In radiopharmaceutical therapy, delivered doses to critical organs must be below a certain threshold therefore internal radiation dosimetry of radiopharmaceuticals is essential. Advantages and disadvantages of radionuclides with different characteristics were evaluated for selection of appropriate radionuclide. The Monte Carlo MCNPX simulation program was used to obtain radial dose and cumulative dose of Sm-153, Lu-177 and Ho-166 used in radiotherapy of bone metastases. A cylindrical geometry with constant density materials was supposed for simulation of femur bone. The radius of bone marrow, bone, and surrounding soft tissue was considered 0.6 cm, 1.3 cm and 4 cm, respectively. It was assumed that the radionuclides were uniformly distributed throughout the tumor. "continuous energy spectrum" of beta particle was used instead of mean beta energy. Our simulations show that absorbed dose in target organ (bone) is greater than other organs and Ho-166 gives a higher dose to the critical organ of bone marrow than either Sm-153 or Lu-177. Absorbed dose versus time demonstrate faster dose delivery for the short half-life radionuclides (Sm-153 and Ho-166). These results are in good agreement with clinical observations which show a pain relief within 1 week after intravenous administration of Sm-153-EDTMP, whereas it occurs within 2 week in the case of Lu-177-EDTMP. According to the results, combination of different radionuclides with different characteristics such as Sm-153-EDTMP and Lu-177-EDTMP could be more advantageous to patients with painful bone metastasis. (C) 2014 Elsevier Ltd. All rights reserved.
