ESTRO 36 Abstract Book

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S6 ESTRO 36 2017
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metastatic melanoma with excellent local control and
indications of systemic antitumor responses in a subset of
patients.
OC-0018 Chemoradiation-induced altered profile of
PD-L1 and CD8+ TILs indicated prognosis in rectal
cancer
Y.J. Lim1 , J. Koh2, S. Kim 2, S.R. Jeon3, E.K. Chie1, K.
Kim 4, G.H. Kang2, S.W. Han5, T.Y. Kim5, S.Y. Jeong6, K.J.
Park6, H.G. Wu1
1 Seoul National University Hospital, Radiation Oncology,
Seoul, Korea Republic of
2 Seoul National University Hospital, Pathology, Seoul,
Korea Republic of
3 Seoul National University, Cancer Research Institute,
Seoul, Korea Republic of
4 Ewha Womans University School of Medicine, Radiation
Oncology, Seoul, Korea Republic of
5 Seoul National University Hospital, Internal Medicine,
Seoul, Korea Republic of
6 Seoul National University Hospital, Surgery, Seoul,
Korea Republic of
Purpose or Objective Cytotoxic chemoradiotherapy
(CRT)-induced impact on the programmed death-1 (PD-1)/
programmed death-ligand 1 (PD-L1) checkpoint activity in
human cancers has not been much explored. This study
evaluated CRT-induced changes in the expression levels of
PD-L1 and CD8+ tumor-infiltrating lymphocytes (TILs) and
prognostic associations in rectal cancer.
Material and Methods We analyzed pre-CRT biopsies and
the corresponding post-CRT resected tissues of 123 rectal
cancer patients undergoing preoperative CRT followed by
surgery between 2005 and 2012. Immunohistochemical
staining of PD-L1 and CD8 was performed for the paired
specimens.
Results The median values of PD-L1 H-score and density
of CD8 + TILs for pre and post-CRT tissues were 0 and 100,
and 319.66 and 787.05 cells/mm2, respectively. CRT
induced increases in the expression levels of PD-L1 and
CD8 + TILs (P < 0.001 for both), and patients with sustained
high level of PD-L1 both at pre and post-CRT showed less
increase in the density of CD8 + TILs than the others (P =
0.020). Defining the low or high level of the PD-L1 and
CD8 + TILs before and after CRT, patients with high-to-high
level of PD-L1 had poorer overall survival (OS) and disease-
free interval (DFI) (P = 0.018 and 0.029, respectively),
whereas the low-to-low density of CD8+ TILs was
associated with inferior DFI (P = 0.010). Considering the
existence or non-existence of the high-to-high PD-L1 level
or low-to-low density of CD8 + TILs, patients with one or
more of the factors showed significantly worse OS and DFI
(P = 0.020 and 0.002, respectively).
Conclusion This study verified that preoperative CRT
resulted in the immunologic shift toward increases in the
PD-L1 expression and density of CD8+ TILs in rectal cancer.
The poor prognostic subset was identified based on the
CRT-induced change profiles, suggesting the potential
candidates who can benefit from combining checkpoint
inhibitors and CRT.
Joint symposium ESTRO-AAPM: New technological and
computational developments in particle therapy
SP-0019 Scaling down proton therapy facilities to fit
into photon vaults
T. Bortfeld1, S. Yan 1, B. Clasie1
1 Mass. General Hospital, Radiation Oncology, Boston-
MA, USA
Proton therapy technology is rapidly evolving. Newer
designs exhibit substantial reduction in size, weight and
cost compared to the first generation. In the first part of
this talk, we will review state of the art compact proton
therapy systems. We will focus particularly on single room
solutions and highlight the physics and technology behind
solutions that enable the size reduction of accelerator and
gantry designs.
In spite of the already achieved and remarkable progress
towards more compact and affordable proton therapy
systems, all current systems require construction of
dedicated buildings to house them which are significantly
larger (and more costly) than conventional treatment
rooms for photon therapy.
In the second part of this talk, we will explore the
potential to build even more compact proton systems. We
will first review a project that is underway at the
Massachusetts General Hospital where we retrofit a proton
therapy system into two neighboring photon vaults within
an existing building. The system is almost installed and
awaiting testing and commissioning. The progress and
challenges with this approach will be discussed.
Finally, we will give an outlook with possible designs that
enable a proton therapy system to be installed in a single
conventional photon therapy vault. We will discuss the
technical hurdles that need to be overcome to realize this
vision. These ultra-compact solutions will likely not
include a gantry but rather a fixed beamline with
advanced robotics and imaging solutions for patient
positioning.
SP-0020 Integrating CBCT in ion beam therapy:
challenges and opportunities beyond anatomical
guidance
K. Teo1
1Hospital of the University of Pennsylvania, Department
of Radiation Oncology TRC 2 West, Philadelphia- PA, USA
Cone beam CT (CBCT) is an important imaging modality
for image guided radiation therapy (IGRT). In ion
beam therapy, volumetric imaging offered by CBCT
has important potential applications beyond
anatomical guidance. Ion beam therapy dose distribution
is sensitive to daily setup variation, motion and
anatomical change such as tumor response,
atelectasis, pleural effusion, bowel gas and organ
filling. While CBCT may be used to assess these
variations in a qualitative manner, a more quantitative
analysis requires accurate Hounsfield units (HUs) for
conversion to ion stopping power. In this
presentation, the methods to improve the accuracy of
CBCT HUs are reviewed. These techniques will enable
water equivalent thickness (WET) measurements and dose
estimation to be performed using CBCT. We demonstrate
both qualitative and quantitative analyses of CBCT for
different treatment sites and discuss the development of
tools that will streamline adaptive proton therapy. These
include extraction of image and dosimetric features that
are predictive of the need for replanning as well as online
replanning tools.
SP-0021 New horizons in probabilistic and robust
treatment planning in particle therapy
M. Alber1
1Alber Markus, Department of Radiation Oncology,
Heidelberg, Germany
Treatment related uncertainties give rise to the risk of
loss in all quality scores of a treatment plan. Risk
mitigation strategies can be largely blind to the
magnitude and frequency of losses, and still be effective,
like the PTV concept in photon therapy. However, all risk
mitigation in one quality score comes at a price in most
others. In particular, risk mitigation of systematic errors
(by treatment planning) can be costly, ineffective and
even in the best case: unfair. For example, whenever a
protocol requires that a larger volume than the CTV is
irradiated because some patients need this, all other
patients pay the price. Ultimately, the precise