Purpose: The "Registry for the Evaluation of Side Effects After Radiotherapy in Childhood and Adolescence" (RiSK) has been established to prospectively characterize dose-volume effects of radiation in terms of side effects. The aim of this analysis was to characterize the function of the thyroid gland after radiotherapy to the head-and-neck region in children and adolescents.
Methods and materials: Detailed information regarding radiation doses to at-risk organs has been collected across Germany since 2001. Thyroid function was evaluated by blood value examinations of thyroid-stimulating hormone, triiodothyronine, and thyroxine. Information regarding thyroid hormone substitution was requested from the treating physicians.
Results: Until May 2009, 1,086 patients from 62 centers were recruited, including 404 patients (median age, 10.9 years) who had received radiotherapy to the thyroid gland and/or hypophysis. Follow-up information was available for 264 patients (60.9%; median follow-up, 40 months), with 60 patients (22.7%) showing pathologic values. In comparison to patients treated with prophylactic cranial irradiation (median dose, 12 Gy), patients with radiation doses of 15 to 25 Gy to the thyroid gland had a hazard ratio of 3.072 (p=0.002) for the development of pathologic thyroid blood values. Patients with greater than 25 Gy to the thyroid gland and patients who underwent craniospinal irradiation had hazard ratios of 3.768 (p=0.009) and 5.674 (p<0.001), respectively. The cumulative incidence of thyroid hormone substitution therapy did not differ between defined subgroups.
Conclusions: Radiation-induced thyroid function impairment, including damage to the thyroid gland and/or hypophysis, can frequently be observed after radiotherapy in children. A structured follow-up examination is advised.
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