Background: Prostate Cancer (PC) is the second leading cause of cancer death in men, and early diagnosis is essential since localized PC is curable. International Commission on Radiological Protection (ICRP) and Medical Internal Radiation Dose (MIRD) guidelines should be followed to guarantee accurate and reliable dosimetry evaluations.
Objective: In this study, the radiation absorbed dose of the human organs of [^113mIn] In-PSMA-617 was estimated using animal data and Monte Carlo simulation in Oak Ridge National Laboratory (ORNL) human phantom to evaluate the dosimetry of a novel Single Photon Emission Computed Tomography (SPECT) agent.
Material and Methods: In this experimental study, the radiolabeled compound was prepared at optimized conditions, and its biodistribution was studied at different intervals. The absorbed dose of human organs was calculated by MCNPX software by tracking a total of 10⁶ particles for a gamma of 391.7 keV.
Results: The biodistribution of the radiotracer in animals showed the activity was removed from the blood circulation very fast, and significant uptake was observed in the kidneys and the PSMA-expressing organs. The kidneys received the highest absorbed dose with 9 ±1 µGy/MBq. 
Conclusion: This agent shows the potential of [^113mIn] In-PSMA-617 for prostate cancer imaging, particularly in regions with limited access to Positron Emission Tomography (PET) imaging. The generator-based production of ^113mIn allows for widespread availability, making it a practical alternative to other PSMA-based radiopharmaceuticals. Additionally, the low radiation burden and efficient renal clearance support its safety for repeated imaging.