47 Retrospective analyses on toxicity in esophageal cancer patients Bootstrap analysis confirmed the robustness of the selection of the MLD into the model. Calibration plots of the observed vs. calculated risk of complications using the Hosmer-Lemeshow test showed a good performance of the model as well (suppl. data figure 1 and 2) .In 69 out of 216 (31.9%) patients, pericardial effusion (PE) was seen on the follow up CT scans. Nine of these patients developed clinical symptoms of heart failure. Two other patients presented with heart failure without signs of pericardial effusion. They both had a cardiac history (1 valvular disease, 1 ischaemic heart disease). Other cardiac events were diverse and are listed in Table 3. The numbers of the separate toxicities were too low for reliable modelling procedures. Combining clinical cardiac events did not result in a predictive model. In univariate analysis, most cardiac, but no lung, dose volume-parameters were related to PE. None of the clinical factors were significantly associated with PE (suppl. data figure 8). In the multivariable analysis, PE was significantly associated with the volume of the RV receiving a dose higher than 35 Gy (V35): OR = 1.03 (95%CI 1.017-1.039). This model had an AUC of 0.73 (95% CI 0.66-0.80) However, most dose volume parameters, including the mean dose values of the WH, pericardium and RV, performed similarly well in predicting PE (table 4). Most of the heart parameters were highly correlated so we eventually decided to present three models for PE with the mean dose to the RV, the whole heart and to the pericardium as explanatory variables, to facilitate a comparison with results from the literature and use of the models in routine daily practice. All models are presented in table 4 and the model using the mean pericardial dose is depicted in figure 1. Figure 1 NTCP curves on radiaton induced pulmonary and cardiac toxicities The bootstrap procedure and calibration curves again confirmed the robust selection of dose volume parameters in the model (suppl. data figure 3, 4); the adjusted AUC’s are included in table 4. With a median follow up of 27 months, 97 out of 216 patients developed locoregional failures. The median disease-free survival was 64 months (95% CI 58.7-69.3 months). The median OS was not reached. 4
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