ESTRO 36 Abstract Book

S495 ESTRO 36 _______________________________________________________________________________________________

available imaging software (MIM Vista, Cleveland OH). On the test dataset the agreement between the manually drawn gold standard contours and atlas-based auto- segmented contours was measured with a Dice- coefficient. To determine the impact of auto-segmented contours on dosimetry calculations we determined the mean radiation dose for the manual contours and the auto- segmented contours for left-sided breast cancer patients. Differences in dose between the two contours were expressed with mean absolute errors. Results Within the test dataset the atlas-based auto-segmentation approach accurately delineated the heart with a Dice- coefficient of 0.87 ± 0.06 (mean ± standard deviation). Auto-segmentation was much less accurate for the LAD with a Dice-coefficient of 0.05 ± 0.06. Among left-sided breast cancer patients the mean heart dose was 1.2 ± 0.9 Gy for the manually contoured heart, and 2.7 ± 0.9 Gy for the manually contoured LAD. The auto-segmented mean heart dose was similar to the manually contoured mean heart dose, with a mean absolute error of 0.1 ± 0.2 Gy (range 0.0 - 0.7 Gy). The auto-segmented mean LAD dose differed moderately from the manual contoured mean LAD dose, with a mean absolute error of 1.0 ± 1.2 Gy (range 0.0 – 1.7 Gy). There were no statistically significant differences between the manual contours and the automated-contours for either the whole heart (p=0.78 by Wilcoxon-rank sum test), or the LAD (p=0.85). Conclusion This study demonstrates that atlas-based auto- segmentation accurately delineates the whole heart, though less accurately captures the LAD. The high concordance in mean heart dose between the manual contours and automated contours suggests that atlas- based auto-segmented contours could play a role in radiation treatment planning. PO-0898 Automated segmentation for breast cancer radiation therapy based on the ESTRO delineation guideline. A.R. Eldesoky 1,2 , E.S. Yates 3 , T.B. Nyeng 3 , M.S. Thomsen 3 , H.M. Nielsen 1 , P. Poortmans 4 , C. Kirkove 5 , M. Krause 6,7 , C. Kamby 8 , I. Mjaaland 9 , E.S. Blix 10,11 , I. Jensen 12 , M. Berg 13 , E.L. Lorenzen 14,15 , Z. Taheri-Kadkhoda 16 , B.V. Offersen 1 1 Aarhus University Hospital, oncology, Aarhus, Denmark 2 Mansoura University, Clinical Oncology and Nuclear Medicine, Mansoura, Egypt 3 Aarhus University Hospital, Medical Physics, Aarhus, Denmark 4 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands 5 Catholic University of Louvain, Radiation Oncology, Louvain, Belgium 6 OncoRay- University Hospital Carl Gustav Carus- Technische Universität Dresden- and Helmholtz-Zentrum Dresden-Rossendorf, Radiation Oncology, Dresden, Germany 7 German Cancer Consortium DKTK Dresden and German Cancer Research Center DKFZ Heidelberg, Radiation Oncology, Dresden, Germany 8 Rigshospitalet, Oncology, Copenhagen, Denmark 9 Stavanger University Hospital, Oncology, Stavanger, Norway 10 University Hospital of North Norway, Oncology, Tromsø, Norway 11 Institute of Medical Biology- UiT The Arctic University of Norway, Immunology Research group, Tromsø, Norway 12 Aalborg University Hospital, Medical Physics, Aalborg, Denmark 13 Hospital of Vejle, Medical Physics, Vejle, Denmark 14 University of Southern Denmark, Institute of Clinical Research, Odense, Denmark 15 Odense University Hospital, Laboratory of Radiation

Conclusion In patients who underwent RT for prosta te cancer treatment, an increase in signal intensity of t he internal obturator muscles was observed. Specifi cally, this enhancement was concentrated in the area near the prostate, likely to be included in high dose regions. This evidence was present both in T2w and T1w post CA injection MRI and can be compatible with an inflammatory status that normally follows RT. This inhomogeneous structural variation may be explained by the spatial dose distribution. Moreover, correlations with toxicity scores should be investigated, considering the involvement of the pelvic floor muscles in the urinary dysfunctions. PO-0897 Atlas-based auto-segmentation of heart structures in breast cancer patients R. Kaderka 1 , R. Mundt 1 , A. Bryant 1 , E. Gillespie 1 , B. Eastman 1 , T. Atwood 1 , J. Murphy 1 1 University of California San Diego, Department of 858- 822-4842, San Diego, USA Purpose or Objective Radiation therapy deposited in the heart increases the risk of ischemic heart disease, and sudden cardiac death. Reproducible contouring of the heart on CT imaging represents a critical component of treatment planning, though the literature demonstrates substantial variability in contouring among providers. In this study we assess the accuracy of an atlas-based auto-segmentation approach of the whole heart and the left anterior descending artery (LAD). Material and Methods We randomly selected a cohort of 38 breast cancer radiotherapy patients treated between 2014 a nd 2016. For all patients the whole heart and LAD were manually contoured according to guidelines published by Feng et al. (2011). The patients were divided into a training dataset (N=18), and a test dataset (N=20). We used the training dataset to create a contouring atlas using commercially