Proposal of a methodology to evaluate occupational internal exposure to Fluorine-18

The increasing use of ¹⁸F for diagnostic procedures in nuclear medicine through PET technology leads to the growth in the number of occupationally exposed workers to this radionuclide. The external and internal exposures may occur both in the production of the radiopharmaceutical fluorodeoxyglucose (¹⁸FDG) and during its clinical use in nuclear medicine departments. Workers involved in such activities are usually monitored routinely for the control of external exposure. However it is important provide methods for internal monitoring promptly after a suspicion of incorporation. Therefore, the objective of this work is to develop procedures for internal monitoring of ¹⁸F to be applied in cases of possible incorporation of fluoride and ¹⁸FDG, using in vivo and in vitro methods of measurements. The NaI(Tl) 8x4 scintillation detector of the IRD-Whole Body Counter was calibrated for in vivo measurements with a whole body anthropomorphic phantom, simulating homogeneous distribution of ¹⁸F in the body. The NaI(Tl) 3x3 scintillation detector of the IRD-Whole Body Counter was calibrated for in vivo measurements with a brain phantom inserted in an artificial skull, simulating ¹⁸FDG incorporation. The HPGe detection system of the IRD-Bioassay Laboratory was calibrated for in vitro measurements of urine samples with 1 liter plastic bottles containing standard liquid source. A methodology for bioassay data interpretation, based on standard ICRP models edited with the software AIDE-version 6, was established. It is concluded that in vivo measurements have sufficient sensitivity for the monitoring of ¹⁸F in the forms of fluoride and ¹⁸FDG. The use of both in vitro and in vivo bioassay data can provide useful information for the interpretation of bioassay data in cases of accidental incorporation in order to identify the most likely route of intake, chemical form of ¹⁸F incorporated and time of intake. (author)