The plane corresponding to the atrio-ventricular groove is approximately at right angles to the septal plane. Once the interventricular septum is located, the anterior and posterior interventricular grooves may be identified as they correspond to the anterior and posterior limits of the interventricular septum (d, e). Scrolling down to the level of the ventricles this line overlies the interventricular septum and points just medial to the cardiac apex (d, e). This represents the location of the interatrial septum which is usually clearly visible on CT (c). The septal plane may be marked with a line through the fat space between the right and left atria proximally, using the ruler tool on the treatment planning system. The plane defined by the atrioventricular grooves is usually perpendicular to the septal plane. The atrial and ventricular septa define the septal plane. (c–e) Axial CT images at the level of the inter-atrial septum (c), the proximal inter-ventricular septum (d) and the distal inter-ventricular septum (e). The obtuse heart border separates the sterno-costal and left surfaces of the heart extending from the left atrium to the cardiac apex. The acute heart border is the horizontal heart border extending from the lower right edge of the heart to the apex, which is formed mainly by the right ventricle. The cardiac axis projects through the centre of the base of the heart (the left atrium) towards the cardiac apex. (a and b) Anterior (a) and posterior (b) view of the whole heart illustrating the cardiac axis, the cardiac chambers, and the atrioventricular and inter-ventricular grooves. Identifying the atrioventricular and inter-ventricular grooves. This cardiac atlas enables reproducible contouring of segments of the left ventricle and main coronary arteries to facilitate future studies relating cardiac radiation doses to clinical outcomes.Ītlas Cardiac structures Contouring Radiotherapy CT-planning scans.Ĭopyright © 2017 The Author(s). This spatial variation resulted in <1Gy dose variation for most regimens and segments, but 1.2-21.8Gy variation for segments close to a field edge. Inter-observer contour separation (mean d→ H,avg) was 1.5-2.2mm for left ventricular segments and 1.3-5.1mm for coronary artery segments. Inter-observer contour overlap (mean DSC) was 0.60-0.73 for five left ventricular segments and 0.10-0.53 for ten coronary arterial segments. The atlas enabled contouring of 15 cardiac segments. The effect of spatial variation on doses was assessed using six different breast cancer regimens. Spatial variation was assessed using the DICE similarity coefficient (DSC) and the directed Hausdorff average distance (d→ H,avg). Six radiation oncologists tested the atlas. Reference atlas contours were delineated and written guidelines prepared. Segments were defined from cardiology models and agreed by two cardiologists. This study presents a reproducible method for contouring left ventricular and coronary arterial segments on radiotherapy CT-planning scans. The heart is a complex anatomical organ and contouring the cardiac substructures is challenging. 10 University of Birmingham NHS Foundation Trust, Birmingham, UK.9 CRUK/MRC Oxford Institute for Radiation Oncology, Gray Laboratories, University of Oxford, UK.8 George Institute for Global Health, University of Oxford, UK.7 Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford, UK.Luke's Radiation Oncology Network, Dublin, Ireland. 5 Laboratory of Radiation Physics, Odense University Hospital, Denmark.4 Department of Radiation Oncology, University of Michigan, Ann Arbor, USA.3 Department of Oncology and Haematology, Queen Alexandra Hospital, Portsmouth, UK.Electronic address: 2 Clinical Trial Service Unit, Nuffield Department of Population Health, University of Oxford, UK. 1 Clinical Trial Service Unit, Nuffield Department of Population Health, University of Oxford, UK Medical Research Council Population Health Research Unit, Nuffield Department of Population Health, University of Oxford, UK.
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