339. Radiometabolic treatment of hyperthyroidism after a patient specific dosimetric study: The radiation protection impact. (December 2018)

• Record Type: Journal Article
• Authors: Canzi, C.; Longari, V.; Castellani, M.; Bardo, M.F.; D'Alessio, A.; Benti, R.
• Is Part Of: Physica medica. Volume 56(2018)Supplement 2
• Page Start: 267
• Publication Date: 2018-12
• Subjects: Medical physics -- Periodicals; Biophysics -- Periodicals; Biophysics -- Periodicals; Imagerie médicale -- Périodiques; Radiothérapie -- Périodiques; Rayons X -- Sécurité -- Mesures -- Périodiques; Physique -- Périodiques; Médecine -- Périodiques; 610.153
• DOI: 10.1016/j.ejmp.2018.04.348
• Languages: English
• ISSNs: 1120-1797

Abstract

Abstract : Purpose: Hyperthyroidism is a diffuse disease mainly treated with 131 I-NaI radiometabolic therapy. Recently published data report that in Europe at least 15.000/y treatments are performed. As hyperthyroidism is a benign condition, the optimization principle stated in art.56 of 2013/59/Euratom Council Directive should be strongly applied and radiometabolic treatment should be performed with the minimum activity necessary to reach the clinical purpose minimizing the exposure of non-target tissues. Aim of the work was to evaluate the radioprotection impact of 131 I therapies for hyperthyroidism after patient-specific dosimetric-studies, with respect to a standard administration of 600 MBq (max activity allowed in Italy for outpatient treatments). Methods: 503 patients who solved hyperthyroidism within 1 year were considered (183 Graves, 383F, median age = 64y 17–89y]). Results: Median 131 I administered activity was 385 MBq [66–629 MBq] and only 29% of the patients had the maximum allowed activity. Total administered activity was 209 GBq; if the standard activity of 600 MBq had been administered to all patients total would have been 302 GBq, 45% greater than the really used one. This acts on the patient mean effective dose and on the mean absorbed dose to the stomach wall (critical organ for 131 I-NaI/ICRP53) that were 5.8 Sv instead of 9.0 Sv and 177 mGy instead of 276 mGy respectively, with a maximum dose saving (9 times) for the patient who was given 66 MBq. The reduction of 131 I administered activity also acts on the exposure of the nuclear medicine staff and of population: the mean dose rate at 1 m at the patient discharge time is 12 μSv/h instead of 20 μSv/h. This approach involves also the environment, as in the first 24 h 60% of administered activity is excreted. Conclusions: The application of a patient specific pretreatment-dosimetric study can reduce of 45% the radioprotection impact of 131 I treatments of hyperthyroidism with clinical results guaranteed and activity administered to the single patient can be decreased down to 9 times.