric absorption spectrum  

NASA Astrophysics Data System (ADS)

TelFit calculates the best-fit telluric absorption spectrum in high-resolution optical and near-IR spectra. The best-fit model can then be divided out to remove the telluric contamination. Written in Python, TelFit is essentially a wrapper to LBLRTM, the Line-By-Line Radiative Transfer Model, and simplifies the process of generating a telluric model.

Gullikson, Kevin

2014-05-01

330

Periodic mesoporous silica gels  

SciTech Connect

We have synthesized monolithic particulate gels of periodic mesoporous silica by adding tetramethoxysilane to a homogeneous alkaline micellar precursor solution. The gels exhibit 5 characteristic length scales over 4 orders of magnitude: fractal domains larger than the particle size (>500 nm), particles that are {approximately}150 to 500 nm in diameter, interparticle pores that are on the order of the particle size, a feature in the gas adsorption measurements that indicates pores {approximately}10-50 nm, and periodic hexagonal arrays of {approximately}3 nm channels within each particle. The wet gel monoliths exhibit calculated densities as low as {approximately}0.02 g/cc; the dried and calcined gels have bulk densities that range from {approximately}0.3-0.5 g/cc. The materials possess large interparticle ({approximately}1.0-2.3 cc/g) and intraparticle ({approximately}0.6 cc/g) porosities.

Anderson, M.T.; Martin, J.E.; Odinek, J.G. [and others

1996-06-01

331

Electrophoresis and Gel Analysis  

NSDL National Science Digital Library

In this animation produced by WGBH and Digizyme, Inc., see how molecules of DNA are separated using gel electrophoresis, and how this process enables scientists to compare the molecular variations of two or more DNA samples.

Foundation, Wgbh E.

2011-09-22

332

Mechanochromic photonic gels.  

PubMed

Polymer gels are remarkable materials with physical structures that can adapt significantly and quite rapidly with changes in the local environment, such as temperature, light intensity, electrochemistry, and mechanical force. An interesting phenomenon observed in certain polymer gel systems is mechanochromism - a change in color due to a mechanical deformation. Mechanochromic photonic gels are periodically structured gels engineered with a photonic stopband that can be tuned by mechanical forces to reflect specific colors. These materials have potential as mechanochromic sensors because both the mechanical and optical properties are highly tailorable via incorporation of diluents, solvents, nanoparticles, or polymers, or the application of stimuli such as temperature, pH, or electric or strain fields. Recent advances in photonic gels that display strain-dependent optical properties are discussed. In particular, this discussion focuses primarily on polymer-based photonic gels that are directly or indirectly fabricated via self-assembly, as these materials are promising soft material platforms for scalable mechanochromic sensors. PMID:23754505

Chan, Edwin P; Walish, Joseph J; Urbas, Augustine M; Thomas, Edwin L

2013-08-01

333

Micro-Fabricated Solid-State Radiation Detectors for Active Personal Dosimetry  

NASA Technical Reports Server (NTRS)

Active radiation dosimetry is important to human health and equipment functionality for space applications outside the protective environment of a space station or vehicle. This is especially true for long duration missions to the moon, where the lack of a magnetic field offers no protection from space radiation to those on extravehicular activities. In order to improve functionality, durability and reliability of radiation dosimeters for future NASA lunar missions, single crystal silicon carbide devices and scintillating fiber detectors are currently being investigated for applications in advanced extravehicular systems. For many years, NASA Glenn Research Center has led significant efforts in silicon carbide semiconductor technology research and instrumentation research for sensor applications under extreme conditions. This report summarizes the technical progress and accomplishments toward characterization of radiation-sensing components for the recommendation of their fitness for advanced dosimetry development.

Wrbanek, John D.; Wrbanek, Susan Y.; Fralick, Gustave C.; Chen, Liang-Yu

2007-01-01

334

Technical Basis Document for PFP Area Monitoring Dosimetry Program.  

National Technical Information Service (NTIS)

This document describes the phantom dosimetry used for the PFP Area Monitoring program and establishes the basis for the Plutonium Finishing Plant's (PFP) area monitoring dosimetry program in accordance with the following requirements: Title 10, Code of F...

2000-01-01

335

Hanford External Dosimetry Technical Basis Manual PNL-MA-842.  

National Technical Information Service (NTIS)

The Hanford External Dosimetry Technical Basis Manual PNL-MA-842 documents the design and implementation of the external dosimetry system used at Hanford. The manual describes the dosimeter design, processing protocols, dose calculation methodology, radia...

B. A. Rathbone

2009-01-01

336

Hanford External Dosimetry Technical Basis Manual PNL-MA-842.  

National Technical Information Service (NTIS)

The Hanford External Dosimetry Technical Basis Manual PNL-MA-842 documents the design and implementation of the external dosimetry system used at Hanford. The manual describes the dosimeter design, processing protocols, dose calculationl methodology, radi...

B. A. Rathbone

2005-01-01

337

Finding the Right Fitness Trainer  

MedlinePLUS

... don’t hurt myself!” — Grace, age 81 Everyday Fitness Ideas from the National Institute on Aging at ... but want some extra help, working with a fitness trainer may be just the thing. A trainer ...

338

SE-FIT  

NASA Technical Reports Server (NTRS)

The mathematical theory of capillary surfaces has developed steadily over the centuries, but it was not until the last few decades that new technologies have put a more urgent demand on a substantially more qualitative and quantitative understanding of phenomena relating to capillarity in general. So far, the new theory development successfully predicts the behavior of capillary surfaces for special cases. However, an efficient quantitative mathematical prediction of capillary phenomena related to the shape and stability of geometrically complex equilibrium capillary surfaces remains a significant challenge. As one of many numerical tools, the open-source Surface Evolver (SE) algorithm has played an important role over the last two decades. The current effort was undertaken to provide a front-end to enhance the accessibility of SE for the purposes of design and analysis. Like SE, the new code is open-source and will remain under development for the foreseeable future. The ultimate goal of the current Surface Evolver Fluid Interface Tool (SEFIT) development is to build a fully integrated front-end with a set of graphical user interface (GUI) elements. Such a front-end enables the access to functionalities that are developed along with the GUIs to deal with pre-processing, convergence computation operation, and post-processing. In other words, SE-FIT is not just a GUI front-end, but an integrated environment that can perform sophisticated computational tasks, e.g. importing industry standard file formats and employing parameter sweep functions, which are both lacking in SE, and require minimal interaction by the user. These functions are created using a mixture of Visual Basic and the SE script language. These form the foundation for a high-performance front-end that substantially simplifies use without sacrificing the proven capabilities of SE. The real power of SE-FIT lies in its automated pre-processing, pre-defined geometries, convergence computation operation, computational diagnostic tools, and crash-handling capabilities to sustain extensive computations. SE-FIT performance is enabled by its so-called file-layer mechanism. During the early stages of SE-FIT development, it became necessary to modify the original SE code to enable capabilities required for an enhanced and synchronized communication. To this end, a file-layer was created that serves as a command buffer to ensure a continuous and sequential execution of commands sent from the front-end to SE. It also establishes a proper means for handling crashes. The file layer logs input commands and SE output; it also supports user interruption requests, back and forward operation (i.e. undo and redo), and others. It especially enables the batch mode computation of a series of equilibrium surfaces and the searching of critical parameter values in studying the stability of capillary surfaces. In this way, the modified SE significantly extends the capabilities of the original SE.

Chen, Yongkang; Weislogel, Mark; Schaeffer, Ben; Semerjian, Ben; Yang, Lihong; Zimmerli, Gregory

2012-01-01

339

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

PubMed

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 4×4cm(2). Computed tomography scans were used to readout the gel dosimeters. In the PDD measurement, the NIPAM gel dosimeter and Gafchromic(TM) 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 5cm depth for different fields compared with that of the Gafchromic(TM) EBT3 film. During gamma evaluation under 3%/3mm 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

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

2014-08-01

340

Methodology Review: Evaluating Person Fit  

Microsoft Academic Search

Person-fit methods based on classical test theory-and item response theory (IRT), and methods investigating particular types of response behavior on tests, are examined. Similarities and differences among person-fit methods and their advantages and disadvantages are discussed. Sound person-fit methods have been derived for the Rasch model. For other IRT models, the empirical and theoretical distributions differ for most person-fit statistics

Rob R. Meijer; Klaas Sijtsma

2001-01-01

341

Experimental verification of internal dosimetry calculations. Annual progress report  

SciTech Connect

During the past year a dosimetry research program has been established in the School of Nuclear Engineering at the Georgia Institute of Technology. The major objective of this program has been to provide research results upon which a useful internal dosimetry system could be based. The important application of this dosimetry system will be the experimental verification of internal dosimetry calculations such as those published by the MIRD Committee.

None

1980-05-01

342

Technical Basis Document for PFP Area Monitoring Dosimetry Program  

SciTech Connect

This document describes the phantom dosimetry used for the PFP Area Monitoring program and establishes the basis for the Plutonium Finishing Plant's (PFP) area monitoring dosimetry program in accordance with the following requirements: Title 10, Code of Federal Regulations (CFR), part 835, ''Occupational Radiation Protection'' Part 835.403; Hanford Site Radiological Control Manual (HSRCM-1), Part 514; HNF-PRO-382, Area Dosimetry Program; and PNL-MA-842, Hanford External Dosimetry Technical Basis Manual.

COOPER, J.R.

2000-04-17

343

Breast dosimetry in clinical mammography  

NASA Astrophysics Data System (ADS)

The objective of this study was show that a clinical dosimetry protocol that utilizes a dosimetric breast phantom series based on population anthropometric measurements can reliably predict the average glandular dose (AGD) imparted to the patient during a routine screening mammogram. In the study, AGD was calculated using entrance skin exposure and dose conversion factors based on fibroglandular content, compressed breast thickness, mammography unit parameters and modifying parameters for homogeneous phantom (phantom factor), compressed breast lateral dimensions (volume factor) and anatomical features (anatomical factor). The protocol proposes the use of a fiber-optic coupled (FOCD) or Metal Oxide Semiconductor Field Effect Transistor (MOSFET) dosimeter to measure the entrance skin exposure at the time of the mammogram without interfering with diagnostic information of the mammogram. The study showed that FOCD had sensitivity with less than 7% energy dependence, linear in all tube current-time product stations, and was reproducible within 2%. FOCD was superior to MOSFET dosimeter in sensitivity, reusability, and reproducibility. The patient fibroglandular content was evaluated using a calibrated modified breast tissue equivalent homogeneous phantom series (BRTES-MOD) designed from anthropomorphic measurements of a screening mammography population and whose elemental composition was referenced to International Commission on Radiation Units and Measurements Report 44 tissues. The patient fibroglandular content, compressed breast thickness along with unit parameters and spectrum half-value layer were used to derive the currently used dose conversion factor (DgN). The study showed that the use of a homogeneous phantom, patient compressed breast lateral dimensions and patient anatomical features can affect AGD by as much as 12%, 3% and 1%, respectively. The protocol was found to be superior to existing methodologies. In addition, the study population anthropometric measurements enabled the development of analytical equations to calculate the whole breast area, estimate for the skin layer thickness and optimal location for automatic exposure control ionization chamber. The clinical dosimetry protocol developed in this study can reliably predict the AGD imparted to an individual patient during a routine screening mammogram.

Benevides, Luis Alberto Do Rego

344

CONFORMANCE IMPROVEMENT USING GELS  

SciTech Connect

This technical progress report describes work performed from June 20 through December 19, 2001, for the project, ''Conformance Improvement Using Gels''. Interest has increased in some new polymeric products that purport to substantially reduce permeability to water while causing minimum permeability reduction to oil. In view of this interest, we are currently studying BJ's Aqua Con. Results from six corefloods revealed that the Aqua Con gelant consistently reduced permeability to water more than that to oil. However, the magnitude of the disproportionate permeability reduction varied significantly for the various experiments. Thus, as with most materials tested to date, the issue of reproducibility and control of the disproportionate permeability remains to be resolved. Concern exists about the ability of gels to resist washout after placement in fractures. We examined whether a width constriction in the middle of a fracture would cause different gel washout behavior upstream versus downstream of the constriction. Tests were performed using a formed Cr(III)-acetate-HPAM gel in a 48-in.-long fracture with three sections of equal length, but with widths of 0.08-, 0.02-, and 0.08-in., respectively. The pressure gradients during gel extrusion (i.e., placement) were similar in the two 0.08-in.-wide fracture sections, even though they were separated by a 0.02-in.-wide fracture section. The constriction associated with the middle fracture section may have inhibited gel washout during the first pulse of brine injection after gel placement. However, during subsequent phases of brine injection, the constriction did not inhibit washout in the upstream fracture section any more than in the downstream section.

Randall S. Seright

2002-02-28

345

ESR dosimetry for atomic bomb survivors and radiologic technologists  

Microsoft Academic Search

An individual absorbed dose for atomic bomb (A-bomb) survivors and radiologic technologists has been estimated using a new personal dosimetry. This dosimetry is based on the electron spin resonance (ESR) spectroscopy of the CO33- radicals, which are produced in their teeth by radiation. Measurements were carried out to study the characteristics of the dosimetry; the ESR signals of the CO33-

Junko Tatsumi-Miyajima

1987-01-01

346

Errors introduced by dose scaling for relative dosimetry.  

PubMed

Some dosimeters require a relationship between detector signal and delivered dose. The relationship (characteristic curve or calibration equation) usually depends on the environment under which the dosimeters are manufactured or stored. To compensate for the difference in radiation response among different batches of dosimeters, the measured dose can be scaled by normalizing the measured dose to a specific dose. Such a procedure, often called "relative dosimetry", allows us to skip the time-consuming production of a calibration curve for each irradiation. In this study, the magnitudes of errors due to the dose scaling procedure were evaluated by using the characteristic curves of BANG3 polymer gel dosimeter, radiographic EDR2 films, and GAFCHROMIC EBT2 films. Several sets of calibration data were obtained for each type of dosimeters, and a calibration equation of one set of data was used to estimate doses of the other dosimeters from different batches. The scaled doses were then compared with expected doses, which were obtained by using the true calibration equation specific to each batch. In general, the magnitude of errors increased with increasing deviation of the dose scaling factor from unity. Also, the errors strongly depended on the difference in the shape of the true and reference calibration curves. For example, for the BANG3 polymer gel, of which the characteristic curve can be approximated with a linear equation, the error for a batch requiring a dose scaling factor of 0.87 was larger than the errors for other batches requiring smaller magnitudes of dose scaling, or scaling factors of 0.93 or 1.02. The characteristic curves of EDR2 and EBT2 films required nonlinear equations. With those dosimeters, errors larger than 5% were commonly observed in the dose ranges of below 50% and above 150% of the normalization dose. In conclusion, the dose scaling for relative dosimetry introduces large errors in the measured doses when a large dose scaling is applied, and this procedure should be applied with special care. PMID:22955658

Watanabe, Yoichi; Hayashi, Naoki

2012-01-01

347

Dosimetry and Risk Assessment: Fundamental Concepts  

SciTech Connect

Radiation dosimetry is important for characterizing radiation exposures and for risk assessment. In a medical setting, dosimetry is important for evaluating the safety of administered radiopharmaceuticals and for planning the safe administration of therapeutic radionuclides. Environmental dosimetry helps establish the safety of radionuclide releases from electric power production and other human activities. Internal and external dosimetry help us understand the consequences of radiation exposure. The absorbed dose is the fundamental quantity in radiation dosimetry from which all other operational values in radiation protection are obtained. Equivalent dose to tissue and effective dose to the whole body are derivatives of absorbed dose and constructs of risk. Mathematical systems supported by computer software facilitate dose calculations and make it possible to estimate internal dose based on bioassay or other biokinetic data. Risk coefficients for radiation-induced cancer rely primarily on data from animal studies and long-term observations of the Hiroshima and Nagasaki bomb survivors. Low-dose research shows that mechanisms of radiation interactions with tissue are dose-dependent, but the resulting biological effects are not necessarily linear with absorbed dose. Thus, the analysis of radiation effects and associated risks must account for the influences of microscopic energy distributions at the cellular level, dose-rate, cellular repair of sub-lethal radiation damage, and modifying factors such as bystander effects, adaptive response, and genomic instability.

Fisher, Darrell R.

2005-12-29

348

Chemical dosimetry system for criticality accidents.  

PubMed

Ruder Boskovi? Institute (RBI) criticality dosimetry system consists of a chemical dosimetry system for measuring the total (neutron + gamma) dose, and a thermoluminescent (TL) dosimetry system for a separate determination of the gamma ray component. The use of the chemical dosemeter solution chlorobenzene-ethanol-trimethylpentane (CET) is based on the radiolytic formation of hydrochloric acid, which protonates a pH indicator, thymolsulphonphthalein. The high molar absorptivity of its red form at 552 nm is responsible for a high sensitivity of the system: doses in the range 0.2-15 Gy can be measured. The dosemeter has been designed as a glass ampoule filled with the CET solution and inserted into a pen-shaped plastic holder. For dose determinations, a newly constructed optoelectronic reader has been used. The RBI team took part in the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002, with the CET dosimetry system. For gamma ray dose determination TLD-700 TL detectors were used. The results obtained with CET dosemeter show very good agreement with the reference values. PMID:15353694

Miljani?, Saveta; Ilijas, Boris

2004-01-01

349

Lung dosimetry of thorotrast patients.  

PubMed

Deposits of intravascularly injected Thorotrast in the reticulo-endothelial system of Thorotrast patients are a continuous source of 220Rn. In this study, we modeled the transport of 220Rn from these deposits through the body into the lungs, exhalation of 220Rn from the lungs, production of 220Rn progeny in the lungs and their exhalation, and mucociliary clearance of 220Rn progeny deposited on airway surfaces. The injection of 1 mL Thorotrast produces annual doses of 0.48 mGy y-1 to the bronchial epithelium and 0.95 mGy y-1 to pulmonary tissue. Based on a mean injected volume of about 25 mL and an average exposure time of 30 y, German Thorotrast patients received a mean bronchial lifetime dose of 357 mGy. Despite these relatively high doses, comparable to exposure in uranium miners, no excess lung cancers could be observed in the epidemiologic follow-up study. This apparent discrepancy between predicted and observed bronchial tumors may have important implications for lung dosimetry and risk assessment of inhaled 222Rn progeny. PMID:2172184

Hofmann, W; Johnson, J R; Freedman, N

1990-12-01

350

Surface tension-induced gel fracture. Part 1. Fracture of agar gels.  

PubMed

This work involves an experimental investigation of the spreading of liquids on gel layers in the presence of surfactants. Of primary interest is the instability that accompanies the cracking of gels through the deposition and subsequent spreading of a drop of surfactant solution on their surfaces. This instability manifests itself via the shaping of crack-like spreading "arms", in formations that resemble starbursts. The main aim of this study is to elucidate the complex interactions between spreading surfactants and underlying gels and to achieve a fundamental understanding of the mechanism behind the observed phenomenon of the cracking pattern formation. By spreading SDS and Silwet L-77 surfactant solutions on the surfaces of agar gels, the different ways that system parameters such as the surfactant chemistry and concentration and the gel strength can affect the morphology and dynamics of the starburst patterns are explored. The crack propagation dynamics is fitted to a power law by measuring the temporal evolution of the length of the spreading arms that form each one of the observed patterns. The values of the exponent of the power law are within the predicted limits for Marangoni-driven spreading on thick layers. Therefore, Marangoni stresses, induced by surface tension gradients between the spreading surfactant and the underlying gel layer, are identified to be the main driving force behind these phenomena, whereas gravitational forces were also found to play an important role. A mechanism that involves the "unzipping" of the gel in a manner perpendicular to the direction of the largest surface tension gradient is proposed. This mechanism highlights the important role of the width of the arms in the process; it is demonstrated that a cracking pattern is formed only within the experimental conditions that allow S/?w to be greater than G', where S is the spreading coefficient, ?w is the change in the width of the crack, and G' is the storage modulus of the substrate. PMID:22512657

Spandagos, Constantinos; Goudoulas, Thomas B; Luckham, Paul F; Matar, Omar K

2012-05-01

351

Sensitization of Parker fittings  

SciTech Connect

At your request, ferrules from 316 SS Parker-Hannifen compression fittings at the FFTF have been examined and evaluated to determine the metallurgical condition as related to carbide precipitation in grain boundaries (known as sensitization) and the implications this may have with regard to corrosion resistance. To accomplish this, two ferrules from new stock, two ferrules from old stock and two ferrules that had seen service were examined metallurgically. The samples were prepared for optical metallography. They were viewed in both the etched and unetched condition and analyzed on the scanning electron microscope (SEM) for elemental content. It was confirmed that the ferrules from new stock had a 5 mil thick nitrided layer on the ferrule ID at the lead end and that the 316 SS ferrule material was in the sensitized condition, indicating low resistance to aqueous corrosion. The material from old stock had no nitride layer but was in the sensitized condition indicating low resistance to aqueous corrosion. The ferrules that had seen service had not been nitrided and were not sensitized indicating high resistance to aqueous corrosion.

Wilber, W.W.

1985-09-01

352

Review of recent advances in radiochromic materials for 3D dosimetry  

NASA Astrophysics Data System (ADS)

Recent papers concerning radiochromic films, plastics and hydrogels for 3D dosimetry are summarized. The utility of Presage", a radiochromic plastic, with optical CT readout was demonstrated for the following applications: motion and gated treatment delivery, commissioning of small fields for radiosurgery, 192Ir high dose rate brachytherapy source commissioning and as a 3D insert for IMRT credentialing tests with Radiological Physics Centre (RPC) phantoms. Preliminary performance for characterizing microbeams from a synchrotron with optic projection tomography readout demonstrated resolution of an 83 micron diameter beam. Hydrogel chemistries based on nonionic micelles for leuco malachite green and leuco crystal violet demonstrated that low diffusion gels can be designed by choosing product dyes that are poorly soluble and water and tend to remain in the micelles. Turnbull blue chemistry has been successfully adapted to form a non-difffusing gel as well. The performance of ferrous xylenol orange hydrogel layers doped with boron to form neutron dosimeters demonstrated another practical application. Polymerization hydrogels are alternate materials that can be read with optical CT scanners. High dose gradient applications in brachytherapy with 90Sr/90Y sources and proton dosimetry are presented for comparison.

Jordan, Kevin

2010-11-01

353

Czech results at criticality dosimetry intercomparison 2002.  

PubMed

Two criticality dosimetry systems were tested by Czech participants during the intercomparison held in Valduc, France, June 2002. The first consisted of the thermoluminescent detectors (TLDs) (Al-P glasses) and Si-diodes as passive neutron dosemeters. Second, it was studied to what extent the individual dosemeters used in the Czech routine personal dosimetry service can give a reliable estimation of criticality accident exposure. It was found that the first system furnishes quite reliable estimation of accidental doses. For routine individual dosimetry system, no important problems were encountered in the case of photon dosemeters (TLDs, film badge). For etched track detectors in contact with the 232Th or 235U-Al alloy, the track density saturation for the spark counting method limits the upper dose at approximately 1 Gy for neutrons with the energy >1 MeV. PMID:15353690

Frantisek, Spurný; Jaroslav, Trousil

2004-01-01

354

A Dynamic Dosimetry System for Prostate Brachytherapy  

PubMed Central

The lack of dynamic dosimetry tools for permanent prostate brachytherapy causes otherwise avoidable problems in prostate cancer patient care. The goal of this work is to satisfy this need in a readily adoptable manner. Using the ubiquitous ultrasound scanner and mobile non-isocentric C-arm, we show that dynamic dosimetry is now possible with only the addition of an arbitrarily configured marker-based fiducial. Not only is the system easily configured from accessible hardware, but it is also simple and convenient, requiring little training from technicians. Furthermore, the proposed system is built upon robust algorithms of seed segmentation, fiducial detection, seed reconstruction, and image registration. All individual steps of the pipeline have been thoroughly tested, and the system as a whole has been validated on a study of 25 patients. The system has shown excellent results of accurately computing dose, and does so with minimal manual intervention, therefore showing promise for widespread adoption of dynamic dosimetry.

Kuo, Nathanael; Dehghan, Ehsan; Deguet, Anton; Song, Danny Y.; Prince, Jerry L.; Lee, Junghoon

2013-01-01

355

Dosimetry procedures for an industrial irradiation plant  

NASA Astrophysics Data System (ADS)

Accurate and reliable dosimetry procedures constitute a very important part of process control and quality assurance at a radiation processing plant. ?-Dose measurements were made on the GBS 84 irradiator for food and other products on pallets or in containers. Chemical dosimeters wre exposed in the facility under conditions of the typical plant operation. The choice of the dosimeter systems employed was based on the experience in chemical dosimetry gained over several years. Dose uniformity information was obtained in air, spices, bulbs, feeds, cosmetics, plastics and surgical goods. Most products currently irradiated require dose uniformity which can be efficiently provided by pallet or box irradiators like GBS 84. The radiation performance characteristics and some dosimetry procedures are discussed.

Grahn, Ch.

356

Patterns in shrinking gels  

NASA Astrophysics Data System (ADS)

POLYMER gels can undergo a volume phase transition (either continuous or discontinuous) when an external condition, such as temperature or solvent composition, is altered1-3. During this transition, the volume may change by a factor of several thousand, and various patterns develop in the gel. The patterns arising from swelling and shrinking differ in both their appearance and their physical mechanisms. The mechanism for the formation and evolution of patterns on swelling gels has been established as being due to a single kind of mechanical instability4-7 in contrast, the shrinking patterns seem to be sensitive to both the initial and final states of the transition. Here we classify the various shrinking patterns in the form of a phase diagram, and explain the poly-morphism in terms of macroscopic phase separation.

Matsuo, Eriko Sato; Tanaka, Toyoichi

1992-08-01

357

Gel-silica science  

SciTech Connect

Sol-gel techniques can be used to produce two new types of optical silicas, termed Type V for the full density material and Type VI for the optically transparent porous material. This paper summarizes the processing differences between these six types of commercial silicas. The primary emphasis of this paper is to discuss the scientific basis for the processing of Types V and VI optical silica. First, however, the use of sol-gel processing of other systems will be briefly reviewed. The controlled hydrolysis of alkoxides has also been used to produce submicrometer TiO{sub 2}, doped TiO{sub 2} (17), ZrO{sub 2} (18), doped ZrO{sub 2} (18), doped SiO{sub 2} (19), SrTiO{sub 3} (20), and corderite (20) powders. Emulsions have been employed to produce spherical powders of mixed cation oxides, such as yttrium aluminum garnets (YAG) and many other systems (20). Sol-gel powder processes have also been applied to fissile elements (21) where spray form sols UO{sub 2}, and rigid gel spheres of UO-PuO{sub 2} are formed during passage through a column of heated liquid. Both crystalline and vitreous ceramic fibers have been prepared using the sol-gel method. Compositions include TiO{sub 2}-SiO{sub 2} and ZrO{sub 2}-SiO{sub 2} glass fibers (22), high purity SiO{sub 2} waveguide fibers (23), Al{sub 2}O{sub 3}, ZrO{sub 2}, ThO{sub 2}, MgO, TiO{sub 2}, ZrSiO{sub 4}, 3AlO{sub 3}-2SiO{sub 2} fibers (24). Sol-gel derived alumina grains are important commercial products (25).

Hench, L.L.; Vasconcelos, W. (Advanced Materials Research Center, Univ. of Florida, Gainesville, FL (US))

1990-01-01

358

NuFit: nutrition and fitness CBPR program evaluation.  

PubMed

The present study combines community-based participatory research (CBPR) and peer education to create NuFit, a nutrition and fitness curriculum, adapted by community and student peer leaders for Latino and African-American high-school students in Chicago. The purpose of this pilot study was to assess the feasibility and efficacy of the NuFit curriculum to improve the knowledge, attitudes, and behaviors regarding nutrition and fitness for minority and adolescent student populations. The NuFit curriculum improved students' short-term self-reported behaviors and attitudes around nutrition and fitness. The NuFit curriculum shows promise as one mechanism to help prevent and combat childhood obesity by fostering healthy attitudes and behaviors during the critical developmental stage of adolescence. Involvement of and collaboration between community stakeholders and youth appeared to increase the likelihood of NuFit's cultural relevance and sustainability. More work is necessary to evaluate the long-term effects of NuFit. PMID:24702662

McKinney, Chelsea; Bishop, Virginia; Cabrera, Kathy; Medina, Roxane; Takawira, Desire; Donate, Nilmari; Rodriguez, Jose Luis; Guevara, Beti

2014-01-01

359

TransFit: Finite element analysis data fitting software  

NASA Technical Reports Server (NTRS)

The Advanced X-Ray Astrophysics Facility (AXAF) mission support team has made extensive use of geometric ray tracing to analyze the performance of AXAF developmental and flight optics. One important aspect of this performance modeling is the incorporation of finite element analysis (FEA) data into the surface deformations of the optical elements. TransFit is software designed for the fitting of FEA data of Wolter I optical surface distortions with a continuous surface description which can then be used by SAO's analytic ray tracing software, currently OSAC (Optical Surface Analysis Code). The improved capabilities of Transfit over previous methods include bicubic spline fitting of FEA data to accommodate higher spatial frequency distortions, fitted data visualization for assessing the quality of fit, the ability to accommodate input data from three FEA codes plus other standard formats, and options for alignment of the model coordinate system with the ray trace coordinate system. TransFit uses the AnswerGarden graphical user interface (GUI) to edit input parameters and then access routines written in PV-WAVE, C, and FORTRAN to allow the user to interactively create, evaluate, and modify the fit. The topics covered include an introduction to TransFit: requirements, designs philosophy, and implementation; design specifics: modules, parameters, fitting algorithms, and data displays; a procedural example; verification of performance; future work; and appendices on online help and ray trace results of the verification section.

Freeman, Mark

1993-01-01

360

Gel Electrophoresis of Dyes  

NSDL National Science Digital Library

In this experiment related to plant biotechnology, learners discover how to prepare and load an electrophoresis gel. They will then run the gels in an electrophoresis system to separate several dyes that are of different molecular sizes and carry different charges. This technique is fundamental to many of the procedures used in biotechnology. This lesson guide includes background information for the educator, safety precautions, and questions with answers for learners. For safety reasons, adult supervision is recommended. Modifications for use with younger learners are described in a related PDF (see related resource).

Stephens, Janice; Leach, Jan

2011-01-01

361

Swelling of Olympic Gels  

NASA Astrophysics Data System (ADS)

The swelling equilibrium of Olympic gels, which are composed of entangled cyclic polymers, is studied by Monte Carlo simulations. In contrast to chemically cross-linked polymer networks, we observe that Olympic gels made of chains with a larger degree of polymerization, N, exhibit a smaller equilibrium swelling degree, Q?N-0.28?0-0.72, at the same polymer volume fraction ?0 at network preparation. This observation is explained by a desinterspersion (reorganization with release of nontrapped entanglements) process of overlapping nonconcatenated rings upon swelling.

Lang, M.; Fischer, J.; Werner, M.; Sommer, J.-U.

2014-06-01

362

A parameterization method and application in breast tomosynthesis dosimetry  

SciTech Connect

Purpose: To present a parameterization method based on singular value decomposition (SVD), and to provide analytical parameterization of the mean glandular dose (MGD) conversion factors from eight references for evaluating breast tomosynthesis dose in the Mammography Quality Standards Act (MQSA) protocol and in the UK, European, and IAEA dosimetry protocols.Methods: MGD conversion factor is usually listed in lookup tables for the factors such as beam quality, breast thickness, breast glandularity, and projection angle. The authors analyzed multiple sets of MGD conversion factors from the Hologic Selenia Dimensions quality control manual and seven previous papers. Each data set was parameterized using a one- to three-dimensional polynomial function of 2–16 terms. Variable substitution was used to improve accuracy. A least-squares fit was conducted using the SVD.Results: The differences between the originally tabulated MGD conversion factors and the results computed using the parameterization algorithms were (a) 0.08%–0.18% on average and 1.31% maximum for the Selenia Dimensions quality control manual, (b) 0.09%–0.66% on average and 2.97% maximum for the published data by Dance et al. [Phys. Med. Biol. 35, 1211–1219 (1990); ibid. 45, 3225–3240 (2000); ibid. 54, 4361–4372 (2009); ibid. 56, 453–471 (2011)], (c) 0.74%–0.99% on average and 3.94% maximum for the published data by Sechopoulos et al. [Med. Phys. 34, 221–232 (2007); J. Appl. Clin. Med. Phys. 9, 161–171 (2008)], and (d) 0.66%–1.33% on average and 2.72% maximum for the published data by Feng and Sechopoulos [Radiology 263, 35–42 (2012)], excluding one sample in (d) that does not follow the trends in the published data table.Conclusions: A flexible parameterization method is presented in this paper, and was applied to breast tomosynthesis dosimetry. The resultant data offer easy and accurate computations of MGD conversion factors for evaluating mean glandular breast dose in the MQSA protocol and in the UK, European, and IAEA dosimetry protocols. Microsoft Excel™ spreadsheets are provided for the convenience of readers.

Li, Xinhua; Zhang, Da; Liu, Bob [Division of Diagnostic Imaging Physics and Webster Center for Advanced Research and Education in Radiation, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114 (United States)] [Division of Diagnostic Imaging Physics and Webster Center for Advanced Research and Education in Radiation, Department of Radiology, Massachusetts General Hospital, Boston, Massachusetts 02114 (United States)

2013-09-15

363

Technical basis for internal dosimetry at Hanford  

SciTech Connect

The Hanford Internal Dosimetry Program, administered by Pacific Northwest Laboratory for the US Department of Energy, provides routine bioassay monitoring for employees who are potentially exposed to radionuclides in the workplace. This report presents the technical basis for routine bioassay monitoring and the assessment of internal dose at Hanford. The radionuclides of concern include tritium, corrosion products ({sup 58}Co, {sup 60}Co, {sup 54}Mn, and {sup 59}Fe), strontium, cesium, iodine, europium, uranium, plutonium, and americium,. Sections on each of these radionuclides discuss the sources and characteristics; dosimetry; bioassay measurements and monitoring; dose measurement, assessment, and mitigation and bioassay follow-up treatment. 78 refs., 35 figs., 115 tabs.

Sula, M.J.; Carbaugh, E.H.; Bihl, D.E.

1991-07-01

364

SNL RML recommended dosimetry cross section compendium  

SciTech Connect

A compendium of dosimetry cross sections is presented for use in the characterization of fission reactor spectrum and fluence. The contents of this cross section library are based upon the ENDF/B-VI and IRDF-90 cross section libraries and are recommended as a replacement for the DOSCROS84 multigroup library that is widely used by the dosimetry community. Documentation is provided on the rationale for the choice of the cross sections selected for inclusion in this library and on the uncertainty and variation in cross sections presented by state-of-the-art evaluations.

Griffin, P.J.; Kelly, J.G.; Luera, T.F. [Sandia National Labs., Albuquerque, NM (United States)] [Sandia National Labs., Albuquerque, NM (United States); VanDenburg, J. [Science and Engineering Associates, Inc., Albuquerque, NM (United States)] [Science and Engineering Associates, Inc., Albuquerque, NM (United States)

1993-11-01

365

Third conference on radiation protection and dosimetry  

SciTech Connect

This conference has been designed with the objectives of promoting communication among applied, research, regulatory, and standards personnel involved in radiation protection and providing them with sufficient information to evaluate their programs. To partly fulfill these objectives, a technical program consisting of more than 75 invited and contributed oral presentations encompassing all aspects of radiation protection has been prepared. General topics include external dosimetry, internal dosimetry, instruments, regulations and standards, accreditation and test programs, research advances, and applied program experience. This publication provides a summary of the technical program and a collection of abstracts of the oral presentations.

Not Available

1991-01-01

366

Practical neutron dosimetry at high energies  

SciTech Connect

Dosimetry at high energy particle accelerators is discussed with emphasis on physical measurements which define the radiation environment and provide an immutable basis for the derivation of any quantities subsequently required for risk evaluation. Results of inter-laboratory dosimetric comparisons are reviewed and it is concluded that a well-supported systematic program is needed which would make possible detailed evaluations and inter-comparisons of instruments and techniques in well characterized high energy radiation fields. High-energy dosimetry is so coupled with radiation transport that it is clear their study should proceed concurrently.

McCaslin, J.B.; Thomas, R.H.

1980-10-01

367

Peculiarities of diffusion in gels  

NASA Astrophysics Data System (ADS)

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Pokusaev, B. G.; Karlov, S. P.; Vyazmin, A. V.; Nekrasov, D. A.

2013-12-01

368

Peculiarities of diffusion in gels  

NASA Astrophysics Data System (ADS)

An optical method was applied to study the peculiarities of diffusion in gel: this method provides real-time visualization of spreading of solutes brought into the gel. It was shown that spectral characteristics of reflected light give additional information about nature of diffusive spreading of solutes and about state of the gel. Gels with different densities and lifetime were studied. These parameters have strong influence on the velocity of diffusion. The study demonstrated critical differences for diffusion process in gels with true solutions and with solutions with nanoparticles. Experiments discovered the anisotropy in 3D diffusion of solutes in gels; physical explanation of this phenomenon was proposed.

Pokusaev, B. G.; Karlov, S. P.; Vyazmin, A. V.; Nekrasov, D. A.

2014-12-01

369

Dose verification of single shot gamma knife applications using VIPAR polymer gel and MRI.  

PubMed

This work describes an experimental procedure with potential to assess the overall accuracy associated with gamma knife clinical applications, from patient imaging and dosimetry planning to patient positioning and dose delivery using the automated positioning system of a Leksell Gamma Knife model C. The VIPAR polymer gel-MRI dosimetry method is employed due to its inherent three-dimensional feature and linear dose response over the range of gamma knife applications. Different polymer gel vials were irradiated with single shot gamma knife treatment plans using each of the four available collimator helmets to deliver a maximum dose of 30 Gy. Percentage relative dose results are presented not only in the form of one-dimensional profiles but also planar isocontours and isosurfaces in three dimensions. Experimental results are compared with corresponding Gammaplan treatment planning system calculations as well as acceptance test radiochromic film measurements. A good agreement, within the experimental uncertainty, is observed between measured and expected dose distributions. This experimental uncertainty is of the order of one imaging pixel in the MRI gel readout session (<1 mm) and allows for the verification of single shot gamma knife applications in terms of acceptance specifications for precision in beam alignment and accuracy. Averaging net R(2) results in the dose plateau of the 4 mm and 18 mm collimator irradiated gel vials, which were MR scanned in the same session, provides a crude estimate of the 4 mm output factor which agrees within errors with the default value of 0.870. PMID:15798319

Karaiskos, P; Petrokokkinos, L; Tatsis, E; Angelopoulos, A; Baras, P; Kozicki, M; Papagiannis, P; Rosiak, J M; Sakelliou, L; Sandilos, P; Vlachos, L

2005-03-21

370

Dose verification of single shot gamma knife applications using VIPAR polymer gel and MRI  

NASA Astrophysics Data System (ADS)

This work describes an experimental procedure with potential to assess the overall accuracy associated with gamma knife clinical applications, from patient imaging and dosimetry planning to patient positioning and dose delivery using the automated positioning system of a Leksell Gamma Knife model C. The VIPAR polymer gel-MRI dosimetry method is employed due to its inherent three-dimensional feature and linear dose response over the range of gamma knife applications. Different polymer gel vials were irradiated with single shot gamma knife treatment plans using each of the four available collimator helmets to deliver a maximum dose of 30 Gy. Percentage relative dose results are presented not only in the form of one-dimensional profiles but also planar isocontours and isosurfaces in three dimensions. Experimental results are compared with corresponding Gammaplan treatment planning system calculations as well as acceptance test radiochromic film measurements. A good agreement, within the experimental uncertainty, is observed between measured and expected dose distributions. This experimental uncertainty is of the order of one imaging pixel in the MRI gel readout session (<1 mm) and allows for the verification of single shot gamma knife applications in terms of acceptance specifications for precision in beam alignment and accuracy. Averaging net R2 results in the dose plateau of the 4 mm and 18 mm collimator irradiated gel vials, which were MR scanned in the same session, provides a crude estimate of the 4 mm output factor which agrees within errors with the default value of 0.870.

Karaiskos, P.; Petrokokkinos, L.; Tatsis, E.; Angelopoulos, A.; Baras, P.; Kozicki, M.; Papagiannis, P.; Rosiak, J. M.; Sakelliou, L.; Sandilos, P.; Vlachos, L.

2005-03-01

371

Reference dosimetry using radiochromic film.  

PubMed

The objectives of this study are to identify and quantify factors that influence radiochromic film dose response and to determine whether such films are suitable for reference dosimetry. The influence of several parameters that may introduce systematic dose errors when performing reference dose measurements were investigated. The effect of the film storage temperature was determined by comparing the performance of three lots of GAFCHROMIC EBT2 films stored at either 4ºC or room temperature. The effect of high (> 80%) or low (< 20%) relative humidity was also determined. Doses measured in optimal conditions with EBT and EBT2 films were then compared with an A12 ionization chamber measurement. Intensity-modulated radiation therapy quality controls using EBT2 films were also performed in reference dose. The results obtained using reference dose measurements were compared with those obtained using relative dose measurements. Storing the film at 4ºC improves the stability of the film over time, but does not eliminate the noncatalytic film development, seen as a rise in optical density over time in the absence of radiation. Relative humidity variations ranging from 80% to 20% have a strong impact on the optical density and could introduce dose errors of up to 15% if the humidity were not controlled during the film storage period. During the scanning procedure, the film temperature influences the optical density that is measured. When controlling for these three parameters, the dose differences between EBT or EBT2 and the A12 chamber are found to be within ± 4% (2? level) over a dose range of 20-350 cGy. Our results also demonstrate the limitation of the Anisotropic Analytical Algorithm for dose calculation of highly modulated treatment plans. PMID:23149793

Girard, Frédéric; Bouchard, Hugo; Lacroix, Frédéric

2012-01-01

372

Preparation of Homogeneous Aluminosilicate Gels by Sol/Gel Techniques.  

National Technical Information Service (NTIS)

The factors affecting the production of homogeneous aluminosilicate gels from alkoxide precursors were investigated. Aluminosilicate gels were made in acidic conditions with a prepolymerization of the silicate precursors followed by the addition of the al...

M. Reese J. Sanchez A. V. McCormick

1993-01-01

373

Dosimetry And Its Enhancement Using Gold Nanoparticles In Synchrotron Based Microbeam And Stereotactic Radiosurgery  

SciTech Connect

Research into the areas of synchrotron generated microbeam radiotherapy (MRT) and stereotactic radiosurgery is increasing. Such MRT techniques are showing potential of tackling some of the more difficult radiotherapy cases such as certain type of brain tumours. Two challenging aspects of these techniques are addressed in this investigation; the difficulty of dose determination and the delivery of the treatments at lower dose levels. In this research polymer gels were used as phantoms and dosimeters and cells were used to confirm outcomes. Normoxic polyacrylamide gels (nPAG) were tested as potential dosimeters for microbeam dosimetry. Following irradiation using microbeam and minibeam radiation from the BL28BU beam-line at Spring-8, Japan, the nPAG were scanned using a Raman spectroscopy technique. Dose enhancement caused by the inclusion of the gold nanoparticles (AuNPs) in the target was investigated using both cells and polymer gels. The use of AuNP could potentially reduce the dose required for the delivery of MRT. In this study it was shown that using endothelial cells with AuNPs, the minimal dose for clear cell killing along the beam line was reduced to 10 Gy. Both studies cell and gel studies indicates significant dose enhancement caused by the gold atoms in the target.

Rahman, Wan Nordiana; Davidson, Robert; Geso, Moshi [Division of Medical Radiation, School of Medical Sciences, RMIT University, Bundoora, Victoria (Australia); Wong, Christopher James [Division of Medical Radiation, School of Medical Sciences, RMIT University, Bundoora, Victoria (Australia); William Buckland Radiotherapy Centre, Alfred Hospital (Australia); Yagi, Naoto [Japanese Synchrotron Radiation Research Institute, Sayo-gun, Hyogo (Japan)

2010-07-23

374

Reactor Dosimetry State of the Art 2008  

NASA Astrophysics Data System (ADS)

Oral session 1: Retrospective dosimetry. Retrospective dosimetry of VVER 440 reactor pressure vessel at the 3rd unit of Dukovany NPP / M. Marek ... [et al.]. Retrospective dosimetry study at the RPV of NPP Greifswald unit 1 / J. Konheiser ... [et al.]. Test of prototype detector for retrospective neutron dosimetry of reactor internals and vessel / K. Hayashi ... [et al.]. Neutron doses to the concrete vessel and tendons of a magnox reactor using retrospective dosimetry / D. A. Allen ... [et al.]. A retrospective dosimetry feasibility study for Atucha I / J. Wagemans ... [et al.]. Retrospective reactor dosimetry with zirconium alloy samples in a PWR / L. R. Greenwood and J. P. Foster -- Oral session 2: Experimental techniques. Characterizing the Time-dependent components of reactor n/y environments / P. J. Griffin, S. M. Luker and A. J. Suo-Anttila. Measurements of the recoil-ion response of silicon carbide detectors to fast neutrons / F. H. Ruddy, J. G. Seidel and F. Franceschini. Measurement of the neutron spectrum of the HB-4 cold source at the high flux isotope reactor at Oak Ridge National Laboratory / J. L. Robertson and E. B. Iverson. Feasibility of cavity ring-down laser spectroscopy for dose rate monitoring on nuclear reactor / H. Tomita ... [et al.]. Measuring transistor damage factors in a non-stable defect environment / D. B. King ... [et al.]. Neutron-detection based monitoring of void effects in boiling water reactors / J. Loberg ... [et al.] -- Poster session 1: Power reactor surveillance, retrospective dosimetry, benchmarks and inter-comparisons, adjustment methods, experimental techniques, transport calculations. Improved diagnostics for analysis of a reactor pulse radiation environment / S. M. Luker ... [et al.]. Simulation of the response of silicon carbide fast neutron detectors / F. Franceschini, F. H. Ruddy and B. Petrovi?. NSV A-3: a computer code for least-squares adjustment of neutron spectra and measured dosimeter responses / J. G. Williams, A. P. Ribaric and T. Schnauber. Agile high-fidelity MCNP model development techniques for rapid mechanical design iteration / J. A. Kulesza.Extension of Raptor-M3G to r-8-z geometry for use in reactor dosimetry applications / M. A. Hunter, G. Longoni and S. L. Anderson. In vessel exposure distributions evaluated with MCNP5 for Atucha II / J. M. Longhino, H. Blaumann and G. Zamonsky. Atucha I nuclear power plant azimutal ex-vessel flux profile evaluation / J. M. Longhino ... [et al.]. UFTR thermal column characterization and redesign for maximized thermal flux / C. Polit and A. Haghighat. Activation counter using liquid light-guide for dosimetry of neutron burst / M. Hayashi ... [et al.]. Control rod reactivity curves for the annular core research reactor / K. R. DePriest ... [et al.]. Specification of irradiation conditions in VVER-440 surveillance positions / V. Kochkin ... [et al.]. Simulations of Mg-Ar ionisation and TE-TE ionisation chambers with MCNPX in a straightforward gamma and beta irradiation field / S. Nievaart ... [et al.]. The change of austenitic stainless steel elements content in the inner parts of VVER-440 reactor during operation / V. Smutný, J. Hep and P. Novosad. Fast neutron environmental spectrometry using disk activation / G. Lövestam ... [et al.]. Optimization of the neutron activation detector location scheme for VVER-lOOO ex-vessel dosimetry / V. N. Bukanov ... [et al.]. Irradiation conditions for surveillance specimens located into plane containers installed in the WWER-lOOO reactor of unit 2 of the South-Ukrainian NPP / O. V. Grytsenko. V. N. Bukanov and S. M. Pugach. Conformity between LRO mock-ups and VVERS NPP RPV neutron flux attenuation / S. Belousov. Kr. Ilieva and D. Kirilova. FLUOLE: a new relevant experiment for PWR pressure vessel surveillance / D. Beretz ... [et al.]. Transport of neutrons and photons through the iron and water layers / M. J. Kost'ál ... [et al.]. Condition evaluation of spent nuclear fuel assemblies from the first-generation nuclear-powered submarines by gamma scanning / A. F. Usatyi. L. A. Serdyuk

Voorbraak, Wim; Debarberis, Luigi; D'Hondt, Pierre; Wagemans, Jan

2009-08-01

375

Calcium tartrate gel.  

PubMed

A method for preparation of a gel for chromatography has been developed. The adsorbent is calcium tartrate treated with potassium phosphate. By changing the temperature of synthesis (10-65 degrees C) and concentration of the salts (calcium chloride and sodium potassium tartrate) from 0.3 to 3.0 M, we have been able to prepare adsorbent crystals of definite sizes in the range 35-200 microns. In all cases, for synthesis of adsorbent, the Ca2+/K+Na+ ratio was greater than 1. After treatment of calcium tartrate crystals with 0.075-1.5 M potassium phosphate at 80-100 degrees C and pH 8.5-9.0, an appropriate chromatographic adsorbent was prepared. The chromatographic properties of calcium tartrate gel have been studied. The adsorbent permits flow rates of 25-150 ml/h, depending on the particle size. The capacity of calcium tartrate gel for binding BSA, RNA, and DNA was similar to that of Tiselius' hydroxyapatite (A. Tiselius, S. Hjerten, O. Levin (1956) Arch. Biochem. Biophys. 65, 132-155). The spheric shape of gel particles permits uniform and compact packing of adsorbent under the conditions of column chromatography. PMID:2757203

Akhrem, A A; Drozhdenyuk, A P

1989-05-15

376

Got Fitness? Addressing Student Fitness Needs within Secondary Physical Education  

ERIC Educational Resources Information Center

Feeling trapped within your daily teaching routine? Are the same curricular activities getting you down, or worse yet ... your students? Perhaps you and your students are craving an injection of new and fun fitness activities designed for the secondary level. The development of health-related fitness has long been associated with primary…

Banks, Aaron; Reimann, Bonnie

2007-01-01

377

Can mobile virtual fitness apps replace human fitness trainer?  

Microsoft Academic Search

The increased need in promoting fitness activity and rapid growth of smart-phones has urged the development of mobile virtual fitness apps (MVFA). Yet, evaluation on these MVFA has been limited and, therefore, this study attempts to conduct preliminary evaluation on randomly sampled MVFA based on our proposed system workflow using theories of social support and persuasive technology, and the American

Ron Kwok Chi-Wai; Stanley Hui Sai-Chuen; Tania Mak So-Ning; Peter Wu Ka-Shun; Ken Lee Wing-Kuen; Clara Wong Choi-Ki

2011-01-01

378

A feasibility study using radiochromic films for fast neutron 2D passive dosimetry  

PubMed Central

The objective of this paper is threefold: (1) to establish sensitivity of XRQA and EBT radiochromic films to fast neutron exposure; (2) to develop a film response to radiation dose calibration curve and (3) to investigate a two-dimensional (2D) film dosimetry technique for use in establishing an experimental setup for a radiobiological irradiation of mice and to assess the dose to the mice in this setup. The films were exposed to a 10 MeV neutron beam via the 2H(d,n)3He reaction. The XRQA film response was a factor of 1.39 greater than EBT film response to the 10 MeV neutron beam when exposed to a neutron dose of 165 cGy. A film response-to-soft tissue dose calibration function was established over a range of 0–10 Gy and had a goodness of fit of 0.9926 with the calibration data. The 2D film dosimetry technique estimated the neutron dose to the mice by measuring the dose using a mouse phantom and by placing a piece of film on the exterior of the experimental mouse setup. The film results were benchmarked using Monte Carlo and aluminum (Al) foil activation measurements. The radiochromic film, Monte Carlo and Al foil dose measurements were strongly correlated, and the film within the mouse phantom agreed to better than 7% of the externally mounted films. These results demonstrated the potential application of radiochromic films for passive 2D neutron dosimetry.

Brady, Samuel L; Gunasingha, Rathnayaka; Yoshizumi, Terry T; Howell, Calvin R; Crowell, Alexander S; Fallin, Brent; Tonchev, Anton P; Dewhirst, Mark W

2013-01-01

379

System for Gel Electrophoretic Immunoassay.  

National Technical Information Service (NTIS)

A micro-analytical platform for performing electrophoresis-based immunoassays was developed by integrating photopolymerized cross-linked polyacrylamide gels within a microfluidic device. The microfluidic immunoassays are performed by gel electrophoretic s...

A. E. Herr A. K. Singh D. J. Throckmorton

2005-01-01

380

Nanostructured Magnetorheological Fluids and Gels.  

National Technical Information Service (NTIS)

Magnetorheological materials having a supramolecular polymer gel as a component of the carrier are disclosed. Useful supramolecular polymers for gels include those having terpyridine ligands which can participate in metal coordination bonding. The magneti...

A. Fuchs B. Hu B. Kavlicoglu F. Gordaninejad

2004-01-01

381

NLINEAR - NONLINEAR CURVE FITTING PROGRAM  

NASA Technical Reports Server (NTRS)

A common method for fitting data is a least-squares fit. In the least-squares method, a user-specified fitting function is utilized in such a way as to minimize the sum of the squares of distances between the data points and the fitting curve. The Nonlinear Curve Fitting Program, NLINEAR, is an interactive curve fitting routine based on a description of the quadratic expansion of the chi-squared statistic. NLINEAR utilizes a nonlinear optimization algorithm that calculates the best statistically weighted values of the parameters of the fitting function and the chi-square that is to be minimized. The inputs to the program are the mathematical form of the fitting function and the initial values of the parameters to be estimated. This approach provides the user with statistical information such as goodness of fit and estimated values of parameters that produce the highest degree of correlation between the experimental data and the mathematical model. In the mathematical formulation of the algorithm, the Taylor expansion of chi-square is first introduced, and justification for retaining only the first term are presented. From the expansion, a set of n simultaneous linear equations are derived, which are solved by matrix algebra. To achieve convergence, the algorithm requires meaningful initial estimates for the parameters of the fitting function. NLINEAR is written in Fortran 77 for execution on a CDC Cyber 750 under NOS 2.3. It has a central memory requirement of 5K 60 bit words. Optionally, graphical output of the fitting function can be plotted. Tektronix PLOT-10 routines are required for graphics. NLINEAR was developed in 1987.

Everhart, J. L.

1994-01-01

382

A-bomb survivor dosimetry update  

SciTech Connect

A-bomb survivor data have been generally accepted as applicable. Also, the initial radiations have tended to be accepted as the dominant radiation source for all survivors. There was general acceptance of the essential reliability of both the biological effects data and the causative radiation dose values. There are considerations casting doubt on these acceptances, but very little quantification of th implied uncertainties has been attempted. The exception was A-bomb survivor dosimetry, where free-field kerma values for initial radiations were thought to be accurate to about 30%, and doses to individual survivors were treated as effectively error-free. In 1980, a major challenge to the accepted A-bomb survivor dosimetry was announced, and was quickly followed by a succession of explanations and displays showing the soundness of that challenge. In fact, a complete replacement set of free-field kerma values was provided which was suitable for use in constructing an entire new dosimetry for Hiroshima and Nagasaki. The new values showed many changes greater than the accepted 30% uncertainty. An approximate new dosimetry was indeed constructed, and used to convert existing leukemia cause-and-effect data from the old to the new dose values, by way of assessing the impact. (ERB)

Loewe, W.E.

1982-06-01

383

From ``micro`` to ``macro`` internal dosimetry  

SciTech Connect

Radiation dose is the amount of radiation energy deposited per unit mass of absorbing tissue. Internal dosimetry applies to assessments of dose to internal organs from penetrating radiation sources outside the body and from radionuclides taken into the body. Dosimetry is essential for correlating energy deposition with biological effects that are observed when living tissues are irradiated. Dose-response information provides the basis for radiation protection standards and risk assessment. Radiation interactions with living matter takes place on a microscopic scale, and the manifestation of damage may be evident at the cellular, multi-cellular, and even organ levels of biological organization. The relative biological effectiveness of ionization radiation is largely determined by the spatial distribution of energy deposition events within microscopic as well as macroscopic biological targets of interest. The spatial distribution of energy imparted is determined by the spatial distribution of radionuclides and properties of the emitted charged-particle radiation involved. The nonuniformity of energy deposition events in microscopic volumes, particularly from high linear energy transfer (LET) radiation, results in large variations in the amount of energy imparted to very small volumes or targets. Microdosimetry is the study of energy deposition events at the cellular level. Macrodosimetry is a term for conventional dose averaging at the tissue or organ level. In between is a level of dosimetry sometimes referred to as multi-cellular dosimetry. The distinction between these terms and their applications in assessment of dose from internally deposited radionuclides is described.

Fisher, D.R.

1994-06-01

384

Radiochromic film for medical radiation dosimetry  

Microsoft Academic Search

Photon, electron and proton radiations are used extensively for medical purposes in diagnostic and therapeutic procedures. Dosimetry of these radiation sources can be performed with radiochromic films, devices that have the ability to produce a permanent visible colour change upon irradiation. Within the last 10 years, the use of radiochromic films has expanded rapidly in the medical world due to

Martin J Butson; Peter K. N Yu; Tsang Cheung; Peter Metcalfe

2003-01-01

385

Distribution effectiveness for space radiation dosimetry  

NASA Technical Reports Server (NTRS)

A simplified risk basis and a theory of hematological response are presented and applied to the problem of dosimetry in the manned space program. Unlike previous studies, the current work incorporates radiation exposure distribution effects into its definition of dose equivalent. The fractional cell lethality model for prediction of hematological response is integral in the analysis.

Wilson, J. W.

1975-01-01

386

Partition and permeation of dextran in polyacrylamide gel.  

PubMed Central

Partition of sized FITC-dextrans in polyacrylamide gel showed a relationship between Kav and solute radius as predicted by the theory of Ogston, which is based solely on geometry of the spaces. Permeability data for the same dextrans were fit to several theories, including those based on geometry and those based on hydrodynamic interactions, and the gel structure predicted by the partition and permeability data were compared. The Brinkman effective-medium model (based on hydrodynamic interactions and requiring a measure of the hydraulic conductivity of the matrix) gave the best fit of permeability data with the values for fiber radius (rf) and void volume of the gel (epsilon) that were obtained from the partition data. The models based on geometry and the hydrodynamic screening model of Cukier, using the rf and epsilon from partition data, all predicted higher rates of permeation than observed experimentally, while the effective-medium model with added term for steric interaction predicted lower permeation than that observed. The size of cylindrical pores appropriate for the partition data predicted higher rates of permeation than observed. These relative results were unaffected by the method of estimating void volume of the gel. In sum, it appears that one can use data on partition of solute, combined with measurement of hydraulic conductivity, to predict solute permeation in polyacrylamide gel.

Williams, J C; Mark, L A; Eichholtz, S

1998-01-01

387

Motivating Students in Fitness Activities  

ERIC Educational Resources Information Center

Physical educators have a responsibility to motivate students to develop personal fitness. This is a critical concept as physical education is the only part of the curriculum capable of meeting the health needs of students regarding physical activity. Current physical educators must promote fitness in ways that motivate students to engage in…

Wilkinson, Carol; Hunter, Mike

2008-01-01

388

Fantastic Disc Activities for Fitness  

ERIC Educational Resources Information Center

Disc activities are an excellent elementary content area for both skill and fitness enhancement. They may occur through progressive skill and drill practice, small sided-game examples, modifications of traditional disc activities appropriate to large groups, and with adjustments designed to increase activity and fitness levels. For games in this…

Griffin, Michael R.; Johnson, Romona; Thomas, Jessica; Spell, Melissa; Popham, John; Croft, Brent; Umpleby, Albert; Verbel, Eric

2005-01-01

389

Transfer of Value From Fit  

Microsoft Academic Search

People experience regulatory fit when they pursue a goal in a manner that sustains their regulatory orientation (E. T. Higgins, 2000). Five studies tested whether the value experienced from regulatory fit can transfer to a subsequent evaluation of an object. In Studies 1 and 2, participants gave the same coffee mug a higher price if they had chosen it with

E. Tory Higgins; Lorraine Chen Idson; Antonio L. Freitas; Scott Spiegel; Daniel C. Molden

2003-01-01

390

My Career: Group Fitness Instructor  

ERIC Educational Resources Information Center

This article presents an interview with Tammy Kenney, who teaches a yoga-Pilates class in several different gyms. In this interview, Kenney talks about her career as a group fitness instructor and gives her best advice for someone who wants to teach group fitness.

Green, Kathleen

2013-01-01

391

Exercise Prescription for Physical Fitness.  

ERIC Educational Resources Information Center

Examines current guidelines for physical fitness, noting issues that may influence the updating of the American College of Sports Medicine exercise statement. Differences between exercise prescription for fitness and physical activity for health are discussed, noting the importance of designing individualized programs with appropriate levels of…

Pollock, Michael L.; And Others

1995-01-01

392

Fitting an Ellipse to Data,  

National Technical Information Service (NTIS)

In the report, the authors consider the problem of fitting an ellipse to data. They first examine the conic section equation and develop a linear least squares model of the data fitting problem which they analyze in terms of its conditioning and numerical...

A. B. Forbes

1987-01-01

393

Fitness and Health. Beginnings Workshop.  

ERIC Educational Resources Information Center

Presents five articles on children's fitness and health: "Relaxation: Every Child's Right to Simply Be" (Patrice Thomas and Wendy Shepherd); "Infant Massage" (Carolyn Oleson); "Fitness and the Young Child" (James M. Poole); "Partners in Health: Helping Families Advocate for Their Children's Health Care" (Karen Sokal-Gutierrez); and "Preventing…

Child Care Information Exchange, 2000

2000-01-01

394

Least Squares Fitting of Circles  

Microsoft Academic Search

Fitting standard shapes or curves to incomplete data (which represent only a small part of the curve) is a notoriously difficult problem. Even if the curve is quite simple, such as an ellipse or a circle, it is hard to reconstruct it from noisy data sampled along a short arc. Here we study the least squares fit (LSF) of circular

Nikolai Chernov; Claire Lesort

2005-01-01

395

Phase Transitions in Ionic Gels  

Microsoft Academic Search

The polymer network of a gel, under certain conditions, undergoes a discrete transition in equilibrium volume with changes in solvent composition or temperature. This Letter demonstrates that ionization of the gel network plays an essential role in the phase transition. The volume collapse is also observed when the pH within the gel is varied.

Toyoichi Tanaka; David Fillmore; Shao-Tang Sun; Izumi Nishio; Gerald Swislow; Arati Shah

1980-01-01

396

FitSKIRT: Oligochromatic Fitting of Dusty Galaxies  

NASA Astrophysics Data System (ADS)

We present the updated version of FitSKIRT, a method to fit radiative transfer models to UV/optical/NIR images of dusty galaxies. Among various improvements made to the code, the most substantial one is the ability to simultaneously fit to several images. This oligochromatic fitting technique (“oligo” stems from Ancient Greek meaning “a few”) can use several reference images, ranging from the UV to NIR, to constrain the parameters of the model more appropriately. Since the alterations made to the code are quite substantial, we revisit the test case used to test the previous version. This new test case is created to check to which degree the improved FitSKIRT is capable of retrieving the initial parameters. Both the images and parameter values are compared to provide insights and valorize the updated fitting procedure. The result is a highly automated fitting routine capable of providing more accurate constraints on both the distribution and properties of stars and dust in dusty galaxies.

De Geyter, G.; Baes, M.

2014-03-01

397

Transfer of value from fit.  

PubMed

People experience regulatory fit when they pursue a goal in a manner that sustains their regulatory orientation (E. T. Higgins, 2000). Five studies tested whether the value experienced from regulatory fit can transfer to a subsequent evaluation of an object. In Studies 1 and 2, participants gave the same coffee mug a higher price if they had chosen it with a strategy that fit their orientation (eager strategy/promotion; vigilant strategy/prevention) than a strategy that did not fit. Studies 3-5 investigated possible mechanisms underlying this effect. Value transfer was independent of positive mood, perceived effectiveness (instrumentality), and perceived efficiency (ease), and occurred for an object that w as independent of the fit process itself. The findings supported a value confusion account of transfer. PMID:12793581

Higgins, E Tory; Chen Idson, Lorraine; Freitas, Antonio L; Spiegel, Scott; Molden, Daniel C

2003-06-01

398

FITS Liberator: Image processing software  

NASA Astrophysics Data System (ADS)

The ESA/ESO/NASA FITS Liberator makes it possible to process and edit astronomical science data in the FITS format to produce stunning images of the universe. Formerly a plugin for Adobe Photoshop, the current version of FITS Liberator is a stand-alone application and no longer requires Photoshop. This image processing software makes it possible to create color images using raw observations from a range of telescopes; the FITS Liberator continues to support the FITS and PDS formats, preferred by astronomers and planetary scientists respectively, which enables data to be processed from a wide range of telescopes and planetary probes, including ESO’s Very Large Telescope, the NASA/ESA Hubble Space Telescope, NASA’s Spitzer Space Telescope, ESA’s XMM-Newton Telescope and Cassini-Huygens or Mars Reconnaissance Orbiter.

Lindberg Christensen, Lars; Nielsen, Lars Holm; Nielsen, Kaspar K.; Johansen, Teis; Hurt, Robert; de Martin, David

2012-06-01

399

Experimental determination of the diffusion coefficient in two-dimensions in ferrous sulphate gels using the finite element method  

Microsoft Academic Search

A novel two-dimensional finite element method for modelling the diffusion which occurs in Fricke or ferrous sulphate type\\u000a radiation dosimetry gels is presented. In most of the previous work, the diffusion coefficient has been estimated using simple\\u000a one-dimensional models. This work presents a two-dimensional model which enables the diffusion coefficient to be determined\\u000a in a much wider range of experimental

C. Baldock; P. J. Harris; A. R. Piercy; B. Healy

2001-01-01

400

Radiation dose distribution in polymer gels by Raman spectroscopy.  

PubMed

The Raman spectroscopy of polymer gel dosimeters has been investigated with a view to developing a novel dosimetry technique that is capable of determining radiation dose within a micrometer of spatial resolution. The polymer gel dosimeter, known as the PAG dosimeter, is typically made up of acrylamide, N,N'-methylene-bis--acrylamide, gelatin, and water. A polyacrylamide network within the gelatin matrix forms in response to an absorbed dose. The loss of monomers may be monitored by corresponding changes to the Raman spectrum. Principal component analysis offers a simple method of quantifying the absorbed radiation dose from the Raman spectrum of the polymer gel. The background luminescence in the spectrum increased significantly with dose and is shown to originate in the glass of the sample vial. The competing effects of elastic scatter, which increases with dose due to the formation of polymer, and sample absorption were quantified and found to introduce errors of up to 5% under certain conditions. Raman spectra as a function of distance from the air-surface interface have been measured for samples that were subjected to doses delivered by a clinical linear accelerator. The depth dose profile thus obtained compared favorably with "gold standard" ion-chamber measurements. PMID:14610936

Rintoul, L; Lepage, M; Baldock, C

2003-01-01

401

Characterizing matrix remodeling in collagen gels using optical coherence tomography  

NASA Astrophysics Data System (ADS)

Optical coherence tomography (OCT) has shown promise at non-destructively characterizing engineered tissues such as collagen gels. However, as the collagen gels develop, the OCT images lose contrast of structures as the gels develop, making visual assessment difficult. Our group proposed quantitatively characterizing these gels by fitting the optical properties from the OCT signals. In this paper, we imaged collagen gels seeded with smooth muscle cells (SMCs) over a 5-day period and used the data to measure their optical properties. Our results showed that over time, the reflectivity of the samples increased 10-fold, corresponding to a decrease in anisotropy factor g, without much change in the scattering coefficient ?s. Overall, the optical properties appeared to be dominated by scattering from the collagen matrix, not the cells. However, SMCs remodeled the collagen matrix, and this collagen remodeling by the cells is what causes the observed changes in optical properties. Moreover, the data showed that the optical properties were sensitive to the activity of matrix metalloproteinases (MMPs), enzymes that break down local collagen fibrils into smaller fragments. Blocking MMPs in the SMC gels greatly impeded both the remodeling process and change in optical properties at day 5. Treating day 1 acellular gels with MMP-8 for 3 hr managed to partially reproduce the remodeling observed in SMC gels at day 5. Altogether, we conclude that matrix remodeling in general, and MMPs specifically, greatly affect the local optical properties of the sample, and OCT is a unique tool that can assess MMP activity in collagen gels both non-destructively and label free.

Levitz, David; Hinds, Monica T.; Hanson, Stephen R.; Jacques, Steven L.

2010-02-01

402

Fit-testing for firefighters.  

PubMed

When fit-testing firefighters who may be required to wear an SCBA unit in the positive pressure mode for IDLH or structural firefighting applications, use these guidelines. 1. The firefighter shall be allowed to pick the most acceptable respirator from a sufficient number of respirator models and sizes so the respirator is acceptable to, and correctly fits, the firefighter. 2. Before a firefighter may be required to use the SCBA, he/she must be fit-tested with the same make, model, style, and size of respirator that will be used. If different makes, models, styles, and sizes of facepieces are used, the firefighter must be fit-tested for each. 3. Based on current interpretations and guidance, OSHA requires firefighters to be quantitatively or qualitatively fit-tested while in the negative pressure mode. 4. Quantitative fit-testing of these respirators shall be accomplished by modifying the facepiece to allow sampling inside the facepiece and breathing zone of the user, midway between the nose and mouth. This requirement shall be accomplished by installing a permanent sampling probe onto a surrogate facepiece or by using a sampling adapter designed to temporarily provide a means of sampling air from inside the facepiece. 5. Qualitative fit-testing can be accomplished by converting the user's actual facepiece into a negative pressure respirator with appropriate filters or by using an identical negative pressure air-purifying respirator facepiece with the same sealing surfaces as a surrogate for the SCBA facepiece. 6. If after passing the fit-test the firefighter subsequently determines the fit of the respirator is unacceptable, he/she shall be given a reasonable opportunity to select a different respirator facepiece and be retested. 7. The new standard requires initial and at least annual fit-testing using quantitative or qualitative fit-testing protocols. 8. Additional fit-testing may be required whenever physical changes to the employee occur that may affect respirator fit, such as facial scarring, dental changes, cosmetic surgery, or an obvious change in body weight. PMID:9891408

Brickman, C P

1999-01-01

403

Microfluidics with Gel Emulsions  

Microsoft Academic Search

Microfluidic processing is usually achieved using single phase liquids. Instead, we use monodisperse emulsions to compartment liquids within microchannel geometries. At low continuous phase volume fractions, droplets self-organize to form well-defined arrangements, analogous to foam. While it is well-known that confined geometries can induce rearrangement of foam compartments at the millimeter-scale, similar dynamics are also expected for gel emulsions. We

Craig Priest; Enkhtuul Surenjav; Stephan Herminghaus; Ralf Seemann

2006-01-01

404

SmartFit: automatic photo fitting for variable data printing  

NASA Astrophysics Data System (ADS)

We present an algorithm for smart image fitting: changing the size of an image so that it may fit "naturally" within a given frame. As the frame's dimensions will generally differ from that of the image, the algorithm preserves important details in their original aspect ratio, while less important details undergo more substantial deformations. This problem is useful for many commercial print applications. One example is the HP SmartStream Designer, which is a tool to create variable and personalized content documents.

Karni, Zachi; Gaash, Amir

2012-02-01

405

Gel architectures and their complexity.  

PubMed

Gels have made the transition from brittle materials with few potential applications to high performance systems with mechanical properties approaching that of rubber. They have a wide variety of structures and provide the opportunity to tailor these structures to achieve well-controlled properties over a range of length scales. In this review we consider and compare the structures and properties of a range of gels that have been studied in recent years. In comparing these gels we highlight the importance of key structural parameters in defining gel mechanical properties. It is hoped that this article will provide authors who discover new gels a resource that will easily enable them to determine the differences of their new gels to existing gels. PMID:24705716

Richtering, Walter; Saunders, Brian R

2014-06-01

406

MissFITS: Basic Maintenance and Packaging Tasks on FITS Files  

NASA Astrophysics Data System (ADS)

MissFITS is a program that performs basic maintenance and packaging tasks on FITS files using an optimized FITS library. MissFITS can: add, edit, and remove FITS header keywords; split and join Multi-Extension-FITS (MEF) files; unpile and pile FITS data-cubes; and, create, check, and update FITS checksums, using R. Seaman's protocol.

Marmo, Chiara; Bertin, Emmanuel

2010-10-01

407

Technical Basis Document for PFP Area Monitoring Dosimetry Program  

Microsoft Academic Search

This document describes the phantom dosimetry used for the PFP Area Monitoring program and establishes the basis for the Plutonium Finishing Plant's (PFP) area monitoring dosimetry program in accordance with the following requirements: Title 10, Code of Federal Regulations (CFR), part 835, ''Occupational Radiation Protection'' Part 835.403; Hanford Site Radiological Control Manual (HSRCM-1), Part 514; HNF-PRO-382, Area Dosimetry Program; and

2000-01-01

408

Physical Fitness of Women Marines.  

National Technical Information Service (NTIS)

The proposed Jewett physical fitness test battery for WMs was evaluated, found consistent with recommendations made in the literature, and administered to 167 WMs. Intercorrelations of the scores demonstrated that each test event measured a separate facto...

P. J. Rasch J. W. Hamby

1967-01-01

409

Physical Fitness Testing and Rewards.  

ERIC Educational Resources Information Center

Fitness testing programs with award systems began in 1958 and proved to be extremely popular. Award programs for students with disabilities are described. The need for award systems for all handicapped students is stressed. (MT)

Stein, Julian U.

1988-01-01

410

Kinematic Fitting of Detached Vertices  

SciTech Connect

The eg3 experiment at the Jefferson Lab CLAS detector aims to determine the existence of the $\\Xi_{5}$ pentaquarks and investigate the excited $\\Xi$ states. Specifically, the exotic $\\Xi_{5}^{--}$ pentaquark will be sought by first reconstructing the $\\Xi^{-}$ particle through its weak decays, $\\Xi^{-}\\to\\pi^{-}\\Lambda$ and $\\Lambda\\to\\pi^{-}$. A kinematic fitting routine was developed to reconstruct the detached vertices of these decays, where confidence level cuts on the fits are used to remove background events. Prior to fitting these decays, the exclusive reaction $\\gamma D\\rightarrow pp\\pi^{-}$ was studied in order to correct the track measurements and covariance matrices of the charged particles. The $\\Lambda\\rightarrow p\\pi^{-}$ and $\\Xi^{-}\\to\\pi^{-}\\Lambda$ decays were then investigated to demonstrate that the kinematic fitting routine reconstructs the decaying particles and their detached vertices correctly.

Paul Mattione

2007-05-01

411

Convex piecewise-linear fitting  

Microsoft Academic Search

We consider the problem of fitting a convex piecewise-linear function, with some specified form, to given multi-dimensional\\u000a data. Except for a few special cases, this problem is hard to solve exactly, so we focus on heuristic methods that find locally\\u000a optimal fits. The method we describe, which is a variation on the K-means algorithm for clustering, seems to work well

Alessandro Magnani; Stephen P. Boyd

2009-01-01

412

Adaptive Walk on Fitness Soundscape  

Microsoft Academic Search

\\u000a We propose a new IEC for musical works based on an adaptive walk on a fitness landscape of sounds. In this system, there is\\u000a a virtual plane that represents the genetic space of possible musical works called fitness soundscape. The user stands on\\u000a the soundscape, and hears the multiple sounds that correspond to one’s neighboring genotypes at the same time.

Reiji Suzuki; Takaya Arita

413

Fitting Cosmological Data CMB Model  

NSDL National Science Digital Library

The Cosmic Microwave Background (CMB) radiation measurements offer some of the most powerful constraints in cosmology for supporting the accelerated expansion of the universe (cosmic acceleration). Rather than fitting a model to the entire dataset, we fit a model to three parameters that represent specific features of the CMB. The simulation allows users to compare and fit theoretical models of cosmology with recent CMB data sets to confirm the accelerated expansion of the universe. This modeling allows the user to vary cosmological parameters within a particular class of dark energy cosmological models to fit a particular cosmological data set. The user can plot several theoretical curves with the data to compare different models. The values of these parameters, for a particular model, determine the physical description and evolution of the universe. The EJS Fitting Cosmological Data CMB model was created using Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_FittingCosmologicalDataCMB.jar file will run the program if Java is installed. You can modify this simulation if you have EJS by right-clicking within the plot and selecting Open Ejs Model from the pop-up menu item.

Moldenhauer, Jacob; Stone, Keenan; Engelhardt, Larry

2012-09-10

414

Absolute and relative dosimetry for ELIMED  

SciTech Connect

The definition of detectors, methods and procedures for the absolute and relative dosimetry of laser-driven proton beams is a crucial step toward the clinical use of this new kind of beams. Hence, one of the ELIMED task, will be the definition of procedures aiming to obtain an absolute dose measure at the end of the transport beamline with an accuracy as close as possible to the one required for clinical applications (i.e. of the order of 5% or less). Relative dosimetry procedures must be established, as well: they are necessary in order to determine and verify the beam dose distributions and to monitor the beam fluence and the energetic spectra during irradiations. Radiochromic films, CR39, Faraday Cup, Secondary Emission Monitor (SEM) and transmission ionization chamber will be considered, designed and studied in order to perform a fully dosimetric characterization of the ELIMED proton beam.

Cirrone, G. A. P.; Schillaci, F.; Scuderi, V. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Institute of Physics Czech Academy of Science, ELI-Beamlines project, Na Slovance 2, Prague (Czech Republic); Cuttone, G.; Candiano, G.; Musumarra, A.; Pisciotta, P.; Romano, F. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania (Italy); Carpinelli, M. [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy)] [INFN Sezione di Cagliari, c/o Dipartimento di Fisica, Università di Cagliari, Cagliari (Italy); Leonora, E.; Randazzo, N. [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Presti, D. Lo [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN-Sezione di Catania, Via Santa Sofia 64, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Raffaele, L. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and INFN-Sezione di Catania, Via Santa Sofia 64, Catania (Italy); Tramontana, A. [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy)] [INFN, Laboratori Nazionali del Sud, Via Santa Sofia 62, Catania, Italy and Università di Catania, Dipartimento di Fisica e Astronomia, Via S. Sofia 64, Catania (Italy); Cirio, R.; Sacchi, R.; Monaco, V. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino, Italy and Università di Torino, Dipartimento di Fisica, Via P.Giuria, 1 10125 Torino (Italy); Marchetto, F.; Giordanengo, S. [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)] [INFN, Sezione di Torino, Via P.Giuria, 1 10125 Torino (Italy)

2013-07-26

415

Patient-specific dosimetry in radionuclide therapy.  

PubMed

This study presents an attempt to compare individualised palliative treatment absorbed doses, by planar images data and Monte Carlo simulation, in two in vivo treatment cases, one of bone metastases and the other of liver lesions. Medical Internal Radiation Dose schema was employed to estimate the absorbed doses. Radiopharmaceutical volume distributions and absorbed doses in the lesions as well as in critical organs were also calculated by Monte Carlo simulation. Individualised planar data calculations remain the method of choice in internal dosimetry in nuclear medicine, but with the disadvantage of attenuation and scatter corrections lack and organ overlay. The overall error is about 7 % for planar data calculations compared with that using Monte Carlo simulation. Patient-specific three-dimensional dosimetric calculations using single-photon emission computed tomography with a parallel computed tomography study is proposed as an accurate internal dosimetry with the additional use of dose-volume histograms, which express dose distributions in cases with obvious inhomogeneity. PMID:21831867

Lyra, Maria; Lagopati, Nefeli; Charalambatou, Paraskevi; Vamvakas, Ioannis

2011-09-01

416

Passive particle dosimetry. [silver halide crystal growth  

NASA Technical Reports Server (NTRS)

Present methods of dosimetry are reviewed with emphasis on the processes using silver chloride crystals for ionizing particle dosimetry. Differences between the ability of various crystals to record ionizing particle paths are directly related to impurities in the range of a few ppm (parts per million). To understand the roles of these impurities in the process, a method for consistent production of high purity silver chloride, and silver bromide was developed which yields silver halides with detectable impurity content less than 1 ppm. This high purity silver chloride was used in growing crystals with controlled doping. Crystals were grown by both the Czochalski method and the Bridgman method, and the Bridgman grown crystals were used for the experiments discussed. The distribution coefficients of ten divalent cations were determined for the Bridgman crystals. The best dosimeters were made with silver chloride crystals containing 5 to 10 ppm of lead; other impurities tested did not produce proper dosimeters.

Childs, C. B.

1977-01-01

417

Thermoluminescent dosimetry in total body irradiation.  

PubMed

The aim of this paper was to develop a thermoluminescent dosimetry method for the absorbed dose determination of 6 MeV high-energy electron beams by thermoluminescent dosimetry. Total body irradiation (TBI) was performed using four dual fields angled at 252° and 285° in high-dose rate (HDR) mode. TBI measurements were investigated to estimate the absorbed dose in different anatomical parts of the patient. Experimental results were obtained using thermoluminescent detectors and solid water phantoms. The TL response of the dosimeters, as a function of the high-energy electron beam (HEEB) absorbed dose, was linear, from 0.1 to 500 cGy. The entrance skin dose (ESD) and isodose distribution on the surface of the treatment were investigated graphically. PMID:23039951

Rodríguez-Cortés, J; Rivera-Montalvo, T; Villaseñor Navarro, L F; Flores-López, O; Roman, J; Hernandez-Oviedo, J O

2012-12-01

418

Radiochromic film dosimetry: past, present, and future.  

PubMed

In radiation therapy, an accurate dose determination and a precise dose delivery to the tumour are directly associated with better treatment outcomes in terms of higher tumour control and lower post radiation therapy complications. Over the years, film dosimetry was developed into a powerful tool for radiotherapy treatment verification and quality assurance. This review summarizes development of GAFCHROMIC™ film models through improvement in their sensitivity and uniformity as two dimensional detectors. The most important characteristics as well as the limitations that can affect the performance of the radiochromic film dosimetry systems have been described. An outline of both clinical and research contemporary applications is given particularly emphasizing new applications like brachytherapy, diagnostic radiology and radiobiological experiments. Review concludes through an overview of future directions in development of this important dosimetric tool revolving around its possible use as a three-dimensional dosimeter and the energy dependence of the film's response. PMID:21050785

Devic, Slobodan

2011-07-01

419

Development of a CCD array imaging system for measurement of dose distributions in doped agarose gels.  

PubMed

An imaging system for agarose gel sections has been investigated for applications in rapid two-dimensional radiation dosimetry. The imaging system, with white light illumination and CCD camera detection, was designed for measurement of the radiation-induced optical density changes in iron- and xylenol orange dye-doped agarose gels. The performance of the imaging system was compared with that of a laser scanning system for the gels and with the accepted dosimetry standard, the ionization chamber. In measurement of beam profiles of two therapeutic radiation fields, relative dose values from the CCD camera imaging system were on average within 3% ranging from 0.005% to 7.5%) of values recorded with a parallel plate ionization chamber. In comparison with the laser scanner, the CCD camera imaging system provided comparable spatial resolution and an increased rate of data acquisition, although a consistently reduced signal to noise ratio was observed. Suggestions for improving the camera imaging technique include noise reduction through camera cooling and further frame averaging. PMID:9304582

Tarte, B J; Jardine, P A; van Doorn, T; Nitschke, K N; Poulsen, M G

1997-09-01

420

Technical basis for internal dosimetry at Hanford  

Microsoft Academic Search

The Hanford Internal Dosimetry Program, administered by Pacific Northwest Laboratory for the US Department of Energy, provides routine bioassay monitoring for employees who are potentially exposed to radionuclides in the workplace. This report presents the technical basis for routine bioassay monitoring and the assessment of internal dose at Hanford. The radionuclides of concern include tritium, corrosion products (⁵⁸Co, ⁶°Co, ⁵⁴Mn,

M. J. Sula; E. H. Carbaugh; D. E. Bihl

1989-01-01

421

Technical basis for internal dosimetry at Hanford  

Microsoft Academic Search

The Hanford Internal Dosimetry Program, administered by Pacific Northwest Laboratory for the US Department of Energy, provides routine bioassay monitoring for employees who are potentially exposed to radionuclides in the workplace. This report presents the technical basis for routine bioassay monitoring and the assessment of internal dose at Hanford. The radionuclides of concern include tritium, corrosion products (⁵⁸Co, ⁶°Co, ⁵⁴Mn,

M. J. Sula; E. H. Carbaugh; D. E. Bihl

1991-01-01

422

Workshop 3: Retrospective Dosimetry and Decommissioning Data  

NASA Astrophysics Data System (ADS)

The workshop had 27 participants. There was an initial discussion of the current status and use of retrospective dosimetry techniques. There was a consensus that this had become a wide-spread and useful technique. The applications have ranged from the well known characterization of reactor vessel neutron exposure to the assessment of the age of metal specimens removed from reactor internals to concrete trepans from concrete shields in a decommissioning context...

Serén, Tom; Fero, Arnold

2009-08-01

423

DNA Length Ranges Exhibiting Distinct Separation Mechanisms in Gel Electrophoresis  

NASA Astrophysics Data System (ADS)

Electrophoresis was performed on double stranded DNA ranging from 200 to 194,000 bp in agarose gel concentrations from 0.4% - 1.3%. The electric field was varied from 0.62 to 6.21 V/cm. A wide range of electric fields and gel concentrations were used to study how the new interpolation equation, frac1?(L) = frac1?L - (frac1?L - frac1?_s)e^-L/? (where ?_L, ?_s, and ? are independent free fitting parameters), helps to distinguish among different mechanisms of molecular transport. This exponential relation fits well when there is a smooth transition from Ogston sieving to reptation. These transitions are distinguished by so-called ``reptation plots" (plotting 3? L/?_rc vs. L) (J. Rousseau, G. Drouin, and G. W. Slater, Phys Rev Lett. 1997, 79, 1945-1948). Fits deviate from the data more than two characteristic trends are observed in the reptation plots. The failure of the fits to follow the data appears to be a consequence of another separation mechanism, ``entropic trapping," occurring between the sieving and reptation regimes. The boundaries between length and field ranges where different separation mechanisms dominate are extracted from reptation plots of the best fits and the data. ``Phase diagrams" expressing these boundaries are derived.

Beheshti, A.; van Winkle, D. H.; Rill, R. L.

2003-03-01

424

Clarification Procedure for Gels  

NASA Technical Reports Server (NTRS)

Procedure developed to obtain transparent gels with consistencies suitable for crystal growth, by replacing sodium ions in silicate solution with potassium ions. Clarification process uses cation-exchange resin to replace sodium ions in stock solution with potassium ions, placed in 1M solution of soluble potassium salt. Slurry stirred for several hours to allow potassium ions to replace all other cations on resin. Supernatant solution decanted through filter, and beads rinsed with distilled water. Rinsing removes excess salt but leaves cation-exchange beads fully charged with potassium ions.

Barber, Patrick G.; Simpson, Norman R.

1987-01-01

425

Hanford Internal Dosimetry Project manual. Revision 1  

SciTech Connect

This document describes the Hanford Internal Dosimetry Project, as it is administered by Pacific Northwest Laboratory (PNL) in support of the US Department of Energy and its Hanford contractors. Project services include administrating the bioassay monitoring program, evaluating and documenting assessment of potential intakes and internal dose, ensuring that analytical laboratories conform to requirements, selecting and applying appropriate models and procedures for evaluating radionuclide deposition and the resulting dose, and technically guiding and supporting Hanford contractors in matters regarding internal dosimetry. Specific chapters deal with the following subjects: practices of the project, including interpretation of applicable DOE Orders, regulations, and guidance into criteria for assessment, documentation, and reporting of doses; assessment of internal dose, including summary explanations of when and how assessments are performed; recording and reporting practices for internal dose; selection of workers for bioassay monitoring and establishment of type and frequency of bioassay measurements; capability and scheduling of bioassay monitoring services; recommended dosimetry response to potential internal exposure incidents; quality control and quality assurance provisions of the program.

Carbaugh, E.H.; Bihl, D.E.; MacLellan, J.A.; Long, M.P.

1994-07-01

426

In vivo dosimetry in external beam radiotherapy  

SciTech Connect

In vivo dosimetry (IVD) is in use in external beam radiotherapy (EBRT) to detect major errors, to assess clinically relevant differences between planned and delivered dose, to record dose received by individual patients, and to fulfill legal requirements. After discussing briefly the main characteristics of the most commonly applied IVD systems, the clinical experience of IVD during EBRT will be summarized. Advancement of the traditional aspects of in vivo dosimetry as well as the development of currently available and newly emerging noninterventional technologies are required for large-scale implementation of IVD in EBRT. These new technologies include the development of electronic portal imaging devices for 2D and 3D patient dosimetry during advanced treatment techniques, such as IMRT and VMAT, and the use of IVD in proton and ion radiotherapy by measuring the decay of radiation-induced radionuclides. In the final analysis, we will show in this Vision 20/20 paper that in addition to regulatory compliance and reimbursement issues, the rationale for in vivo measurements is to provide an accurate and independent verification of the overall treatment procedure. It will enable the identification of potential errors in dose calculation, data transfer, dose delivery, patient setup, and changes in patient anatomy. It is the authors' opinion that all treatments with curative intent should be verified through in vivo dose measurements in combination with pretreatment checks.

Mijnheer, Ben [Department of Radiation Oncology, Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam 1066 CX (Netherlands); Beddar, Sam [Department of Radiation Physics, University of Texas MD Anderson Cancer Center, Houston, Texas 77030 (United States); Izewska, Joanna [Division of Human Health, International Atomic Energy Agency, Vienna 1400 (Austria); Reft, Chester [Department of Radiation and Cellular Oncology, University of Chicago Medical Center, Chicago, Illinois 60637 (United States)

2013-07-15

427

Sensitivity studies associated with dosimetry experiment interpretation  

SciTech Connect

Document available in abstract form only, full text of document follows: Interpretation of reactor dosimetry experiments with C/E comparison requires precise knowledge of parameters involved in modeling. Some parameters have more weight than others on the calculated values. So, sensitivity studies should be conducted to verify the importance of these parameters. The conclusions of these studies are used to refine the experiment modeling, or to correct uncertainty calculations. The results of these sensitivity studies allow a post-irradiation analysis, which can justify the discarding of some atypical C/M values. Derived uncertainties may be improved by the sensitivity analyses. Beyond classical parameters as geometry or composition, this paper describes some specific sensitivity studies conducted for dosimetry irradiation in reactor, and presents conclusions. These studies are based on dosimeters irradiated in the EOLE reactor facility at Cadarache CEA center. Conclusions drawn from these studies are generic and can be applied to any dosimetry study. Calculations performed for these studies were realized using TRIPOLI-4 Monte Carlo code. (authors)

Bourganel, S.; Soldevila, M. [CEA/DANS/DM2S/SERMA, CEA Saclay, 91191, Gif sur Yvette (France); Ferrer, A.; Gregoire, G.; Destouches, C.; Beretz, D. [CEA/DEN-CAD/DER/SPEX, CEA Cadarache, F13108, Saint Paul lez Durance (France)

2011-07-01

428

EPR dosimetry with tooth enamel: A review.  

PubMed

When tooth enamel is exposed to ionizing radiation, radicals are formed, which can be detected using electron paramagnetic resonance (EPR) techniques. EPR dosimetry using tooth enamel is based on the (presumed) correlation between the intensity or amplitude of some of the radiation-induced signals with the dose absorbed in the enamel. In the present paper a critical review is given of this widely applied dosimetric method. The first part of the paper is fairly fundamental and deals with the main properties of tooth enamel and some of its model systems (e.g., synthetic apatites). Considerable attention is also paid to the numerous radiation-induced and native EPR signals and the radicals responsible for them. The relevant methods for EPR detection, identification and spectrum analyzing are reviewed from a general point of view. Finally, the needs for solid-state modelling and studies of the linearity of the dose response are investigated. The second part is devoted to the practical implementation of EPR dosimetry using enamel. It concerns specific problems of preparation of samples, their irradiation and spectrum acquisition. It also describes how the dosimetric signal intensity and dose can be retrieved from the EPR spectra. Special attention is paid to the energy dependence of the EPR response and to sources of uncertainties. Results of and problems encountered in international intercomparisons and epidemiological studies are also dealt with. In the final section the future of EPR dosimetry with tooth enamel is analyzed. PMID:20599388

Fattibene, Paola; Callens, Freddy

2010-11-01

429

DNA Electrophoresis in Agarose Gels: Mobility vs. Length Dependence  

NASA Astrophysics Data System (ADS)

Over the years, many different models have been applied to the migration of DNA fragments during gel electrophoresis. These models have been limited to describing DNA motion over specific size ranges. We propose a frictional and charge based model relating the electrophoretic mobility to length that fits data for DNA fragment lengths from 100 base pairs (bp) to 50 kilobase pairs (kbp). Excellent fits have been obtained from both published sources and experiments we have performed, with agarose gel concentrations of 0.5% to 1.5%. The length range of DNA for which the model works spans the range where a DNA fragment behaves like a semi-rigid rod to best described as a random coil polymer

Beheshti, Afshin; van Winkle, David; Rill, Randolph

2001-03-01

430

Inexpensive and safe DNA gel electrophoresis using household materials.  

PubMed

Gel electrophoresis is the single most important molecular biology technique and it is central to life sciences research, but it is often too expensive for the secondary science classroom or homeschoolers. A simple safe low-cost procedure is described here that uses household materials to construct and run DNA gel electrophoresis. Plastic containers are fitted with aluminum foil electrodes and 9-V batteries to run food-grade agar-agar gels using aquarium pH buffers and then stained with gentian violet. This activity was tested in a high school biology classroom with significantly positive responses on postactivity reflective surveys. The electrophoresis activity addresses several Life Science Content Standard C criteria, including aspects of cell biology, genetics, and evolution. It also can be used to teach aspects of motion and force in the physical science classroom. PMID:22615228

Ens, S; Olson, A B; Dudley, C; Ross, N D; Siddiqi, A A; Umoh, K M; Schneegurt, M A

2012-01-01

431

Rapid (ten-minute) pore-gradient electrophoresis of proteins and peptides in Micrograd gels.  

PubMed

Precast gradient gels of short migration length (25 mm) have been developed to provide rapid electrophoretic separation without loss of resolution. These Micrograd gels have been prepared in gel ranges (conventional and unique) to match pore-gradient electrophoresis conditions to proteins/peptides ranging in size from several hundreds to millions. The Hylinx Micrograd gel combines an extreme gel range (6 to 48% polyacrylamide) with a novel crosslinker to provide sieving of polypeptides, and pore-limit electrophoresis of the smallest proteins (e.g. insulin monomer). All gel ranges (such as 3 to 30%) provide zone sharpening in routine analysis of conventional protein mixtures (e.g. serum) within 10 min electrophoresis at 200 to 300 volts. The gels are thin (1 mm) and thus stain quickly, but the gel cassette is of conventional overall width (83 mm), thus fitting many apparatus designs and accommodating 12 samples. The gels are finding valuable use in screening applications, requiring the electrophoretic analysis of many samples, and in cases where a rapid answer is needed, such as monitoring protein purification. The gels have proved particularly useful, in-house, for the latter application in developing Gradipore's new large-scale preparative electrophoresis system, the Gradiflow. PMID:1599958

Wrigley, C W; Margolis, J

1992-01-01

432

Fitness  

MedlinePLUS

... even fun times, like watching movies and playing video games, don’t require us to move . This is a problem because we now know that how much you move is as important as what you eat to your overall health. But don’t worry — girlshealth.gov can help ...

433

Polyoxometalate-based Supramolecular Gel  

NASA Astrophysics Data System (ADS)

Self-assemblyings of surfactant-encapsulated Wells-Dawson polyoxometalates (SEPs) nanobuilding blocks in butanone and esters yielded supramolecular gels showing thermo and photo responsive properties. The gels can be further polymerized if unsaturated esters were used and subsequently electrospinned into nanowires and non-woven mats. The as-prepared non-woven mats have a Young's modulus as high as 542.55 MPa. It is believed that this supramolecular gel is a good platform for polyoxometalates processing.

He, Peilei; Xu, Biao; Liu, Huiling; He, Su; Saleem, Faisal; Wang, Xun

2013-05-01

434

Polyoxometalate-based Supramolecular Gel  

PubMed Central

Self-assemblyings of surfactant-encapsulated Wells-Dawson polyoxometalates (SEPs) nanobuilding blocks in butanone and esters yielded supramolecular gels showing thermo and photo responsive properties. The gels can be further polymerized if unsaturated esters were used and subsequently electrospinned into nanowires and non-woven mats. The as-prepared non-woven mats have a Young's modulus as high as 542.55?MPa. It is believed that this supramolecular gel is a good platform for polyoxometalates processing.

He, Peilei; Xu, Biao; Liu, Huiling; He, Su; Saleem, Faisal; Wang, Xun

2013-01-01

435

Measured, modeled, and causal conceptions of fitness  

PubMed Central

This paper proposes partial answers to the following questions: in what senses can fitness differences plausibly be considered causes of evolution?What relationships are there between fitness concepts used in empirical research, modeling, and abstract theoretical proposals? How does the relevance of different fitness concepts depend on research questions and methodological constraints? The paper develops a novel taxonomy of fitness concepts, beginning with type fitness (a property of a genotype or phenotype), token fitness (a property of a particular individual), and purely mathematical fitness. Type fitness includes statistical type fitness, which can be measured from population data, and parametric type fitness, which is an underlying property estimated by statistical type fitnesses. Token fitness includes measurable token fitness, which can be measured on an individual, and tendential token fitness, which is assumed to be an underlying property of the individual in its environmental circumstances. Some of the paper's conclusions can be outlined as follows: claims that fitness differences do not cause evolution are reasonable when fitness is treated as statistical type fitness, measurable token fitness, or purely mathematical fitness. Some of the ways in which statistical methods are used in population genetics suggest that what natural selection involves are differences in parametric type fitnesses. Further, it's reasonable to think that differences in parametric type fitness can cause evolution. Tendential token fitnesses, however, are not themselves sufficient for natural selection. Though parametric type fitnesses are typically not directly measurable, they can be modeled with purely mathematical fitnesses and estimated by statistical type fitnesses, which in turn are defined in terms of measurable token fitnesses. The paper clarifies the ways in which fitnesses depend on pragmatic choices made by researchers.

Abrams, Marshall

2012-01-01

436

Fit Effect of Motorcycle Helmet  

NASA Astrophysics Data System (ADS)

Optimized assessment of the adequacy of fit conditions between a motorcycle helmet and head size in relation to prevention of head injury remains unclear and is complicated by wide variations in the size and shape characteristics of helmet and wearer’s heads. A finite element model (LS-DYNA3D) based on realistic geometric features of a motorcycle helmet was established to simulate the standard shock absorption test for evaluating the dynamic response and fit effects of a helmet. The model was used to simulate crown, rear and side sites impacts of the helmet. The peak acceleration and Head Injury Criterion (HIC) were employed to assess the protective performance of the helmet against head injuries. The results show that this helmet model had various dynamic responses at different impact sites due to its geometric shape, but that the impact-absorbing capability did not vary markedly within these sites. The fit conditions between the headform and the helmet dramatically affected the assessment of the impact-absorbing capability of the helmet in the standard shock absorption test. However, for a motorcyclist, the helmet fit would have only minor influence on the protection against head injuries. This observation suggests that a better fitting helmet with stable fixation should provide more protection against head injury.

Chang, Li-Tung; Chang, Chih-Han; Chang, Guan-Liang

437

Fitting Cosmological Supernovae Data Model  

NSDL National Science Digital Library

The Fitting Cosmological Supernovae Data Model allows users to compare and fit cosmological models with recent supernovae type Ia datasets to confirm the accelerated expansion of the universe. The 2011 Nobel Prize in Physics was awarded for the discovery of the cosmic acceleration using Supernovae Type Ia. This simulation allows the user to vary cosmological parameters within a particular class of dark energy cosmological models to fit a particular supernovae dataset. The simulation can plot several theoretical curves with the supernovae data to compare different models. The values of these parameters, for a particular model, determine the physical description and evolution of the universe. The Fitting Cosmological Supernovae Data Model model was created using Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_Fitting_Cosmological_Models_Supernovae.jar file will run the program if Java is installed. You can modify this simulation if you have EJS by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item.

Moldenhauer, Jacob; Engelhardt, Larry; Stone, Keenan

2011-12-08

438

Dosimetry tools and techniques for IMRT  

SciTech Connect

Intensity modulated radiation therapy (IMRT) poses a number of challenges for properly measuring commissioning data and quality assurance (QA) radiation dose distributions. This report provides a comprehensive overview of how dosimeters, phantoms, and dose distribution analysis techniques should be used to support the commissioning and quality assurance requirements of an IMRT program. The proper applications of each dosimeter are described along with the limitations of each system. Point detectors, arrays, film, and electronic portal imagers are discussed with respect to their proper use, along with potential applications of 3D dosimetry. Regardless of the IMRT technique utilized, some situations require the use of multiple detectors for the acquisition of accurate commissioning data. The overall goal of this task group report is to provide a document that aids the physicist in the proper selection and use of the dosimetry tools available for IMRT QA and to provide a resource for physicists that describes dosimetry measurement techniques for purposes of IMRT commissioning and measurement-based characterization or verification of IMRT treatment plans. This report is not intended to provide a comprehensive review of commissioning and QA procedures for IMRT. Instead, this report focuses on the aspects of metrology, particularly the practical aspects of measurements that are unique to IMRT. The metrology of IMRT concerns the application of measurement instruments and their suitability, calibration, and quality control of measurements. Each of the dosimetry measurement tools has limitations that need to be considered when incorporating them into a commissioning process or a comprehensive QA program. For example, routine quality assurance procedures require the use of robust field dosimetry systems. These often exhibit limitations with respect to spatial resolution or energy response and need to themselves be commissioned against more established dosimeters. A chain of dosimeters, from secondary standards to field instruments, is established to assure the quantitative nature of the tests. This report is intended to describe the characteristics of the components of these systems; dosimeters, phantoms, and dose evaluation algorithms. This work is the report of AAPM Task Group 120.

Low, Daniel A.; Moran, Jean M.; Dempsey, James F.; Dong Lei; Oldham, Mark [Washington University, St. Louis, Missouri 63110 (United States); University of Michigan, Ann Arbor, Michigan 48109 (United States); Viewray Incorporated, Cleveland, Ohio 44106 (United States); M. D. Anderson Cancer Center, Houston, Texas 77013 (United States); Duke University Medical Center, Durham, North Carolina 27710 (United States)

2011-03-15

439

Electrically controlled polymeric gel actuators  

DOEpatents

Electrically controlled polymeric gel actuators or synthetic muscles are described capable of undergoing substantial expansion and contraction when subjected to changing pH environments, temperature, or solvent. The actuators employ compliant containers for the gels and their solvents. The gels employed may be cylindrical electromechanical gel fibers such as polyacrylamide fibers or a mixture of poly vinyl alcohol-polyacrylic acid arranged in a parallel aggregate and contained in an electrolytic solvent bath such as salt water. The invention includes smart, electrically activated devices exploiting this phenomenon. These devices are capable of being manipulated via active computer control as large displacement actuators for use in adaptive structure such as robots. 11 figures.

Adolf, D.B.; Shahinpoor, M.; Segalman, D.J.; Witkowski, W.R.

1993-10-05

440

Electrically controlled polymeric gel actuators  

DOEpatents

Electrically controlled polymeric gel actuators or synthetic muscles capable of undergoing substantial expansion and contraction when subjected to changing pH environments, temperature, or solvent. The actuators employ compliant containers for the gels and their solvents. The gels employed may be cylindrical electromechanical gel fibers such as polyacrylamide fibers or a mixture of poly vinyl alcohol-polyacrylic acid arranged in a parallel aggregate and contained in an electrolytic solvent bath such as salt water. The invention includes smart, electrically activated devices exploiting this phenomenon. These devices are capable of being manipulated via active computer control as large displacement actuators for use in adaptive structure such as robots.

Adolf, Douglas B. (Albuquerque, NM); Shahinpoor, Mohsen (Albuquerque, NM); Segalman, Daniel J. (Albuquerque, NM); Witkowski, Walter R. (Albuquerque, NM)

1993-01-01

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