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S6

ESTRO 36 2017

_______________________________________________________________________________________________

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. Lim

1

, J. Koh

2

, S. Kim

2

, S.R. Jeon

3

, E.K. Chie

1

, K.

Kim

4

, G.H. Kang

2

, S.W. Han

5

, T.Y. Kim

5

, S.Y. Jeong

6

, K.J.

Park

6

, H.G. Wu

1

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/mm

2

, 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. Bortfeld

1

, S. Yan

1

, B. Clasie

1

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. Teo

1

1

Hospital 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. Alber

1

1

Alber 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