ESTRO 36 Abstract Book

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S608 ESTRO 36 2017
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Conclusion
The presence of oligodendroglial features and IDH 1
mutation in patients underwent complete surgical
resection allowed to identify a subgroup with better
outcome in which radiation therapy can be delayed at
disease progression.
EP-1122 TSPO PET imaging RT treatment planning in
malignant glioma
D.F. Fleischmann1,3, N.L. Albert2, M. Unterrainer2, P.
Bartenstein2, C. Belka1,3 , M. Niyazi1,3
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
TSPO PET imaging has been recently hypothesized to
accurately display biologically active tumor in high-grade
glioma patients and is of major interest for radiotherapy
(RT) treatment planning. Biological tumor volumes (BTVs)
with different thresholds were analyzed retrospectively
for their concordance with MRI-based gross tumor volumes
(GTVs).
Material and Methods
TSPO PET images of 12 patients were retrospectively
analyzed. Eleven GBM patients and one patient with
anaplastic astrocytoma (IDH wt) were included into the
analyses. Five patients underwent primary definitive
radiochemotherapy (RCx) with temozolomide, three
patients hypofractionated RT and four patients re-
irradiation at HGG recurrence. Median dose was 2 to 60 Gy
for primary RCx, 2.67 to 40.05 Gy for hypofractionated RT
and 2.4/2 Gy to 43.2/36 Gy (three patients) with SIB or 2
to 36 Gy (one patient due to a very large recurrence) at
re-irradiation with concomitant bevacizumab.
Results
Different BTV thresholds were tested, BTV1.6, BTV1.8 or
BTV2.0. As per definition, BTV1.6 was largest (86.5 cc >
72.3 cc > 59.3 cc). Median PTV volume was 341.8 cc
(primary RCx) or 82.2 cc (PTV36) and 34.9 cc (PTV43.2).
The Sorensen-DICE coefficient of BTVs vs. GTV (solely MRI-
based) was 0.48 (BTV1.6), 0.54 (BTV1.8) or 0.58 (BTV2.0).
Volumetric comparisons revealed significantly larger BTVs
in comparison to the median GTV volume of 29.4 cc
(respectively p=0.002/0.003/0.008, paired Wilcoxon
tests). It was tested whether the BTV volume was included
within the PTV (60 Gy) or PTV36/43.2. For this purpose,
the amount of BTV included within the PTV was calculated
as (BTV∩PTV)/BTV. For a threshold of 1.6, the amount was
median 0.99 in primary GBM and median 0.70 for PTV36
(four patients) and 0.43 for PTV43.2 (three patients). At a
threshold of 1.8, the corresponding values were 0.996,
0.80 and 0.60, and at a threshold of 2.0, the values were
0.997, 0.88 and 0.71.
Conclusion
TSPO PET imaging seems to be a very interesting approach
for GBM delineation at primary RT and re-RT. GTV and BTV
concordance was poor, but almost the whole BTV content
was included within the primary PTV (60 Gy). TSPO might
have a high relevance for re-irradiation as margins are far
tighter than for primary GBM (8 mm added to the GTV for
PTV36, 3 mm for the PTV43.2 as SIB). Future studies on
recurrence patterns are warranted to analyze the initial
tumor coverage of the boost volume.
EP-1123 To contour or not contour hippocampus in
stereotactic brain radiotherapy? A dosimetric study.
C. Di Carlo1, S. Di Biase1, L. Caravatta1, G. Caponigro1, C.
Rosa1, M. Di Biase 1, F. Perrotti1, M. Trignani1, A.
Vinciguerra1, A. Augurio1, S. Giancaterino1, A. De Nicola1,
M.D. Falco1, D. Genovesi1
1 Ospedale Clinicizzato S.S. Annunziata, Radiotherapy,
Chieti, Italy
Purpose or Objective
To evaluate hippocampal irradiation in patients treated
with fractionated stereotactic brain radiotherapy (FSRT).
Material and Methods
We performed a dosimetric analysis on 22 patients with 1-
4 brain metastases treated with 24 Gy/3 fractions or 20
Gy/4 fractions using volumetric intensity-modulated arc
therapy (VMAT). Original plans did not include
hippocampus as a structure to avoide in optimization
criteria. All cases were then retrospectively replanned for
the VMAT planning hippocampus-spared study.
Hippocampus was delineated on diagnostic T1-weighted
Magnetic Resonance images (MRI) co-registered with
planning computed tomography (CT) images. A planning
risk volume (PRV) for hippocampus sparing was generated
adding an isotropic 5 mm margin. Hippocampus was
defined both as a single (Hu) and as pair organ (Hdx, Hsn).
Delineation was performed using RTOG atlas as reference
than revised by neuroradiologist. Assuming an α/β ratio of
2 Gy, biologically equivalent dose in 2 Gy fractions (EQD2)
was calculated. Constraints analyzed were: Dmax<16 Gy,
D40%<7.3 Gy, D100%=Dmin<9 Gy. In addition, neurological
status (NS) was investigated at baseline and during follow-
up and memory or other neurologic deficit were evaluated
by CTACE 4.0 scale.
Results
Among constraints analyzed, Dmax and D40% have been
exceeded in 10/22 cases (20 Gy in 6 cases, 24 Gy in 4),
whereas D100% was respected in all cases. Hu Dmax
ranged between 17-58.9 Gy, with a mean of 31.1 Gy.D40%
ranged between 8.9-13.7 Gy and mean D40% was 11.4 Gy.
PRV Hu showed a mean Dmax of 33.2 Gy (range 21.5-60.5
Gy) and a mean D40% of 10.8 Gy (7.7-13.7 Gy). When
considered as pair organ, Hdx and Hsn respectively, mean
Dmax was 33.2 Gy (range 17-58.9 Gy) and 18.4 Gy (range
16.5-20.9 Gy), while mean D40% was 17.5 Gy (7.6-44.2 Gy)
and 10.7 Gy (range 8.2-14.3 Gy). PRV Hdx received a mean
Dmax of 35.5 Gy (range 23.4-60.5 Gy) and mean D40% was
15.9 Gy (7.5-36.4 Gy); PRV Hsn received a mean Dmax of
22.6 Gy (range 16-28.7 Gy) and a mean D40% of 9.9 Gy
(8.7-12.4 Gy). At 3-months follow-up, at least, 14/22
patients were clinically evaluable; NS was investigated in
9/14 patients while missed in 5/14. Neurological deficits
occurred in 4/9 patients and 3 of these presented Dmax
and D40% exceeding limit.
Conclusion
Our data showed that hippocampus might be often over-
irradiated if not considered in the optimization of the
treatment plan in brain FSRT. Hippocampal delineation
should be performed especially in case of good life
expectation where its saving could be reasonable avoiding
relevant damage.
EP-1124 PET-MRI prior to re-irradiation of high-grade
glioma patients - a planning study
D.F. Fleischmann1,3 , M. Unterrainer2, S. Corradini1, M.
Rottler1, P. Bartenstein2, C. Belka1,3, N.L. Albert2, M.
Niyazi1,3
1LMU Munich, Radiation Oncology, Munich, Germany
2LMU Munich, Nuclear Medicine, Munich, Germany
3German Cancer Consortium (DKTK) German Cancer
Research Center (DKFZ) Heidelberg, Germany,
Purpose or Objective
Imaging of positron emission tomography (PET) combined
with MRI was conducted prior to re-irradiation for 7 high-
grade glioma patients. MRI-based treatment planning of
three independent raters was compared with biological
tumor volumes (BTVs) automatically generated from PET-
MRI data in this prospective phase I clinical trial
(NCT01579253).
Material and Methods
MRI-based treatment plans for 7 high-grade glioma
patients with PET-MR imaging preceding re-irradiation
were created by three independent raters including all