ESTRO 2023 - Abstract Book

S792

Monday 15 May 2023

ESTRO 2023

All the plans were delivered with 3 coplanar or no-coplanar 10 MV-FFF arcs, the mean value of Monitor Units was 7700, while the mean treatment time was 3 minutes. The average mean dose for heart and LAD were 3.9 and 6.3 Gy respectively; while mean values observed for the maximum dose of LAD, spinal cord, left and right bronchus and esophagus were 11.2, 7.5, 14.3, 12.4 and 13.6 Gy respectively. Conclusion The reported STAR dosimetric data showed an optimal target coverage, sparing surrounding tissue, in a 3 minute of OTT. Considering the large diffusion of LINAC in the world and the large AF elderly population, the present collected data are interesting, LINAC-based STAR for AF could represent a valid non-invasive alternative for elderly who were excluded from catheter ablation. OC-0944 Dosimetric impact of auto-mapping heart contour and motion uncertainty in lung cancer radiotherapy V. Chin 1,2,3 , R. Finnegan 4,5,6 , P. Chlap 7,2,6 , L. Holloway 7,5,2,6 , D. Thwaites 5,8 , J. Otton 7,9 , G. Delaney 7,2,3 , S. Vinod 7,2,3 1 University of New South Wales, South Western Sydney Clinical School, Sydney , Australia; 2 Liverpool and Macarthur Cancer Therapy Centres, Department of Radiation Oncology, Sydney, Australia; 3 Ingham Institute for Applied Medical Research, Radiation Oncology, Sydney, Australia; 4 Northern Sydney Cancer Centre, Royal North Shore Hospital, Sydney, Australia; 5 University of Sydney, Institute of Medical Physics, Sydney, Australia; 6 Ingham Institute for Applied Medical Research, Medical Physics, Sydney, Australia; 7 University of New South Wales, South Western Sydney Clinical School, Sydney, Australia; 8 St James's Hospital and University of Leeds, Leeds Institute of Medical Research, Radiotherapy Research Group, Leeds, United Kingdom; 9 Liverpool Hospital, Department of Cardiology, Sydney, Australia Purpose or Objective Contour variation (inter- or intra-observer) and organ motion produce uncertainty in radiation dose delivery, which is challenging to quantify. Most automatic segmentation tools generate a single “most likely” contour, but other contours are possible, especially for small difficult-to-see structures. A technique is proposed to generate additional feasible auto contours from visualisation and quantification of contour and motion uncertainties on lung cancer planning CTs, with evaluation of the dosimetric impact. Materials and Methods We previously developed a fully-automated segmentation tool to delineate 18 cardiac structures (Finnegan et al, Radiother Oncol 170(2022)S1,670): the heart via a deep learning (DL) model and substructures within the DL-heart using multi-atlas mapping (M-AM) and geometric segmentation. To map contour variation, the tool was used on 27 curative lung cancer planning CTs, with each of the 10 atlases from the M-AM step providing a separate substructure contour (Fig 1). For motion mapping, 9/27 cases had 4D planning CTs, and cardiac motion was mapped through all respiration phases. Dose volume histograms (DVH) for each probable contour and motion-changed contour were generated for comparison.

Results Dose differences from contour variation and motion depend on tumour position relative to organs at risk (OARs) and not simply on magnitude of contour differences. For example, motion mapping showed mean dose to right atrium (RA) and right coronary artery (RCA) differed by 0.7-7.4Gy and 0.5-5.9Gy respectively across the cases, with Fig 2A showing the case with high dose difference of these right sided structures (7.4Gy and 5.8Gy difference respectively). The right-sided tumour means right cardiac structures lie in a high dose gradient, hence wider dose differences in DVH. Conversely, left sided