INDIVIDUAL MONITORING OF INTERNAL EXPOSURE FOR NUCLEAR MEDICINE WORKERS IN SWITZERLAND

Monitoring of internal exposure for nuclear medicine workers requires frequent measurements due to the short physical half-lives of most radionuclides used in this field. The aim of this study was to develop screening measurements performed at the workplace by local staff using standard laboratory instrumentation, to detect whether potential intake has occurred. Such measurements do not enable to determine the committed effective dose, but are adequate to verify that a given threshold is not exceeded. For radioiodine, i.e. I-123, I-124, I-125 and I-131, a calibrated surface contamination monitor is placed in front of the thyroid to detect whether the activity threshold has been exceeded. For radionuclides with very short physical half-lives (<= 6 h), such as Tc-99m and those used in positron emission tomography imaging, i.e. C-11, O-15, F-18 and Ga-68, screening procedures consist in performing daily measurements of the ambient dose rate in front of the abdomen. Other gamma emitters used for imaging, i.e. Ga-67, In-111 and Tl-201, are measured with a scintillation detector located in front of the thorax. For pure beta emitters, i.e. Y-90 and Er-169, as well as beta emitters with low-intensity gamma rays, i.e. Sm-153, Lu-177, Re-186 and Re-188, the procedure consists in measuring hand contamination immediately after use. In Switzerland, screening procedures have been adopted by most nuclear medicine services since such measurements enable an acceptable monitoring while taking into account practical and economic considerations.