Session Item

We aimed to externally validate normal tissue complication probability (NTCP) models for radiation-related toxicity in head and neck (HN) cancer patients (pts) treated with curative radiotherapy (RT)

Retrospective analysis of pts treated from 2015 to 2021. Four NTCP models were evaluated: 1) physician-rated swallowing dysfunction at 6 months (m) (Christianen et al.); 2) tube feeding dependence at 6 m (Wopken et al.) 3) Incidence of G≥2 laryngeal edema within 15 m from RT (Rancati et al.); 4) acute oral and oropharyngeal mucositis (OM) G≥3 at any time during RT and OM mean G during RT treatment weeks ≥1.5 (Orlandi et al.). Pts already undergone oncological treatments on the HN district and/or with distant metastases and/or synchronous tumors or treated with altered fractionation RT schedule were excluded. Toxicities were retrieved from electronic medical charts. Validation analyses included: 1) Model performance using the Brier score 2) discrimination ability using the area under the receiver operating characteristic curve (AUC) 3) calibration using calibration intercept and slope 4) Hosmer–Lemeshow goodness-of-fit test to evaluate the calibration of the model. The model’s predictions fit the data at an acceptable level if the Hosmer– Lemeshow goodness-of-fit test statistic is>0.05

150 pts were eligible for the analyses; pts’ and tumor’s characteristics are reported in Table 1. Of these, those available for NTCP analysis and incidence of corresponding toxicities were distributed as follows: 1) 97 pts eligible for dysphagia at 6 months (5% events); 2) 88 pts eligible for tube feeding dependence (3% events); 3) 102 pts eligible for G≥2 laryngeal edema (21% events); 4)  113 pts eligible for mucositis G≥3 (42% events); 5) 114  pts for mucositis  G≥1.5 (63% events). All AUC of NTCP models are reported in Fig.1. Considering all validation tests, all the models, except for Christianen model, show adequate fit. The best discrimination is reached by Wopken model (AUC = 0.73), but the limited number of cases influences the precision of the estimates, as can be seen by the wide confidence interval (CI 95%: 0.67-0.98). No model has evidence of good calibration. Non parametric tests concerning different scores show a significant difference between pts with events and other pts, only for Rancati model (p-value = 0.02 for laryngeal edema). The low number of events for NTCP models of dysphagia at 6 months and tube feeding dependence prevented statistically robust results

All the model (except for Orlandi OM mean G≥1.5) suggest a good discrimination and a sufficient fit (except for Christianen). Calibration, considered as distance as observed and predicted probabilities, is low probably because of the low number of events. Further analyses are currently ongoing to confirm the assessment of the performance of both dysphagia and tube-feeding NTCP models.