Room: AAPM ePoster Library
Purpose: Anisotropy of the 192Ir source causes a lack of dose coverage at the apex in HDR vaginal cylinder brachytherapy. In this study, we took advantage of the GEANT4 Monte Carlo code to design a new DMBT vaginal applicator so that it maintains the dose coverage of the current vaginal cylinder at periphery everywhere while improving the apex coverage.
Methods: The new DMBT vaginal applicator was designed to have a typical range of 20-35 mm diameter, single lumen vaginal cylinder, made of PPSU plastic. The central part of the applicator which includes the lumen was considered to be a detachable 8 mm diameter tandem rod. In order to provide directional modulation, a tungsten rod similar to the dimensions of the detachable tandem was added to simulation. The applicator works in two steps. First, we get a typical dose distribution based on the planning system using the applicator with a detachable PEEK tandem in place. Second, the detachable tandem is replaced with a tungsten tandem to compensate for lack of coverage at the apex utilizing directional radiation beam generated. The same source dwell positioning is used for both steps while the dwell time for the second step is a small added fraction of the first step. The MATLAB software was used for data analysis.
Results: The analysis showed that the new applicator can address the lack of coverage at the apex due to anisotropy (~2 mm), while simultaneously preventing from overdosing the periphery.
Conclusion: This new DMBT concept design can be considered as a possible solution for the lack of apex coverage due to anisotropy as there is a subset of patients who experience recurrences after brachytherapy, frequently in the vaginal apex.