Tehran University of Medical Sciences Frontiers in Biomedical Technologies 2345-5837 0 0 2026 08 19 1239 1239 Hossein Rajabi Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares Universiy, Tehran, Iran. Parisa Abdoli Department of Medical Physics, Faculty of Medical Sciences, Tarbiat Modares Universiy, Tehran, Iran. 2025 03 11 2025 05 13 Background: Radiosynovectomy (RSV) is a therapeutic modality for inflammatory joint diseases, traditionally employing beta-emitting radionuclides. However, the clinical potential of alpha-emitting radionuclides has not been extensively explored. This study seeks to compare the dosimetric profiles of alpha (225Ac and 227Th) and beta-emitting radionuclides (32P, 188Re, and 90Y) within a voxelized knee joint phantom.  Methods: A three-dimensional graphic model of the knee joint was transformed into a high-resolution voxelized phantom. Monte Carlo simulations were performed to assess the distribution of absorbed doses within critical anatomical structures: the joint cavity, synovial membrane, articular cartilage, and bone. Dose-Volume Histograms (DVHs) were generated to analyze the spatial distribution of radiation doses for each radionuclide, with maximum and mean absorbed doses and the Homogeneity Index (HI) calculated   Results: The alpha-emitting radionuclides demonstrated markedly superior maximum and mean absorbed doses in comparison to their beta-emitting counterparts. Notably, 227Th provided the highest doses (Dmax: 266.10 Gy/MBq in the joint cavity), while 225Ac exhibited considerable localized energy deposition. The HI values for alpha emitters (0.34 for 227Th) indicated a greater degree of dose uniformity compared to beta emitters (e.g., HI of 4.30 for 90Y). Nevertheless, the use of alpha emitters resulted in increased radiation exposure to surrounding tissues, raising concerns about their appropriateness for the treatment of rheumatoid arthritis.  Conclusions: This study underscores the dosimetric advantages of alpha-emitting radionuclides in terms of localized dose delivery and uniformity within targeted tissues. However, the risk of heightened exposure to non-target tissues suggests that beta-emitting radionuclides may continue to be the preferred option for clinical applications in RSV. https://fbt.tums.ac.ir/index.php/fbt/article/view/1239