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 (X(2) 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.