932 / 1096
S916
ESTRO 36
_______________________________________________________________________________________________
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 mm
3
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/mm
2
.
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 0
o
C 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-Pérez
1
, E. Arana
2
, J. Cruz
3
, M. Barrios
2
, F.
Blázquez
1
, A. Bartrés
4
, L. Oliver
1
, V. Campo
1
, C. Bosó
1
, P.
Sanamaría
5
, V. Crispín
1
1
Fundación Instituto Valenciano de Oncología, Servicio de
Radiofísica y Protección Radiológica, Valencia, Spain
2
Fundación Instituto Valenciano de Oncología, Servicio de
Radiología, Valencia, Spain
3
Fundación Instituto Valenciano de Oncología, Servicio de
Anatomía Patológica, Valencia, Spain
4
Onkologikoa, Servicio de Radiofísica y Protección
Radiológica, San Sebastián, Spain
5
Fundación Instituto Valenciano de Oncología, Servicio de
Radioterapia, Valencia, Spain
Purpose or Objective
To assess if dual energy computed tomography (DECT)
quantitative imaging can distinguish necrotic tumours in
lung cancer.
Material and Methods
From July 2013 to June 2016, 83 patients who underwent
a DECT study were reviewed for their lung tumour necrosis
status (33 positive; 50 negative).
Lesion size varied considerably: the mean lesion volume
was 15 cm
3
(range 0.05-138 cm
3
). Malignant lesions were
predominantly adenocarcinoma (77.1%), squamous cell
carcinoma (13.2%) and metastases (7.2%).
DECT examination was performed on a Discovery CT 750
HD scanner (GE Healthcare, WI, USA). Patients were
injected with 1.35 ml/kg of body weight of non-ionic
iodinated contrast material at 4 ml/s (Iopamidol, 300
mg/ml; Bracco, Italy). A Gemstone Spectral Imaging (GSI)
DECT exam of the entire chest was performed at arterial
phase.
Lesion volume was semi-automatically segmented using
Dexus lung nodule function (ADW4.6; GE Healthcare, USA)
by two radiologists. Images for quantitative iodine content
ρ
I
(mg/cm
3
) and effective atomic number (Z
eff
) were
reconstructed. Maximum, mean and standard deviation
values were recorded for both parameters and for
conventional HU image. Lesion volume and diameter were
also registered. Inter- and intra-observer intraclass
correlation coefficient (ICC) was studied.
Bilateral statistical analysis was performed using the
Mann-Whitney U test. Due to multiple comparisons,
Bonferroni adjustment was made and significance was set
at p < 0.007. Receiver operating characteristic (ROC)
curves were generated and diagnostic capability was
determined by calculating the area under the ROC curve
(AUC). The licensed statistical software package SPSS 20
(IBM, Somers, NY, USA) was used.
Results
Reproducibility of intraobserver lung lesion the ICC was
0.95 (CI 95% 0.80–0.98) and interobserver ICC was 0.92 (CI
95% 0.70–0.98).
The bivariate analysis for distinguishing necrotic from non-
necrotic lesions revealed statistically significant
differences. Larger lesions presented more necrosis than
smaller ones, as previously known in the literature. Values
for p, AUC and its 95% confidence level interval are shown
in
Table 1.
Box-whisker and ROC plots are displayed in Fig. 1 for mean
Z
eff
variable, which presented highest AUC (0.890). Mean