BRACHYTHERAPY OPTIMIZATION AT MEMORIAL HOSPITAL.

Computer-assisted optimization of source-strength configuration has proved useful for intracavitary brachytherapy both with a manually afterloaded applicator (for cervix cancer) and a stepping-source remote afterloader. Optimization for cervix cancer treatments uses a method in which Cs-137 source strengths are selected iteratively to minimize the sum of squares of differences between desired and achieved doses at specified points of interest. For the remote afterloader, source strength for optimizing purposes is identified with the (continuously variable) dwell time of the Ir-192 source at each stepping-motor-selected location. Both a variant of the Rosenstein algorithm and an analytic algorithm have been used to produce shaped dose contours at depth for vaginal treatments.