A GORTEC survey on low-risk CTV-P2 delineation in head and neck cancers.

Purpose: An international consensus was established in 2018 to standardise practice using geometric (5 + 5 mm) expansion around GTV-P for definitive radiotherapy of squamous cell carcinomas of the head and neck (HNC). The GORTEC (French HNC Oncology and Radiotherapy Group) conducted a survey to assess the level of agreement about CTV-P2 delineation using a "formalised consensus method". Methods: The 32 proposals of the 2018 consensus on CTV-P2 and 6 additional GORTEC proposals were submitted to 13 GORTEC radiation oncologists (RO). Proposals were rated as "suitable" for median scores ≥7, "unsuitable" for scores ≤3.5 or "uncertain." The degree of agreement was high (≥85 %), moderate (75-84 %) or low (<75 %). Suitable proposals were reviewed by 40 other RO for final recommendations. Results: The 2018 proposals were "uncertain" with low degrees of agreement (41.5-69 %), except for T1 tumors, which had 89 % agreement. Five out of 6 GORTEC proposals were "suitable" and one "uncertain." The final recommendation was "suitable and to be retained" by 97.5 % of RO, as follows: To obtain CTV-P2, GORTEC recommends applying a "geo-anatomical" approach. Using the geometric concept, 10 mm-isotropic margins are applied to the GTV, for all locations but the hypopharynx (10 mm antero-posterior, laterally and 15 mm craniocaudally). CTV-P2 is further modified using the anatomical concept (anatomical barriers, dissemination routes) and accounting the benefit/risk balance and proximity of organs at risk. Conclusion: The GORTEC survey derived from the 2018 international CTV-Ps delineation consensus suggests a "geo-anatomical" approach for the delineation of CTV-P2 in HNC.