Comparisons of normal tissue complication probability models derived from planned and delivered dose for head and neck cancer patients

Background and purpose: Normal tissue complication probability (NTCP) models are typically derived from the planned dose distribution, which can deviate from the delivered dose due to anatomical dayto-day variations. The aim of this study was to compare NTCP models derived from the planned and the delivered dose for head and neck cancer (HNC) patients. Material and method: 322 HNC patients who received radiotherapy with daily CBCT guidance were included in this retrospective study. The delivered dose was estimated by deformably accumulating dose from daily CBCT to planning anatomy. We used a Lyman-Kutcher-Burman NTCP model, to relate the equivalent uniform dose (EUD) of organs at risk (OAR) with oral mucositis, xerostomia and dysphagia respectively. We compared the model parameters and performances. Results: The median differences between planned and delivered EUD to the OARs were significantly larger for patients with toxicity than without for acute dysphagia (>G2 and >G3) and late dysphagia (>G3) (p < 0.05). Those differences resulted in small differences in steepness and agreement to the data between delivered-and planned-fitted NTCP curves, and the differences were not significant. The differences in AUC were less than 0.01. Conclusion: Differences between delivered and planned dose did not lead to significant differences in NTCP curves. The additional clinical relevance of NTCP models using accumulated dose for oral mucositis, xerostomia and dysphagia in HNC radiotherapy is likely to be limited. (c) 2021 Elsevier B.V. All rights reserved. Radiotherapy and Oncology 164 (2021) 209-215