PET and SPECT for detection of tumor progression in irradiated low-grade astrocytoma: a receiver-operating-characteristic analysis.
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-[(123)I]iodo-alpha-methyl-L-tyrosine (IMT) and (99m)Tc(I)-hexakis(2-methoxyisobutylisonitrile) (MIBI) and the PET tracer (18)F-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 (18)F-FDG PET and by (99m)Tc-MIBI and (123)I-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
(123)I-IMT yielded the best ROC characteristics and was the most accurate for classification, with an area under the ROC curve (A(z)) of 0.991. The A(z) of (18)F-FDG (0.947) was not significantly lower than that of (123)I-IMT. The difference in the A(z) of (99m)Tc-MIBI (0.713) from the A(z) of the other tracers used in our study was highly significant (P </= 0.01). (99m)Tc-MIBI SPECT was of low accuracy and, especially, of poor sensitivity even at modest specificity values.


CONCLUSIONS
(123)I-IMT SPECT imaging of amino acid transport accurately detects tumor progression in patients with irradiated LGA. In contrast to (123)I-IMT, (18)F-FDG PET was slightly less accurate for classification, and (99m)Tc-MIBI SPECT was of limited value. Imaging of amino acid transport with (123)I-IMT is a valuable additional tool for the follow-up of LGA, allowing early, noninvasive differentiation of lesions with ambiguous morphology after irradiation.
Henze
Marcus
M
Department of Nuclear Medicine, University of Heidelberg, Heidelberg, Germany. marcus.henze@med.uni-heidelberg.de
Mohammed
Ashour
A
Schlemmer
Heinz P
HP
Herfarth
Klaus K
KK
Hoffner
Simone
S
Haufe
Sabine
S
Mier
Walter
W
Eisenhut
Michael
M
Debus
Jürgen
J
Haberkorn
Uwe
U
D000328:Adult; D001254:Astrocytoma / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008781:Methyltyrosines; D009361:Neoplasm Invasiveness / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000517:prevention & control; D009364:Neoplasm Recurrence, Local / Q000175:diagnosis / Q000000981:diagnostic imaging*; D011182:Postoperative Care / Q000379:methods; D011237:Predictive Value of Tests; D012372:ROC Curve; D019275:Radiopharmaceuticals; D017256:Technetium Tc 99m Sestamibi; D014055:Tomography, Emission-Computed / Q000379:methods*; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods; D016896:Treatment Outcome
D008781:Methyltyrosines; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D017256:Technetium Tc 99m Sestamibi; C030855:3-iodo-alpha-methyltyrosine