Margriet Kwint

Chapter 6 116 Patients and methods Patient selection Between January 2008 and November 2010, patients with locally advanced NSCLC treated with CCRT in our institute were prospectively followed. Inclusion criteria for this study were treatment with CCRT, histology or cytology proven NSCLC, WHO≤2, adequate renal and hepatic functions and life expectancy >6 months. The clinical AET grades as well as the dose-volume-parameters of the esophagus were available for all patients. Former studies reported different dosimetric predictors for AET for SCRT and RT-only, compared to CCRT [6,7]. Therefore only patients were selected who received at least 50% of the planned chemotherapy dose and 100% of the radiotherapy dose. All patients were treated with IMRT of 66 Gy in 24 fractions, once daily, 5 times per week. The concurrent chemotherapy regimen consisted of daily low dose Cisplatin intravenous (6 mg/m²) 1-2h before irradiation. Radiotherapy preparation For all patients a 3D-midventilation-CT (MidV-CT) was selected out of a respiration correlated 4DCT, in which the moving tumor was closest to its time-averaged mean position [11]. The gross tumor volume (GTV) and all pathological lymph nodes were delineated on the MidV-CT which was also registered with a recent fludeoxyglucose- positron-emission-tomography-(FDG-PET)-scan. Delineations were discussed in a multidisciplinary meeting. The GTV was expanded to a planning target volume (PTV) using margins of 12 mm +¼ of the 4DCT peak-to-peak tumor amplitude in orthogonal directions. For the lymph nodes a uniform PTV margin of 12 mm was used [12]. Critical organs were delineated according to a written protocol: heart, spinal cord, lungs and esophagus (from cricoïd to gastro-esophageal-junction). The planning- constraints used for the organs at risk were; esophagus V35<65%, mean lung-dose ≤20 Gy, spinal cord ≤50 Gy, total heart ≤40 Gy and ⅔ of the heart ≤50 Gy and ⅓ of the heart ≤66 Gy. Equally spaced, 7-field IMRT-plans were calculated using 10 or 6 MV photons and direct machine parameter optimization in the homo-lateral lung (Pinnacle version 9.0, Philips, Best, the Netherlands) [10]. The prescription-dose was specified at a representative point in the PTV. The dose inhomogeneity within the PTV was >90% and <115%.