BLOOD RADIOIODINE CONCENTRATION AND BLOOD RADIATION DOSAGE DURING I131THERAPY FOR METASTATIC THYROID CARCINOMA*

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Abstract
The radiation delivered to the blood of 23 patients following 53 oral therapeutic doses of I131 was detd. from the I131 concn. of serial blood samples taken after ingestion of the isotope. Assuming that the ratio of the avg. I131 concn. in tissue is half that in blood, the avg. specific radiation dosage to the blood (Roentgen equivalent physical (REP)/100 mc I131 admd.) was 52 [plus or minus] 31. The range was from 20-182 REP/100 mc. The max. total body radiation delivered following a single dose of radioiodine was calculated to equal 160 REP. No untoward effects followed the admn. of a single therapeutic dose of radioiodine other than temporary leukopenia. On the other hand, after extensive treatment with several large doses of radioiodine, 2 out of 13 patients developed persistent leukopenia. Although the blood I131 concn. is lower for the 1st 2 days following a radiation thyro-idectomizing dose than during the same period following a post-thyroidectomy dose, the reverse is usually observed after the 1st 2 days. A characteristic rise in the blood radioiodine concn. was observed following thyroidectomizing doses to euthyroid patients and following 25% of the therapeutic doses to thyroidectomized patients with functioning thyroid metastases. This rise was attributed to irradiation trauma on radioiodine-containing tissue.