Differences in geometric patterns of failure in human papillomavirus (HPV)‐associated and HPV‐non‐associated oropharyngeal cancer after definitive radiotherapy

Introduction The aim of this study was to evaluate and compare the spatial pattern of locoregional recurrences in patients diagnosed with HPV‐associated and HPV‐non‐associated oropharyngeal SCC (OPSCC) treated with definitive radiotherapy. Methods and materials Patients who had locoregional recurrence following definitive intensity‐modulated radiation therapy were identified at a single tertiary institution. Target volumes were delineated according to the latest consensus international guidelines. Recurrences were classified into five categories based on radiotherapy dose distribution and target volume, using a previously validated methodology; type A (central high dose), type B (peripheral high dose), type C (central elective dose), type D (peripheral elective dose), and type E (extraneous dose). The types of failure were compared between p16‐positive and p16‐negative tumors using the Pearson chi‐square test. Results Fifty‐eight locoregional recurrences were observed in 36 patients. The majority of recurrences were in nodal locations (66%, 38/58). Among these, 34 (59%) were classified as type A, 6 (10%) as type B, 9 (15%) as type C, 5 (9%) as type D, and 4 (7%) as type E failure. A significant difference was found in the types of failure between p16‐positive and p16‐negative tumors (X2 9.52, p = 0.044). p16‐negative tumors were more likely to have recurrences in a peripheral location compared to p16‐positive tumors (32% vs. 7%). p16‐positive tumor were more likely to have extraneous recurrences (17% vs. 0%). Conclusion Our study results identified a significant difference in patterns of locoregional failure among patients diagnosed with oropharyngeal cancer following consensus‐based tumor delineation and modern radiotherapy. Further confirmatory pattern of failure studies are required to enable greater individualization of radiotherapy for patients diagnosed with oropharyngeal malignancy in the future.