ESTRO 36 Abstract Book

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S707 ESTRO 36 2017
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A. Otero-Romero1, A. Pérez-Rozos1, R. Correa-Generoso 1,
I. Jerez-Sainz1, M.J. García-Anaya1, I. Zapata-Martínez1,
A. Román-Jobacho1 , M.D. Toledo-Serrano1, R. Ordoñez-
Marmolejo1, I. García-Ríos1, J. Goméz-Millan1, J.A.
Villalobos-Martín2, T. Díaz-Antonio2, J.A. Medina-
Carmona1
1 Hospital Virgen de la Victoria, Radiation Oncology,
Málaga, Spain
2 Hospital Virgen de la Victoria, Radiology, Málaga, Spain
Purpose or Objective
CT (Computer Tomography) is the standard for conformal
radiotherapy treatment planning of prostate cancer,
however T2-weighed MRI (Magnetic Resonance) allows
better definition of apex of prostate, seminal vesicles and
the rectum-prostate interface.
Analyse intra and inter-observer variability and whether
implementing systematic image fusion with CT and MRI
could improve prostate contouring accuracy.
Material and Methods
MR was requested to complete tumour staging and
performed in a different centre due to the unavailability
of MRI scan in our hospital. Planning CT was carried out in
our department, slices of 3 mm, with empty bladder and
rectum, in supine position using knee and feet
immobilization devices. Image fusion was performed with
T2-weighed MRI and CT scans matching on bony structures
of the pelvis.
We conducted the study in two parts.
First part of the study consisted in contouring the prostate
and seminal vesicles of a single patient on CT images and
then on MRI fusion images by 9 Radiation Oncologists
(including training doctors)
In the second part of the study two Radiation Oncologists,
specialized in prostate cancer, and a Radiologist trained
in MRI contoured the prostate of 5 patients on CT images
and then on MRI fusion images. The contour of the
Radiologist was considered the gold standard.
Comparison of volumes measured on CT and MRI using
Pinnacle planning system was made. Intraobserver and
interobserver variability was assessed taking into account
the percentage of coincident volume with the gold
standard, analysing the distance of the direction with
more differences, and calculating sensitivity (S) and
Paccard indexes (Ipaccard ;P=delineated prostate; C=gold
standard).
Results
Accurate CT-MRI image fusion was not always achieved
with bony matching due to the different pelvis position
and needed soft tissue correction.
Volumes of the first part of the study range was 29.1-52.4
cc for prostate and 10.8-16.7 cc for seminal vesicles on
CT, and 29.5-57.2 cc for prostate and 11.6-16.1 cc for
seminal vesicles on MRI. Comparing CT and MRI volumes
the intraobserver ratio was 1.13 (1.02-1.26) for prostate
and 1.12 (1.01-1.21) for seminal vesicles.
In the second part of the study mean volumes range on CT
scan was 13-21 cm3 while on MRI was 18-26 cm3. Mean
volume% comparing to the gold standard volume range was
62%-67% on CT and 81%-86% on MR. Variability in distance
in the different directions were 3-9 mm in the longitudinal
axis, 3-4 mm in the lateral axis and 2-3 mm in the anterior-
posterior axis. Mean sensitivity index was 0.58 on CT and
0.80 on MRI, and mean Paccard index was 0.48 and 0.76
on CT and MRI respectivel
y.
Conclusion
Prostate MRI enables more accurate planning contouring
than CT. In our study CT volumes tend to be smaller than
on MRI. The longitudinal axis is the direction where more
contouring differences have been found.
MRI and CT could be made in the same pelvis position to
achieve reduced uncertainty image registration.
EP-1333 Impact of 18F-Choline PET scan acquisition
time on delineation of GTV in Prostate cancer
C. Parkinson1, J. Chan2, I. Syndikus2, C. Marshall3, J.
Staffurth4, E. Spezi1
1Cardiff University, School of Engineering, Cardiff,
United Kingdom
2Clatterbridge Cancer Centre, Clinical Oncology,
Liverpool, United Kingdom
3Cardiff and Vale University Health Trust, Wales
Research & Diagnostic PET Imaging Centre, Cardiff,
United Kingdom
4Velindre Cancer Centre, Clinical Radiotherapy Trials,
Cardiff, United Kingdom
Purpose or Objective
Dose painting radiotherapy requires accurate outlining of
primary tumour volumes in the prostate. T2-Weighted
(T2W) Magnetic Resonance Imaging (MRI) is the best
imaging method for defining the gross tumour volume
(GTV). Choline positron emission tomography (PET) is
currently a controversial tracer. The image acquisition
differs significantly in published studies. Many used early
static imaging. One study found that 18F-choline PET/CT
with late image acquisition has superior accuracy to T2W
MR and functional MR alone. We investigate whether
increasing 18F-Choline PET scan acquisition time from 60
(PET-60) to 90 (PET-90) minutes improves GTV TVD.
Material and Methods
Analysis was performed on 9 18F-Choline PET scans.
Patients were injected with 370MBq of activity. Three
clinicians (C1, C2 and C3) independently and without
reference to each other contoured GTVs on each of the
T2W-MRI, PET-60 and PET-90 scans at differing times.
Scans were registered by a clinician using rigid co-
registration. The treating clinicians MRI contour was used
as a reference contour. The resulting PET and MRI GTVs
were transferred to the PET-60 and PET-90 scans after
image registration. The Dice Similarity Coefficient (DSC),
Specificity (Sp) and Sensitivity (S) were calculated from
contour mask voxel analysis.
Results
Table 1 shows the mean and range DSC, S and Sp scores on
MRI, PET-60 and PET-90 for C1, C2 and C3 in comparison
to the treating clinicians contour on MRI (C1). A 2 sampled
T-test (P < 0.01) showed, no significant difference in the
Sp, S and DSC between GTVs on PET-60 and PET-90 scans.
Further to this, as shown in Figure 1, variability in GTV
delineation is significant between observers in a singular
case as well as across imaging modalities.