Biological dosimetry applied to treatment with 131 radio-iodine in thyroid cancers

This study had 2 objectives: Firstly to compare the number of unstable chromosomal anomalies (dicentrics, rings and fragments) obtained by the method of conventional cytogenetics with the number of translocations revealed by in situ hybridization (FISH) and secondly to estimate the mean whole body dose after treatment with 3.7 GBq (100 mCi) of 131I. The estimated mean total body dose is 2 to 4 times higher than that based on MIRD calculations (0.13 Gy). In fact, MIRD calculations were derived from individuals with normal thyroid function and normal metabolic activity. Thyroid cancer patients are hypothyroid at the time of 131I administration. The hypothyroid status decreases the renal clearance of radioiodine and thus increases the whole body dose which can explain the discrepancy between the MIRD estimation and the values found by biological dosimetry. (author)