Source configuration and dose rates for the selectron afterloading equipment for gynecologic applicators

This paper describes source train configurations of the Selectron LDR-6 that can be used to duplicate commonly used manually afterloadable source configurations for gynecological intracavitary brachytherapy. We demonstrate that the recommended source configuration using 2.5 mm ¹³⁷Cs spheres is dosimetrically equivalent to its manually afterloaded counterparts using 3M ¹³⁷Cs sources (20 mm overall length, 14 mm active length). Isodose distributions are in agreement to within 5% for the Fletcher-Suit-Delclos family of tandems, colpostats, and vaginal cylinders. Our data also demonstrate that the isotropic point source model used by most computerized treatment planning systems is a good approximation to source trains of filtered, spherical sources interspersed with solid steel spacers. We conclude that the use of 2.5 mm ¹³⁷Cs sources in the Selectron remote afterloading system can accurately reproduce the isodose distribution achieved with linear ¹³⁷Cs manually afterloaded sources.