Margriet Kwint

Summary 177 were identified. Surprisingly, these subgroups did not differ in their risk of treatment outcomes, whereas baseline volume of the primary tumor was significantly associated with OS. Therefore, risk stratification at baseline might already be accurate enough in identifying the best treatment strategy for most patients. However, further research is needed to optimize current prediction models. Part III Acute esophagus toxicity Intensity Modulated Radiotherapy (IMRT) results in amore conformal dose distribution leading to increased organ sparing compared to 3D-conformal-radiotherapy (3DCRT). The change of radiotherapy technique from 3D-CRT to IMRT can influence the accuracy of dose volume parameters to predict toxicity. In chapter 6 the dose-effect- relation between acute esophageal toxicity (AET) and dose-volume-parameters of the esophagus after IMRT and concurrent chemotherapy in 139 NSCLC patients were investigated. The outcome was compared to the clinically (at that time in our institute) used esophagus V35 (volume of the esophagus receiving ≥35 Gy) prediction model for grade ≥2 after radical 3D-CRT treatment. The conclusion of this study was that the incidence of AET did not differ between patients treated with IMRT or 3D-CRT. The V50 (volume of the esophagus receiving ≥50 Gy) turned out to predict grade ≥2 significantly better compared to the clinical V35-model. At present the V50 of the esophagus is used as planningsconstraint in clinical practice in the Netherlands Cancer Institute. Data obtained from sources outside of randomized clinical trials are often referred to as ‘real world data’ (RWD). By introducing electronic toxicity registration within our institute, a more systematic and accurate recording of toxicity was implemented in clinical practice. The RWD collected from this electronic toxicity registration, can be used to audit normal tissue complication probability (NTCP) models. The dose reduction of the involved mediastinal lymph nodes as described in chapter 2 might have impact on the NTCP-model to predict AET. The aim of the study described in chapter 7 was to assess the validity of the RWD derived from the electronic toxicity registration and to show the feasibility of this registration to audit toxicity prediction models and dose constraints used in daily clinical practice. As a showcase, 2 NTCP- models (V50 and V60; volume of the esophagus receiving ≥50 Gy and ≥60 Gy) of AET for CCRT for NSCLC patients were used to validate the electronic toxicity registration of AET before/after dose de-escalation of the prescribed dose to the mediastinal lymph