Individualized dosimetry for patients with graves’ disease

Introduction Following Directive 2013/59 Euratom, all therapeutic exposures of target volumes shall be individually planned and their delivery appropriately verified. We have developed a home-made software for I-131 dosimetry in hyperthyroid patients using gammacamera and capture probe for prior and post treatment. Purpose This study describes the dosimetry method, the differences between pre and post treatment purposes, and compare its results. Materials and methods We base our procedure on the EANM Dosimetry Committee Guidelines using an INa Probe for uptake measurements at 2, 24 and 96 h after administration of 25 μCi tracer activity (also measured before its administration) and two Tc-99m planar images to estimate the thyroid mass. A two compartimental model is used to calculate the required activity to achieve 160 Gy to the target. Two uptake measurements are acquired at 96 and 168 h post-treatment to calculate the real absorbed dose to the thyroid, using a monocompartimental model and dead time correction for saturation effect through a previous probe calibration curve. 78 patients treated during 2015 have been analyzed. Results 163,1 Gy and 37,7 Gy are the average and standard deviation of administered absorbed doses, ranging from 87,3 Gy to 240,1 Gy. The mean activity to be administered according the used model is 9,1 mCi which differs from previously used (Marinelli algorithm, 7,3 mCi) and administered (8,9 mCi). Differences of means between activities by Marinelli and by our method using t-Student are significant (p  Conclusion Individualized pre and post treatment dosimetry for hyperthyroidism I-131 therapy is mandatory.