ESTRO 36 Abstract Book

S486 ESTRO 36 2017 _______________________________________________________________________________________________

Treatment CT scans from up to 8 randomly selected patients included in the trial had target volumes auto delineated with MIM Maestro™ software version 6.5 (MIM Software Inc., Cleveland, OH) and manually edited according to ESTRO target volume delineation guidelines. Post editing of contours were verified by an observer (BVO),and considered as a gold standard reference (GS). Dice similarity coefficient (DSC) between original delineation (OD) and GS was calculated. Protocol compliance and dose distribution of delineated volumes (Dmin, Dmax, D2%, D95%, D98% and Homogeneity index (HI) for breast and nodal target volumes) were assessed in OD. HI and D95% were compared between OD and GS delineation of primary (CTVp),CTVn_L2-4- interpectoral (CTVn), internal mammary CTV (CTVn_ IMN) and CTVn_L1.

Conclusion There was low interobserver variability across all centres. Low rates of protocol deviations ensured high compliance of the participating centres. Targets were adequately and homogeneously covered in the majority of patients. Dose parameters were comparable between OD and GS and confirmed that interobserver variability did not influence treatment outcomes.

Results 88 treatment plans from 12 centres in 4 countries were assessed. Delineation of all target volumes and organs at risk was complete in 99% and 96% of the patients,respectively. DSC showed high agreement in contouring, with average values of 0,9 for CTVp and 0,77 for nodal volumes.Complete dosimetric assessment was available in all patients for CTVp, but 1 patient with missing target volume delineation required integration with data extrapolated from GS. No deviations for target dose distribution were found in 76% of the patients, and 82% and 95%of the patients had successful target coverage of CTVp and CTVn, with 95% of volume covered by >95% and >90% of prescribed dose, respectively. Dose comparison for CTVp was performed in all patients, but 17 patients were excluded from CTVn comparison due to incomplete target delineation or exclusion of one or more nodal levels from target volume according to institutional policy. No differences were found for CTVp HI and D95% between OD and GS. CTVn, CTVn_L1 and CTVn_IMN were successfully covered (D95>90% of prescribed dose) in both delineations. Minimal differences were found in D95% and HI for CTVn (p<0,001 for both), CTVn_IMN (p=0,001 for D95%) and CTVn_L1 (p=0,02 for HI andp=0,03 for D95%).

Poster: Physics track: Images and analyses

PO-0892 Automatic quality assurance of rectal contours on image guidance scans M. Romanchikova 1 , D.I. Johnston 1 , M.P.F. Sutcliffe 2 , K. Harrison 3 , S.J. Thomas 1 , J.E. Scaife 4 , N.G. Burnet 4 1 Cambridge University Hospitals, Medical Physics and Clinical Engineering, Cambridge, United Kingdom 2 University of Cambridge, Engineering, Cambridge, United Kingdom 3 University of Cambridge, Physics, Cambridge, United Kingdom 4 University of Cambridge, Oncology, Cambridge, United Kingdom Purpose or Objective Assessment of the quality of contours produced by automatic methods is labour-intensive and inherently dependant on the skills of the evaluator. The utilisation of these contours in radiotherapy requires objective quality metrics and efficient tools for contour quality assurance. We present a method to determine the quality of automated rectum contours on daily image guidance scans (IG). Material and Methods We analysed 11519 automatically produced rectum contours on 1062 pelvic IG scans of 33 prostate cancer patients. Each contour was evaluated by 1) a trained clinician and 2) an automated classification software that applied a set of binary and numeric metrics to each contour. The metrics included 1) centre-to-centre contour distances, 2) differences in contour areas between