933 / 1082
S917
ESTRO 36 2017
_______________________________________________________________________________________________
minutes and 2 minutes, respectively. Three x-ray energies
were used including 10MV, 25MV and 45MV. The radiation
dose ranged from 1.0Gy to 10.0Gy per treatment. The
dose distribution can be calculated from the activity
distribution of
11
C and
15
O.
Results
It was confirmed that no activity was detected at 10 MV
beam energy, which was far below the energy threshold
for photonuclear reactions. At 25 MV x-ray beams could
produce photonuclear reactions and activity distribution
images were observed on PET. But it needed much higher
radiation dose in order to obtain good quality images. For
45 MV photon beams, good quality activation images were
obtained with 2-3Gy radiation dose, which is the typical
daily dose for radiation therapy.
Conclusion
The PET image and the activity distribution of
15
O and
11
C
positron emitter nuclei could be used to derive the dose
distribution of 45MV x-ray irradiation at the regular daily
dose level. This method can potentially be used to verify
in situ dose distributions delivered to the patient using the
LA45 accelerator.
EP-1700 Prognostic value of FCH PET/CT in response
to radical radiotherapy for localized prostate cancer
M. Sepulcri
1
, L. Evangelista
2
, M. Fusella
3
, S. Galuppo
1
, L.
Corti
1
, G. Saladini
2
, M. Paiusco
3
1
Veneto Institute of Oncology IOV-IRCCS, Radiation
Oncology Unit, Padua, Italy
2
Veneto Institute of Oncology IOV-IRCCS, Nuclear
Medicine and Molecular Imaging Unit, Padua, Italy
3
Veneto Institute of Oncology IOV-IRCCS, Medical Physics
Unit, Padua, Italy
Purpose or Objective
To assess the value of FCH PET/CT in predicting the
outcome of patients with localized prostate cancer
treated by radical radiotherapy.
Material and Methods
From a mono-centric PET/CT database, we retrospectively
reviewed pre-treatment FCH PET/CT scans of 24 patients
who underwent radiotherapy for the treatment of
localized prostate cancer. For each study, SUVmax,
SUVavg and metabolic tumor volume (MTV) were
evaluated. Moreover, the value of PSA before
radiotherapy (PSAp) was recovered. Regarding radiation
therapy, all patients underwent to a radical treatment for
a total equivalent dose of 78-80 Gy, reached with a
standard fractionation (2 Gy/fraction) or with an
hypofractionated schedule (2.5 Gy/fraction). A follow-up
period after PET/CT scan, of at least one-year, was
required. In accordance with the observational period,
patients were classified as disease free (DF) if the increase
of PSA value after radiotherapy was less than 2 ng/mL
respect to PSA nadir value, conversely with an increase of
PSA higher than 2 ng/ml they were classified as recurrent
(not
disease free,
NDF).
A Kolgomorov-Smirnov test was used to compare the
distribution of semi-quantitative PET and PSA data of the
two
patient groups.
For all patients a simulated plan with a dose escalation on
intraprostatic dominant lesion (IDL) was made.
Results
Mean, minimum and maximum values of SUVmax, SUVavg,
MTV and PSAp were 9 (3.1-29.6), 4.2 (3.1-9.4), 13.3 (0.1-
49.1) and 18.3 ng/mL (4.5-88.7 ng/mL), respectively.
After one year of follow-up, 20 patients were considered
as DF and 4 patients were considered as NDF. The values
of DF patients were 8.2 (3.1-29.6), 3.9 (3.1-6.7), 11.6
(0.1-29.7) and 16 ng/mL (4.5-54.8 ng/mL) respectively for
SUVmax. SUVavg, MTV and PSAp. For NDF patients the
corresponding obtained values were 14.3 (8.7-22.7), 6.4
(3.8-9.4), 24.8 (7.1-49.1) and 33.7 ng/mL (8.7-88.7
ng/mL). In NDF patients, the mean values of SUVmax and
SUVavg were significantly higher than in DF group (both
p<0.05, fig.1) while MTV and PSAp were not statistically
different between the two groups. This data, in
accordance with the well known radiobiology of prostate
cancer, suggest to increase the dose to the tumor. The
analysis of OAR's DVH (bladder and rectum) showed that
there are no significant changes between the standard
treatment and the simultaneous integrated boost (SIB)
approach, reaching a total dose to IDL volume around 105
Gy.
Conclusion
High values of FCH SUV's in prostate cancer for patients
who are candidates to radiotherapy result predictive of
poor outcome after one year of follow-up. Therefore, the
SUV values could be useful to identify those patients who
could benefit from a boosted radiotherapy dose to the
intraprostatic dominant tumor lesion.
EP-1701 FDG-PET Background Definition in Rectal
Cancer Patients Using Differential Uptake Volume
Histograms
J. Schneider
1
, N. Tomic
1
, T. Vuong
1
, R. Lisbona
2
, M.
Hickeson
2
, G. Chaussé
2
, F. DeBlois
1
, J. Seuntjens
1
, S.
Devic
1
1
McGill University, Oncology, Montreal, Canada
2
McGill University, Diagnostic Radiology, Montreal,
Canada
Purpose or Objective
According to Erdi et al. [Cancer 1997;80:S2505-9] signal to
background ratio (S/B) reflects the activity specific for
local normal tissue, rather than making an assumption the
activity is uniformly distributed over the whole body and
recommended S/B as a quantity of choice for radiotherapy
target definitions. In the case of paired organs (lung) Devic
et al. [Int J Rad Oncol Biol Phys 2010; 78: 1555-62]
sampled background uptake in contra-lateral healthy lung
and scaled it by physical densities to obtain S/B for NSLC
patients.
Material and Methods
Differential uptake volume histogram (dUVH) method
[Devic et al. BJR 2016;89:20150388] was used on a group
of 20 rectal adenocarcinoma patients that received pre-
operative endorectal brachytherapy [Vuong et al, J Cont
Brachyther 2015;7:183-8]. All patients had PET/CT scan
prior to brachytherapy for staging purposes. Based on
post-surgery pathology results half of the patients had
complete response after brachytherapy (pT0) while the
other half had no or minimal response. Uptake values (in
Bq/ml) were sampled on PET images, using CT, and co-
registered PET/CT images (Fig.1 top) by placing the
sampling region of interest (ROI) over both tumor and
healthy rectal tissue, and at the same time by avoiding air
(gas) and feces.