ESTRO 36 Abstract Book

S496 ESTRO 36 2017 _______________________________________________________________________________________________

contour propagation. For the automatic contouring strategy the daily propagated contours were based on an intra-patient atlas consisting of the manual contours of the first day and propagated contours of other previous days.The semi-automatic contouring strategy included additional manual adjustments made by a technologist after each daily automatic contour propagation serving as input for the following days. All automatic and semi- automatic contours were compared with the manual contours of the corresponding day by calculating dice coefficients, mean and Hausdorff distances. Timing measurements were done for both strategies. Results Higher median dice coefficients with smaller ranges were found for the semi-automatic strategy compared to the automatic strategy (figure 1). However, large variations after manual adjustments were still found for the GTV. Outliers found in the mean and Hausdorff distances of the automatic strategy were not seen in the semi-automatic strategy (figure 2). The contours were automatically propagated for day 2, 3, 4 and 5 in respectively 18, 38, 54 seconds and 1:13 minutes on average. The propagated contours of the semi- automatic strategy were manual adjusted with an average time of 14:49 minutes (in comparison with approximately 45 minutes for full manual contouring). Manual adjustments of the cranial and caudal slices of the contours were most time consuming.

Conclusion Automatic propagated contours for target and OARs need manual adjustments for clinical acceptance. Mesorectum and OARs adjustments can be made by an experienced technologist and are not clinically relevant different from the manual contours of an experienced radiation oncologist. This semi-automatic contouring strategy can be used in an online workflow for rectal boost treatment, however further speed-optimisation is desirable. PO-0906 Textural analysis of MR images to improve the characterisation of recurrent prostate cancer J. Stirling 1 , R. Alonzi 2 , P.J. Hoskin 2 , N.J. Taylor 1 , W.L. Wong 1 , A.R. Padhani 1 , B. Sanghera 1 1 Paul Strickland Scanner Centre, Research, Northwood, United Kingdom 2 Mount Vernon Hospital, Academic Oncology Unit, Northwood, United Kingdom