Hypothyroidism after 3‐dimensional conformal radiotherapy and intensity‐modulated radiotherapy for head and neck cancers: Prospective data from 2 randomized controlled trials

Abstract Background The purpose of this study was to determine the incidence of hypothyroidism after chemoradiation in head and neck squamous cell cancer (HNSCC). Methods One hundred twenty‐two patients treated with 3‐dimensional conformal radiotherapy (3DCRT; 70 Gy/35#) or intensity‐modulated radiation therapy (IMRT; 66 Gy/30#) in 2 identical simultaneous randomized trials were studied. Thyroid function was assessed at baseline and every 3 to 6 monthly thereafter. Development of subclinical (thyroid‐stimulating hormone [TSH] >4.67 μIU/mL) or biochemical (T4 <4.5 μg/dL) hypothyroidism was noted. Multivariate analyses were done to determine the factors associated with hypothyroidism. Results At a median of 41 months, 55.1% of the patients developed hypothyroidism (39.3% subclinical, 15.7% biochemical). The IMRT arm had higher subclinical hypothyroidism (51.1% vs 27.3%; p = .021) peaking around 1 year postradiotherapy in both arms. Younger age, hypopharynx/larynx primary, node positivity, higher dose/fraction (IMRT arm), and D100 were statistically significant factors for developing hypothyroidism. Conclusion Postradiotherapy hypothyroidism peaks at 1 year. Higher dose per fraction possibly led to greater incidence of hypothyroidism in the IMRT cohort. © 2014 Wiley Periodicals, Inc. Head Neck 36: 1573–1580, 2014