Monitoring Cytogenetic Effects in Peripheral Blood Lymphocytes of Thyroid Cancer Patients Receiving Radioiodine Treatment

This study investigated cytogenetic damage in peripheral blood lymphocytes of 10 differentiated thyroid cancer patients who received multiple 131I radioiodine (RAI) treatments following total thyroidectomy. Blood samples were collected before the RAI therapy course and 2–3 days after the course for a few selected courses (from 1 to 3) for each patient. The cumulative average number of chromosome aberrations (CAs) per cell and its increment due to a selected RAI course were evaluated using the multiplex fluorescence in situ hybridization method (mFISH). An increase in the number of CAs was observed with the accumulation of RAI activity. The yield of these CAs per unit of accumulated RAI activity was, however, approximately three-fold lower than the respective yield for the incremented number of CAs in a selected course, thus demonstrating the elimination of CAs and/or aberrant cells with time. Biological dosimetry was performed based on the number of all types of CAs and in vitro mFISH calibration curves. With an average administered RAI activity of 3.40 ± 0.39 GBq, the average absorbed blood dose was 0.61 Gy (0.31–0.89:95% CI). Our results demonstrate that one-time administration of such activities of RAI was safe, since the commonly accepted threshold of 2 Gy for the blood dose was not exceeded.