Impact of Metallic Implants on Dose Distribution in Radiotherapy with Electrons, Photons, Protons, and Very-High-Energy Beams

Metallic implants in radiotherapy patients alter dose distributions due to their high density and unique composition, potentially compromising treatment precision. This study evaluates the effects of three metallic materials, Co-Cr-Mo alloy, titanium alloy, and stainless steel, on dose distribution across four radiotherapy modalities: 6 MV photons, 15 MeV electrons, 170 MeV protons, and very-high-energy electrons (100 and 150 MeV). Monte Carlo simulations in the TOol for PArticle Simulations Monte Carlo (TOPAS MC) generated percentage depth dose curves and dose profiles, with dosage data standardized to a reference point and uncertainties addressed via error propagation. Results revealed that the Co-Cr-Mo alloy produced the most significant alterations. For instance, at 100 MeV Very High Electron Energy (VHEE), the dose at a 15 cm depth was 34.57% lower than in water; 6 MV photons showed a 15.16% reduction, and the proton Bragg peak shifted 9.5 cm closer to the source. These pronounced changes along the central beam axis affected dose distributions anterior and posterior to the metal. A prostate cancer simulation further demonstrated considerable dose reduction with deeply embedded metallic implants. The findings underscore the critical impact of implant properties on radiotherapy dose distributions, emphasizing the need to integrate these factors into clinical protocols to improve dosimetric accuracy and treatment safety.