Predicting the Clinical Gains Associated With Further Reduction of Normal Tissue Dose Constraints in Oropharynx Cancer Radiotherapy

Abstract

<h3>Purpose/Objective(s)</h3> Toxicity mitigation is a salient focus in the treatment of HPV-associated oropharyngeal cancer. As the standard of care evolves, toxicity mitigation can be facilitated by adopting more stringent normal tissue constraints. We hypothesize that further reduction in currently accepted constraints leads to reductions in normal tissue complication probabilities (NTCP) without compromising disease outcomes. <h3>Materials/Methods</h3> This was a retrospective, single-institution study of patients with oropharynx cancer treated with adjuvant volumetric modulated arc therapy to standard doses (60-66 Gy) and volumes (i.e., bilateral neck) from 2015-2018. Doses delivered to organs at risk were compared to recommended dose acceptance criteria from a recent, cooperative trial of RT to 60 Gy (NRG HN002). We applied validated, published NTCP models for xerostomia, dysphagia, dysgeusia, oral mucositis and esophagitis relevant to oropharyngeal cancer. <h3>Results</h3> 92 patients were identified. Median follow-up was 2.2 years. The doses achieved and corresponding estimates of NTCP are shown in Table 1, as compared to a nationally recognized standard (NRG HN002). Notable NTCP reductions were observed for salivary flow, dysphagia, dysgeusia, mucositis, and esophagitis. The use of more stringent constraints did not impact disease outcome, with only a total of 3 patients having experienced locoregional recurrence (1 local, 2 regional), for an overall locoregional control of 96.7%. <h3>Conclusion</h3> Improved normal tissue sparing compared to current dose constraint standards is achievable with contemporary RT planning techniques. These improved constraints may lead to decreased toxicity, while preserving excellent disease outcomes. Our constraints can easily be adopted as standard of care and used in conjunction with other efforts to mitigate toxicity.