RecruitingRadiation therapyA Pilot Study of Ultra-High Dose Rate (ConformalFLASH®), for Reirradiation of Carcinoma of the Head and NeckThis pilot study is designed to evaluate the feasibility of delivering ultra-high dose-rate conformal proton therapy (ConformalFLASH) in participants requiring re-irradiation for head and neck cancer who are not amenable to surgical resection. ConformalFLASH treatment planning and delivery workflows are comparable to those of conventional Stereotactic Body Radiation Therapy (SBRT), a standard approach for re-irradiation in this population.