Doses from nuclear medicine examinations: A 25-year follow-up study

New radiopharmaceuticals have been introduced in nuclear medicine examinations, and on the other hand, the amount of many routine nuclear medicine procedures have been replaced with clinical methods utilising non-ionisating radiation (ultrasonography, MRI). To clarify the situation in Finland, a country wide survey on the use of radiopharmaceuticals in diagnostics and therapy was made in 1975, 1982, 1989, 1994, 1997 and will be made in 2000. A questionnaire was sent to all hospitals and institutes using unsealed sources in both diagnostic and therapeutic nuclear medicine procedures. For each procedure, the pharmaceutical used, the number of procedures and the typical administered activities were recorded. The collective effective doses from nuclear medicine examinations were calculated according to the ICRP formulae similarly for each survey. In Finland, in each of these years, more than 50,000 procedures in more than 30 different laboratories were performed. Significant changes in collective doses were observed: for example, the collective dose from I-131 was 350 manSv in 1975, and 20 manSv in 1997. In 1975, 68% (n=23967) of collective dose originated from I-131, whereas in 1997 the percentage of I-131 in collective dose was 10 % (n=1118). In 1994 and 1997, the use of the three radionuclides (Tc-99m, I-131 and Tl-201) accounted for 96% and 95% of the collective effective dose. Our results indicate that the collective effective dose from nuclear medicine examinations has decreased in last 25 years. National surveys form the basis when setting reference levels for typical nuclear medicine examinations. By introducing reference levels based on national practice it is possible to even decrease the collective effective dose. (author)