Abstract In radiation treatments of some types of brain tumors, such as craniopharyngiomas, selection of an appropriate radionuclide is critical. The aim of this work was to calculate distributions of dose rates from 32P and 186Re in radiocolloids injected into craniopharyngioma cysts. The calculations were performed with the MCNP4C radiation transport code. Analytical calculations based on the Loevinger formula were also performed for 32P with the MATLAB software. The results of the two techniques for identical models were compared. The effects of the cyst wall type and of the density of the cyst inner fluid were investigated. The 32P activities required for providing 200, 250, and 300 Gy to cysts of different sizes were calculated.