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Conclusion
This work presents a methodology to e stimate the
parameters of a mechanistic, radiobiological l TCP model
based on pre-treatment FMISO and FDG PET scans. The
method is able to predict mean and median values of
intra-treatment hypoxia for each of the lesions in a
validation dataset held out from the analysis. This could
potentially be used in the future to, for example, select
patients for a de-escalation protocol based on their
expected response. More patients will be added to the
analysis in order to refine the prediction, find the defining
characteristics of the outliers, and consolidate the results.
PO-0891 Quality assessment of target volume
delineation and dose planning in the Skagen Trial 1
G. Francolini
1
, M. Thomsen
2
, E. Yates
2
, C. Kirkove
3
, I.
Jensen
4
, E. Blix
5
, C. Kamby
6
, M. Nielsen
7
, M. Krause
8
, M.
Berg
9
, I. Mjaaland
10
, A. Schreiber
11
, U. Kasti
12
, K. Boye
13
,
B. Offersen
14
1
Azienda Ospedaliera Universitaria Careggi, Department
of Radiation oncology, Firenze, Italy
2
Aarhus University hospital, Department of Medical
physics, Aarhus, Denmark
3
Catholic University of Louvain, Department of Radiation
Oncology, Brussels, Belgium
4
Aalborg University Hospital, Department of Medical
Physics, Aalborg, Denmark
5
University Hospital of North Norway, Department of
Oncology, Tromso, Norway
6
Rigshospitalet, Department of Oncology, Copenhagen,
Denmark
7
Odense University Hospital, Department of Oncology,
Odense, Denmark
8
University Hospital Carl Gustav Carus, Department of
Radiation Oncology, Dresden, Germany
9
Hospital of Vejle, Department of Physics, Vejle,
Denmark
10
Stavanger University Hospital, Department of
Oncology, Stavanger, Norway
11
Praxis für Strahlentherapie, Department of Radiation
oncology, Dresden, Germany
12
Sørlandet Sykehus HF, Department of Oncology,
Kristiansand, Norway
13
Zealand University Hospital, Department of Oncology,
Naestved, Denmark
14
Aarhus University Hospital, Department of Oncology,
Aarhus, Denmark
Purpose or Objective
Skagen Trial 1 is a multicenter, non-inferiority trial
randomising early breast cancer patients to loco-regional
irradiation with 50 Gy/25 fractions vs 40 Gy/15fractions.
Primary endpoint is arm lymphedema.
The protocol has pre-specified criteria for target volume
delineation and dose planning, and quality assessment of
this is reported. Inter-observer variability in delineation
and its impact on dose parameters were assessed.
Automated atlas-based segmentation was used in order to
streamline assessment procedure.
Material and Methods
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%).