Rabbit internal dosimetry for iodine-131 using GATE Monte Carlo simulation code: a preclinical trial

Introduction: One of the main concerns in administration of radiotracers, especially in therapeutic arm, is the amount of delivered dose to the different organs. Individual variations of anatomy, physiology and underlying pathology in the patients lead to alteration of administered activity. In the current study we preclinically applied internal dosimetry using an animal model   Materials and Methods: The SPECT/CT imaging of a rabbit 24 hours after administration of 288μci Iodine-131 was done. Biodistribution of radiotracer was obtained from SPECT, and the CT was used to define attenuation map and the target volume of interest (VOIs). Dosimetry calculations were performed with GATE Monte Carlo code and S-values for beta and gamma radiation of different organs were calculated.   Results: The S-values of thyroid as target organ are 1.09×10-4(mGy/MBq/sec) for beta and 1.05×10- 5 for gamma radiation. And S-values of kidneys, lungs, spine, and heart as critical organs are 1.10×10-5, 1.58×10-5, 7.62×10-6, 6.75×10-6 for beta, respectively and 3.9×10-6, 2.69×10-6, 2.63×10-6, 3.27×10-6 for gamma, respectively Conclusion: The internal dosimetry is applicable clinically. The response to therapy would be increased and the side effect would be minimized if the prescription using patient specific dosimetry is optimized.