Radiation dose from routine nuclear medicine procedures: lung imaging with /sup 99m/Tc microspheres

Perfusion lung scanning with /sup 99m/Tc labeled particles (microspheres or macroaggregates) is one of the most important and popular nuclear medicine procedures. It permits the early diagnosis of pulmonary embolism before x-ray changes have occurred. Because this can be a life-threatening condition and therapy (anticoagulation and surgery) is possible, lung scanning plays an important role in patient management. Unlike many nuclear medicine procedures which are gradually being replaced by CAT scanning, no other effective study exists for the early diagnosis of pulmonary embolism. The radiation dose to the lungs from this procedure is of the order of a few rads and possibly as much as a rad to the liver and kidney. While these doses are not prohibitive, they are far from trivial. The willingness of a physician to order lung scans in a patient with a low level of clinical suspicion of pulmonary embolism will depend on the magnitude of the radiation dose because the procedure is otherwise without risk. Therefore, the best estimate of the radiation dose delivered is necessary for lung scanning to be used optimally in screening patients with pulmonary embolism symptoms or who may have increased risk but are asymptomatic. A discussion is given of one of the problems of radiation dose calculations for this procedure, i.e., the somewhat complex fate of the injected radioactive particles