Correlative study of dose to thyroid and incidence of subsequent dysfunction after head and neck radiation

Background Thyroid dysfunction is common after radiotherapy (RT) for patients with head and neck cancers. We attempted to discover RT dose parameters that correspond with RT‐induced thyroid dysfunction. Methods Records of 102 patients who received RT from 2008 to 2010 were reviewed with respect to thyroid function. Abnormalities were grouped in 2 ways: (1) none, transient, or permanent; and (2) overt or subclinical. Results At median follow‐up of 33.5 months, incidence of any thyroid abnormality was 39.2% (women vs men – 50% vs 35%). Permanent dysfunction was seen in 24.5% with higher incidence in women versus men (42.9% vs 17.6%; p = .0081). Permanent abnormalities most strongly correlated with D 50% ( p = .0275). V 50Gy also correlated with thyroid dysfunction post‐RT ( p = .0316). Concurrent chemotherapy increased permanent dysfunction ( p = .0008). Conclusion Achieving D 50% <50 Gy, V 50 <50%, and mean dose <54.58 Gy during RT planning may decrease the incidence; whereas female sex and concurrent chemotherapy seem to increase the risk of RT‐induced hypothyroidism.