ESTRO 37 Abstract book

S107

ESTRO 37

PV-0200 Benchmark Case results from the EORTC Lungtech trial of SBRT for patients with centrally NSCLC M. Lambrecht 1 , E. Clement 2 , J.J. Sonke 3 , U. Nestle 4,5 , S. Adebahr 5 , M. Guckenberger 6 , D.C. Weber 7 , C.W. Hurkmans 1 1 Catharina Hospital, Department of Radiation Oncology, Eindhoven, The Netherlands 2 EORTC, Headquarters, Brussels, Belgium 3 The Netherland Cancer Institute, Department of Radiation Oncology, Amsterdam, The Netherlands 4 Kliniken Maria Hilf, Department of Radiation Oncology, Moenchengladbach, Germany 5 University Medical Center Freiburg, Department of Radiation Oncology, Freiburg, Germany 6 University Hospital Zurich, Department of Radiation Oncology, Zurich, Switzerland 7 Paul Scherrer Institute- ETH DomainSwitzerland, Center for Proton Therapy, Villigen, Switzerland Purpose or Objective The European Organisation for Research and Treatment of Cancer (EORTC) prospective multicentre Lungtech trial assesses the safety and effectiveness of SBRT in patients with inoperable centrally located non-small cell lung cancer. As part of the quality assurance, a Benchmark Case (BC) was distributed for delineation and planning. Material and Methods BCs were reviewed stepwise; only when delineations were deemed acceptable the treatment plan was generated and subsequently reviewed. A retrospective study was performed of the 15 first accepted submissions looking at the dice similarity coefficients of the OARS and the target delineations. In addition, a set of gold standard CTV contours combined with each institutions specific CTV to PTV margin were linked to the dose submissions to evaluate the influence of delineation on dosimetry. Results Four (27%) BCs were accepted at their first attempt. Ten (67%) institutions had to revise their delineation at least once and three had to revise their planning once. The mean dice coefficient varied significantly between OARs: The lowest values were found for the brachial plexus 0.23 (0.11-0.58;average volume 9.0 cm 3 ) and the highest for the spinal cord 0.88 (0.78-0.94;average volume 57.8 cm 3 ). The mean PTV dice coefficient was 0.71 (0.63- 0.95). Applying the gold standard contours, only one institution remained compliant with the dose coverage criteria. PTV and gold standard-PTV V100% were on average 93.6 %(70.5-99.3) and 83.3% (54.2-93.9), respectively, indicating that delineation variations have a larger influence on PTV coverage than variations in planning and irradiation techniques.

Conclusion Clinical guidelines and radiotherapy protocols should be further improved and are not a substitute for timely RTQA procedures. Furthermore, delineation remains the main source of BC rejection. Plan review without first reviewing delineation may not be efficient as contour variations significantly deteriorate dose coverage. PV-0201 Automated proton planning by mimicking the reference photon dose for patient selection R.G.J. Kierkels 1 , A. Fredriksson 2 , S. Both 1 , J.A. Langendijk 1 , D. Scandurra 1 , E.W. Korevaar 1 1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands 2 RaySearch Laboratories AB, Stockholm, Sweden