An occupational dose distribution study in a positron emission tomography service

Resumo

Positron emission tomography (PET) is a powerful diagnostic tool, especially for Oncology. In PET procedures, the hands exposition of the workers is potentially higher than the thorax exposition due to the direct handling of the high-energy photons radionuclide. As the dose distribution in the extremities is non-uniform, the conventional monitoring methods (dosimetric ring and bracelet) may underestimate the skin dose equivalent in the most exposed part of the hand, which usually are the fingertips. In this study, two PET services had their workers monitored during the tasks of preparation and injection of the radiopharmaceutical 18F-fluorodeoxyglucose ( 18F-FDG) in patients, using chips of LiF:Mg,Cu,P thermoluminescent dosimeters (TLD-100H). Each employee worn TLD sets attached on the wrist and fingers of the dominant hand, and on the thorax. The highest dose values were measured on the index finger, which received doses up to 0.4 mSv in a single procedure of 18F-FDG dose preparation and 0.27 mSv in one injection. In a potential annual dose extrapolation, assuming that this technician performs 840 PET scans (preparation and injection), with these doses values, in one year, his skin dose equivalent on the index finger would be 564 mSv, exceeding the annual skin dose equivalent limit of 500 mSv. Despite the hands dose distribution is very sensitive of how to hold the syringe, the dose near to the index fingertip are always the highest, can be, respectively, 4 and 12 times greater than in the position where dosimetric rings and bracelets are commonly used for routine individual monitoring. Thus, extremity individual monitoring, in addition to the mandatory whole body individual monitoring with thorax dosemeters, are important tools for occupational dose optimization and should also be mandatory for PET technician.