Abstract
This study investigated both internal and external dose estimation in nuclear medicine. Three widely used radioactive nuclides 99mTc, 18F, and 131I were considered. For internal dose assessment, the MIRD schema provides a general approach for the dosimetry of incorporated radionuclides. Two crucial factors for dose estimation, the specific absorbed fraction and S-value, were calculated by Monte Carlo simulations with anthropomorphic phantoms and the results were found to be generally consistent with literature values. The OLINDA/EXM computer software was also used to estimate the resulting effective doses for patients administered three interested radiopharmaceuticals. For external radiation protection, various source models, ranging from simplified point, line, and cylinder sources to high-fidelity anthropomorphic phantoms were applied to calculate dose rates near a nuclear medicine patient. This systematical comparison led to the following observations and conclusions. The Monte Carlo calculated results based on detailed phantom models are realistic but time-consuming. The point source model is simple but too conservative while both the line and cylinder source models gave reasonable predictions. The line source model was found to be comparable to the cylinder source model due to the cancellation of radiation attenuation and buildup in the source volume. The effects of various source energies and cylinder sizes on the cancellation were investigated. The line source model, relatively easy in calculation and predicting dose rates slightly conservative than the phantom results by approximately 7-18% for the three radionuclides, is therefore considered the most practical method of dose calculation for patient release criteria. An application of the line source model to 51 post-thyroidectomy patients in Taiwan was demonstrated and its comparison with measurements was discussed. The agreement between calculations and measurements is reasonable after taking the room-scattering effect into account.