Dose-volume predictors of post-radiation primary hypothyroidism in head and neck cancer: A systematic review

•This systematic review included 29 studies (n = 4,530 patients) on dosimetric predictors of primary hypothyroidism in HNC.•Average crude incidence of primary hypothyroidism after HNC radiotherapy was 41.4%.•Thyroid Dmean and V50 were the most widely reported dosimetric predictors for hypothyroidism.•Thyroid volume is a predictor of hypothyroidism (pooled aOR 0.89 per 1 cc increment) independent of radiation dosimetry.•Thyroid gland constraints individualized for thyroid volume are crucial in HNC radiotherapy.