Late dysphagia after changes in high-dose clinical tumour volume margin for head and neck cancer patients.

Background and purpose: One of the factors influencing disease control and toxicity risk after radiotherapy is selection of treatment volume margin. This study evaluates whether different gross tumour volume (GTV) to high-dose clinical target volume (CTV1) margins impact dysphagia in a cohort of head and neck squamous cell carcinoma (SCC) patients. Patient/material and methods: Data of patients receiving primary IMRT-based radiotherapy for SCC for the oropharynx, hypopharynx, and larynx at three treatment centres between 2010 and 2015 were retrospectively collected. Treatment planning followed two DAHANCA guideline periods: pre-2013 (varying GTV-CTV1 margins), and post-2013 (isotropic 5 mm margin). Treatment plans were collected for 1,913 patients. GTV-CTV1 margins were calculated as median surface distance from GTV to CTV1. Dysphagia was graded using modified DAHANCA ordinal scale. For each patient, the highest score of dysphagia during 5-year follow-up period was chosen for analysis.

Results: Dysphagia data were available for 1,706 patients (89%). The median GTV-CTV1 margin was 9.0 mm in 2010-2012 and 4.7 mm in 2013-2015. The severity of dysphagia was more pronounced in patients treated during 2010-2012 (p = 0.003). Predictors of grade ≥ 2 dysphagia included larger GTV (odds ratio [OR]: 1.7; p < 0.001), larger GTV-CTV1 margin (odds ratio [OR] of 1.3 per cm; p = 0.04), and tumour localisation other than oropharyngeal p16+carcinomas (p = 0.002). Male sex, non/previous smoking status, and application of chemotherapy were associated with less severe dysphagia.

Interpretation: Tumour volume and GTV-CTV1 margin are dominant geometric parameters influencing dysphagia risk following curative radiotherapy.