Patient Specific Dosimetry based in excreted urine measurements

One of the limiting factors in utilising therapeutic radiopharmaceuticals in the I-131 thyroid therapy is the potential hazard to the bone marrow, kidneys, and other internal organs. In this work, by means of daily dose rate measurements at a point in contact of the can with the urine excreted by the patient undergoing radio-iodine therapy, activities and associated absorbed doses in total body are calculated. The urine can is characterised by a geometric and materials model for MC simulation with MCNP. Knowing the conversion factor from activity in urine to dose rate in the measurement point of the can for each filling volume, the urine and patient activity can be obtained at each measurement time. From the fitting of these activities, the time evolution, the effective half life in the patient and the cumulative whole body activity are calculated. The emission characteristics of I-131 are using after to estimate the maximum whole body absorbed dose. The results for 2 hyperthyroidism and 4 carcinoma treatments are presented. The maximum total body absorbed dose are 673 and 149 Gy for the carcinoma and hyperthyroidism. The corresponding range of T1/2) eff is o.2 to 2.5 days (carcinoma) and 5.4 to 6.6 days (hyperthyroidism). (Author)