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S695
ESTRO 36 2017
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Abbreviations,
Pre-CT; pre-radiotherapy computed tomography;
Pre-RT, baseline Magnetic Resonance Imaging (MRI);
Mid-RT, MR image at mid-point of the radiotherapy course
(about
38
Gy);
Post-RT, MR image at completion of the radiotherapy
course.
Results
There was no significant difference between the
estimated sizes of prostate during RT in all phases.
A retreatment plan was well implemented in all patients.
Conclusion
In this study, no significant change in prostate size was
observed during the course of IMRT. On revising the
radiation plan according to change in prostate size, no
significant difference with respect to clinical outcomes
associated with the use of a revised plan was observed.
The mean prostate volume in our study population was 37
cc. The relatively smaller prostate may have led to this
result.
EP-1310 68Ga-PSMA-PET/CT imaging of localized
prostate cancer patients for IMRT with integrated
boost
L. Thomas
1
, S. Kantz
2
, A. Hung
1
, D. Monaco
1
, M. Essler
3
,
H. Strunk
4
, C. Thomas
1
, W. Laub
1
, R. Bundschuh
3
1
Oregon Health & Science University, Department of
Radiation Oncology, Portland, USA
2
LMU Klinikum der Universität München, Klinik und
Poliklinik für Strahlentherapie und Radioonkologie,
Munich, Germany
3
Universitaetsklinikum Bonn, Nuklearmedizinische Klinik
und Poliklinik für Nuklearmedizin, Bonn, Germany
4
Universitaetsklinikum Bonn, Radiologische Klinik, Bonn,
Germany
Purpose or Objective
The purpose of our study was to show the potential
benefits of using
68
Ga-PSMA-PET/CT imaging for integrated
boost treatment planning or boost only treatment planning
of prostate cancer patients. The potential gain of such an
approach is the improvement of tumour control and
reduction of the dose to organs at risk at the same time.
Material and Methods
21 prostate cancer patients (70yrs average) without
previous local therapy received
68
Ga-PSMA-PET/CT
imaging. Body contour and organs at risk were manually
defined on the obtained datasets. A PTV70 and PTV5920
were defined as planning target volumes. A PET active
volume GTV_PET was segmented with a 40% of the
maximum activity uptake in the lesion as threshold. Five
different treatment plan variations were calculated for
each patient (Monaco, Version 5.11.00, Elekta, St. Louis,
MO) – Table 1. Analysis of derived treatment plans was
done according to QUANTEC with in-house developed
software. TCP (Tumor Control Probability) and NTCP
(Normal Tissue Complication Probability) was calculated
for
Prostate
and
ProstatePET
(TCP) as well as Rectum and
bladder (NTCP). Student’s t-test method was applied for
statistical analysis (paired, two-sided). A p level of smaller
0.05 was considered to be statistically significant.
Results
The median TCP of the PET-positive volume was found to
be (89.9 ± 2.7) % for conventional
Prostate
plans.
Comparing the
conventional plans to the plans with
integrated boost and plans just treating the PET-positive
tumor volume, we found that the TCP increased to (95.2
± 0.5) % for an integrated boost with 75.6 Gy, (98.1 ±
0.3) % for an integrated boost with 80 Gy, (94.7 ± 0.8) %
for treatment of the PET-positive volume with 75 Gy,
and
to (99.4 ± 0.1) % for treating the PET-positive volume
with 95 Gy (all p < 0.0001). For the integrated boost with
80 Gy, a statistically significant, but moderate increase
of the median NTCP of the rectum was found. Only
patients with a tumour directly adjacent to the rectum
wall were found to have a significantly higher NTCP
rectum
.
At the same time of course, these patient’s median TCP
of the PET-positive volume was found to be significantly
improved as well, if compared to TCPs of conventional
plans. For all other plan variations no statistical
significant increase of the rectum or bladder NTCP was
found.
Conclusion
Our study demonstrates that the use of
68
Ga-PSMA-PET/CT
image information would allow for more individualized
prostate treatment planning and better targeting of active
tumour volumes. TCP values of identified active tumour
volumes can be increased, while rectum and bladder NTCP
values either remain the same or are even lower for most
plans. Clinical studies should be performed to confirm the
theoretical benefits of PET target optimized prostate
cancer treatment planning.
EP-1311 Beyond IMRT for Prostate Cancer: The Effect
of Modern Technique on Treatment Quality and
Outcome
J. Kao
1
, A. Zucker
1
, J. Timmins
1
, A. Wong
1
, A. Woodall
2
,
E. Loizides
2
1
Good Samaritan Hospital Medical Center, Radiation
Oncology, West Islip, USA