ESTRO 36 Abstract Book

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S386 ESTRO 36 2017
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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.
Poster: Clinical track: Sarcoma
PO-0742 Target delineation conformity in extremity
STS within the UK phase II multi-centre IMRiS trial
H. Yang1, R. Simões1, F. Le Grange2, S. Forsyth 3, D.
Eaton1, 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
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
(DSC) as: , 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.
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