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S316
ESTRO 36 2017
_______________________________________________________________________________________________
Purpose or Objective
Danish national guidelines (GL) for head and neck cancer
radiotherapy (RT) have been available since 1990 and
were revised in 2013. One of the major revision points was
the change of GTV to CTV margins from mainly
anatomically driven expansions to symmetric geometric
expansion. The purpose of this study was to analyse the
consistency of generated CTV contours by the new
approach and to evaluate the impact on CTVs and any
differences between four centres involved in RT before
and after the guideline revision.
Material and Methods
Prior to the GL change in 2013, four centres were asked to
delineate CTV1, CTV2 and CTV3 of a stage IV oropharynx
patient with three prescription levels: 66 Gy, 60 Gy and 50
Gy in 33 fractions. The contours of the tumour GTV and
the lymph node GTV were provided together with the
organs at risk (OAR). Each centre made a RT plan from the
CTVs. After the new GL was implemented, the centres
were asked to repeat the CTV contouring and the dose
planning. Likewise, the centres were asked in 2016, three
years after the GL, to re-contour and re-plan to test the
consistency over time of the GL.
The difference in contouring was evaluated by the
difference in CTV volume, Dice Similarity Coefficient
(DSC) and average minimum surface distance (MSD)
between the CTV contours. The difference in dose plans
was evaluated by mean dose to OAR and dose-specific
treated volumes (V
62.7Gy
, V
57Gy
, V
47.5 Gy
and V
25Gy
)
.
The
statistical difference was tested with a paired two-sided
Student's t-test (p<0.05).
Results
The contours from GL 2004 were less uniform and showed
large volume differences (Table 1). The MSD showed a
mean difference of 0.6 cm and a relatively large standard
deviation (SD) of 0.45 cm for the CTV1. The GL 2013
provided a more operational margin expansion and hence
resulted in a high DSC and very similar volumes, however
with a mean increase of 40% and 32% for the CTV1 and
CTV2, respectively. The re-contouring in 2016 was similar
to 2013 indicating that the interpretation of GL 2013 is not
affected by time.
The similarity of the CTV targets in 2013-16 resulted in
more uniform dose plans, however, the different planning
approaches resulted in only slight difference to the OAR,
and the SD of mean doses did not improve significantly.
The SD of the irradiated volume improved with the GL
2013 and further improved in 2016 dose plans. It is obvious
that the larger CTVs of the GL 2013 increased the
irradiated volume (figure 1), however improved planning
and familiarity of the GL reduced this difference in the
2016 plans.
Conclusion
The GL 2013 showed more uniform CTV1 and CTV2
contouring between centres, which was reproduced in
2016. The more geometric GTV to CTV expansion allows
for an easier operational delineation which leaves less
room for misinterpretation. This transforms into more
uniform treatment plans and very similar irradiated
volumes across all centres.
PO-0614 The prognostic role of 18F-FDG PET/CT in
head and neck cancer and the importance of HPV status
J.M. Moan
1
, E. Malinen
2
, J.G. Svestad
3
, C.D. Amdal
1
, T.V.
Bogsrud
4
, E. Dale
1
1
Oslo University Hospital, Department of Oncology, Oslo,
Norway
2
University of Oslo, Department of Physics, Oslo, Norway
3
Oslo University Hospital, Department of Medical
Physics, Oslo, Norway
4
Oslo University Hospital, Department of Nuclear
Medicine, Oslo, Norway
Purpose or Objective
Standardized uptake value (SUV) and related parameters
derived from 18F-FDG PET/CT prior to radiochemotherapy
of head and neck cancer have been shown in several
studies to correlate with survival. We wanted to validate
this finding in our own patient cohort, but also to see the
PET parameters together with clinical risk factors
including HPV status.
Material and Methods
We retrospectively reviewed 225 patient cases from 2007
to 2014 with complete sets of 18F-FDG PET/CT and
potential clinical risk factors (age, sex, ECOG status,
Charlson comorbidity status, pack years of smoking, TNM
stage, tumor differentiation, tumor site, HPV DNA status
(tested for oropharyngeal cancers [OPC]), treatment
duration, days on nimorazole and numbers of weekly
cisplatinum. All patients received radiotherapy with 68-70
Gy in 2 Gy fractions. Patients older than 70 years or with
comorbidity did not receive concomitant cisplatinum
(26%). Clinical endpoints were overall survival (OS), local
control, regional control, distant control, and disease-free
survival (DFS). We investigated the image parameters; 1)
Gross tumor volume (GTV) based on CT and PET, 2) PET
tumor volume delineated by the nuclear medicine
specialist, 3) metabolic tumor volume (MTV), 4) total