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EGSnrc‐based Monte Carlo dosimetry of CSA1 and CSA2 C 137 s brachytherapy source models
Author(s) -
Selvam T. Palani,
Sahoo S.,
Vishwakarma R. S.
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3176936
Subject(s) - kerma , brachytherapy , monte carlo method , dosimetry , physics , imaging phantom , nuclear medicine , computational physics , nuclear engineering , optics , medicine , mathematics , radiation therapy , statistics , radiology , engineering
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 C137 s 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 encapsulatedC137 s sources such as RTR, 3M, and selectron/LDRC137 s . 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 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/LDRC137 s 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 diameter × 80 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 Kper unit source activity,S K / A for the CSA1 and CSA2 sources is 7.393 ( 7 ) × 10 − 8cGycm 2 / ( hBq ) . 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 pelletC137 s 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 3MC137 s 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 3MC137 s 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.