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Radiation-induced hypothyroidism after radical head and neck cancer treatment has the potential to worsen the quality of life of patients. Thyroid-sparing techniques are sparingly employed in locally advanced head and neck cancers. This pilot study was designed to evaluate the clinical outcomes of Thyroid Sparing Simultaneous Integrated Boost Volumetric Modulated Arc Radiotherapy (SIB-VMAT) in the treatment of Stage III and IV Head and Neck cancers.

This two-arm pilot study recruited patients of Stage III and IV squamous cell carcinomas of the head and neck for treatment with radical chemoradiation using SIB-VMAT technique. Patients in the study group received radiotherapy by thyroid-sparing SIB-VMAT technique to a dose of 70 Gy and 59.4 Gy (to the gross disease and subclinical disease) in 33 fractions over 6 ½ weeks with concurrent three weekly cisplatin (100mg/m2 on days 1,22,43). The thyroid constraint employed was V50Gy<75%. The control group consisted of patients treated with the same schedule without thyroid constraints. Thyroid profile was evaluated at the end of radiotherapy, 6 months, 9 months after radiotherapy, and at the last follow-up. Survival analysis was done using the Kaplan-Meir method and the Progression Free Survival (PFS) was compared using the log-rank test.

Twenty-six patients were evaluated in this study (thirteen in each arm). There were twenty-five males (96.2%) and one female patient (3.8%). The median age was 51.5 years (range 35-65 years). Thirteen (50%) patients had Stage III and the other half were Stage IVA at diagnosis. All patients were euthyroid at diagnosis. The median follow-up duration was 20.7 months. On last follow up the mean TSH, T3 and T4 values in the non thyroid sparing and the thyroid sparing group were 7.03 vs 3.92 μIU/L (p=0.307), 1.39 vs 1.11 ng/ml (p=0.422) and 6.65 vs 7.67 mcg/dL (p=0.268). At nine months post-radiotherapy, three patients in the non-thyroid-sparing group and two patients in the thyroid-sparing group developed any degree of hypothyroidism (both clinical and subclinical). At a median follow-up of 20 months, six out of thirteen patients (46.15%) developed any degree of hypothyroidism in the non-thyroid sparing group whereas three out of thirteen patients (23.07%) developed any degree of hypothyroidism in the thyroid-sparing group (p=0.216). The thyroid V50Gy in the Thyroid sparing group was 65.33±6.63 % (volume in %) compared to 80.35 ±13.40 % in non-thyroid sparing radiotherapy (p=0.003). The median PFS of the study group was found to be comparable to that of the control group (8.9 v 10.2 months; p=0.578).

The usage of thyroid constraint of V50Gy<75% halved the incidence of any degree of hypothyroidism in our study without affecting the survival outcomes. The routine use of thyroid constraints can reduce the risk of radiation-induced hypothyroidism and must be evaluated in a larger study.