Assessment of occupational hazard in handling syringes containing radiopharmaceuticals, using Monte Carlo technique

In recent years, the use of various radionuclides in nuclear medicine has increased significantly. Determination of true radiation exposure received by the hands of technologists handling radiopharmaceuticals is essential in order to confirm that the exposure is within the acceptable limits. A Monte Carlo computer code has been developed to calculate absorbed dose rates at surface sites on unshielded syringes containing radiopharmaceuticals for diagnostic and therapeutic injections. The code includes dose due to characteristic x-rays, gamma rays, beta particles and secondary electrons, and makes allowances for absorption in source and syringe wall region. The system used in the code consisted of radioactive fluid, plastic syringe and skin-tissue surrounding it. Water was taken as tissue-equivalent material and the syringe-barrel as a right circular cylinder. The code provides both axial and radial dose distribution at various locations in the skin and can handle various types and sizes of syringes, different amount, activity and type of radiopharmaceutical. Test cases were run for commonly used Technetium-99m on IBM 370/145 computer for 100,000 histories. Results using 1 ml (4.6mm I.D., 6.6mm O.D.) and 5 ml (12.8mm I.D., 14.4mm O.D.) fully filled syringes were 35-68 and 20-30 mrad/mCi-minute respectively, to the active layers of fingertips. Dose rates to the palm and wrist were much smaller. It was evaluated that fingertips of a technologist can receive 70-250 rems/year by performing 25 administrations per week (40 working week in a year) of 10 mCi activity each, when average administration time was 25 seconds. Similar results using the code can be utilized to determine the possible occupational risks in using unshielded syringes and to design an appropriate shield to avoid undesirable effect of excessive and unnecessary radiation exposure. (author)