SU-E-T-382: Revision of the Dosimetric Parameters of the CSM11 LDR Cs-137 Source

Abstract

Purpose: The clinical use of brachytherapy sources requires the existence of dosimetric data with enough quality for the proper application of treatments in clinical practice. It has been found that the published data for the low dose rate CSM11 Cs‐137 source [Ballester et al. Med Phys 2000;27:2182–2189] lacks of smoothness in some regions because data are too noisy. The purpose of this study is to calculate the dosimetric data for this source to improve the quality dosimetric data of Ballester et al. Methods: To obtain the dose rate distributions Monte Carlo simulations were done using the GEANT4 code. A spherical phantom 40 cm in radius with the Cs‐137 source located at the centre of the phantom was used. Results: The results from Monte Carlo simulations were used to derive AAPM Task Group 43 dosimetric parameters: Anisotropy function, radial dose function, air kerma strength, and dose rate constant. The dose rate constant obtained has been 1.094±0.002 cGy ĥ‐1 U‐1. Conclusions: The new calculated data agrees within statistical uncertainties with the old data of Ballester et al. being the present data much less nosisy. The present data fulfils now all the requirements of the TG‐43U1 and thus it can be used in clinical practice.