A Monte Carlo study of dose rate distribution around the specially asymmetric CSM3-a Cs-137 source

The CSM3 Cs-137 type stainless-steel encapsulated source is widely used in manually afterloaded low close rate brachytherapy. A specially asymmetric s ource. CSM3-a, has been designed by CIS Bio International (France) substitu ting the eyelet side seed with an inactive material in the CSM3 source. Thi s modification has been done in order to allow a uniform dose level over th e upper vaginal surface when this 'linear' source is inserted at the top of the dome vaginal applicators. In this study the Monte Carlo GEANT3 simulat ion code. incorporating the source geometry in detail, was used to investig ate the dosimetric characteristics of this special CSM3-a Cs-137 brachyther apy source. The absolute dose rate distribution in water around this source was calculated and is presented in the form of an along-away table. Compar ison of Sievert integral type calculations with Monte Carlo results are dis cussed.