URINARY-EXCRETION AND EXTERNAL RADIATION-DOSE FROM PATIENTS ADMINISTERED WITH RADIOPHARMACEUTICALS

Patients who have received radiopharmaceuticals become a source of exp osure to those near them, such as nursing staff or visiting relatives. In order to provide quantitative information to propose protective me asures for carers attending patients administered diagnostic amounts o f Tc-99m, Ga-67 or Tl-201 (the most frequently used radiophamiaceutica ls) the dose rate at various distances from 84 patients was measured u sing an ionising chamber, and the radioactivity of these compounds in urine collected from some patients was also measured using dose calibr ation equipment and an auto-well-type gamma scintillation counter. The dose rates were proportional to powers from -1.4 to -1.2 of the dista nces at 5 to 100 cm from the patient. The urinary excretion of Tc-99m- DTPA and Tc-99m-MDP was rapid: about 30% of the administered activity was excreted within 40 min, and about 50% within 4 h of injection, res pectively. For Ga-67 compounds the urinary excretion rate was slow: on ly about 25% of the administered activity being lost within three days of injection. The accumulated first-day doses to carers attending to patients administered Tc-99m accounted for about 100% of the total acc umulated doses. Thus, significant exposure from the patients was mainl y limited to that occurring on the day of administration. Protective m easures are emphasised for the day of radiopharmceutical administratio n.