TSH use before radiotherapy for thyroid cancer reduces iodine isotope half-life

Compared with thyroxine withdrawal, treatment with thyroid stimulating hormone before radioiodine therapy for thyroid cancer significantly reduces the half-life of 131-iodine, according to a new report.

The findings, which are published in the July issue of The Journal of Nuclear Medicine, are based on a study of 227 patients who were treated with radioiodine therapy for thyroid cancer. The preparation for radiotherapy included thyroxine withdrawal in 163 patients and treatment with recombinant human TSH in 64 patients.Radioactive iodine was cleared from the body significantly faster in the TSH group compared with the thyroxine withdrawal group (p < 0.001), report Dr. Christian Menzel and colleagues, from the Johann W. Goethe University Hospital in Frankfurt, Germany.Moreover, the TSH treatment appeared to be well tolerated with no serious adverse effects occurred, the researchers add.Although the study provides important information, it really does not answer which pre-treatment method should be used, Dr. Richard J. Robbins and Dr. Keith S. Pentlow, from Memorial Sloan-Kettering Cancer Center in New York, note in a related editorial. The principal difference between the two methods is that thyroxine withdrawal results in hypothyroidism, whereas treatment with TSH does not. While avoiding hypothyroidism is definitely beneficial, it may not be worth it if the reduced 131-iodine half-life means that cancerous lesions are being inadequately treated. While the current findings indicate that TSH treatment reduces whole-body exposure to 131-iodine, the editorialists note, it remains unclear whether this means that cancerous lesions also receive less exposure.Before TSH treatment can be recommended as a means to avoid hypothyroidism, it must first be shown that such treatment does not adversely affect the ability of 131-iodine to destroy target tissues, Drs. Robbins and Pentlow conclude.(Source: J Nucl Med 2003;44:1065-1068: Reuters Health: July 18, 2003: Oncolink)