For partial breast irradiation, multi-lumen brachytherapy applicators are used in place of single lumen applicators when dose asymmetry is desired in an attempt to avoid intolerable normal tissue doses. According to RTOG-0413 criteria, the minimum balloon-to-skin distance is 7 mm. With this small of a balloon-to-skin distance, dose asymmetry may be desired to reduce the skin dose to tolerable levels (<145% prescription dose). Special consideration needs to be accounted for by the physicist when planning to ensure proper dose distribution. This includes the lack of tissue heterogeneity corrections of most treatment planning systems, which may lead to an inaccurate dose distribution.
The purpose of this investigation is to show the difference between the measured dose distribution and that predicted by the treatment planning system. This will be done for two brachytherapy applicators, which include ConturaTM (Bard, Inc.) and SAVITM (Cianna Medical, Inc.). For each applicator, both symmetric and asymmetric plans will be examined to show which produces a larger difference from the dose distribution predicted by the planning system. Also, the effects of the air cavity present in the SAVITM applicator will be investigated.