ESTRO 2022 - Abstract Book

S379

Abstract book

ESTRO 2022

Conclusion Presence of the stem cell marker SLC3A2 is significantly more frequent in HPV/p16 negative HNSCC and is together with tumor volume a poor prognostic factor. SLC3A2 may be a putative marker of radioresistance in primary RT of HNSCC.

OC-0436 External validation of NTCP models for dysphagia and xerostomia in the elderly patients with HNSCC

L. Sommers 1 , H.P. van der Laan 1 , L. van den Bosch 1 , J. van den Hoek 1 , T. van Zon-Meijer 1 , E. Oldehinkel 1 , H. Verbeek 1 , G. Halmos 2 , R. Steenbakkers 1 , J. Langendijk 1 1 University Medical Centre Groningen, Radiation Oncology, Groningen, The Netherlands; 2 University Medical Centre Groningen, Otorhinolaryngology/Head & Neck Surgery, Groningen, The Netherlands Purpose or Objective We recently reported on a comprehensive individual toxicity risk (CITOR) profile, including normal tissue complication probability (NTCP) models for toxicities after radiotherapy for head and neck squamous cell carcinoma (HNSCC). It has often been assumed that elderly patients (age ≥ 70 years) are generally more susceptible to radiation-induced toxicities. Therefore, this study aimed to externally validate these models in a cohort of elderly HNSCC patients. Materials and Methods Prospectively collected data of all consecutive elderly patients with HNSCC treated with definitive RT from April 2007 to July 2020 were analysed. Toxicity outcomes consisted of 4 dichotomised outcomes: CTCAEv4.0 physician-rated dysphagia ≥ Grade 2; dysphagia ≥ Grade 3; EORTC QLQ-H&N35 patient-rated moderate-to-severe xerostomia and severe xerostomia. The NTCP- models for dysphagia at 6, 12, 18 and 24 months after RT included the mean dose to the oral cavity and the pharyngeal constrictor muscles, baseline dysphagia, and primary tumour site as predictors The NTCP-models for late xerostomia (same time points) included the mean dose to the parotid and submandibular glands and baseline xerostomia as predictors. The original NTCP-models after RT treatment were externally validated in a general HNSCC population. Discrimination (ROC-AUC) and calibration among elderly patients were evaluated, and appropriate model updates were done when needed. Results The study population consisted of 310 elderly (29.6%) of the total HNSCC population of 1047 patients. Compared to the development cohort, the prevalence of dysphagia increased with time in the elderly cohort, with a lower prevalence at six months and a higher prevalence at 24 months (Table 1). Models developed for dysphagia ≥ Grade 2 had high discrimination