ESTRO 36 Abstract Book

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S903 ESTRO 36 2017
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the repeatability of semi-automatic contouring was also
tested.
Results
A total of 73 TA were extracted on each contour. A strong
disagreement was found between automatic SUVmax
threshold contours and manual or semi-automatic
contours in terms of both DICE and TA agreement (9/73 TA
for HNC and 10/73 for pancreas pts with p-
value>0.05,Figure 2). Instead, both the inter-observer as
well as the agreement between manual and semi-
automatic contour was relatively high, for both volume
(median DICE=0.71,range=0.36-0.96) and TA extraction
(72/73 with p-value>0.05 for both HNC and pancreas pts).
A high intra-observer agreement and a high contour
repeatability were found for manual contours (median
DICE=0.75,range:0.13-0.92) and for the semi-automatic
method for lesions with high uptake values (median
DICE=0.95,range=0.42-1.00). No statistically significant
difference was found among scanners (p-value=0.12).
Conclusion
Almost the totality of the selected radiomic features were
sufficiently robust against the delineation when using
manual and semi-automatic methods, while threshold
based methods resulted to be less robust. The satisfactory
results with a semi-automatic PET contouring method
suggests, for the two clinically situations considered in
this work, possible promising applications for consistent
and fast textural feature extraction in multi-centric
studies.
EP-1679 Preliminary functional imaging study on an
integrated 1.5T MR-Linac machine
M. Kadbi1, Y. Ding2, J. Wang2, C.D. Fuller3
1 Philips, MR Therapy, Gainesville, USA
2 MD Anderson, Department of Radiation Physics,
Houston, USA
3 MD Anderson, Department of Radiation Oncology,
Houston, USA
Purpose or Objective
Diffusion-weighted imaging (DWI) is a promising technique
in MR guided radiotherapy (MRgRT) to delineate the
tumor, predict response to induction chemotherapy,
response to radiation therapy, and has been demonstrated
as a biomarker of recurrence. This is the first attempt to
investigate the performance of DWI technique in an
integrated MR-Linac which combines Philips 1.5T MRI with
7 MV photon beam Elekta Linear accelerator
(Linac). Conventional EPI-based DWI was compared with
Spin-Echo (SE)-based DWI and geometrical distortion of
the sequences were benchmarked with CT images as
reference for geometric fidelity.
Material and Methods
Clinical single-shot EPI-DWI sequence is a rapid imaging
technique commonly used for functional imaging.
However, EPI techniques are very sensitive to hardware
and software imperfection (e.g. B0 inhomogeneity and
eddy current) as well as susceptibility effect causing
geometrical distortion. The system imperfection is more
problematic in MR-Linac with split magnet and less
homogeneous magnetic field compared to diagnostic MR
systems. SE DWI techniques can reduce the geometrical
distortion with the penalty of longer imaging time. Split
acquisition of fast spin-echo signals for diffusion imaging
(SPLICE) is a DWI technique combined with modified spin
echo approach in which is insensitive to the phase of the
magnetization.
A commercial DWI phantom designed by The Radiological
Society of North America Quantitative Imaging Alliance
(QIBA) with known Apparent Diffusion Coefficient (ADC) at
ice temperature was used in order to determine the
optimum ADC measurement sequence for future clinical
development. Use of the phantom also allows spatially
accurate assessment of geometric distortion compared to
CT images acquired using GE Discovery CT 750 HD with
Slice thickness of 1.25mm and Voxel size of
0.4883x0.4883x1.25 mm3
DWI imaging was performed using SS EPI (TR/TE =
10000/115 ms) and SS SPLICE (TR/TE = 10000/99 ms) with
voxel size = 1.72x1.72mm; slice thickness = 4mm; number
of slices=25; and b values = 0, 500, 900, 2000 s/mm2 .
Results
Qualitative assessment of the geometrical distortion
shows significant improvement using SPLICE-DWI against
EPI-DWI compared to CT images as shown in figure 1.
Quantitative ADC measurement revealed a consistency
between measured values using DWI-EPI sequence
acquired on Diagnostic MRI system and MR-Linac system in
room temperature. The measured values in room
temperature are about 33% larger than ADC values
measured in 0oC which is in agreement with our previous
experiments on diagnostic MRI systems. However, the
measured ADC values using SPLICE have larger variations
specifically in higher b-values.
Conclusion
The SPLICE DWI showed improved spatial fidelity
compared to EPI-DWI. This is particularly beneficial in
MRgRT due to importance of geometrical fidelity. The
SPLICE-DWI sequence needs further modifications and
calibrations to achieve more accurate ADC measurement.
EP-1680 Assessing tumour necrosis in lunvg cancer with
dual energy CT quantitative imaging
V. González-Pérez1, E. Arana2, J. Cruz3, M. Barrios2, F.
Blázquez 1, A. Bartrés4, L. Oliver1, V. Campo1, C. Bosó1, P.
Sanamaría 5, V. Crispín1
1Fundación Instituto Valenciano de Oncología, Servicio de
Radiofísica y Protección Radiológica, Valencia, Spain
2Fundación Instituto Valenciano de Oncología, Servicio de
Radiología, Valencia, Spain
3Fundación Instituto Valenciano de Oncología, Servicio de
Anatomía Patológica, Valencia, Spain
4Onkologikoa, Servicio de Radiofísica y Protección
Radiológica, San Sebastián, Spain