The use of international radiotherapy consensus guidelines for primary clinical target volume delineation for oropharyngeal carcinoma: case series with recurrence pattern analysis

International consensus guidelines for head and neck cancer primary clinical target volume (CTV) delineation based upon a geometric ‘5+5’ expansion and anatomical editing were published in 2018. Analysis of recurrence patterns in relation to target volumes is required to validate this approach. Patients with oropharyngeal carcinoma treated between 2019-22 with definitive (chemo)radiotherapy using the guideline approach to primary CTV delineation were identified. Patterns of locoregional recurrence were analysed using combined spatial and dosimetric analysis. Central, high dose recurrences were defined by mapped a centroid of the volume of recurrence (Vrec) to within the high dose planning target volume (PTV) and >95% of Vrec receiving >95% of prescribed dose to high dose PTV. 133 patients were treated using the consensus outlining guidelines. Median follow up was 3.9 years. 78.9% had p16 positive disease. 3-year local and regional control rates were 96% and 94.7y. Locoregional recurrence occurred in 6/133 (4.5%) of patients including 3 patients with primary site recurrences. All primary site recurrences were classified as central high dose recurrences. All primary tumour site recurrences were within the high dose volume with no evidence of marginal or out-of-field recurrences. There results provide evidence for the safety of the consensus outlining approach for primary tumour CTVs. • Head and neck clinical target volume delineation guidelines were published in 2018. • Patients with oropharyngeal cancer treated according to guidelines analysed. • High rates of local control • Recurrence pattern analysis shows all primary site recurrences in high dose area. • Provides validation for use of delineation guidelines.