501 / 1082
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.
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%).
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.
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