Dosimetric comparison of 90Y, 32P, and 186Re radiocolloids in craniopharyngioma treatments

Purpose: In the radionuclide treatment of some forms of brain tumors such as craniopharyngiomas, the selection of the appropriate radionuclide for therapy is a key element in treatment planning. The aim was to study the influence by considering the beta-emitter radionuclide dose rate in an intracranial cyst. Methods: Dosimetry was performed using the MCNP4C radiation transport code. Analytical dosimetry was additionally performed using the Loevinger and the Berger formulas in the MATLAB software. Each result was compared under identical conditions. The advantages and disadvantages of using 90Y versus 32P and 186Re were investigated. Results: The dose rate at the inner surface of the cyst wall was estimated to be 400 mGy/h for a 1 MBq/ml concentration of 90Y. Under identical conditions of treatment, the corresponding dose rates were 300 mGy/h for 32P and 160 mGy/h for 186Re. For a well-defined cyst radius and identical wall thickness, higher dose rates resulted for 90Y. Conclusions: To achieve the same radiological burden, the required amount of physical activity of injectable solution is lower for 32P. This is found to be a consequence of both the radionuclide physical half-life and the pattern of energy deposition from the emitted radiation. According to the half-life and dose-rate results, 90Y would be a good substitute for 32P.