Delineation of the post-operative primary tumour and nodal clinical target volumes in oral cavity squamous cell carcinoma: European Society for Radiotherapy and Oncology (ESTRO) clinical guidelines.

BACKGROUND AND PURPOSE: To date, no consensus guidelines have been published that systematically guide delineation of primary and nodal Clinical Target Volumes (CTVs) in patients who require post-operative radiotherapy (PORT) for mucosal Head and Neck squamous cell carcinoma (HNSCC). As a result, significant individual, institutional and national variation exists in the way that CTVs are delineated in the post-operative setting, leading to considerable heterogeneity in radiotherapy treatment.

METHODS

A multi-disciplinary group of experts convened by the European Society for Radiotherapy and Oncology (ESTRO) set-out principles for the multi-disciplinary management of oral cavity squamous cell carcinoma (OCSCC). Building on these, and adapting the geometric expansion approach described in previous primary CTV delineation guidelines, new consensus guidelines for the delineation of post-operative CTVs, both for the primary tumour and nodal regions, were proposed by the expert group, before being shared with a second tier of international experts to ensure their worldwide acceptability and applicability.

RESULTS

These guidelines propose that surrogate volumes representing the resected primary and nodal Gross Tumour Volumes (GTV-P and GTV-N respectively) are re-created on the radiotherapy planning scan, either by registration with diagnostic imaging or via reference to anatomical landmarks. A post-operative CTV for the primary tumour (CTV-P) is created as a composite volume that includes: i) geometric expansion around the surrogate GTV-P, and ii) geometric expansion around the surgical defect and/or reconstruction flap. A post-operative CTV for the nodal region (CTV-N) is created as a composite volume that includes: i) geometric expansion around the surrogate GTV-N, and ii) the involved nodal level (CTV-N1). Guidelines for delineating at-risk nodal levels in a prophylactic dose CTV (CTV-N2) are included, and for making decisions regarding the need for unilateral and/or bilateral neck treatment.

CONCLUSIONS

Implementation of these guidelines into clinical practice should reduce variation, and by promoting consistency of approach, facilitate multi-institutional audits and clinical trials including Radiation Therapy Quality Assurance (RTQA) in patients with OCSCC. It is anticipated that they will form the basis for future guidelines aiming to standardise post-operative CTV delineation in other head and neck subsites.