Acute effects on the thyroid gland after non-directed radiation therapy in children and adolescents

Background: During radiation therapy, unwanted scatter to healthy tissues outside the target field may occur. Children and adolescents are more sensitive to radiation injury, and the thyroid gland is particularly susceptible to these effects. Purpose: To assess acute changes in thyroid function and volume in children and adolescents undergoing radiotherapy for a variety of non-thyroid cancers. Materials and Methods: Thirty-one children and adolescents underwent radiation therapy of various body areas in which the thyroid was not included. Thyroid-stimulating hormone (TSH), thyroxine (T4), free thyroxine (fT4), triiodothyronine (T3), anti-thyroperoxidase antibodies and thyroglobulin were measured before, on the last day and at 1 and 3 months after the end of radiotherapy. Ultrasound scans were taken and 6- and 24-hour¹³¹I uptake was measured before and after treatment. The scattered dose to the thyroid region was estimated with a treatment planning system or measured with thermoluminescent dosimeters. Results: The median radiation dose scattered to the thyroid was 296∙6 cGy (IQR 16∙7–1,709∙0). Levels of TSH (p=0∙575), T4 (p=0∙950), fT4 (p=0∙510), T3 (p=0∙842), thyroglobulin (p=0∙620) and anti-thyroid peroxidase antibodies (p=0∙546) were statistically similar at all four time points. There were no differences between pre- and post-radiotherapy thyroid volume and ¹³¹I uptake (p=0∙692 and 0∙92, respectively). Conclusion: More sensitive methods may be required to ascertain whether acute injury to the follicular epithelium occurs with lower radiation doses scattered to the thyroid