ESTRO 36 Abstract Book

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S489 ESTRO 36 2017
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Conclusion
System-related GD was present in all 3T and 7T MR images
but remained within the 2mm tolerance limit. Near the
magnetic isocenter, 7T anatomical images showed no
difference in geometric reliability to 3T MR images.
Careful selection of 7T sequences and judicious use of GD
correction methods can warrant the geometrical quality
required for incorporation of 7T MR into image-guided
interventions
PO-0895 MRI-based analysis of volumetric changes of
healthy brain tissue in glioma patients after photon RT
A. Gommlich 1,2,3, H. Wahl4, F. Raschke2, M.
Baumann 1,2,3,5,6, M. Krause1,2,3,5,6, E.G.C. Troost1,2,3,5,6
1 Institute of Radiooncology, Helmholtz-Zentrum
Dresden-Rossendorf, Dresden, Germany
2 OncoRay - Center for Radiation Research in Oncology,
Translational and Clinical Radiation Oncology, Dresden,
Germany
3 NCT - National Center for Tumor Diseases- partnersite
Dresden- Germany, partnersite, Dresden, Germany
4 Institute of Neuroradiology- University Hospital Carl
Gustav Carus, Institute of Neuroradiology, Dresden,
Germany
5 University Hospital Carl Gustav Carus, Department of
Radiotherapy and Radiation Oncology, Dresden, Germany
6 DKTK - German Cancer Consortium, Partnersite,
Dresden, Germany
Purpose or Objective
State-of-the-art Linac-based photon beam irradiation
achieves highly conformal target volume coverage in
glioma patients, but is also known to cause side-effects to
surrounding tissues and organs. Apart from subjective
measures (e.g., questionnaires, function tests) objective
means to quantify tissue damage, e.g., anatomical or
functional magnetic resonance imaging (MRI) are urgently
needed to compare different treatment techniques and
beam qualities (e.g., protons vs. photons) and to develop
predictive measures for optimal sparing of normal brain
tissue. As initial part of our program for dose-dependent
spatial mapping of structural and functional radiation
induced brain damage, we assessed here a retrospectively
collected MRI-dataset in order to potentially detect
volumetric changes of the healthy brain tissue (gray and
white matter) in the non-affected hemisphere of glioma
patients treated with photon irradiation.
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. Scalco1, I. Pirovano1, T. Rancati2, A. Cicchetti2, F.
Palorini2, B. Avuzzi3, A. Messina4, R. Valdagni 2, (3), (5),
G. Rizzo1
1Istituto di Bioimmagini e Fisiologia M olecolare, CNR,
Segrate Milano, Italy
2Fondazione IRCCS Istituto Nazionale dei Tumori,
Prostate Cancer Program, Milano, Italy
3Fondazione IRCCS Istituto Nazionale dei Tumori,
Radiation Oncology 1, Milano, Italy
4Fondazione IRCCS Istituto Nazionale dei Tumori,
Radiology, Milano, Italy
5Università 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