Whole-body (131)I washout in a patient with metastatic well-differentiated papillary thyroid carcinoma treated with repeated (131)I administration.

We describe the case of a 37-year-old male patient suffering from papillary carcinoma of the thyroid gland with pulmonary metastases who after total thyroidectomy on 29/07/1998 was submitted to three treatments with high doses of (131)I and studied as to the whole body clearance of (131)I by measuring the dose rate of (131)I. The patient was referred to us for total ablation of post surgery remnant of thyroid tissue on 19/09/1998. Due to lymphadenic metastases and high Tg values: 450 ng/ml, he was purposely given therapeutically a high dose of 5146 MBq (131)I. On the whole body post-operative scintiscan that followed, a diffuse uptake of (131)I in the lungs and in the thyroid remnant was found. The patient was given 7307 MBq (131)I after 7 months and 5154 MBq of (131)I after another 10 months, because Tg was increased. Whole body scintiscan after the third treatment as mentioned above, showed poor uptake of (131)I in the thyroid gland area and in the lungs. No side effects were noticed, Tg fell to 4.5-7 ng/ml and the patient was in good condition with no abnormal findings on the X-rays or CT of the thorax. After iodine administration whole body measurements of the dose rate of the clearance of (131)I measured by an ionization chamber at a distance of 2 m from the thorax, were performed. For the first treatment effective half-lives of (131)I of the patient, as measured for the two components of the clearance curve, were 4.4 h and 16.8 h respectively. For the second and third treatment clearance curve had only one component and effective half-lives were 22.5 h and 11 h respectively. Remaining activity of (131)I at 48 h was for the first, second and third treatment: 13.3% (685 MBq), 22.8% (1670 MBq) and 4.2% (222 MBq) respectively. We do not know any similar case in the literature with whole body measurements of (131)I clearance in patients undergoing repeated (131)I treatment as above, especially with diffuse pulmonary uptake of (131)I indicating metastatic lesions after the first treatment of (131)I post total thyroidectomy. The interest of the above case also lies on the fact that there were three successive treatments with (131)I and three whole body (131)I measurements. Clearance rate indicated the need for additional treatment and the treatment followed was successful.