ESTRO 36 Abstract Book

S386 ESTRO 36 2017 _______________________________________________________________________________________________

investigated for the first time within the UK in IMRiS, a prospective multi-centre phase II trial. As part of radiotherapy trials quality assurance, we determined the conformity of volume delineation of an extremity STS benchmark training case in the post- operative setting, and report target outlining variation in relation to the trial protocol. Material and Methods The clinical history, operation/histology reports, pre- operative magnetic resonance imaging and planning scans of the training case were made available to participating clinicians, who submitted outlines based on the protocol. Both first and re-submissions were evaluated by two clinicians, where GTV, CTV_6000 and CTV_5220 were compared to the reference contours. The volumes were quantitatively assessed using Dice Similarity Coefficient , where A and B represent regions of interest. Individual feedback based on trial protocol variations was provided for all submissions. Results There was a total of 25 submissions from 23 centres. Delineation of GTV, CTV_6000 and CTV_5220 were deemed unacceptable according to the protocol in 5(20%), 10(40%) and 5(20%) submissions respectively. The table details the unacceptable variations from the protocol. All unacceptable GTV contours failed to reconstruct the pre-operative disease in its entirety. Incorrect margin expansion constituted the majority of the unacceptable submissions for both CTVs. (DSC) as:

Conclusion Our experience suggests that the combination of Ipi+SRS/SRT in MBMs pts can obtain a better survival with a low toxicity profile related to combined treatment. The high precision of treatment with Cyberknife allows to reduce radiation of organs at risk. The optimal timing of combination Ipi+RT is not clear, but from our experience it would seem to be a benefit of using the Ipi before SRS/SRT on LC. The recruitment of a greater number of pts and a longer follow-up are needed to demonstrate the role of Ipi also in the treatment of melanoma pts with BMs and the better sequence with RT. PO-0742 Target delineation conformity in extremity STS within the UK phase II multi-centre IMRiS trial H. Yang 1 , R. Simões 1 , F. Le Grange 2 , S. Forsyth 3 , D. Eaton 1 , B. Seddon 2 1 Mount Vernon Cancer Centre, National Radiotherapy Trials Quality Assurance Group, Northwood, United Kingdom 2 University College Hospital, Sarcoma Unit, London, United Kingdom 3 University College London, Cancer Research UK & University College London Cancer Trials Centre, London, United Kingdom Purpose or Objective Accurate target volume delineation is essential in the use of intensity-modulated radiotherapy, where its role in the treatment of bone and soft tissue sarcoma (STS) is being Poster: Clinical track: Sarcoma

The mean DSCs were systematically lower for the unacceptable contours compared to accepted contours for GTV [0.61 (range 0.55–0.66) vs 0.77 (range 0.60–0.81), p<0.001], CTV_6000 [0.75 (range 0.53–0.82) vs 0.82 (range 0.77–0.89), p=0.036] and CTV_5220 [0.15 (range 0.02– 0.36) vs 0.43 (range 0.11–0.64), p=0.002]. CTV_5220 was incorrectly positioned in 5 submissions due to the contouring inaccuracies of GTV/CTV_6000. Other variations in the inclusion of the scar/seroma were seen where it was not fully encompassed axially (CTV_6000: 8 submissions, CTV_5220: 6 submissions), and wh ere CTV_6000 was extended beyond margins longitudinally to include it (5 submissions). In addition, some volumes were tapered where the anatomical planes were not followed lengthwise (CTV_6000: 5 submissions, CTV_5220: 13 submissions). There were five re-submissions after feedback, for which all target volumes had either acceptable, or no variation from the protocol (mean DSC GTV: 0.75, CTV_6000: 0.83, CTV_5220: 0.48). Conclusion High numbers of unacceptable variations from the trial protocol were seen in the first submission of the training case; the adherence to the protocol improved following individualised feedback. As the outlining of both CTVs is dependent on the accuracy of the reconstructed GTV in the post-operative setting, this should be done with