PRKDC and head and neck squamous cell carcinoma: We are also acutely aware of the availability of more potent and selective inhibitors than the ones used in the current study, specifically those targeting ATM (e.g., AZD1390), ATR (e.g., AZD6738) and DNA-Pkcs (e.g., AZD7648), which require examination of their potential to radiosensitise HNSCC cell models following photon and proton irradiation.