Assessment of S values for I 131 and Y 90 based on the Digimouse voxel phantom.

Introduction: Most preclinical studies using radiopharmaceuticals have been carried out on mice. In nuclear medicine and radioimmunotherapy procedures, I-131 and Y-90 have been widely used. For better estimation of doses from these procedures, S value plays a vital role. In this study, we have evaluated S values for major source and target combinations of Digimouse voxel phantom. Materials and Methods: We have used the Digimouse voxel phantom which was incorporated in Monte Carlo code FLUKA. Simulation studies were performed using Monte Carlo simulation code FLUKA. Latest publication of International Commission on Radiological Protection (ICRP) report 110 was used for assigning the values of organ compositions and densities. Photon and electron spectra for I-131 and Y-90 have been taken from the ICRP publication 107. For Digimouse voxel phantom, we have simulated 9 source regions with an assumed uniform distribution of I-131 and Y-90. Results and Discussion: S values have been evaluated for I-131 and Y-90 for different source and target combinations of Digimouse voxel phantom and presented in tabular form. The S values can be applied prospectively or retrospectively to the calculation of radiation doses internally exposed to I-131 and Y-90, including nuclear medicine and radioimmunotherapy procedures. These S values have been very important for the calculation of absorbed doses for various organs similar in size to present study for mice. Conclusion: In this study S value for I-131 and Y-90 were evaluated for major organs of digimouse voxel phantom. These S values are very important for absorbed dose calculation for various organs of a mouse.