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Characterization of 68Ga-DOTA-D-Phe1-Tyr3-Octreotide
Kinetics in Patients with Meningiomas
Henze M, Dimitrakopoulou-Strauss A, Milker-Zabel S, Schuhmacher J,
Strauss LG, Doll J, Macke HR, Eisenhut M, Debus J, Haberkorn U
Department of Nuclear Medicine, University of Heidelberg, Heidelberg,
Germany.
Because biopsy has a high risk of hemorrhage and the findings of CT and MRI
are often ambiguous, especially at the base of the skull, additional methods
for the characterization of intracranial tumors are needed.
Meningiomas show
high expression of the somatostatin receptor subtype 2 and thus offer the
possibility of receptor-targeted imaging.
We used the somatostatin analog
(68)Ga-DOTA-d-Phe(1)-Tyr(3)-octreotide (DOTA-TOC) labeled with the positron
emitter (68)Ga (half-life, 68 min), obtained from a (68)Ge/(68)Ga generator,
for PET of these tumors.
In contrast to (18)F-FDG, this ligand shows high
meningioma-to-background ratios.
The aim was to evaluate kinetic parameters
in meningiomas before radiotherapy.
Methods. Dynamic PET scans
(3-dimensional mode; 28 frames; ordered-subsets expectation maximization
reconstruction) were acquired for 21 patients (mean age +/- SD, 51 +/- 13 y)
before radiotherapy during the 60 min after intravenous injection of 156 +/-
29 MBq of (68)Ga-DOTA-TOC.
We analyzed 28 meningiomas (median grade [I]
according to the system of the World Health Organization) with volumes of at
least 0.5 mL (mean volume, 13.1 mL) and nasal mucosa as reference tissue,
showing a slight to moderate physiologic uptake.
For evaluation of the
(68)Ga-DOTA-TOC kinetics, the vascular fraction (vB) and the rate constants
(k1, k2, k3, and k4 [1/min]) were computed using a 2-tissue-compartment
model.
Furthermore, receptor binding (RB) (k1 - k1 x k2) and the ratios
k1/k2 and k3/k4 were calculated.
Results. Significant differences (P <
0.05; t test) between meningiomas and the reference tissue were found for
the mean standardized uptake value (10.5 vs.1.3), vB (0.42 vs. 0.11), k2
(0.12 vs. 0.56), k3 (0.024 vs. 0.060), k4 (0.004 vs. 0.080), and RB (0.49
vs. 0.13).
Although there was no significant difference for k1 (0.54 vs.
0.40), the ratios k1/k2 (4.50 vs. 0.71) and k3/k4 (6.00 vs. 0.75) were
markedly greater in meningiomas than in reference tissue.
Conclusion. The
high uptake of (68)Ga-DOTA-TOC in meningiomas can be explained by the high
values for vB and by the remarkably low values for k2 and k4, leading to
significantly greater k1/k2 and k3/k4 ratios and RB in meningiomas than in
reference tissue.
Thus, pharmacokinetic modeling offers a more detailed
analysis of biologic properties of meningiomas.
In further studies, these
data might serve as a basis for monitoring the somatostatin receptors of
meningiomas after radiotherapy.
PMID: 15872348 [PubMed - in process]
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