A Quantitative Clinical Decision-support Strategy Identifying Which Oropharyngeal Head and Neck Cancer Patients may Benefit the Most from Proton Radiation Therapy.

PURPOSE: Developing a quantitative decision-support strategy estimating the impact of normal tissue complications from definitive radiation therapy (RT) for head and neck cancer (HNC). We developed this strategy to identify oropharyngeal HNC patients that may benefit most from receiving proton RT.

METHODS AND MATERIALS: Recent normal tissue complication probability (NTCP) models for dysphagia, esophagitis, hypothyroidism, xerostomia and oral mucositis were used to estimate NTCP for 33 oropharyngeal HNC patients previously treated with photon IMRT. Comparative proton therapy plans were generated using clinical protocols for HNC RT at a collaborating proton center. Organ-at-risk (OAR) doses from photon and proton RT plans were used to calculate NTCPs, Monte Carlo sampling 10,000 times for each patient to account for model parameter uncertainty. The latency and duration of each complication were modeled from calculated NTCP, accounting for age-, sex-, smoking- and p16-specific conditional survival probability. Complications were then assigned quality-adjustment factors based on severity to calculate quality-adjusted life years (QALYs) lost from each complication.

RESULTS: Based on our institutional delivered photon IMRT doses, and the achievable proton therapy doses, the average QALY reduction from all HNC RT complications for photon and proton therapy was 1.52 QALYs vs. 1.15 QALYs, with proton therapy sparing 0.37 QALYs on average (composite 95% CI: 0.27 , 2.53 QALYs). Long-term complications dysphagia and xerostomia contributed most to the QALY reduction. The QALYs spared with proton RT varied considerably between patients, from 0.06 to 0.84 QALYs. Younger patients with p16-positive tumors who smoked ≤10 pack-years may benefit most from proton therapy, although this finding should be validated using larger patient series. A sensitivity analysis reducing photon IMRT doses to all OARs by 20% resulted in no overall estimated benefit with proton therapy with -0.02 QALYs spared, although some patients still had an estimated benefit in this scenario, ranging from -0.50 to 0.43 QALYs spared.

CONCLUSIONS: This quantitative decision-support strategy allowed us to identify oropharyngeal cancer patients that might have the greatest benefit from proton RT, although the estimated benefit of proton therapy ultimately depends on the organ-at-risk doses achievable with modern photon IMRT solutions. These results can help radiation oncologists and proton therapy centers optimize resource allocation and improve HNC patients' quality of life.