Comparison of point, line and volume dose calculations for exposure to nuclear medicine therapy patients

This work compared the predicted dose to an individual due to exposure from a radioactive patient using three models (point, line, and volume), for three therapeutic regimens (hyperthyroidism, thyroid cancer, and non-Hodgkin's lymphoma). For the volume source calculations, Monte Carlo simulations employing the Visual Monte Carlo (VMC) code and the voxel phantom FAX were used. For hyperthyroid patients, the point, line, and volume source models predicted doses to exposed individuals of 54, 24, and 14 mSv, respectively, at a distance of 0.3 m, and 4.8, 4.0 and 3.3 mSv at a distance of 1 m. For thyroid cancer patients, the dose values were 85, 38, and 18 mSv at 0.3 m, and 7.6, 6.4, and 4.4 mSv at 1 m, respectively. For non-Hodgkin's lymphoma (NHL) subjects, the doses were 230, 103, and 36 mSv at 0.3 m, and 21, 17, and 10 mSv at 1 m. These results show that patient release based on point source calculations involves unnecessary conservatism.