ESTRO 36 Abstract Book

S136 ESTRO 36 _______________________________________________________________________________________________

Using multi-atlas (MIR) compared to single-atlas (RS) for prostate RT showed better in 19, similar in 2 and worse in 3 out of the 24 volumetric parameters. Even though the results are promising, discordances could lead to large DVH parameters differences. OC-0264 Assessment of Atlas based auto-segmentation in Breast Contouring P.H. Fok 1 , W.K. Fung 1 , C.H.P. Ho 1 , G. Chiu 1 1 Hong Kong Sanatorium & Hospital, Department of Radiotherapy, Happy Valley, Hong Kong SAR China Purpose or Objective To investigate the efficiency and accuracy of atlas based auto-contour segmentation (ABAS) for radiotherapy of Contour sets of 80 breast cancer patients were recruited to build an atlas in MIM Software for ABAS purpose. They consisted of structures including CTV, PTV, and OARs including the esophagus, heart, liver, spinal cord and contralateral breast. ABAS was evaluated by comparing auto segmented contours with manually drawn contours using Dice Similarity coefficients (DSC) and Hausdroff distance (HD). CTV and contralateral breast were dissected into superior, inferior, medial, lateral, anterior and posterior portions (Fig.1) for individual evaluations of their accuracy of ABAS. The study consisted of two parts. Part A: All patients from the atlas were used as the test subjects and the patient who was selected as the test subject would be excluded from the atlas. Manual contours of each subject were compared with those that were generated by ABAS. Part B: Another 16 patients with breast cancer were randomly recruited to evaluate the efficacy of ABAS in clinical practice. The time required for manual contouring and contouring by ABAS with or without manual refinement were compared. Radiation Oncologists (ROs) were asked for their satisfactory levels regarding the ABAS generated contours. breast cancer patients. Material and Methods

The comparison results of the ABAS generated contours and the manual contours were listed in Table 1. High levels of agreement (DSC=0.8 to 1) were shown in the right lung, left lung, liver, heart, spinal cord and left breast PTV; moderate levels of agreement (DSC=0.7 to 0.79) were shown in the left breast (CTV, contralateral breast) and the right breast (CTV, PTV, contralateral breast); poor agreement (DSC<0.69) was shown in the esophagus. The lateral portions of the CTV, PTV and contralateral breast for both left and right sided breast cancer patients had the largest volume differences among the other portions. Thus, the lateral portion of the breast contour required the most refinement. Part B Level of agreement and s atisfaction improvement were shown after refinement on AB AS generated TVs, with the mean DSC increased from 0.861 to 0.979 and the satisfaction score (range:1-5 ) increased from 2.2 to 4.3. The mean time for ROs to manually contour TVs and to modify ABAS generated TVs with refinement was 26.8 and 15.3mins respectively. The DSC, mean time for manually contouring OARs and that for ABAS generated contours with refinement were as follows: heart (DSC=0.949; 8.2 and 7.3mins), liver (DSC=0.904; 24.8 and 20.5mins), esophagus (DSC=0.556; 7.6 and 11.3mins), spinal cord (DSC=0.855; 9.2 and 10.4mins) and contralateral breast (DSC=0.904; 24 and 18mins).

Fig.1

Conclusion ABAS could speed up the contouring process especially in target delineation during breast patient treatment planning. However, improvement in the a lgorithm is still needed and auto post-ABAS refinement has to be developed to further increase its efficiency for clinical practice. OC-0265 Evaluating variability of contouring using ESTRO guidelines for elective breast cancer radiotherapy D. Megias 1 , M. Sydenham 2 , D. Wheatley 3 , M. Maclennan 4 , E. Spezi 5 , A.M. Brunt 6 1 Mount Vernon Hospital, National Radiotherapy Trials Quality Assurance Group RTTQA, Northwood, United Kingdom 2 Institute of Cancer Research, ICR Clinical Trials and Statistics Unit, Sutton, United Kingdom 3 Royal Cornwall Hospital, Clinical Oncology, Truro, United Kingdom 4 Edinburgh Cancer Centre, Cancer Services, Edinburgh, United Kingdom 5 Cardiff University, School of Engineering, Cardiff, United Kingdom 6 Royal Stoke University Hospital & Keele University, Cancer Centre, Stoke on Trent, United Kingdom Purpose or Objective Outlining of target and OAR volumes is an integral part of the radiotherapy pathway but inherently subject to variability. With an emerging body of evidence supporting regional nodal irradiation in early breast cancer, there is continued emphasis for optimal, standardised and

Results Part A