499 / 1082
S484
ESTRO 36 2017
_______________________________________________________________________________________________
Conclusion
The post-treatment and response SUV
max
of the LNs were
found to be significant prognostic factors for regional
failure and OS in patients with locally advanced NSCLC
treated with hypofractionated CCRT. These parameters
might be useful in the selection of patients for additional
therapy.
PO-0889 FLT PET kinetic analysis biomarkers of
resistance to radiotherapy for nasal tumours in canines
U. Simoncic
1
, T.J. Bradshaw
2
, L. Kubicek
3
, L.J. Forrest
4
,
R. Jeraj
5
1
Jozef Stefan Institute, F-8, Ljubljana, Slovenia
2
University of Wisconsin, Department of Radiology,
Madison, USA
3
Angell Animal Medical Center, Angell Animal Medical
Center, Boston, USA
4
University of Wisconsin, Department of Surgical
Sciences- School of Veterinary Medicine, Madison, USA
5
University of Wisconsin, Department of Medical Physics,
Madison, USA
Purpose or Objective
Imaging biomarkers of resistance to radiotherapy are
prerequisite for precise treatment. Multiple imaging
biomarkers are typically provided by a separate multi-
tracer or multimodal imaging. This study assessed kinetic
analysis as a means to create multiple imaging biomarkers
of resistance to radiotherapy from a dynamic 3’-
(
18
F)fluoro-3’-deoxy-L-thymidine (FLT) positron emission
tomography (PET) scan.
Material and Methods
Sixteen canine cancer patients with spontaneous nasal
tumours were imaged dynamically with FLT PET before
and during the radiotherapy. Images were analysed for
kinetics on a voxel basis using a two tissue, four rate-
constant compartmental model. Overall parameter values
(mean and median over the region of intrests (ROI)) and
heterogeneity measures (coefficient of variation (COV),
ratio of interquartile range to median (IQR/median)) were
evaluated over the tumour gross target volume for the
transport (K
i
=K
1
k
3
/(k
2
+k
3
)), perfusion/permeability (K
1
)
and vascular fraction (V
b
) parametric images. Response
biomarkers were evaluated as a ratio of mid-therapy to
pre-therapy regional values, (i.e. mean, median, COV,
IQR/median). Alternative, spatial responses were
evaluated as a mean, median, COV or IQR/median taken
on a ratio of mid-therapy to pre-therapy prametric
images. The time to progression after radiotherapy (TTP)
was estimated by assessing the therapy response
according to the RECIST. Kaplan-Meier analysis and
univariate Cox proportional hazards (PH) regression were
used to assess the impact of each imaging biomarker on
the TTP.
Results
Pre- or mid-therapy overall
K
i
parameters were significant
predictors of TTP after the radiotherapy. However, many
imaging biomarkers based on
K
1
and
V
b
parameters had
higher predictive power for the radiation therapy
response. Table shows results of univariate Cox
proportional hazard regression for imaging biomarkers
derived from FLT PET parametric images. Hazard is
significantly increased for higher pre- or mid-therapy
overall
K
i
parameter values, higher or increasing pre- or
mid-therapy overall
K
1
parameter value, lower or
decreasing pre- or mid-therapy
K
1
spatial heterogeneity,
higher but decreasing pre- or mid-therapy overall
V
b
parameter value, and lower pre-therapy
V
b
spatial
heterogeneity.
Figure shows selected results of Kaplan-Meier analyses
that illustrates prognostic power of some imaging
biomarkers based on FLT PET parametric images.
Conclusion
Worse outcome after radiotherapy was significantly
associated with higher pre- or mid-therapy overall K
i
.
Additionally, we found that various imaging biomarkers
derived from vascular parameters or their change through
the therapy, contains even stronger prognostic
information than the FLT transport parameter, which
justify use of kinetic analysis.
PO-0890 PET-based radiobiological modeling of changes
in tumor hypoxia during chemoradiotherapy
M. Crispin Ortuzar
1
, M. Grkovski
1
, B.J. Beattie
1
, N.Y.
Lee
2
, N. Riaz
2
, J.L. Humm
1
, J. Jeong
1
, A. Fontanella
1
,
J.O. Deasy
1
1
Memorial Sloan Kettering Cancer Center, Medical
Physics, New York, USA
2
Memorial Sloan Kettering Cancer Center, Radiation
Oncology, New York, USA
Purpose or Objective
To develop a mechanistic radiobiological model of tumor
control probability (TCP) for predicting changes in tumor
hypoxia during chemoradiotherapy, based on pre-
treatment imaging of perfusion and hypoxia with
18
F-
Fluoromisonidazole (FMISO) dynamic PET and of glucose
metabolism with
18
F-Fluorodeoxyglucose (FDG) PET.