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A Comprehensive Study to Design A Novel Direction Modulated Brachytherapy (DMBT) Vaginal Cylinder (VC) Using GEANT4 Monte Carlo Simulation Code

M Meftahi*, W Song, Virginia Commonwealth University, Henrico, VA

Presentations

SU-IePD-TRACK 6-4 (Sunday, 7/25/2021) 12:30 PM - 1:00 PM [Eastern Time (GMT-4)]

Purpose: To design a new DMBT VC applicator to address the lack of dose coverage at the VC apex due to anisotropy effect and to provide directional modulation for coverage of legions that cannot be covered using the common VC applicators at the very critical region of the vaginal cuff.

Methods: The new DMBT-VC was modeled in GEANT4 MC code, as single lumen and made of PPSU plastic. The central part of that including the lumen was considered to be a detachable 8 mm diameter tandem rod made of PEEK plastic. First, we extracted a standard dose distribution from BrachyVision TPS of the VC applicator with PEEK tandem. Second, to provide directional intensity modulation, the PEEK tandem was replaced with MR-compatible tungsten alloy or alternatively iridium tandems, with similar dimensions to optimize the coverage at the apex utilizing directional radiation beam generated. Two widely used 192Ir sources, Varian’s GammaMedPlus and VS2000 were simulated. Further, we studied the applicator functionality for improving coverage for legions that are located beyond the typical 5mm isodose prescription line from the surface using both DMBT tandems.

Results: The analysis showed that the new applicator can improve the lack of coverage at the apex due to anisotropy which were about 2mm and 4mm for GammaMedPlus and VS2000, respectively, using all DMBT tandems. In addition, the DMBT applicator was able to successfully modulate the prescription isodose line by up to 13 mm and 18mm using tungsten and iridium tandems, respectively, beyond the VC surface at vaginal apex without overdosing the peripheral sides through inverse optimization.

Conclusion: Results showed that the novel DMBT VC can remedy the anisotropy effect and provide coverage for deep-seated legions at vaginal cuff. This is of major clinical value as the vaginal apex is a frequent site of recurrence in patients.

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    Keywords

    Not Applicable / None Entered.

    Taxonomy

    TH- Brachytherapy: HDR Brachytherapy

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