Margriet Kwint

Chapter 5 88 Materials and Methods Patient selection An observational study was performed, including 394 consecutive patients treated with CCRT for cytologically or histologically proven LA-NSCLC in our institute between 2007 and 2013. Medical records and treatment characteristics of these patients were registered. The concurrent chemotherapy regimen consisted of daily low-dose cisplatin intravenous (6 mg/m²) 1-2h before irradiation. All patients were treated with intensity modulated radiotherapy (IMRT) to 66Gy/24 fractions to the primary tumor and the involved mediastinal lymph nodes in, 5 times per week on a linear accelerator equipped with a CBCT. Exclusion criteria were: other CCRT schedules or the absence of available CBCT-data. The Institutional Review Board of our institute approved the study for retrospective data collection according to the European Privacy Law Radiotherapy preparation A 3D-midposition-CT (MidP-CT) was selected for all patients from a respiration correlated 4D-planning-CT, in which the moving tumor was reconstructed at time averagemean position (22). A recent FDG-PET-scan was registered to theMidP-CT, and the gross tumor volume (GTV) and all pathological lymph nodes were delineated on the MidP-CT. 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. A uniform PTV margin of 12 mm was used for the lymph nodes (23) according to our institutional protocol. Organs at risk were delineated according to the institutional protocol: heart, spinal cord, lungs and esophagus. Equally spaced, 7-field IMRT-plans were designed using 6 or 10 MV photons and direct machine parameter optimization (Pinnacle, Philips, Best, the Netherlands) (24). The prescription-dose was specified at a representative point in the PTV. The dose distribution within 99% of the PTV was >90% and <115% of the prescribed dose. Setup correction protocol From January 2007 to December 2012 an off-line shrinking-action level setup correction protocol was used (25). In this protocol CBCT’s were acquired during the first three fractions, using Elekta Synergy 4.6 (Elekta Oncology Systems Ltd., Crawley, UK) augmented with in-house developed software. If no correction was necessary