External radiation exposure of personnel working with 99mTechnetium

Radiation from 99mTc was measured at typical locations in those areas of a nuclear medicine department where approximately 50 Ci 99mTc is used per year. In addition, measurements of shielded and unshielded syringes containing 99mTc-labelled radiopharmaceuticals were carried out. From these data radiation exposure of hands and of the whole body of personnel was calculated, taking into consideration the mean working times in the areas and the times of direct and indirect handling of 99mTc. They were compared with the mean values obtained by personnel dosimetry through quartz fibre pocket dosimeters and TLD finger ring dosimeters. The whole body radiation calculated from local measurements for technicians (163 +/- 15 mR/year) (mean +/- SE) and for physicians (260 +/- 15 mR/year) was very low judged by the maximum permissible dose of 5,000 mrem/year and correlated well with those of personnel dosimetry (165 +/- 15 R and 265 +/- 15 R/year respectively). Although local radiation was rather high during generator elution and while preparing radiopharmaceuticals (13 +/- 1.2 mR/h) the radiation exposure to the hands of the radiochemists measured by the TLD finger ring dosimeter was low (2.6 +/- 0.2 R/year). This was attained by consistently using long distance tools in order to avoid direct contact with 99mTc-containing vials and syringes. The most critical point of radiation exposure in our investigation were the finger tips during injection of 99mTc, when syringe shielding was not used (80-130 mR/injection of 10 mCi). Under our conditions this amounts to 330-560 R/year when a total of 40 Ci is injected by the same physician. This by far exceeds the maximum permissible dose of 60 rem/year. The dose can be reduced extensively to only 2-3 R/year when tungsten shielding of the syringe is consistently used.