###### Abstract  
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. Article Implants, Dose Distribution in Radiotherapy with Electrons, Photons, Protons, and Very-High-Energy Beams 2025 15 April  
methods like FLASH radiotherapy with very high electron energy (VHEE), which may interact differently with metallic implants than more conventional methods. VHEE is a new modality with unique physical diametric properties that is promising for dose delivery. If we compare VHEE with other modalities, they show lower lateral scattering than photon beams [4]. They are more insensitive to inhomogeneities than other charged particle therapies [5]. VHEE may also have the advantage of ultra-high dose rate (UHDR) capability [6]. The combination of VHEE and UHDR contributes to faster and, therefore, more precise radiation treatment of the patient and limits the occurrence of inhomogeneities associated with patient movement or patient organ movement. Metal prostheses are widely employed in orthopedics to substitute damaged joints and bones. There is a growing trend among patients to choose surgical procedures, such as metal prostheses, due to the increasing prevalence of arthritis, osteoporosis, and other degenerative joint disorders. In the case of metastatic bone disease in cancer patients, metal plates and screws are used for stabilization. Orthopedics practitioners commonly employ knee and hip joint replacements because of the high incidence of degenerative alterations that affect these weight-bearing articulations [7]. The occurrence of degenerative alterations frequently necessitates joint replacement procedures to restore functionality and reduce the accompanying pain. Patients' prosthesis replacement procedures do not consider radiotherapy treatment; thus, problematic situations may arise in the future during the treatment of oncological diseases. In contemporary orthopedics, various materials for fabricating metallic prostheses are being used. Each of these materials has significant implications for their application in the human body. Stainless steel has become known for its excellent robustness and corrosion resistance [8]. This characteristic renders it a preferred option for a wide range of joint replacements. In recent times, titanium and its alloys have garnered significant attention as formidable candidates due to their remarkable biocompatibility and low mass [9]. The attributes above contribute to mitigating stress shielding and enhancing implant durability, particularly in hip and knee replacement procedures.