Reducing target volume in definitive radiotherapy for human papillomavirus-associated tonsil cancer.

BACKGROUND: To evaluate the efficacy and safety of reducing target volume in definitive radiotherapy for HPV-associated tonsil cancer. METHODS: A single-institution cohort of 90 patients with human papillomavirus (HPV)-associated tonsil cancer who received definitive radiotherapy with a 5-mm expansion from the gross tumor volume to clinical target volume between 2008 and 2019 were included. The overlapping volume of initial planning target volume and the recurrent tumor was calculated and categorized as one of three failure types: in-field: >/=95%; marginal-field: 50%-94%; and out-field: <50%. RESULTS: With a median follow-up of 59.4 months, the 3-year and 5-year local control rates were 94.4% and 92.8%, respectively. A total of seven local failures were identified, of which 4 (4.4%) were in-field, 2 (2.2%) were marginal-field, and 1 (1.1%) was out-field. Grade 3 acute and late toxicities developed in 30 (33.3%) and 5 (5.6%) patients, respectively. CONCLUSIONS: Reducing target volume could be an alternative option for selected patients with HPV-associated tonsil cancer.