Feasibility of Primer Shot Radiotherapy for Non-small Cell Lung Cancer - PRIMER

Intro/rationale: Radiotherapy employs uniform, equally spaced weekday fractions that do not account for changes in tumor radiosensitivity. However, radiobiological characteristics evolve during the radiotherapy schedule as reoxygenation increases radiosensitivity. In tumor-response simulations and preclinical experiments, it was superior to prime the tumor with one radiotherapy fraction, followed by a treatment break permitting mitotic cell death and reoxygenation of tumor cells. Objective: To determine the safety and feasibility of primer shot fractionation for NSCLC. Study design: A prospective non-randomized feasibility trial to test the safety of primer shot fractionation in a 3+3 phase with increasing treatment breaks, followed by an expansion cohort. Study population: Patients with NSCLC stage 2-4, referred for palliative radiotherapy of the primary tumor and possibly (lymph node) metastases. Patients are allowed to receive systemic treatments, except for VEGFR-inhibitors. The 3+3 phase is followed by an expansion phase of 22 patients. Intervention: All treatments are 5x6 Gy to all targets. Patients receive an increasing primer shot treatment break. In the 3+3 phase, the break between the first and the second radiotherapy fraction is: 1, 2 and 3 weeks. The maximum tolerated break length will be used for the expansion cohort. Main study parameters/endpoints: The main study endpoint is the ability of patients to finish the radiotherapy schedule as planned. Secondary endpoints are tumor response at the end of treatment and 3 months thereafter, and acute toxicity. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Based on simulations and preclinical data, primer shot treatment breaks increase tumor control. However, the increased overall treatment time could potentially increase the chance a patient drops out before the radiotherapy schedule is finished. Because of the gradually prolonged break, this risk