Abstract Book

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ESTRO 37

Results The median distance of the out-of-field failures to the median boost volume, is 5.8 cm, range 1.5 to 8.9 cm (Fig. 1). In-field failures received on average 46 Gy. Out-of- field failures received on average 16 Gy, while the population-based incidental dose in the locations of the out-of-field failures was 18 Gy +/- 10Gy (difference non- significant). The observed pattern of failures (increasing with distance) is inconsistent with general expectation, i.e., tumour deposits decrease with distance to the primary. To model the increase in failures at larger distances, we assumed an exponential decrease model of tumour deposit probability, and combined it with a TCP model based on the incidental dose to the failure locations (Fig. 2a). Since the incidental dose reduces at distance, the chance of not controlling occult disease increases with distance. Using a steep dose-response with D 50 in the order of 20 Gy, failure rates are modelled that are consistent with the observations (Fig. 2b).

and University Hospital Carl Gustav Carus, Dresden, Germany 7 Helmholtz-Zentrum Dresden-Rossendorf- PET Center, Institute of Radiopharmaceutical Cancer Research, Dresden, Germany 8 Department of Radiotherapy, Hospital Dresden- Friedrichstadt, Dresden, Germany 9 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Berlin, Berlin, Germany 10 Department of Radiooncology and Radiotherapy, Charité University Hospital, Berlin, Germany 11 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Essen, Essen, Germany 12 Department of Radiotherapy, Medical Faculty University of Duisburg-Essen, Essen, Germany 13 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Frankfurt, Frankfurt, Germany 14 Department of Radiotherapy and Oncology, Goethe- University Frankfurt, Frankfurt, Germany 15 Heidelberg Ion Therapy Center HIT, Department of Radiation Oncology- University of Heidelberg Medical School, Heidelberg, Germany 16 Department of Radiation Oncology, Ludwig- Maximilians-Universität, Munich, Germany 17 Clinical Cooperation Group, Personalized Radiotherapy in Head and Neck Cancer- Helmholtz Zentrum, Munich, Germany 18 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Munich, Munich, Germany 19 Department of Radiation Oncology, Technische Universität München, Munich, Germany 20 Institute of Innovative Radiotherapy iRT, Helmholtz Zentrum München, Munich, Germany 21 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Tübingen, Tübingen, Germany 22 Department of Radiation Oncology, Faculty of Medicine and University Hospital Tübingen- Eberhard Karls Universität Tübingen, Tübingen, Germany 23 Helmholtz-Zentrum Dresden – Rossendorf, Institute of Radiooncology - OncoRay, Dresden, Germany Purpose or Objective Radiomics aims to characterise the tumour phenotype using advanced image features to predict patient-specific outcome. Commonly, image features are calculated from the entire gross tumour volume (GTV e ). However, tumours are biologically complex, e.g. , expressing necrosis merely in the core and tumour cell proliferation at the periphery. The identification of sub-volumes to incorporate regional tumour variation into the risk models may lead to an improved outcome prediction. Therefore, we investigated different sub-volumes of the GTV e using CT imaging, developed radiomic signatures, and compared prognostic power and stratification performance of the signatures. Material and Methods A multicentre cohort consisting of 302 patients with advanced stage head and neck squamous cell carcinoma (HNSCC) was collected and divided into an exploratory and a validation cohort (208 and 94 patients, respectively). All patients received primary radio- chemotherapy at one of the six DKTK partner sites and underwent a non-contrast-enhanced CT scan for treatment-planning purposes. The analysis was divided into two subsequent steps (Fig. 1): (a) two distinct sub- regions were extracted from GTV e : the tumour boundary of different widths (3,5,10 mm) and the corresponding remaining core volumes. (b) extension of the highest prognostic tumour-boundary sub-volume by different widths (1,2,3,5 mm) beyond the GTV e . 1555 image

Conclusion To our knowledge, this study is the first to combine patterns of loco-regional failure in anal cancer (the primary endpoint for the UK national PLATO trial) with incidental dose data. Out of field failure locations tend to be far from the high dose region. To model this pattern, incidental dose has to be taken into account. Our model suggests a steep dose-response curve for occult tumour deposits with D 50 in the order of 20Gy. OC-0508 Identification of tumour sub-volumes for improved radiomic risk modelling in locally advanced HNSCC S. Leger 1,2 , A. Zwanenburg 1,2,3,4 , K. Pilz 1,2,3,5 , F. Lohaus 1,2,3,5 , A. Linge 1,2,3,5 , K. Zöphel 6,7 , J. Kotzerke 6,7 , A. Schreiber 8 , I. Tinhofer 9,10 , V. Budach 9,10 , A. Sak 11,12 , M. Stuschke 11,12 , P. Balermpas 13,14 , C. Rödel 13,14 , U. Ganswindt 15,16,17 , C. Belka 15,16,17,18 , S. Pigorsch 18,19 , S.E. Combs 18,19,20 , D. Mönnich 21,22 , D. Zips 21,22 , M. Krause 1,2,3,5,23 , M. Baumann 1,2,3,4,5,23 , C. Richter 1,2,5,23 , E.G.C. Troost 1,2,3,5,23,24 , S. Löck 1,2,5,24 1 OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden- Helmholtz-Zentrum Dresden – Rossendorf, Dresden, Germany 2 German Cancer Research Center DKFZ, Heidelberg and German Cancer Consortium DKTK partner site Dresden, Dresden, Germany 3 National Center for Tumor Diseases NCT, partner site Dresden, Dresden, Germany 4 German Cancer Research Center DKFZ, DKFZ, Heidelberg, Germany 5 Department of Radiotherapy and Radiation Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus- Technische Universität Dresden, Dresden, Germany 6 Department of Nuclear Medicine, Faculty of Medicine