A Monte Carlo investigation of the dosimetric characteristics of the CSM11Cs-137 source from CIS

The purpose of this study is to calculate basic dosimetry data for a CSM11 low dose rate Cs-137 source in water. This source is widely used in afterlo adable dome cylinders designed to homogeneously irradiate the vaginal cuff alone or additional areas of the vagina in hysterectomized patients. In thi s study, the Monte Carlo simulation code GEANT, incorporating in detail sou rce geometry, is used to investigate the dosimetric characteristics of the source. The calculated data were analyzed using a fitting procedure that is described in detail. Absolute dose rate distributions in water were calcul ated around this source and are presented as conventional 2D Cartesian look up tables (classically along-away tables). Also, the dose calculation forma lism endorsed by the Interstitial Collaborative Working Group and the AAPM Task Group 43 have been calculated. The calculated dose rate constant for t his source is Lambda = 1.096+/-0.002 cGy h(-1) U-1. The anisotropy function results in about 50% deviations from isotropy at positions near the long a xis of the source. The radial dose function is given as a polynomial that r eproduces the calculated data up to 20 cm. Best-fit values of attenuation c oefficients suitable for use in Sievert integral calculations have been der ived. (C) 2000 American Association of physicists in Medicine. [S0094-2405( 00)02309-9].