SU-E-T-337: Intensity Modulated Brachytherapy for Rectal Cancer Using A Novel Grooved Shielding Design

Abstract

Purpose: To create a novel HDR (192‐Ir) brachytherapy applicator for treatment of rectal carcinomas that uses tungsten shielding to make it dosimetrically superior to all commercially available applicators, despite being no larger than them. Methods: A set of 16 new applicators were designed and simulated using Monte Carlo (MCNPX). All designs were made of a 16‐mm diameter, high density tungsten alloy cylinder with inset grooves running along its length for the source to travel along. The designs varied regarding the number and depth of these grooves. Each design was optimized on 36 clinically treated plans (using 8‐channel Intracavitary Mold Applicator (Nucletron)) with asymmetrical CTVs, on in‐house written intensity modulated brachytherapy planning optimization software. Additionally, a 10 channel device with two channels per groove at varying depths was considered. All results were compared against the clinically treated plans. Results: First, all device designs outperformed the Intracavitary Mold Applicator in EVERY metric, except the total dwell times (about 30% increase). There were clear but relative tradeoffs regarding both the number of channels and the depth of each channel. Overall, the 12‐channel, 1‐mm depth design had the best results of the simpler designs, sparing the healthy rectal tissues the most while achieving comparable CTV coverage. All designs significantly outperformed the clinically treated plans using the Intracavitary Mold Applicator. Conclusions: Our extensive simulations and planning showed that our device designs have the ability to conform to the CTV and spare OAR with previously unmatched quality compared to existing commercial brachytherapy devices.