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Title: SU-F-T-12: Monte Carlo Dosimetry of the 60Co Bebig High Dose Rate Source for Brachytherapy

Abstract

Purpose: The purpose of this work is to obtain the dosimetry parameters in accordance with the AAPM TG-43U1 formalism with Monte Carlo calculations regarding the BEBIG 60Co high-dose-rate brachytherapy. The geometric design and material details of the source was provided by the manufacturer and was used to define the Monte Carlo geometry. Methods: The dosimetry studies included the calculation of the air kerma strength Sk, collision kerma in water along the transverse axis with an unbounded phantom, dose rate constant and radial dose function. The Monte Carlo code system that was used was EGSnrc with a new cavity code, which is a part of EGS++ that allows calculating the radial dose function around the source. The XCOM photon cross-section library was used. Variance reduction techniques were used to speed up the calculation and to considerably reduce the computer time. To obtain the dose rate distributions of the source in an unbounded liquid water phantom, the source was immersed at the center of a cube phantom of 100 cm3. Results: The obtained dose rate constant for the BEBIG 60Co source was 1.108±0.001 cGyh-1U-1, which is consistent with the values in the literature. The radial dose functions were compared with the valuesmore » of the consensus data set in the literature, and they are consistent with the published data for this energy range. Conclusion: The dose rate constant is consistent with the results of Granero et al. and Selvam and Bhola within 1%. Dose rate data are compared to GEANT4 and DORZnrc Monte Carlo code. However, the radial dose function is different by up to 10% for the points that are notably near the source on the transversal axis because of the high-energy photons from 60Co, which causes an electronic disequilibrium at the interface between the source capsule and the liquid water for distances up to 1 cm.« less

Authors:
;  [1]
  1. Universidade do Estado do Rio de Janeiro, Rio De Janeiro, Rio de Janeiro (Brazil)
Publication Date:
OSTI Identifier:
22642262
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; BRACHYTHERAPY; COBALT 60; CROSS SECTIONS; DOSE RATES; DOSIMETRY; KERMA; MONTE CARLO METHOD; NUCLEAR DATA COLLECTIONS; PHANTOMS; RADIATION DOSES; REACTION KINETICS

Citation Formats

Campos, L T, and Almeida, C E V de. SU-F-T-12: Monte Carlo Dosimetry of the 60Co Bebig High Dose Rate Source for Brachytherapy. United States: N. p., 2016. Web. doi:10.1118/1.4956146.
Campos, L T, & Almeida, C E V de. SU-F-T-12: Monte Carlo Dosimetry of the 60Co Bebig High Dose Rate Source for Brachytherapy. United States. doi:10.1118/1.4956146.
Campos, L T, and Almeida, C E V de. 2016. "SU-F-T-12: Monte Carlo Dosimetry of the 60Co Bebig High Dose Rate Source for Brachytherapy". United States. doi:10.1118/1.4956146.
@article{osti_22642262,
title = {SU-F-T-12: Monte Carlo Dosimetry of the 60Co Bebig High Dose Rate Source for Brachytherapy},
author = {Campos, L T and Almeida, C E V de},
abstractNote = {Purpose: The purpose of this work is to obtain the dosimetry parameters in accordance with the AAPM TG-43U1 formalism with Monte Carlo calculations regarding the BEBIG 60Co high-dose-rate brachytherapy. The geometric design and material details of the source was provided by the manufacturer and was used to define the Monte Carlo geometry. Methods: The dosimetry studies included the calculation of the air kerma strength Sk, collision kerma in water along the transverse axis with an unbounded phantom, dose rate constant and radial dose function. The Monte Carlo code system that was used was EGSnrc with a new cavity code, which is a part of EGS++ that allows calculating the radial dose function around the source. The XCOM photon cross-section library was used. Variance reduction techniques were used to speed up the calculation and to considerably reduce the computer time. To obtain the dose rate distributions of the source in an unbounded liquid water phantom, the source was immersed at the center of a cube phantom of 100 cm3. Results: The obtained dose rate constant for the BEBIG 60Co source was 1.108±0.001 cGyh-1U-1, which is consistent with the values in the literature. The radial dose functions were compared with the values of the consensus data set in the literature, and they are consistent with the published data for this energy range. Conclusion: The dose rate constant is consistent with the results of Granero et al. and Selvam and Bhola within 1%. Dose rate data are compared to GEANT4 and DORZnrc Monte Carlo code. However, the radial dose function is different by up to 10% for the points that are notably near the source on the transversal axis because of the high-energy photons from 60Co, which causes an electronic disequilibrium at the interface between the source capsule and the liquid water for distances up to 1 cm.},
doi = {10.1118/1.4956146},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • An ytterbium-169 high dose rate brachytherapy source, distinguished by an intensity-weighted average photon energy of 92.7 keV and a 32.015{+-}0.009 day half-life, is characterized in terms of the updated AAPM Task Group Report No. 43 specifications using the MCNP5 Monte Carlo computer code. In accordance with these specifications, the investigation included Monte Carlo simulations both in water and air with the in-air photon spectrum filtered to remove low-energy photons below 10 keV. TG-43 dosimetric data including S{sub K}, D(r,{theta}), {lambda}, g{sub L}(r), F(r,{theta}), {phi}{sub an}(r), and {phi}{sub an} were calculated and statistical uncertainties in these parameters were derived and calculatedmore » in the appendix.« less
  • The MCNP5 Monte Carlo code was used to simulate the dosimetry of an M-19 iridium-192 high dose rate brachytherapy source in both air/vacuum and water environments with the in-air photon spectrum filtered to remove low-energy photons below {delta}=10 keV. Dosimetric data was organized into an away-along table and was used to derive the updated AAPM Task Group Report No. 43 (TG-43U1) parameters including S{sub K}, D(r,{theta}), {lambda}, g{sub L}(r), F(r,{theta}), {phi}{sub an}(r), and {phi}{sub an} and their respective statistical uncertainties.
  • Purpose: The objective was to characterize a new Yb-169 high dose rate source for brachytherapy application. Methods: Monte Carlo simulations were performed using the MCNP5 F6 energy deposition tallies placed around the Yb-169 source at different radial distances in both air-vacuum and water environments. The calculations were based on a spherical water phantom with a radius of 50 cm. The output from the simulations was converted into radial dose rate distribution in polar coordinates surrounding the brachytherapy source. Results: The results from Monte Carlo simulations were used to calculate the AAPM Task Group 43 dosimetric parameters: Anisotropy function, radial dosemore » function, air kerma strength, and dose rate constant. The results indicate a dose rate constant of 1.12{+-}0.04 cGy h{sup -1} U{sup -1}, anisotropy function ranging from 0.44 to 1.00 for radial distances of 0.5-10 cm and polar angles of 0 deg. - 180 deg. Conclusions: The data from the Yb-169 HDR source, Model M42, presented in this study show that this source compares favorably with another source of Yb-169, Model 4140, already approved for brachytherapy treatment.« less
  • Purpose: A novel {sup 32}P brachytherapy source has been in use at our institution intraoperatively for temporary radiation therapy of the spinal dura and other localized tumors. We describe the dosimetry and clinical implementation of the source. Methods and Materials: Dosimetric evaluation for the source was done with a complete set of MCNP5 Monte Carlo calculations preceding clinical implementation. In addition, the depth dose curve and dose rate were measured by use of an electron field diode to verify the Monte Carlo calculations. Calibration procedures using the diode in a custom-designed phantom to provide an absolute dose calibration and tomore » check dose uniformity across the source area for each source before treatment were established. Results: Good agreement was established between the Monte Carlo calculations and diode measurements. Quality assurance measurements results are provided for about 100 sources used to date. Clinical source calibrations were usually within 10% of manufacturer specifications. Procedures for safe handling of the source are described. Discussion: Clinical considerations for using the source are discussed.« less
  • Purpose: An integrated software platform was developed to perform a patient-specific dosimetric study on high-dose-rate {sup 192}Ir endorectal brachytherapy. Monte Carlo techniques were used to examine the perturbation effects of an eight-channel intracavitary applicator with shielding and a liquid-inflatable balloon. Such effects are ignored in conventional treatment planning systems that assume water-equivalent geometries. Methods and Materials: A total of 40 Task Group 43-based rectal patient plans were calculated using the PTRAN{sub C}T Monte Carlo photon transport code. The silicone applicator, tungsten or lead shielding, contrast solution-filled balloon, and patient anatomy were included in the simulations. The dose to water andmore » dose to medium were scored separately. The effects of heterogeneities and uncertainties in source positioning were examined. A superposition calculation method using pregenerated Monte Carlo dose distributions about the shielded applicator in water was developed and validated for efficient treatment planning purposes. Results: On average, metal shielding decreases the mean dose to the contralateral normal tissues by 24% and reduces the target volume covered by the prescribed dose from 97% to 94%. Tissue heterogeneities contribute to dose differences of <1% relative to the prescribed dose. The differences in the dose volume indices between dose to water and dose to medium-based calculations were <1% for soft tissues, <2% for bone marrow, and >20% for cortical bone. A longitudinal shift of {+-}2.5 mm and a rotational shift of {+-}15{sup o} in applicator insertion reduced the target volume receiving the prescribed dose by {<=}4%. Conclusion: The shielded applicator improved dose conformity and normal tissue sparing; however, Task Group 43-based treatment planning might compromise target coverage by not accounting for shielding.« less