SU-E-T-349: An Optimized Dosimetric Study of a Multi-Channel Vaginal Cylindrical Applicator in Brachytherapy

Abstract

Purpose: Toptimized dosimetry of a CT/MRI multi‐lumen brachytherapy applicator was planned to treat vaginal cancer after hysterectomy. Multichannel design of cylinder includes several peripheral channels isotropically placed 5mm inside cylinder from surface with a separate central channel to allow single lumen brachytherapy as an option. The optimized dosimetry plans were compared between single‐channel versus multi‐channel to determine the sufficient coverage to the vaginal apex and other potential dosimetric advantages. Methods: CT simulation for each treatment of vaginal brachytherapy of postoperative endometrial or vaginal cancer. Seventeen CT image data sets were collected in this study. Standard single channel treatment was planned. Prescribed dose was to the 5mm cuff from the cylinder surface. PTV of 5mm rind with prescribed length was constructed. Doses to PTV and ROIs such as bladder and rectum were documented in DVH. Dose point to the apex of 5mm rind which locates at 5mm from applicator tip was specified. A second brachytherapy plan was generated using a multi‐channel loading. DVH of 5mm rind coverage, doses to apex, bladder and rectum were optimized in Oncentra brachytherapy planning system. Results: Optimized 95% to V95 and lower dose to adjacent structures were reported in multi‐channel plan. Improvements to apex dose by 3‐5% and organ sparing by 7‐14% were achieved. At the apex, inverse planning was further optimized by adjusting unequal contribution selectively from multi‐channel end. It is difficult for single channel to eliminate the cold spot at apex and maintain the dose uniformity to the 5mm cuff simultaneously. Conclusion: Possible optimization of brachytherapy treatment planning of vagina is investigated in this study by using a new multi‐lumen vaginal cylinder. The new device can increase the therapeutic ratio by improving target coverage and at the apex region as well. A reduction in the potential toxicity to the adjacent critical organs is feasible.