Comparative study with new accuracy metrics for target volume contouring in pet image guided radiation therapy

International audienceThe impact of PET on radiation therapy is held 1 back by poor methods of defining functional volumes of interest. 2 Many new software tools are being proposed for contouring 3 target volumes but the different approaches are not adequately 4 compared and their accuracy is poorly evaluated due to the ill-5 definition of ground truth. This paper compares the largest cohort 6 to date of established, emerging and proposed PET contouring 7 methods, in terms of accuracy and variability. We emphasise 8 spatial accuracy and present a new metric that addresses the 9 lack of unique ground truth. 30 methods are used at 13 different 10 institutions to contour functional VOIs in clinical PET/CT and 11 a custom-built PET phantom representing typical problems in 12 image guided radiotherapy. Contouring methods are grouped 13 according to algorithmic type, level of interactivity and how they 14 exploit structural information in hybrid images. Experiments 15 reveal benefits of high levels of user interaction, as well as 16 simultaneous visualisation of CT images and PET gradients to 17 guide interactive procedures. Method-wise evaluation identifies 18 the danger of over-automation and the value of prior knowledge 19 built into an algorithm. 2