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Title: Brachytherapy dosimetry parameters calculated for a {sup 131}Cs source

Abstract

A comprehensive analysis of the IsoRay Medical model CS-1 Rev2 {sup 131}Cs brachytherapy source was performed. Dose distributions were simulated using Monte Carlo methods (MCNP5) in liquid water, Solid{sup TM}, and Virtual Water{sup TM} spherical phantoms. From these results, the in-water brachytherapy dosimetry parameters have been determined, and were compared with those of Murphy et al. [Med. Phys. 31, 1529-1538 (2004)] using measurements and simulations. Our results suggest that calculations obtained using erroneous cross-section libraries should be discarded as recommended by the 2004 AAPM TG-43U1 report. Our {sub MC}{lambda} value of 1.046{+-}0.019 cGy h{sup -1} U{sup -1} is within 1.3% of that measured by Chen et al. [Med. Phys. 32, 3279-3285 (2005)] using TLDs and the calculated results of Wittman and Fisher [Med. Phys. 34, 49-54 (2007)] using MCNP5. Using the discretized energy approach of Rivard [Appl. Radiat. Isot. 55, 775-782 (2001)] to ascertain the impact of individual {sup 131}Cs photons on radial dose function and anisotropy functions, there was virtual equivalence of results for 29.461{<=}E{sub {gamma}}{<=}34.419 keV and for a mono-energetic 30.384 keV photon source. Comparisons of radial dose function and 2D anisotropy function data are also included, and an analysis of material composition and cross-section libraries was performed.

Authors:
 [1]
  1. Department of Radiation Oncology, Tufts-New England Medical Center, Tufts University School of Medicine, Box 246, 750 Washington Street, Boston, Massachusetts 02111 (United States)
Publication Date:
OSTI Identifier:
20951064
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 2; Other Information: DOI: 10.1118/1.2432162; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ANISOTROPY; BRACHYTHERAPY; CESIUM 131; DOSIMETRY; KEV RANGE 10-100; MONTE CARLO METHOD; NUCLEAR DATA COLLECTIONS; PHANTOMS; PHOTON BEAMS; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; SIMULATION; THERMOLUMINESCENT DOSEMETERS

Citation Formats

Rivard, Mark J. Brachytherapy dosimetry parameters calculated for a {sup 131}Cs source. United States: N. p., 2007. Web. doi:10.1118/1.2432162.
Rivard, Mark J. Brachytherapy dosimetry parameters calculated for a {sup 131}Cs source. United States. doi:10.1118/1.2432162.
Rivard, Mark J. Thu . "Brachytherapy dosimetry parameters calculated for a {sup 131}Cs source". United States. doi:10.1118/1.2432162.
@article{osti_20951064,
title = {Brachytherapy dosimetry parameters calculated for a {sup 131}Cs source},
author = {Rivard, Mark J.},
abstractNote = {A comprehensive analysis of the IsoRay Medical model CS-1 Rev2 {sup 131}Cs brachytherapy source was performed. Dose distributions were simulated using Monte Carlo methods (MCNP5) in liquid water, Solid{sup TM}, and Virtual Water{sup TM} spherical phantoms. From these results, the in-water brachytherapy dosimetry parameters have been determined, and were compared with those of Murphy et al. [Med. Phys. 31, 1529-1538 (2004)] using measurements and simulations. Our results suggest that calculations obtained using erroneous cross-section libraries should be discarded as recommended by the 2004 AAPM TG-43U1 report. Our {sub MC}{lambda} value of 1.046{+-}0.019 cGy h{sup -1} U{sup -1} is within 1.3% of that measured by Chen et al. [Med. Phys. 32, 3279-3285 (2005)] using TLDs and the calculated results of Wittman and Fisher [Med. Phys. 34, 49-54 (2007)] using MCNP5. Using the discretized energy approach of Rivard [Appl. Radiat. Isot. 55, 775-782 (2001)] to ascertain the impact of individual {sup 131}Cs photons on radial dose function and anisotropy functions, there was virtual equivalence of results for 29.461{<=}E{sub {gamma}}{<=}34.419 keV and for a mono-energetic 30.384 keV photon source. Comparisons of radial dose function and 2D anisotropy function data are also included, and an analysis of material composition and cross-section libraries was performed.},
doi = {10.1118/1.2432162},
journal = {Medical Physics},
number = 2,
volume = 34,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}
  • Dosimetry measurements of a {sup 131}Cs brachytherapy source have been performed in liquid water employing thermoluminescence dosimeters. A search of the literature reveals that this is the first time a complete set of dosimetric parameters for a brachytherapy ''seed'' source has been measured in liquid water. This method avoids the medium correction uncertainties introduced by the use of water-equivalent plastic phantoms. To assure confidence in the results, four different sources were employed for each parameter measured, and measurements were performed multiple times. The measured dosimetric parameters presented here are based on the AAPM Task Group 43 formalism. The dose-rate constantmore » measured in liquid water was (1.063{+-}0.023) cGy h{sup -1} U{sup -1} and was based on the air-kerma strength standard for this source established by the National Institute of Standards and Technology. Measured values for the 2D anisotropy function and the radial dose function are presented.« less
  • Purpose: The formalism recommended by Task Group 60 (TG-60) of the American Association of Physicists in Medicine (AAPM) is applicable for {beta} sources. Radioactive biocompatible and biodegradable {sup 153}Sm glass seed without encapsulation is a {beta}{sup -} emitter radionuclide with a short half-life and delivers a high dose rate to the tumor in the millimeter range. This study presents the results of Monte Carlo calculations of the dosimetric parameters for the {sup 153}Sm brachytherapy source. Methods: Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate two-dimensional dose distributions around the source. The dosimetric parameters ofmore » AAPM TG-60 recommendations including the reference dose rate, the radial dose function, the anisotropy function, and the one-dimensional anisotropy function were obtained. Results: The dose rate value at the reference point was estimated to be 9.21{+-}0.6 cGy h{sup -1} {mu}Ci{sup -1}. Due to the low energy beta emitted from {sup 153}Sm sources, the dose fall-off profile is sharper than the other beta emitter sources. The calculated dosimetric parameters in this study are compared to several beta and photon emitting seeds. Conclusions: The results show the advantage of the {sup 153}Sm source in comparison with the other sources because of the rapid dose fall-off of beta ray and high dose rate at the short distances of the seed. The results would be helpful in the development of the radioactive implants using {sup 153}Sm seeds for the brachytherapy treatment.« less
  • A new x-ray source, the model S700 Axxent trade mark sign X-Ray Source (Source), has been developed by Xoft Inc. for electronic brachytherapy. Unlike brachytherapy sources containing radionuclides, this Source may be turned on and off at will and may be operated at variable currents and voltages to change the dose rate and penetration properties. The in-water dosimetry parameters for this electronic brachytherapy source have been determined from measurements and calculations at 40, 45, and 50 kV settings. Monte Carlo simulations of radiation transport utilized the MCNP5 code and the EPDL97-based mcplib04 cross-section library. Inter-tube consistency was assessed for 20more » different Sources, measured with a PTW 34013 ionization chamber. As the Source is intended to be used for a maximum of ten treatment fractions, tube stability was also assessed. Photon spectra were measured using a high-purity germanium (HPGe) detector, and calculated using MCNP. Parameters used in the two-dimensional (2D) brachytherapy dosimetry formalism were determined. While the Source was characterized as a point due to the small anode size, <1 mm, use of the one-dimensional (1D) brachytherapy dosimetry formalism is not recommended due to polar anisotropy. Consequently, 1D brachytherapy dosimetry parameters were not sought. Calculated point-source model radial dose functions at g{sub P}(5) were 0.20, 0.24, and 0.29 for the 40, 45, and 50 kV voltage settings, respectively. For 1<r<7 cm, measured point-source model radial dose functions were typically within 4% of calculated results. Calculated values for F(r,{theta}) for all operating voltages were within 15% of unity along the distal end ({theta}=0 deg. ), and ranged from F(1 cm,160 deg. )=0.2 to F(15 cm,175 deg. )=0.4 towards the catheter proximal end. For all three operating voltages using the PTW chamber, measured dependence of output as a function of azimuthal angle, {psi}, was typically on average {+-}3% for 0 deg. {<=}{psi}{<=}360 deg. . Excluding an energy response function, measurements of normalized photon energy spectra were made for three operating voltages, and were typically within 2% agreement with the normalized Monte Carlo calculated spectra. In general, the model S700 Source exhibited depth dose behavior similar to low-energy photon-emitting low dose rate sources {sup 125}I and {sup 103}Pd, yet with capability for variable and much higher dose rates and subsequently adjustable penetration capabilities. This paper presents the calculated and measured in-water brachytherapy dosimetry parameters for the model S700 Source at the aforementioned three operating voltages.« less
  • Monte Carlo (MC) simulations were performed to estimate brachytherapy dose distributions for Collaborative Ocular Melanoma Study (COMS) eye plaques. Brachytherapy seed models 200, 6711, and CS-1 Rev2 carrying {sup 103}Pd, {sup 125}I, and {sup 131}Cs radionuclides, respectively, were modeled and benchmarked against previously published values. Calculated dose rate constants {sub MC}{lambda} were 0.684, 0.924, and 1.052 cGy h{sup -1} U{sup -1} ({+-}2.6%, k=1 uncertainty) for models 200, 6711, and CS-1 Rev2, respectively. The seeds were distributed into 10, 12, 14, 16, 18, 20, and 22 mm-diameter COMS eye plaques. Simulations were performed in both heterogeneous and homogeneous environments, where themore » latter were in-water and the former included the silastic seed carrier insert and gold-alloy plaque. MC-based homogenous central axis dose distributions agreed within 2%{+-}1% ({+-}1 s.d.) to hand-calculated values. For heterogeneous simulations, notable photon attenuation was observed, with dose reduction at 5 mm of 19%, 11%, and 9% for {sup 103}Pd, {sup 125}I, and {sup 131}Cs, respectively. A depth-dependent correction factor was derived to correct homogenous central-axis dose distributions for plaque component heterogeneities, which were found to be significant at short radial distances.« less