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distant brain failure, 41 % have been re-irradiated with
stereotactic radiotherapy for the additional lesions.
Radionecrosis occurred in 35 patients (18.8 %), at a
median time of 15 months (3,0 - 38,1) and was associated
with the infratentorial location of the metastasis (HR =
2.97 [1.47 - 6.01], p = 0.0025).
Conclusion
This study demonstrated the safety and efficacy of a 3 x
7.7 Gy HFSRT regimen for irradiation of cerebral
metastasis resection cavities. These results compare
favorably to historical data undergoing WBRT, SRS or
HFSRT. It is an alternative to adjuvant WBRT after surgery,
and allow the implementation of salvage therapies.
PO-0638 FET PET prior to primary RT of glioblastoma
patients - a recurrence pattern analysis
D.F. Fleischmann
1,3
, M. Unterrainer
2
, R. Schön
1
, S.
Corradini
1
, C. Maihöfer
1
, P. Bartenstein
2
, C. Belka
1,3
, N.L.
Albert
2
, M. Niyazi
1,3
1
LMU Munich, Radiation Oncology, Munich, Germany
2
LMU Munich, Nuclear Medicine, Munich, Germany
3
German Cancer Consortium (DKTK) German Cancer
Research Center (DKFZ) Heidelberg, Germany,
Purpose or Objective
18
F-fluoroethyltyrosine (FET) PET imaging for primary RT
treatment planning is of increasing importance. It remains
unclear if margin adjustment and reduction is possible
through additional FET PET imaging. Margins for FET PET
derived biological tumor volumes (BTVs) were compared
to MRI-based gross tumor volumes (GTVs) on a recurrence
pattern analysis.
Material and Methods
Treatment plans and clinical outcome of 36 glioblastoma
patients receiving FET PET scans before primary
radiotherapy were retrospectively analyzed. The minimal
margin including the entire tumor recurrence was
calculated for the GTV and a union of GTV and BTV with a
threshold of 1.6. Recurrence pattern analysis was
performed for the original PTV consisting of the clinical
target volume (CTV = GTV + 20 mm) and a 3 - 5 mm PTV
margin, the original 95-percent isodose, a synthetic PTV
derived from the GTV with a fixed 23 mm margin and a
union of GTV and BTV with a 18 mm margin. Treatment
planning was performed on OTP-Masterplan® and GTV
delineation was based on contrast-enhancing regions on
MRI or postoperative resection cavity, respectively.
Results
36 glioblastoma patients receiving FET PET before initial
RT were included in the recurrence pattern analysis.
Median age was 65.5 years and median KPS was 90 at the
beginning of RT. Median follow-up time from the start of
RT was 47 months, median overall survival 23 months and
median progression-free survival 7 months. The minimal
margin including the recurrent tumor was smaller for the
union of GTV and BTV (median 12.5 mm) than for the GTV
alone (median 17 mm) with statistical significance on
Wilcoxon-Test (p<0.001). Recurrence pattern analysis
revealed 33 (91.6%) central, 1 (2.8%) in-field, 1 (2.8%)
marginal, 1 (2.8%) ex-field recurrences for the original
PTV, 30 (83.3%) central, 3 (8.3%) in-field, 2 (5.6%)
marginal, 1 (2.8%) ex-field recurrence for the 95-percent
isodose line, 30 (83.3%) central, 4 (11.1%) in-field, 2 (5.6%)
ex-field recurrences for GTV with a 23 mm margin and 32
(88.8%) central, 2 (5.6%) in-field and 2 (5.6%) ex-field
recurrences for the union of GTV and BTV with a 18 mm
margin. The union of GTV and BTV with a 18 mm margin
was smaller than the GTV alone with a 23 mm margin
(p=0.053 in Wilcoxon-Test).
Conclusion
FET PET derived BTVs may reduce the minimal margin at
the primary RT of glioblastoma patients with an improved
delineation of biologically active tumor. The union of GTV
and BTV with 18 mm was smaller than GTV with a 23 mm
margin and had better results on recurrence pattern
analysis (which corresponds to a 15 mm CTV expansion).
These findings have to be prospectively validated.
PO-0639 Feasibility of tract based dosimetric analysis
in brain tumor patients
M. Conson
1
, L. Cella
2
, E. D'Ippolito
3
, F. Piccolo
3
, S.
Cocozza
3
, V. D'Avino
2
, R. Liuzzi
2
, M. Quarantelli
1
, R.
Pacelli
3
1
Intituto di Biostrutture e Bioimmagini, University of
Naples "Federico II"- Department of Diagnostic Imaging
and Radiation Oncology- Napoli- Italy, Napoli, Italy
2
Intituto di Biostrutture e Bioimmagini, National Council
of Research CNR, Napoli, Italy
3
Department of Advanced Biomedical Sciences,
University of Naples "Federico II"- Department of
Diagnostic Imaging and Radiation Oncology- Napoli- Italy,
Napoli, Italy
Purpose or Objective
Radiation induced white matter injuries are feared side
effects of brain irradiation that may cause cognitive
dysfunction. Diffusion tensor imaging (DTI) analysis is a
valid tool to evaluate white matter (WM) integrity. A
framework for the integrated analysis of tractographic and
dosimetric data in brain tumor patients undergoing
radiotherapy is proposed. The tool is able to
simultaneously measure in specific white matter tracts the
diffusion changes due to microstructural alterations and
the radiation dose.
Material and Methods
Ten consecutive patients affected by high grade glioma
were treated by conformal radiotherapy with multiple
non-coplanar 6 MV photon beams from a linear accelerator
with a total dose of 60 Gy in 30 daily fractions of 2
Gy. Two different time-points were planned for MRI
execution (before starting RT and one month after RT).
Each MRI study included, beside the DTI, three-
dimensional T1-weighted gradient-echo sequence
(MPRAGE) before and after i.v. injection of contrast
medium, as well as FLAIR and TSE-T2W images in the axial
plane. The MPRAGE and the TSE-T2W images were co-
registered with the
b0
image and were used for the
delineation of the area of parenchymal distortion
(deformed area, DA). The DA included the surgical cavity
and/or the area of contrast enhancement and/or the area
of abnormal signal on TSE-T2W images. Deterministic fiber
tracking across the whole WM was then performed using
the fiber assignment continuous tracking algorithm.
Fractional anisotropy (FA), radial diffusivity (RD) and axial
diffusivity (AD) maps were generated. A ROI-based
approach was used to select the fiber tracts. All fiber
tracts passing through the DA were excluded though
belonging to one of the three structures considered. The
fiber tracts were converted in DICOM-RT format. The
MPRAGE sequences without contrast medium were used as
reference images for the co-registration with the
corresponding planning CT-scan. The RT structure-set files
were transferred from the MRI-space into the planning CT-
space using the resulting co-registration matrix.
Superimposing the dose map from each patient, the
dosimetric evaluation was performed. The detailed
scheme of our framework is reported in Figure 1.