Abstract Book

S766

ESTRO 37

EP-1406 Feasibility study of contouring heart structures and development of atlas for lung cancer planning N. Mohammed 1 , K. McLellan 2 , B. McCann 1 , Y. Flannigan 3 , R. Woodward 4 , P. Kelso 3 , M. Glegg 3 , K. Mangion 5 , P. McLoone 6 , S. Smith 3 , M. Sankaralingham 1 1 Beatson West of Scotland Cancer Centre, Radiation Oncology, Glasgow, United Kingdom 2 Edinburgh Cancer Centre, Radiation Oncology, Edinburgh, United Kingdom 3 Beatson West of Scotland Cancer Centre, Radiation Phyiscs, Glasgow, United Kingdom 4 Glasgow Research Imaging Facility, Cardiovascular, Glasgow, United Kingdom 5 British Heart Foundation Cardiovascular Research Facility, Glasgow University, Glasgow, United Kingdom 6 Glasgow University, Statistics, Glasgow, United Kingdom Purpose or Objective Lung cancer has the highest mortality rate and new data suggests, noncancer deaths affect survival outcomes in patients treated with radiotherapy. Subsequent studies have investigated radiation dose to the whole heart and found contradictory results. The heart is a complex organ with multiple sub-structures, therefore it is likely that simply one DVH parameter will not be sufficient to identify acute cardiac toxicity. We developed a detailed contouring atlas to contour heart sub-structures, in order to investigate the relationship of radiation dose to those substructures in patients treated with thoracic radiotherapy. Material and Methods

reproducible predictors for survival

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References [1] Aerts, Hugo J. W. L., et al. (2015). The Cancer Imaging Archive. DOI: 10.7937/K9/TCIA.2015.PF0M9REI EP-1405 Assessment of Heart Motion in lung Radiotherapy: making sure your heart’s in the right place. D.C.P. Cobben 1,2 , M.S. Iqbal 3 , A. Bedair 4 , J. Byrne 5 , H. McCallum 5 1 Christie Hospital NHS, Radiotherapy Related Research, Manchester, United Kingdom 2 University of Manchester, Division of Cancer Sciences- School of Medical Sciences - Faculty of Biology- Medicine and Health, Manchester, United Kingdom 3 Northern Centre for Cancer Care- Freeman Hospital, Radiotherapy, Newcastle upon Tyne, United Kingdom 4 North West Cancer Centre, Clinical Oncology, Derry- Londonderry, United Kingdom 5 Northern Centre for Cancer Care- Freeman Hospital, Radiotherapy Physics, Newcastle upon Tyne, United Kingdom Purpose or Objective The use of 4D planning CT scans has enabled us to the take the lung tumour motion into account with high precision. Yet, it has not been utilised with the same precision to study the impact of cardiac motion on the dose delivered to the heart. This has become a more pertinent topic, since radiation induced cardiac toxicity has been found to occur more frequently and earlier after treatment than previously thought. Therefore, the purpose of this hypothesis generating study was to assess the range of heart motion using 4D planning CT dataset and compare with conventional process of heart delineation on single 3D CT acquisition. Material and Methods A cohort of 10 lung cancer patients previously treated with SABR was considered in the study. The heart was delineated on both the 3D CT and the Maximum Intensity Projection (MaxIP) by an experienced clinical oncologist (MSI). Initially, we calculated the difference in volume between these two delineations using a paired, one-tailed t-test. Then, the change in volume was characterised by measuring the maximum distance between the 3D CT and MaxIP contours in six directions: superior, inferior, left, right, anterior and posterior in the coordinate system of the scan-set. A positive value indicated that the MaxIP defined contour was larger than the contour defined on the 3DCT. A negative value indicated that the MaxIP defined contour was smaller than the contour defined on the 3DCT. Results A statistically significant difference in volume was observed between the 4DCT maxIP and the 3DCT volume (p=0.007). The mean percentage increase in heart volume delineated on the MaxIP 4DCT compared to the 3DCT based delineations, was 12%, ranging between 4 and 27%. The mean of the measured distances between the delineations defined on the MaxIP and 3DCT in each of the directions was: 0.2 cm ( - 0.04 – 0.9 cm) superiorly, 1.1 cm (0.5 – 2.4 cm) inferiorly, 0.1 cm ( - 0.9 – 1.0 cm) to the left, 0.4 cm ( - 0.3 – 1.2 cm) to the right, 0.4 cm (0.2 – 0.5 cm) anteriorly and 0.6 cm ( - 0.5 – 0.8 cm) posteriorly. Conclusion The results of this hypothesis generating study indicate large patient specific differences in heart volume and heart motion on 4D CT. This will encourage us to further investigate individualised Planning Organ at Risk volume of the heart, to reduce cardiac toxicity not only for lung radiotherapy, but also for other indications of thoracic radiotherapy (e.g. breast, lymphoma and oesophageal cancers).

The atlas was developed by a team involved in a cardiac toxicity study (CART study). The atlas was used to assess reproducibility of contouring heart substructures. Fifteen structures were contoured on 5 lung cancer patients by 3 oncologists. Contouring variability was assessed using Eclipse Treatment Planning System v15.5 [Varian Medical Systems, Palo Alto, CA, USA] to compute concordance