## 4 Discussion
While adapting the radiation modality or modifying the treatment schedule may be clinically desirable in patients with metallic implants, the feasibility of such changes can be limited by institutional resources and infrastructure. Not all treatment centers have access to advanced modalities such as VHEE or proton therapy, and even within a center, re-planning may depend on the availability of trained personnel and appropriate imaging and verification systems. Therefore, any proposed change must be evaluated within the context of the specific clinical environment, and decisions should be based on a multidisciplinary assessment involving medical physicists, radiation oncologists, and treatment planning staff. To improve the consistency and safety of patient care across different institutions, it is essential to establish and implement clear, accessible, and standardized clinical guidelines for managing radiotherapy in patients with metallic implants. These guidelines should be readily available and applicable in daily clinical practice, supporting harmonized treatment planning workflows across centers worldwide. Simulations for VHEE (100 MeV and 150 MeV) showed a more modest dose attenuation than electrons but still significant differences between materials. For 100 MeV VHEE, the Co-Cr-Mo alloy proved to be the most influential on the dose profile, with a decrease in maximum dose of up to 30% compared to water, with titanium and stainless steel causing a more minor but still significant decrease. At 150 MeV VHEE, this effect was even more pronounced, with Co-Cr-Mo causing a shift in the depth of the maximum dose and a decrease in its value, indicating the high ability of metallic materials to affect energy deposition even at high energies. VHEEs are an exciting alternative for deep irradiation because they have significant penetration compared to lower electron energies. However, interaction with metal implants remains a significant challenge. Although lower-density alloys such as titanium show less dose reduction, there is still a shift of maximum energy deposition towards the surface, which could lead to underdosing in deeper target tissues. This effect could be addressed by adjusting the beam energy or optimizing the irradiation angle. Protons pose a specific challenge in the presence of metal implants due to the shift of the Bragg peak. The results for 170 MeV protons showed a dramatic shift of the Bragg peak due to the presence of metal, particularly Co-Cr-Mo alloy. In water, the Bragg peak was at a depth of 19.4 cm, while for Co-Cr-Mo, this peak shifted to 9.9 cm, indicating a nearly 50% reduction in rank. Titanium and steel also affected the shift of the Bragg peak, but to a lesser extent, with values of 15 cm and 12.4 cm, respectively. In addition to the shift of the Bragg peak, a significant reduction of the maximum dose in metals was also observed. The maximum dose reached 100% in water, while Co-Cr-Mo reduced this value to 70.87%, a more than 29.00% reduction. Titanium and steel also reduced the maximum dose, with titanium reaching 73.07% and steel reaching 71.36%. These results are significant for proton treatment, where precise planning depends on the exact location of the Bragg peak. Metal implants can significantly shorten the proton range and reduce treatment efficacy if these factors are not considered. The results obtained for all modalities demonstrate that metal implants significantly impact distribution and depth of maximum energy deposition. High-density metallic materials, such as Co-Cr-Mo, have the greatest impact, leading to a significant shift of the Bragg peak for protons and a sharp drop in dose behind the implant for electrons and VHEE. On the other hand, lower-density materials, such as titanium, have a more moderate effect but still cause measurable changes in the dose profiles. Clinically, these results are significant in radiation planning for patients with metal implants.