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PET
and SPECT for Detection of Tumor Progression in Irradiated Low-Grade
Astrocytoma: A Receiver-Operating-Characteristic Analysis
Marcus
Henze, MD, Ashour Mohammed, PhD, Heinz P. Schlemmer, MD, Klaus K.
Herfarth, MD, Simone Hoffner, MD, Sabine Haufe, MD, Walter Mier, PhD,
Michael Eisenhut, PhD, Jürgen Debus, MD, PhD and Uwe Haberkorn, MD
Department
of Nuclear Medicine, University of Heidelberg, Heidelberg, Germany
[M.H., A.M.. S.Ho., S.Ha., W.M., U.H.]. Clinical Cooperation Unit
Nuclear Medicine, German Cancer Research Center, Heidelberg, Germany
[M.H., S.Ho., U.H.]. Department of Diagnostic Radiology,
Eberhard-Karls University, Tübingen, Germany [H.P.S.]. Department of
Radiation Oncology, University of Heidelberg, Heidelberg, Germany
[K.K.H., J.D.]. Division of Radiochemistry and Radiopharmacology,
German Cancer Research Center, Heidelberg, Germany [M.E.].
Differentiation
between tumor progression and radiation necrosis is one of
the most difficult tasks in oncologic neuroradiology.
Functional imaging
of tumor metabolism can help with this task, but the choice
of tracer is still controversial.
This prospective
study following up irradiated low-grade astrocytoma (LGA) was,
to our knowledge, the first receiver-operating-characteristic
(ROC) analysis that intraindividually evaluated the diagnostic
performance of the SPECT tracers 3-[123I]iodo-α-methyl-L-tyrosine
(IMT) and 99mTc(I)-hexakis(2-methoxyisobutylisonitrile)
(MIBI) and the PET tracer 18F-FDG.
Methods.
We examined 17 patients, initially with histologically
proven LGA and treated by stereotactic radiotherapy, who
presented with new gadolinium-diethylenetriaminepentaacetic acid–enhancing
lesions (n = 26) on MRI.
At that time, MRI
could not differentiate between progressive tumor and nonprogressive
tumor.
This MRI
examination was closely followed by 18F-FDG PET
and by 99mTc-MIBI and 123I-IMT SPECT.
Lesions were
classified as progressive tumor (n = 17) or
nonprogressive tumor (n = 9) on the basis of
prospective follow-up (through clinical examination, MRI,
and proton MR spectroscopy) for 26.6 ± 6.6 mo after PET or
SPECT.
Results.
123I-IMT yielded the best ROC characteristics and
was the most accurate for classification, with an area under the
ROC curve (Az) of 0.991.
The Az
of 18F-FDG (0.947) was not significantly lower
than that of 123I-IMT.
The difference in
the Az of 99mTc-MIBI (0.713) from the Az
of the other tracers used in our study was highly
significant (P ≤0.01).
99mTc-MIBI
SPECT was of low accuracy and, especially, of poor sensitivity
even at modest specificity values.
Conclusion.
123I-IMT SPECT imaging of amino acid transport
accurately detects tumor progression in patients with
irradiated LGA.
In contrast to 123I-IMT,
18F-FDG PET was slightly less accurate for
classification, and 99mTc-MIBI SPECT was of
limited value.
Imaging of amino
acid transport with 123I-IMT is a valuable
additional tool for the follow-up of LGA, allowing early,
noninvasive differentiation of lesions with ambiguous
morphology after irradiation.
Key
Words: 18F-FDG, 3-123I-iodo-α-methyl-L-tyrosine,
99mTc(I)-hexakis(2-methoxyisobutylisonitrile), radiotherapy,
astrocytoma
©
2004 by Society
of Nuclear Medicine
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