Author: Hungcheng Hank Chen, Laura A. Doyle, Helena Frisbie-Firsching, Amy S. Harrison, Jackson D Reeves, Lindsay B Romak, Jon Strasser 👨🔬
Affiliation: Christiana Care 🌍
Purpose: Brass mesh bolus (BMB) is a high-density woven metal mesh which is an excellent alternative to tissue equivalent bolus in photon beams, offering improved surface conformality. Unlike utilization of BMB in photon beams, there are few publications summarizing dosimetric characteristics of BMB in electron beams. The goal of this research is to assess dosimetric effects and evaluate the feasibility of dose calculation utilizing a Monte Carlo (MC) algorithm in a commercial treatment planning system for BMB in electron beams.
Methods: A solid water phantom and parallel plate ion chamber were arranged to collect measurements at the surface and depth of d-max for electron energies of 6, 9, and 12 MeV. The experimental set up included solid water set to 100cm SSD with a 10x10cm electron cone and repeated delivery of 200 MU. Measurements at d-max were taken without bolus. Measurements at the phantom surface were repeated with no bolus, 1.5mm BMB, and 5mm Superflab bolus. The experimental setup was modeled in RayStation 2023B and calculated with Monte Carlo Clinical v5.0 to 0.5% uncertainty, using solid brass to approximate the BMB.
Results: Phantom measurements demonstrated surface dose enhancement with BMB, comparable to Superflab. Surface doses with BMB, Superflab, and no bolus as a percentage of dose at d-max were BMB: 95.9%, 95.3%, 96.7%, Superflab: 92.2%, 95.3%, 98.0%, and no bolus: 79.3%, 84.5%, 87.5%, for beam energies of 6, 9, and 12 MeV, respectively.
Conclusion: BMB shows promise for increasing surface dose in electron therapy, with similar effects as Superflab. Further research will include phantom measurements using film, at various depths with bolus, and at various incident angles to more comprehensively characterize the BMB. The experimental setup will be re-modeled based on additional findings, modifying the BMB model to best align calculations with measured data.