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RESEARCH PRODUCT

SU-E-T-508: Monte Carlo Dosimetric Study of the CSM40 Low Dose Rate Source

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Purpose: There is a LDR 137Cs brachytherapy source, CSM40, developed by Eckert & Ziegler BEBIG. Fundamental dosimetric datasets to be used on treatment planning systems do not exist for this source. This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO. Methods: Penelope2008 and GEANT4 Monte Carlo codes were used to characterize this source dosimetry. Water composition and mass density was that recommended by AAPM. Due to the typical energies of the 137 Cs, dose for small distances can be approximated by collisional kerma. Therefore, we have considered collisional kerma for r<20 cm. To provide adequate spatial resolution, cells were 0.05 cm in thickness. Angular sampling was taken every 1°. Additional simulations were performed to obtain SK as recommended by AAPM. Mass‐energy absorption coefficients in water and air were consistently derived and used to calculate collisional kerma. Along‐away tables and TG‐43 formalism parameters and functions were derived, as recommended by HEBD from AAPM‐ESTRO. Results: TG‐43 dosimetry parameters with L = 1.65 cm were obtained. Results performed with both radiation transport codes showed agreement typically within 0.05%. Using Penelope 2008 and GEANT4, an average of α = 0.9265 +/− 0.0005 cGy/(h U) (with k = 1, Type A uncertainties) was obtained. Dose rate constant, radial dose function and anisotropy functions for the CSM40 are compared with published data for other 137 Cs sources. Conclusion: Dosimetric data are provided for the CSM40 source not studied previously in the literature. Using the data provided by this study in the treatment planning systems, it can be used in clinical practice. Partially funded under a research agreement with E&Z BEBIG