A Pilot Study of Ultra-High Dose Rate (ConformalFLASH®), for Reirradiation of Carcinoma of the Head and Neck

C-FLASH-01 is a pilot study evaluating the feasibility of delivering ultra-high dose-rate conformal proton therapy (ConformalFLASH) to participants requiring re-irradiation for head and neck cancer who are not amenable to surgical resection. Stereotactic Body Radiation Therapy (SBRT) re-irradiation is a standard approach that enables highly conformal dose delivery over a limited number of fractions. ConformalFLASH is an investigational approach that applies SBRT principles using proton therapy delivered at ultra-high dose rates (≥ 40 Gray Relative Biological Effectiveness (GyRBE)/second), with the potential to reduce normal tissue toxicity while maintaining tumor control. Participants will undergo treatment planning and delivery consistent with standard SBRT workflows. Treatment consists of five fractions (8 GyRBE per fraction) delivered over approximately 1.5 to 2 weeks. The primary objective is to assess the feasibility of delivering conformal proton SBRT at dose rates ≥ 40 GyRBE/second, along with evaluation of acute toxicity. Secondary objectives include assessment of treatment delivery accuracy, late toxicity, clinical outcomes, and patient-reported quality of life.