Impacts of Oropharyngeal Cancer PTV Coverage Prescription Levels on Clinical Outcomes
Abstract
Purpose
Definitive radiotherapy for oropharyngeal cancer (OPC) requires adequate PTV coverage, but the optimal degree of target coverage is unknown. Some protocols require a PTVD95≥95% whereas others require PTVD95≥100% of prescription dose. Prescribing higher PTV dose coverage (i.e. PTVD95≥100%) may improve cancer control but requires trade-offs in healthy-tissue dose potentially increasing radiation-related toxicities. Quantitative evidence is limited on whether radiotherapy prescribed to PTVD95≥100% improves overall survival (OS) or recurrence. This retrospective study evaluates the difference in treatment outcomes for OPC patients prescribed to PTVD95≥95% or 100%.
Methods
Patients were identified using existing databases of OPC patients treated with radiotherapy. For this analysis, we pooled two databases, one from 2010-2019 and the other from 2022-2025 for a total of n=404 patients (median age: 61 years) treated with 70 Gy/35fx. Patients were stratified by PTV prescription dose, with all patients having a 5 mm expanded PTV margin. Kaplan-Meier analysis was used with the log-rank test to assess significance.
Results
101(25%) patients were prescribed to PTVD95≥95%, and 303(75%) prescribed to PTVD95≥100%. 306(76%) patients were HPV-positive, 60(15%) HPV-negative, 39(10%) were indeterminate. The proportion of Stage I, II, III, IV patients were 76(18%), 140(35%), 92(23%), and 96(24%) respectively. Analyses compared OS and recurrence between the PTVD95≥95% and PTVD95≥100% groups (median follow-up of 3.9 years; 95% CI [3.3, 4.1]). The five-year OS was 75.6% and 71.7% for PTVD95≥95% and 100%, respectively. No statistically significant difference in OS was found between those prescribed to PTVD95≥95% and 100% (p=0.399). The likelihood of recurrence was not significantly different between the prescription groups (p=0.359), following the five-year follow-up.
Conclusion
Delivery of 100% of the prescription dose to 95% of the target volume (PTV) did not significantly alter the cancer outcomes when compared to the standard of care (PTVD95≥95%) in a large cohort of OPC patients treated with definitive radiotherapy.