Effects of Thyroid Hormone Withdrawal and Recombinant Human Thyroid Stimulating Hormone in Glomerular Filtration Rate During Radioiodine Therapy

Radioiodine therapy in thyroid carcinoma is a procedure performed for over six decades, and there is a vast literature in respect of its value in the complementary treatment of this neoplasia. This procedure also promotes a reliable follow-up based on sequential thyroglobulin dosages and makes possible to reduce the disease recurrence rate. One of the main aspects of the patients preparation before receiving the radioiodine consists in promoting stimulation for an effective uptake of the radioiodine, obtained either by endogenously TSH level elevation after post-surgical thyroid hormone withdrawal, or exogenously after use of recombinant human TSH. This last alternative does not demand suspension of thyroid hormone reposition after total thyroidectomy. Although not fully comprehended, it is known that hypothyroidism results in renal function hazard, which is reverted after hormonal reposition. It is also known that renal function modifies the radioiodine residence time and that the longer this time, the greater the patient's radiation exposure will be, and consequently with undesired irradiation of healthy tissues and organs. So theoretically stimulating the patient with recombinant human TSH could avoid the transient deficient renal function, promoting a lower radioiodine residence time and consequently lowering radiation exposure in this therapy.

This project aims to evaluate the effects of the different stimulation, endogenous and exogenous, over renal function by glomerular filtration rate determined by 51Cr-EDTA. This will be a controlled and randomized study in which 44 patients that has clinical indication of remnant ablative radioiodine treatment will be prepared by either one of the TSH stimulation procedures. Additionally radiation dosimetry calculus will be done to analyze the levels of the patient's radiation exposure associated with each of the uptake stimulation procedures for radioiodine therapy.