Thyroid abnormalities after therapeutic external radiation

• Published in: International journal of radiation oncology, biology, physics Vol. 31; no. 5; pp. 1165 - 1170
• Main Authors: Hancock, Steven L., McDougall, I.Ross, Constine, Louis S.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY Elsevier Inc 30.03.1995; Elsevier
• Subjects: Benign and malignant thyroid neoplasms; Biological and medical sciences; Endocrinopathies; Graves' disease; Humans; Hyperthyroidism; Hyperthyroidism - etiology; Hypopituitarism; Hypothyroidism; Hypothyroidism - etiology; Medical sciences; Neoplasms, Radiation-Induced - etiology; Non tumoral diseases. Target tissue resistance. Benign neoplasms; Radiation injury; Radiotherapy - adverse effects; Thyroid diseases; Thyroid Diseases - etiology; Thyroid Diseases - therapy; Thyroid Gland - anatomy & histology; Thyroid Gland - physiology; Thyroid Gland - physiopathology; Thyroid Gland - radiation effects; Thyroid Neoplasms - etiology; Thyroid. Thyroid axis (diseases); Thyroidectomy; Thyroiditis; Thyroiditis; Hypopituitarism; Graves' disease; Hyperthyroidism; Benign and malignant thyroid neoplasms; Thyroid diseases; Radiation injury; Hypothyroidism; Thyroidectomy
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/0360-3016(95)00019-U

The thyroid gland is the largest pure endocrine gland in the body and one of the organs most likely to produce clinically significant abnormalities after therapeutic external radiation. Radiation doses to the thyroid that exceed approximately 26 Gy frequently produce hypothyroidism, which may be clinically overt or subclinical, as manifested by increased serum thyrotropin and normal serum-free thyroxine concentrations. Pituitary or hypothalamic hypothyroidism may arise when the pituitary region receives doses exceeding 50 Gy with conventional, 1.8–2 Gy fractionation. Direct irradiation of the thyroid may increase the risk of Graves' disease or euthyroid Graves' ophthalmopathy. Silent thyroiditis, cystic degeneration, benign adenoma, and thyroid cancer have been observed after therapeutically relevant doses of external radiation. Direct or incidental thyroid irradiation increases the risk for well-differentiated, papillary, and follicular thyroid cancer from 15- to 53-fold. Thyroid cancer risk is highest following radiation at a young age, decreases with increasing age at treatment, and increases with follow-up duration. The potentially prolonged latent period between radiation exposure and the development of thyroid dysfunction, thyroid nodularity, and thyroid cancer means that individuals who have received neck or pituitary irradiation require careful, periodic clinical and laboratory evaluation to avoid excess morbidity.