ESTRO 36 Abstract Book

S138 ESTRO 36 _______________________________________________________________________________________________

OC-0267 Automatic contour propagation of breast and heart for re-planning in breast cancer radiotherapy G.G. Sikkes 1 , L.T.C. Meijers 1 , A.N.T.J. Kotte 1 , I.E. Van Dam 1 , B. Van Asselen 1 , H.J.G.D. Van den Bongard 1 1 UMC Utrecht, Radiation Oncology Department, Utrecht, The Netherlands Purpose or Objective Adaptive radiotherapy (RT) can improve the radiotherapy treatment when target volume, patient anatomy or treatment position has changed during treatment. Automatic, non-rigid, contour propagation in a clinical setting is expected, in comparison with rigidly transferred contours, to reduce delineation time and can increase the efficiency of adaptive radiotherapy. For breast cancer patients, adaptive radiotherapy is mainly performed due to breast contour changes (e.g. oedema) or reduction in seroma volume. The aim of this study was to determine the applicability of non-rigid contour propagation of breast (clinical target volume, CTVbreast) and heart for re-planning in breast cancer RT. Material and Methods 25 breast cancer patients, each with a RT planning- CT(CT1) and a subsequent CT(CT2) taken before or during (fraction 0-9) treatment, were selected for this prospective study. For 11 of the 25 patients the changes visible on CT2 were clinically acceptable, consequently, no re-planning was needed. In 14 patients, 15 new RT plans (including patient with bilateral breast cancer) were performed, due to changes in target (n=11), treatment position (n=2) or switch from Breath hold technique to free breathing CT (n=1). Heart and CTVbreast were manually delineated on CT1 by a radiation oncologist according to clinical delineation guidelines. Contours on CT1 were transferred to CT2 using a rigid registration technique, equal to the standard clinical procedure. The CT1 contours were also transferred to CT2 via deformable automatic contour propagation using ‘Advanced Medical Image Registration Engine’(ADMIRE research software v1.12/v1.13.3/v1.13.5, Elekta AB, Sweden). The rigidly transferred contours as well as the deformable propagated contours were compared to the clinical contours on CT2 using comparison measures target volume, DICE, Hausdorff distance and mean distance. Results The volume, DICE, Hausdorff distance and mean distance, presented in table1 and figure1, depict differences between the deformable propagated and rigidly transferred contours relative to the clinical contours. 14 of the 15 patients receiving new RT plans (including patient with bilateral breast cancer) had a higher DICE, a smaller Hausdorff distance and mean distance and had less volume differences between the deformable propagated CTVbreast and heart contours relative to the clinically used contours in contrast to the rigidly transferred contours.

Conclusion These results shows that the deformable propagated CTVbreast and heart contours are, as expected, more close to the clinical used contours than the r igidly transferred contours. Therefore, deforma ble contour propagation can reduce delineation time and can be used to optimize the workflow of adaptive RT for breast cancer. OC-0268 Volumetric comparison between PET/CT and CT simulation for target delineation in esophageal cancer E. Jimenez-Jimenez 1 , P. Mateo s 2 , N. Aymar 1 , I. Ortiz 1 , R. Roncero 1 , M. Vidal 1 , M. Gimenez 3 , F. Romero 4 , S. Sabater 5 1 Hospital Universitari Son Espases, Radiation Oncology Department, Palma de Mallorca, Spain 2 Hospital Can Misses, Medical Physics Department, Ibiza, Spain 3 Hospital Universitari Son Espases, Nuclear Medicine Department, Palma de Mallorca, Spain 4 Hospital Universitari Son Espases, Medical Physics Department, Palma de Mallorca, Spain 5 Complejo Hospitalario Universitario de Albacete, Radiation Oncology Department, Albacete, Spain Purpose or Objective FDG-PET/CT has proven to be useful in the staging process of esophageal tumors. However, evidence supporting the use of FDG-PET/CT in the tumor delineation process and radiotherapy planning is limited. Our objective was to compare the volumes defined by PET- CT vs. CT simulation in esophageal planning. Material and Methods Nineteen esophageal carcinoma patients were referred for concomitant radio-chemotherapy with radical or neoadjuvant intent. Each patient underwent CT and FDG-PET/CT for simulation treatment in the same treatment position. Two separate GTVs were defined; one based on CT data alone (GTV-CT) and another based on combined PET/CT data (GTV-PET/CT). Volume sizes for both data sets were compared and the spatial overlap was assessed by the Dice similarity coefficient (DSC), which represents the ratio of volume overlap between 2 contours.