Thyroid-optimized and thyroid-sparing radiotherapy in oral cavity and oropharyngeal carcinoma: A dosimetric study

Highlights • This feasibility study showed thyroid sparing in head and neck cancer patients. • Thyroid sparing with acceptable target volume coverage was possible with IMRT. • Average mean dose to thyroid was significantly reduced with thyroid optimization. • Thyroid optimized plans had relatively unchanged doses to surrounding OARs.
Background Radiation-induced hypothyroidism is a common toxicity of head and neck radiation. Our re-planning study aimed to reduce thyroid dose while maintaining target coverage with IMRT. Methods We retrospectively identified patients with oral-cavity (n = 5) and oropharyngeal cancer (n = 5). Treatment plans were re-optimized with 45 Gy thyroid mean dose constraint, then we cropped the thyroid out of PTVs and further reduced thyroid dose. Target coverage was delivering 100% dose to ≥ 93% of PTV and 95% of dose to > 99% of PTV. Results Originally, average mean dose to thyroid was 5580 cGy. In model I, this dropped to 4325 cGy (p