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The Design of a Novel Direction Modulated Brachytherapy (DMBT) Vaginal Cylinder (VC) Using GEANT4 Monte Carlo (MC) Simulation Code

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

Presentations

SA-B-Therapy Room-8 (Saturday, 4/17/2021) 12:30 PM - 2:30 PM [Eastern Time (GMT-4)]

Purpose: In this study, we utilized the MC to design a new DMBT VC applicator to address the lack of dose coverage at the VC apex due to anisotropy effect and to minimize the effect of the air gap at the very critical region of the vaginal cuff.

Methods: The new DMBT-VC was simulated 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 a MR-compatible tungsten alloy tandem 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 abating the effect of the apical air gaps.

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. In addition, the DMBT applicator was able to successfully modulate the prescription isodose line by up to 1 cm at apex without overdosing the peripheral sides through inverse optimization.

Conclusion: Results showed the novel DMBT VC can remedy the lack of apex dose coverage due to anisotropy and is very flexible in minimizing the effect of air gaps. This is of major clinical value as the vaginal apex is a frequent site of recurrence in patients. In addition, the applicator can help to potentially reduce dose where to mitigate toxicities (including vaginal mucosa), where anisotropy and airgaps would’ve been a big barrier in the past.

Keywords

Brachytherapy, HDR, Intensity Modulation

Taxonomy

TH- Brachytherapy: Computational dosimetry: Monte Carlo

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