509 / 1096
S494
ESTRO 36
_______________________________________________________________________________________________
Material and Methods
Structural MRI-scans (T1-weighted) from 18 glioma
patients (grade II and III), who underwent high dose
radio(chemo)therapy (54-60 Gy) with curative intent have
been analyzed. MRIs were acquired before treatment and
at several time intervals thereafter. Because of the
individual characteristics of these data e.g., voxel size
(0.5…6 mm³) and the field strength (1…3 T) a standardized
image processing approach was developed. For bias field
correction, registration with atlas data, resampling, and
segmentation of different tissue types, image processing
methods from the ANTs-, FSL- and SPM-toolbox were used,
respectively. Based on these images the volumes of white
matter and gray matter have been longitudinally
analyzed.
Results
Figure 1 shows the changes of brain tissue volume
depicted as box plots with the median values highlighted
in red. While the entire brain volume on average remains
constant over two years after therapy, in the same time
period the volume of gray matter and white matter varies
conversely in a wide range. Noteworthy, this work points
out the difficulties of retrospectively analyzing clinically
acquired data due to differences in acquisition parameters
and in investigation intervals.
Conclusion
The observed changes over time underpin the importance
of exact follow-up protocols in quantitative e valuation of
structural brain changes after radiotherapy. Together with
the data on interpatient heterogeneity, our findings
allowed to design a prospective study in a larger cohort of
patients treated by photons vs. protons for assessing the
dependence of MRI-detected volumetric changes with
delivered dose.
PO-0896 Quantitative MRI-based characterization of
obturator muscles after prostate cancer radiotherapy
E. Scalco
1
, I. Pirovano
1
, T. Rancati
2
, A. Cicchetti
2
, F.
Palorini
2
, B. Avuzzi
3
, A. Messina
4
, R. Valdagni
2
, (3), (5),
G. Rizzo
1
1
Istituto di Bioimmagini e Fisiologia M olecolare, CNR,
Segrate Milano, Italy
2
Fondazione IRCCS Istituto Nazionale dei Tumori,
Prostate Cancer Program, Milano, Italy
3
Fondazione IRCCS Istituto Nazionale dei Tumori,
Radiation Oncology 1, Milano, Italy
4
Fondazione IRCCS Istituto Nazionale dei Tumori,
Radiology, Milano, Italy
5
Università di Milano, Department of Oncology and
Hemato-oncology, Milano, Italy
Purpose or Objective
To investigate radiation-induced alterations in
periprostatic muscles, such as internal obturators, in
prostate cancer patients treated with external-beam
radiotherapy (RT). These tissues are usually included in
the high dose radiation field and can be involved in genito-
urinary toxicity. In this work, a texture analysis for
quantitative
image-based
structural
tissue
characterization was performed.
Material and Methods
T2-weighted and T1-weighted MRI after contrast agent
(CA) injection at 1.5T were acquired in thirteen patients
before RT (MRI1) and at about 12 months of follow-up
(MRI2). In order to reduce possible errors due to non-
quantitative values of signal intensity, a normalization
step was performed between MRI1 and MRI2 of each
patient, using a histogram matching method.
Right and left internal obturator muscle contours were
manually delineated upon T2w MRI1 by an expert and then
automatically propagated on MRI2 by an elastic
registration method.
The following textural features were extracted in each
volume: histogram-based indices (mean intensity,
variance, 95
th
percentile, entropy, skewness, kurtosis),
GLCM (Grey-Level Co-occurrence Matrix)-based indices
(energy, correlation, homogeneity, entropy, contrast,
dissimilarity), NGTDM (Neighborhood Grey-Tone Different
Matrix)-based indices (coarseness, contrast, busyness,
complexity, strength) and fractal dimension.
To assess changes in internal obturator muscles, a
comparison of the parameters extract on MRI1 and MRI2
was carried out by Wilcoxon test, with significant p-value
< 0.05.
Results
Exemplificative T1w MRI1 and MRI2 with relative muscles
histograms were shown in Figure 1.
From a qualitative
assessment, a homogenous higher enhanced area (red
circle in Figure 1) was localized in MRI2 in a region near
the prostate.
Quantitatively, significant increase in mean, variance and
95
th
percentile values on both T1w MRI and T2w MRI2 was
also found, as well as variation of indices describing
histogram shape as visible by the histograms reported in
Figure 1.
Moreover, changes of GLCM and NGTDM-based indices
confirmed that the spatial distribution of this intensity
enhancement was concentrated in a homogeneous local
area, as suggested by increased homogeneity and
correlation indices and decreased complexity and fractal
dimension (Table 1).