EGSnrc-based Monte Carlo dosimetry of CSA1 and CSA2 {sup 137}Cs brachytherapy source models

Journal Article · Tue Sep 15 04:00:00 EDT 2009 · Medical Physics

DOI:https://doi.org/10.1118/1.3176936· OSTI ID:22102071

Selvam, T. Palani; Sahoo, S.; Vishwakarma, R. S. ^[1]

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1. Radiological Physics and Advisory Division, Health, Safety and Environment Group, Bhabha Atomic Research Centre, Mumbai 400094 (India)

Purpose: AAPM TG-56 recommends the use of a specific dosimetric dataset for each brachytherapy source model. In this study, a full dosimetric dataset for indigenously developed {sup 137}Cs source models, namely, the CSA1 and CSA2, in accordance with the AAPM TG-43U1 formalism is presented. The study includes calculation of dose-to-kerma ratio D/K in water around these sources including stainless steel encapsulated {sup 137}Cs sources such as RTR, 3M, and selectron/LDR {sup 137}Cs. Methods: The Monte Carlo-based EGSnrcMP code system is employed for modeling the sources in vacuum and in water. Calculations of air-kerma strength, S{sub K} for the investigated sources and collision kerma in water along the transverse axis of the RTR source are based on the FLURZnrc code. Simulations of water-kerma and dose in water for the CSA1, CSA2, RTR, 3M, and selectron/LDR {sup 137}Cs sources are carried out using the DOSRZnrc code. In DOSRZnrc calculations, water-kerma and dose are scored in a cylindrical water phantom having dimensions of 80 cm diameterx80 cm height. Results: The calculated dose-rate constants for the CSA1 and CSA2 sources are 0.945(1) and 1.023(1) cGy/(h U), respectively. The calculated value of S{sub K} per unit source activity, S{sub K}/A for the CSA1 and CSA2 sources is 7.393(7)x10{sup -8} cGy cm{sup 2}/(h Bq). The EGSnrcMP-based collision kerma rates for the RTR source along the transverse axis (0.25-10 cm) agree with the corresponding GEANT4-based published values within 0.5%. Anisotropy profiles of the CSA1 and CSA2 sources are significantly different from those of other sources. For the selectron/LDR single pellet {sup 137}Cs spherical source (modeled as a cylindrical pellet with dimensions similar to the seed selectron), the values of D/K at 1 and 1.25 mm from the capsule are 1.023(1) and 1.029(1), respectively. The value of D/K at 1 mm from the CSA1, CSA2, RTR, and 3M {sup 137}Cs source capsules (all sources have an external radius of 1.5 mm) is 1.017(1) and this ratio is applicable to axial positions z=0 to z={+-}L/2. This is in contrast to a published GEANT4-based Monte Carlo dosimetric study on RTR and 3M {sup 137}Cs sources wherein the authors have assumed that collision kerma is approximately equal to absorbed dose at 1 mm from the source capsules. Collision kerma is approximately equal to absorbed dose for distances {>=}2 mm from source capsules as opposed to {>=}1 mm reported in published studies. A detailed electron transport is necessary up to 2 mm from source capsules. Conclusions: The Monte Carlo-calculated dose-rate data for the CSA1 and CSA2 sources can be used as input data for treatment planning or to verify the calculations by radiotherapy treatment planning system.

• OSTI ID: 22102071
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 9 Vol. 36; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
97 MATHEMATICS AND COMPUTING
BRACHYTHERAPY
CESIUM 137
CYLINDRICAL CONFIGURATION
DOSE RATES
DOSIMETRY
KERMA
MONTE CARLO METHOD
PHANTOMS
RADIATION DOSES
STAINLESS STEELS
WATER