IntensityModulated Tomotherapy with Stereotactic Radiosurgery for Brain Tumors: Validation of a supp

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Intensity-Modulated Tomotherapy with Stereotactic
Radiosurgery for Brain Tumors Validation of a
supplementary value of C11-Methionine-PET images
in treatment planning.
Masayuki Matsuo, Jun Shinoda, Kazuhiro
Miwa, Naoya Yamamoto, Hirofumi Asano, Shinji
Furukawa, Yutaka Takahashi, Iori Sumida, Takashi
Yamashita Jitsuhiro Yamada, Shigetoyo Saji
Department of Radiation Oncology, Neurosurgery
and Surgery Kizawa Memorial Hospital Department
of Neurosurgery, Chubu Medical Center Department
of Physics, Cancer Institute Hopsital
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Background
CT/MRI fusion technology is commonly used in
radiation treatment planning of brain tumors.
Recently the gross tumor volume (GTV) delineation
in brain tumors, based traditionally on computed
tomography (CT) and magnetic resonance imaging
(MRI), was improved in using biologic imaging
11C-methionine positron emission tomography
(MET-PET). The higher specificity and
sensitivity of MET-PET for brain tumors, in
comparison to anatomic imaging (CT and MRI), was
demonstrated in previous studies and is the
rationale for the integration of biologic imaging
in the radiation treatment planning.
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Purpose
The goal of our work is to evaluate the
feasibility of intracranial radiosurgery by means
of helical tomotherapy system (Hi-Art from
Tomotherapy Inc.) and to assess the
supplementary value of C11-Methionin-PET images
in treatment planning.
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Materials/Methods
Eight patients (4 malignant gliomas and 4 brain
metastases) with 17 brain tumors . Median age
was 58 years (range, 2978 years). Median
Karnofsky performance status (KPS) was 80
(range, 40100). CT, gadolinium enhanced
T1-weighted MRI and MET-PET were performed for
stereotactic radiosurgery treatment planning.
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Materials/Methods
These image sets (CT/MRI and CT/ MET-PET) were
then fused utilizing the Pinnacle System. CT/MRI
GTV (GTV1) was defined as the contrast-enhanced
area on CT/T1 gadolinium-MRI image fusion images
and CT/MET-PET GTV (GTV2) was defined as the area
of an accumulation of CT/ MET-PET apparently
higher than that of normal tissue on CT/ MET-PET
fusion images. The planning target volume (PTV)
encompassed the GTV plus 2-mm margin. The initial
PTV was prescribed a dose of 20 Gy.
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Materials/Methods
This dose was prescribed to the 95 isodose line,
which covered the PTV. Stereotactic radiosurgery
was performed with the helical tomotherapy system
and an adapted 6 MV linear accelerator. Precise
and reproducible patient immobilization was
achieved with a thermoplastic mask. GTV, PTV and
Homogeneity Index were assessed, and compared
CT/MR fusion plan to CT/MET-PET fusion plan using
dose statistics, dosevolume histograms (DVH),
and the Radiation Therapy Oncology Group (RTOG)
stereotactic radiosurgery criteria.
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Results
mean
range
Standard deviation
GTV1
15.1cc
0.2 54.9cc
16.1cc
PTV1
27.1cc
1.1 88.0cc
25.1cc
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Results
mean
range
Standard deviation
GTV2
17.9cc
0 62.2cc
19.1cc
PTV2
31.1cc
0 105.0cc
31.6cc
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Results
mean
number
GTV1 gt GTV2
9.2cc 1.9cc
1
GTV1 GTV2
6.2cc
0.5 18.1cc
3
GTV1 GTV2
17.9cc 22.9cc
3.1 54.9cc 4.6 62.2cc
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GTV1 lt GTV2
GTV1 GTV2
0.2cc
0.1 0.3cc
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GTV2 could not show the tumor
GTV1
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Tumor on CT/MET-PET was larger than CT/MR plan.
CT
MRI
PET
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Tumor on CT/MET-PET fusion plan could not be
detected.
CT
MRI
PET
Tumor volume 0.3cm3
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Tumor that was radiation necrosis on CT/MET-PET
was smaller than CT/MR plan.
Radiation necrosis
CT
MRI
PET
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Results
Homogenity Index
Conformity Index
CT/MRI plan
106
95
CT/PET plan
107
95
RTOG clinical setting
Maximum isodose in the target
Homogenity Index
Reference isodose
Lesion volumes covered by the reference isodose
Conformity Index
Target volume
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CT/MRI plan
CT/PET plan
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Conclusion
CT/MET-PET volumes were, in general, only
slightly larger than the CT/MRI volumes.
However, a few patients had a marked difference.
Regardless of the size of the target, both
Homogenity Index and Conformity Index were good.
We recommend CT/MET-PET fusion planning in
irradiation to facilitate normal tissue sparing
and toxicity reduction on one hand and to
decrease the likelihood of geographical misses
in target volume definition on the other hand.
This study also show that intracranial
radiosurgery by means of helical tomotherapy
system is feasible.