PO-0932: Preliminary clinical study to evaluate an interactive system to segment OARs in thoracic oncology

Purpose: Radiotherapy aims at delivering the highest possible dose to the tumor while minimizing the irradiation of surrounding healthy tissue, and especially to the organs at risk (OARs). Therefore, accurate delineation of 15 OARs is required for radiation treatment planning (RTP). In thoracic oncology, delineation of some OARs remains manual, making the task time consuming and prone to inter observer variability. Various (semi-) automatic approaches have been proposed to segment OARs on CT but the task still remains challenging. Here, a system to interactively segment OARs in thoracic oncology on CT images is presented and its clinical acceptability evaluated. 20 Methods: The proposed framework has been implemented using MITK platform. User interaction lies in the easy definition of few manual seeds for the OARs and background using a u0027paintbrushu0027 tool, which can be interactively added in any view (axial, sagittal or coronal), and is subsequently propagated within the whole volume. Once the user is content with the seeds placement, the system automatically performs the segmentation. If the outcome is not satisfying, the user can modify the seeds, which involves adding and/or removing existing seeds, and perform 25 again the automatic segmentation. Number of tries has been limited to five in the current study. If after the five modifications the segmentation result is not sufficient to be usable in the RTP, the user shall reject it; otherwise, he shall accept it. A hybrid approach based on our previous work [1, 2] which combines watershed transformation and graph cuts [3] is used for the segmentation task. Results: The system was evaluated on multivendor CT datasets of 10 patients presenting from early stage to 30 locally advanced NSCLC or pulmonary metastases. OARs taken into consideration in this study were: heart, lungs, oesophagus, proximal bronchus tree, spinal canal and trachea. Interactive contours were generated by a physician using the proposed system. Delineation of the OARs obtained with the presented system was approved to be usable for RTP in more than 90% of the cases, excluding the oesophagus, which segmentation was never approved (Fig 1). On the accepted reported cases, more than 90% of the interactive contours reached a Dice 35 Similarity Coefficient higher than 0.7 with respect to manual segmentations (Fig 2). Therefore, our interactive delineation approach allows users to generate contours of sufficient quality to be used in RTP up to three times faster than manually. Conclusions: An interactive, accurate and easy-to-use computer-assisted system for OARs segmentation in tho-racic oncology was presented and clinically evaluated. The introduction of the proposed approach in clinical 40 routine might offer a valuable new option to radiation therapists (RTTs) in performing OARs delineation task. Consequently, further experiments have been conducted on larger databases and with the participation of additional RTTs to investigate its potential use in daily clinical practice [4].