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isodose overlay and gamma analysis. Pilot audits were
conducted at two radiotherapy centres.
Results
The end-to-end audit was performed for both IMRT and
VMAT treatments. Figure 1 shows the dose-area-histogram
for the film measurement plane, for the target and lung
OAR, for VMAT delivery at one centre, with and without
phantom motion. Dose received by 95% of the GTV area
was 263 cGy with the phantom static, 260 cGy with the
phantom moving, confirming an appropriate ITV planning
margin. Gamma analysis (3% global, 2mm, 20% cut-off)
between planned and measured dose had mean passing
rates of 98.3% with static phantom, 87.6% with moving
phantom. There was no significant difference between
IMRT and VMAT modes. Figure 2 shows an isodose
comparison between planned and measured doses for a
VMAT treatment. Motion blurring reduces the dose
gradient around the target in the direction of motion. The
95% isodose of the TPS plan covers the ITV, while the film
measured 95% isodose covers the GTV of the moving
phantom.
Conclusion
A novel, practical method for the dosimetric assessment
of motion management strategies in radiotherapy planning
and delivery has been designed and successfully piloted at
two radiotherapy centres using IMRT and VMAT, enabling
independent end-to-end dosimetry audit for mobile RT
targets. The results showed the local 4DCT treatment
planning approach was sufficient to deliver the required
dose to the moving target structure at treatment delivery,
and any adverse effects of MLC/gantry motion and target
motion interplay were not detrimental. Initially 12 centres
in the UK are being audited.
Poster Viewing : Session 5: Lung and breast
PV-0233 A Radiosensitivity Gene Signature &PD-L1
Predict Clinical Outcome of Breast Cancer in TCGA
dataset
B.S. Jang
1
, I.A. Kim
2
1
Seoul National University Graduate School of Medicine,
Department of Radiation Oncology, Seoul, Korea
Republic of
2
Seoul National University- School of Medicine,
Department of Radiation Oncology, Seoul, Korea
Republic of
Purpose or Objective
Radiosensitivity gene signature including 31 genes was
identified using microarray data of NCI-60 cancer cells,
however, has not been validated in independent datasets
for breast cancer patients. We investigated the link
between the radiosensitivity gene signature & PD-L1 and
clinical outcome in order to identify a group of intensifying
clinical benefit of radiotherapy (RT) combined with anti-
PD1/PD-L1 therapy.
Material and Methods
We validated an identified gene signature alleged to
radiosensitivity and analyzed PD-L1 status of invasive
breast cancer in The Cancer Genome Atlas (TCGA) dataset
using bioinformatic tools. First, we downloaded TCGA
breast carcinoma (BRCA) gene expression data sets of
1,215 samples achieved from the Illumina HiSeq 2000 RNA
Sequencing platform using UCSC Cancer Genomics
Browser. To validate gene signature of our interest, 1,065
patients (or samples) were divided into two clusters using
consensus clustering algorithm, then assigned
radiosensitive (RS) or radioresistant (RR) group according
to their prognosis. Patients were also stratified PD-L1 high
or PD-L1 low group by median value of CD274 mRNA
expression level as surrogates of PD-L1. Relationship
between RS/RR groups and PD-L1 status was also assessed,
visualized with heat maps, and their prognostic value was
evaluated by Kaplan-Meier analysis and Cox proportional
hazard models.
Results
Patents assigned to RS group had better 5-year
recurrence-free survival (RFS) rate compared with RR
group on univariate (89 % vs. 75 %, p-value = 0.017) only
when treated with radiotherapy. RS group was
independently associated with PD-L1 high group compared
with RR group, as well as CD274 expression was
significantly higher in RS group (p-value < 0.001). In a PD-
L1 high group, RS group had better 5-year RFS rate over
RR group (89 % vs. 72 %, p-value = 0.015), which was also
significant on multivariate analysis. The level of PD-L1
expression could represent immunogenicity of tumors, we
speculated that the PD-L1 high group had more
immunogenic tumors which should be more sensitive to
radiation-induced immunologic cell death.
Conclusion
We first validated the predictive value of radiosensitivity
gene signature following adjuvant RT in TCGA data set for
invasive breast cancer and also found a relationship with
this radiosensitivity gene signature and PD-L1.
Radiosensitivity gene signature and PD-L1 status were
important factors to predict a clinical outcome of RT in
patients with invasive breast cancer and could be used for
selecting patients who benefit from radiation therapy
combined with anti-PD1/PDL1 therapy.
PV-0234 SPECT-CT visualization of axillary lymph
nodes in breast cancer: the guide for radiotherapy
planning
S. Novikov
1
, P. Krzhivitskiy
2
, S. Kanaev
1
, P. Krivorotko
3
,
A. Artemeva
4
, E. Turkevich
4
1
Prof. N.N. Petrov Research Institute of Oncology,
Radiation Oncology, St. Petersburg, Russian Federation
2
Prof. N.N. Petrov Research Institute of Oncology,
Nucleear Medicine, St. Petersburg, Russian Federation
3
Prof. N.N. Petrov Research Institute of Oncology, Breast
Surgery, St. Petersburg, Russian Federation
4
Prof. N.N. Petrov Research Institute of Oncology,
Pathology, St. Petersburg, Russian Federation