THE IMPACT ON THE ENVIRONMENT AND ON THE POPULATION DUE TO THE RELEASE OF THE PATIENTS AFTER THERAPY WITH UNSEALED SOURCES: A COMPARISON BETWEEN THE NEW INTERNATIONAL RECOMMENDATIONS AND THE ITALIAN REGULATIONS

The radiopharmaceutical therapy is the administration of unsealed sources of radioactivity designed to elicit a therapeutic response as a result of irradiation of a target human tissue. Historically, radioiodine (131I) therapy for thyroid diseases, including hyperthyroidism as well as localized and metastatic thyroid cancer, has been the most studied and successful application of radionuclide therapy. This success has largely resulted from the high, rapid, and long-retained uptake of iodide in thyroidal tissue, whereas little uptake occurs in extra-thyroidal tissues. After diagnostic nuclear medicine procedures, precautions for the public are rarely required. In the other hand, after some therapeutic procedures, exposures to the public, patient's relatives, and others should be limited. The decision to hospitalise or release a patient after the therapy with unsealed radioactive sources should be determined on an individual basis, and on the factors such as the residual activity in the patient, the patient's wishes, the occupational and public exposures, cost, family and environmental aspects. The ICRP Publication 94 sets a limit for the radio nuclide activities, depending on external dose to other people, that can decide if patients may be or may not be hospitalised after the therapy. The International Commission on Radiological Protection (ICRP) has relied upon the dose limit of 1mSv/year for the public, and the dose constraint of 5 mSv/episode for relatives, visitors, and caregivers (ICRP, 1991, 1996). These recommendations have been interpreted in various Countries, and the dose constraint has often been inappropriately interpreted as a rigid annual dose limit. As iodine-131 is a frequently used high-energy gamma emitter and has an 8-days physical half-life, it results in the largest dose to medical staff, the public, and relatives after procedures involving therapeutic administration of unsealed radionuclides. If we consider 1 mSv as the dose effective for the general public, the remaining activity in the patient of 240 MBq of 131I is sufficient to hospitalise the patients. The Italian regulation establishes that it could not be necessary the patient's hospitalisation after hyperthyroidism therapy with 131I if the administered activity is less than 600 MBq. (D. L.vo 187/2000, All.I, part II, codicil 6). On the basis of the previous considerations, in this paper the authors compare the ICRP recommendations with the Italian procedures adopted in the nuclear medicine practices, either from the point of view of the correct management of the patients or from the point of view of the radioprotectione and of the dose contribution to the population. This comparison takes into account either the environmental release and its contribution to the public dose, or the good protection measurement, which should have been adopted for limiting the exposure of the medical staff, relatives, caregivers and the general public, both in the case of the patient's hospitalisation and of his release.