ESTRO 36 Abstract Book

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S719 ESTRO 36 2017
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(figure 1).
Material and Methods
Twenty-five consecutive patients with T3-T4 prostatic
cancer were included for high-dose radiotherapy. Proton
and Carbon-ion treatment planning was performed by the
ROCOCO trial partners following a strict clinical protocol,
prescribing 78 Gy (biologically equivalent dose) to the
target and compared pair-wise to generated IMRT
treatment plans. All 75 plans were analysed centrally to
compare the dose in the rectum (the main organ at risk)
and the NTCP for late rectal bleeding.
A validated multi-factorial NTCP model used the mean
dose (Gy) in the rectum and the percentage of the rectum
receiving more than 75 Gy (V75) as dosimetric predictors.
It also included a set of clinical predictors such as
haemorrhoids and hormonal therapy. Results
An overview of the results is shown in table 1.
The mean dose in the rectum resulting from the IMRT,
proton and carbon-ion plans was 42.9 Gy [range: 30.8-47.2
Gy], 30.8 Gy [range: 23-45.2 Gy] and 18.9 Gy [range: 11.8-
33.3 Gy] respectively. The V75 for the IMRT, proton and
carbon-ion was 3.2% [range: 0.3-10.8 %], 2.1% [range: 0.5-
4.3 %] and 1.9% [range: 0.6-3.9 %] respectively. Both
proton and carbon-ion plans showed improvement with
respect to the IMRT plans in both dosimetric parameters,
and for carbon-ions it showed an improvement when
compared to protons.
The NTCP predicted for the IMRT, proton and carbon-ion
plans was 8.7% [range: 6-14.5 %], 6.7% [range: 5-9.2 %] and
5.7% [range: 4.7-7.2 %] respectively. On average these
treatments didn’t show large improvements in NTCP,
however, individuals with significant improvement were
identified. One patient showed that proton therapy would
lower the NTCP with 5.3%, and 4 patients showed that
carbon-ion therapy would lower the NTCP with 7.3, 5.2
and twice with 4.1%.
Conclusion
Particle therapy offers the opportunity to significantly
reduce the NTCP, but require decision support systems,
using multi-factorial prediction models and ultimately
including cost-effectiveness analyses to choose the
optimal treatment modality and justify the accompanying
increased costs.
EP-1356 SBRT benefit in oligometastatic prostate
cancer patients detected by [18F]fluoromethylcholine
PET/CT
E. Bouman-Wammes1, J.M. Van Dodewaard- de Jong 1, M.
Dahele2, M.C.F. Cysouw3, O.S. Hoekstra 3, A.H.M. Piet2,
A.J.M. Van den Eertwegh1, H.M.W. Verheul1, D.E. Oprea-
Lager3, V.M. H.4
1VU University Medical Center, Medical Oncology,
Amsterdam, The Netherlands
2VU University Medical Center, Radiotherapy,
Amsterdam, The Netherlands
3VU University Medical Center, Nuclear Medicine,
Amsterdam, The Netherlands
4VU University Medical Center, Urology, Amsterdam, The
Netherlands
Purpose or Objective
For patients with oligometastatic recurrence of prostate
cancer, stereotactic body radiation therapy (SBRT)
represents an attractive treatment option as it is generally
safe without major side effects. The aim of this study is to
investigate the impact of SBRT in postponing the start of
androgen deprivation therapy (ADT), and assessthe
pattern of recurrence post SBRT
Material and Methods
Forty-three patients treated with SBRT for oligometastatic
recurrence of prostate cancer were included. Also, a
control group of 20 patients not treated with SBRT was
identified from other hospitals. Data was retrospectively
collected and analyzed.
Results
A post-SBRT PSA response was seen in 29/43 patients
(67.4%), with undetectable PSA in 6/43 patients (14.0%).
The median ADT free survival (ADT-FS), defined as time
between the start of SBRT and start of ADT, was 15.6
months (95% CI 11.7-19.5) for the whole group, and 25.7
months (95% CI 9.0-42.4) for patients with an initial PSA
response.
Seven patients were treated with a second course of SBRT
because of oligometastatic disease recurrence; the ADT-
FS in this group was 32.1 months (95% CI 7.8-56.5).
We compared the data of SBRT-treated patients with a
group of 20 patients, managed in another hospital, by
watchfull waiting followed by ADT. Compared to the
control group, ADT-FS (from the date of first diagnosis of
metastasis until start of SBRT) was significantly longer for
SBRT treated patients with 17.3 months (95% CI 13.7-20.9)
versus 4.19 months (95% CI 0.0-9.0), p<0.001. Once ADT
had been started, the subsequent PFS during ADT
treatment was comparable between both groups (median
31.5 months for SBRT-treated patients, versus 26.9
months for the control group, p=0.54). This results in a
significanty longer period between the diagnosis of
oligometastatic disease and development of castration
resistant prostate cancer (see figure).
Seventeen patients had a [18F]fluoromethylcholine PET/CT
performed because of a rising PSA after the first course of
SBRT. In 15 patients the rise in PSA could be attributed to
lesions which were outside the high-dose SBRT volume, in
2 patients no cause was found, no local failures were
identified on these scans. One patient had progressive
disease in a previously non-suspicious 3mm lymph node
adjacent to the irradiated node. Another patient had
persistent disease in a partially irradiated lymph node
adjacent to the index node treated at first SBRT.
Seven patients (16.2%) had some form of toxicity recorded
in their medical chart: 2 of the patients with bone