TSH Suppression During Radiotherapy on Thyroid Site to Prevent Iatrogenic Hypothyroidism in Pediatric Cancer Patients

To offer the possibility of a treatment that could achieve a meaningful reduction in the incidence of post-radiation therapy hypothyroidism. Thyroid dysfunction may develop from a few months to several years after patients have completed their radiation treatment. In children with chronic diseases, or given lengthy anti-neoplastic treatments, recurrent or persistent endocrine disorders may have a negative effect on growth and development into adulthood.

Patients will undergo basal thyroid ultrasound and FT3, FT4, TSH assay. Simulations with computed tomography, and computer assisted three-dimensional treatment planning with a dose volume histogram will be used to identify thyroid volumes and corresponding RT isodose distributions. The enrolled patients will be randomly assigned (1:1) to TSH suppression group (experimental group) or non-TSH suppression group (control group). Random allocation will be managed centrally by Clinical epidemiology and Trial organization of the Fondazione IRCCS Istituto Nazionale dei Tumori. The randomization list will be generated by SAS software. Investigators and patients will not be masked to treatment allocation. From 14 days beforehand and throughout their RT, patients in the experimental arm will receive L-thyroxine in the morning on an empty stomach (half an hour before breakfast), starting with 1-2 μg/kg, and adjusting the dose every 3 days to ensure TSH \< 0.3 μIU/mL before RT beginning. The 0.3 μIU/mL threshold is just below normal range not causing hyperthyroidism, and is defined as "mild" TSH suppression. Based on hormone status, L-thyroxine doses will be gradually increased to patients' individual minimum TSH-suppressive dose before starting RT, maintained throughout the treatment, then rapidly tapered off (half dose the next day after RT, 25% the following day and stop).