- - - MSc, Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran
- - - PhD, Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran
- - - PhD, Social Determinants of Health Research Center, Semnan University of Medical Sciences, Semnan, Iran
- - - MSc, Department of Medical Physics, Faculty of Medicine, Semnan University of Medical Sciences, Semnan, Iran

Background: ۹۰Y and ۱۷۷Lu are two well-known radionuclides used in radionuclide therapy to treat neuroendocrine tumors. Objective: This current study aims to evaluate, compare and optimize tumor therapy with ۹۰Y and ۱۷۷Lu for different volumes of the tumor using the criterion of self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and dose-volume histogram (DVH) curve using Gate Monte Carlo simulation code.Material and Methods: In our analytical study, Gate Monte Carlo simulation code has been used to model tumors and simulate particle transport. Spherical tumors were modeled from radius ۰.۵ to ۲۰ mm. Tumors were uniformly designed from water (soft tissue reagent). The full energy spectrum of each radionuclide of ۱۷۷Lu and ۹۰Y was used in the total volume of tumors with isotropic radiation, homogeneously. Self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and DVH curve parameters were evaluated. Results: The absorbed dose for ۹۰Y is higher than ۱۷۷Lu in all tumors (p-value <۵%). The uniformity of the absorbed dose for ۱۷۷Lu is much greater than ۹۰Y. As the tumor size increases, the DVH graph improves for ۹۰Y. Conclusion: Based on self-absorbed dose, cross-absorbed dose, absorbed dose uniformity, and DVH diagram, ۱۷۷Lu and ۹۰Y are appropriate for smaller and larger tumors, respectively. Next, we can evaluate the appropriate cocktail of these radionuclides, in terms of the type of composition, for the treatment of tumors with a specific size.

Radionuclide Tumor Therapy, Gate Monte Carlo, Dosimetry, DVH, Lutetium-۱۷۷, Yttrium-۹۰