Margriet Kwint

Acute esophagus toxicity after IMRT and concurrent chemoradiation 123 6 ▲ Figure 3: Probability of developing grade ≥2 AET using the current clinical model based on V35 (solid line). The datapoints illustrate the actual incidence of AET based on the V35, and their 95% confidence intervals. Discussion To the best of our knowledge, this is the first analysis of dosimetric predictors of AET performed within a large patient group treated with IMRT and the same concurrent chemotherapy-regimen. Several studies have shown that treatment with CCRT gives an increased risk of AET [2,3,5-7], as was also confirmed in the current study. We showed that in the setting of CCRT, the incidence of AET was not significantly changed by the introduction of IMRT compared to 3DCRT. Our current clinical AET prediction model, using V35, resulted in inadequate prediction of AET grade ≥2 when treating with CCRT. With increasing incidence of grade 3 AET, prediction of grade 3 is deemed to be clinically more relevant, and we therefore propose to use the V50. With the introduction of IMRT the volume of the esophagus receiving 5 to 40 Gy was significantly reduced, and simultaneously, the volume receiving 70 Gy was significantly increased (Figure 1). Using the historic prediction model based on V35 [2], one would expect that the incidence of grade ≥2 AET would have been reduced with IMRT, which was actually not the case. The inability of predicting AET using the V35 model in CCRT was indicated by the discrepancies between the actual incidence and the V35 prediction model (Figure 3). With use of CCRT, there were a substantial