Intra-individual comparison of p-[123I]-iodo-L-phenylalanine and L-3-[123I]-iodo-alpha-methyl-tyrosine for SPECT imaging of gliomas.
OBJECTIVE
Radioactive amino-acids accumulate in gliomas even with an intact blood-brain-barrier. L-3-[(123)I]-iodo-alpha-methyl-tyrosine (IMT) is well established for SPECT imaging of gliomas. Recently, we introduced p-[(123)I]-iodo-L-phenylalanine (IPA) for the characterisation of brain lesions. This study compares both tracers in glioma patients.


METHODS
Eleven patients with gliomas (1 WHO grade 1, 5 grade 2, 1 grade 3, 2 grade 4 gliomas, 1 unconfirmed upgrading and 1 post-therapeutic non-neoplastic lesion) underwent SPECT imaging with IPA (early and delayed acquisitions at 30 min and 3 h) and IMT (early only). Maximum tumour-to-brain ratios (TBR) were calculated using region-of-interest analysis to assess uptake of IMT and IPA. Imaging results were compared to histopathological findings.


RESULTS
Early TBRs of IMT and IPA were strongly correlated (r = 0.828, p = 0.002). TBRs were higher for IMT than IPA (1.95+/-0.50 versus 1.79+/-0.42; p < 0.05), but independent from tumour cell density (p > 0.1). Visual interpretation by different observers was more concordant for IMT-SPECT than IPA-SPECT (kappa 1.0 versus 0.774). No differences in early TBRs were observed between low-grade and high-grade gliomas for IMT (1.97+/-0.53 versus 2.21+/-0.44, p > 0.5) or IPA (1.70+/-0.23 versus 2.21+/-0.56, p = 0.167) with a trend to higher TBRs in low-grade tumours for IMT (p = 0.093). In contrast to the known wash-out of IMT, we observed persistent accumulation of IPA in gliomas.


CONCLUSIONS
IPA shows lower TBRs than IMT, especially in low-grade tumours, so IMT should be preferred for the delineation of low-grade gliomas by SPECT imaging. Due to its prolonged retention, however, IPA remains promising for therapeutic use in gliomas after labelling with I-131.
Hellwig
Dirk
D
Department of Nuclear Medicine, Saarland University Medical Center, 66421, Homburg, Germany. Dirk.Hellwig@uniklinik-saarland.de
Romeike
Bernd F M
BF
Ketter
Ralf
R
Moringlane
Jean R
JR
Kirsch
Carl-Martin
CM
Samnick
Samuel
S
D000328:Adult; D000368:Aged; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D002452:Cell Count; D005260:Female; D005910:Glioma / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008297:Male; D008781:Methyltyrosines / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics*; D008875:Middle Aged; D010649:Phenylalanine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D015899:Tomography, Emission-Computed, Single-Photon
D008781:Methyltyrosines; D019275:Radiopharmaceuticals; D010649:Phenylalanine; C030855:3-iodo-alpha-methyltyrosine; C049181:4-iodophenylalanine