RADIATION-DOSE TO TECHNICIANS PER NUCLEAR-MEDICINE PROCEDURE - COMPARISON BETWEEN TC-99M, GA-67, AND I-131 RADIOTRACERS AND F-18 FLUORODEOXYGLUCOSE

The aim of this study was to determine the non-extremity gamma dose re ceived by a technician while performing an ordinary nuclear medicine p rocedure or a static (i.e. without blood sampling) fluorine-18 fluorod eoxyglucose (FDG) positron emission tomography (PET) study, The dose p er patient was measured by means of a commercial electronic pocket Gei ger Mueller dosimeter, worn in the upper left pocket of the overalls. This was previously tested by exposure to known point sources of techn etium-99m, gallium-67, iodine-131 and fluorine-18 in the air. A furthe r test was performed with Tc-99m, I-131 and F-18 sources inserted in a water phantom to simulate the condition of high scattering degradatio n of the primary radiation due to the patient's tissues, Subsequently, the dose was measured by two technicians for a total of 314 clinical cases, covering the most common nuclear medicine procedures, including 44 static, two-level FDG PET studies with repositioning of lire patie nt on the couch between the transmission and the emission scan and sev en whole-body PET studies. The dose read by the dosimeter was correcte d for environmental background and for detector efficiency measured wi th sources in the air. For a limited subset of cases, the time spent c lose to patients was also measured. Doses were then estimated by a cru de non-absorbing point source approximation and by using experimental dose rates. A comparison between experimental. and estimated doses, as well as with previously published data, completed the work. For most of the conventional procedures, the measured dose per procedure proved to be within the range 0.2-0.4 mu Sv, except for equilibrium angiocar dioscintigraphy (1.0 +/- 0.5 mu Sv) and Tc-99m-sestamibi single-photon emission tomography (1.7 +/- 1.0 mu Sv), Comparison with data publish ed in the last 20 years shows that our values are generally lower. The current more favourable working conditions are a result of technologi cal improvements (for instance two-head gamma cameras capable of whole -body studies), and safer shielding and distance from patients. Two-le vel PET gave 11.5 +/- 4.4 mu Sv and whole-body PET 5.9 +/- 1.2 mu Sv. In a subset of patients these values could be subdivided into the sepa rate contributions from each phase of the procedure. They were: 0.11 /- 0.04 mu Sv for daily quality assurance, 2.9 +/- 3.0 mu Sv for two t ransmission scans, 0.3 +/- 0.1 mu Sv for syringe preparation, 2.8 +/- 1.8 mu Sv for injection and escorting the patient to the waiting room, 1.7 +/- 1.5 mu Sv for a whole body emission scan, 7.7 +/- 5.2 mu Sv f or two emission scans, and 0.8 +/- 0.2 mu Sv for patient departure. Th e higher value from PET by comparison with conventional procedures is attributable to the higher specific gamma constant of F-18, as well as the longer time required for accurate positioning.