Nuclear medicine: workplace monitoring and internal occupational exposure during a ventilation/perfusion single-photon emission tomography

The administration of 99mTc-HDP to diagnose pulmonary thromboembolisms leads to the presence of 99mTc in the environment of a nuclear medicine department, which could pose a potential risk of internal contamination to medical staff. Therefore, air samples from the administration room, gamma camera room and corridor of such a department were taken for the purpose of performing a workplace monitoring program of the medical centre under study, with maximum activity values of 640 ± 30 kBq/m3, 1.5 ± 0.1 kBq/m3 and 54 ± 3 kBq/m3, respectively, being obtained. These results correspond to committed effective doses received by exposed employees, via inhalation, when one ventilation/perfusion single-photon emission tomography study was performed, of 0.7 μSv, 0.004 μSv and 0.2 μSv, respectively. As inhalation is the employees’ main exposure pathway to radio-aerosols, the internal dose of the nuclear medicine department’s medical staff was also evaluated via urine bioassay measurements. Nuclear medicine nurses showed the highest 99mTc activity in 24-h urine samples (2100 ± 130 Bq/day), resulting in a committed effective dose of 21 μSv for each diagnostic study performed. Even so, the performance of ventilation/perfusion diagnostic studies did not constitute a substantial radiological risk since the annual dose limit for exposed employees was not exceeded.