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S715
ESTRO 36
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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.
Conclusion
Compared to MRI delineated GTVs, 18F-Choline PET GTVs
are significantly different. This study found however that
increasing the PET scan acquisition time from 60 to 90
minutes did not improve the performance of GTV TVD in
comparison to MRI delineated GTV
.
EP-1334 Stereotactic radiotherapy with cyberknife®
system in localized prostate cancer
S. Falivene
1
, V. Borzillo
1
, R. Di Franco
1
, G. Totaro
1
, V.
Ravo
1
, G. Quarto
2
, D. Sorrentino
2
, S. Perdonà
2
, P. Muto
1
1
Istituto Nazionale Tumori Fondazione Pascale,
Radioterapia, Napoli, Italy
2
Istituto Nazionale Tumori Fondazione Pascale,
Uorologia, Napoli, Italy
Purpose or Objective
Hypofractionated stereotactic radiotherapy (SRT) is an
emerging technique in the treatment of localized prostate
carcinoma (LPC). Considering that α/β ratio prostate
cancer is very low (1.5), SRT is advantageous because
consent to deliver higher dose/fraction on target respect
conventional radiotherapy. In this study we reported our
initial experience with SRT using CyberKnife® System (CK)
in the treatment of LPC.
Material and Methods
From February 2013 to April 2016 ninety-six patients with
LPC, mean age 70,6 years, were treated with CK-SRT. All
patients were submitted to the eco-guided implants of 4
intraprostatic fiducial markers 7-10 days before the SRT in
order to follow, to detect and to correct the intrafraction
target movements. The fusion between CT scan and basal
RM was made in order to optimize the contouring for
treatment planning.
All patients were treated with SRT in 5 fractions of 7-7,25
Gy/fraction for a total dose of 35-36,25 Gy.
It was evaluated acute and late gastrointestinal and
genitourinary toxicity using RTOG scale, biochemical
control using mean decrease of PSA level during the
different phases of follow up.
In this study we have analyzed the results in the 77
patients with almost 3 months of follow up.
Results
All patients have completed CK SRT without severe
complication. Median follow up was 17 months. Three
patients died for non related cancer causes.
Gastrointestinal acute toxicity G2 for perineal pain and
rectal tenesmus was reported in only 13% and was
decreased in all patients. Genitourinary acute toxicity G2
for urgency and nicturia was reported in only 4% and G1
for dysuria in 61% of cases which persist in 27,3% of
patients. (Table 1)
All patients obtained biochemical response with decrease
of PSA. The PSA drop between the start of the therapy and
at 21 months of follow up, was significant with p<0,01
(p=0,00001)