To the Editor:
We read with great interest the recent article by Cornelius et al1 discussing the value of positron emission tomography (PET) imaging in intracranial meningiomas. The authors reviewed the role of the current PET tracers for meningiomas imaging. They suggested that PET holds promise for the preoperative grading of meningiomas and identifying aggressive tumor areas that should be resected, provides better tumor delineation, and allows the assessment of metabolic response to chemotherapy earlier than the volume response measured by magnetic resonance imaging. The authors also discussed some important PET limitations and concluded that this molecular imaging modality is promising for brain tumor management.
In addition to PET, single-photon emission computed tomography (SPECT) is a molecular imaging modality that has been used in nuclear medicine. The most important advantages of SPECT over PET are its lower cost and wider availability. Furthermore, some PET tracers have a short half-life, necessitating an onsite cyclotron for synthesis. SPECT tracers are stable, are readily available, do not require a cyclotron, and have a relative long half-life. On the other hand, PET imaging has a higher sensitivity and provides images of better resolution compared with SPECT.
Over the last years, we have investigated the brain tumor imaging properties of technetium-99m-tetrofosmin (99mTc-TF), a SPECT tracer routinely used for myocardial perfusion imaging. We demonstrated in vivo that, contrary to 99mTc-MIBI, an extensively studied SPECT tracer, 99mTc-TF uptake is not related to the multidrug-resistant phenotype of brain tumors. Thus, 99mTc-TF is superior for brain tumor imaging.2 Furthermore, compared with several PET tracers,99mTc-TF does not cross the intact blood-brain barrier. Consequently, brain lesions are readily identifiable, even if there is faint tracer uptake.
In our previous studies, we have shown that 99mTc- TF may accurately differentiate malignant from benign meningiomas. A lesion-to-normal uptake value of 9.6 was demonstrated as the optimal cutoff value thresholding the discrimination between the 2 groups, with 96% sensitivity and 100% specificity. In addition, the intensity of 99mTc-TF uptake correlated significant with meningioma aggressiveness as assessed by the Ki-67 index, the cell percentage on the S phase, and DNA ploidy.3,4
In conclusion, we believe that 99mTc-TF brain SPECT may offer a valuable alternative to PET imaging, especially in healthcare units without an onsite PET facility. Further well-designed comparative studies between 99mTc-TF and PET tracers are needed.
Alexiou, George A.; Tsiouris, Spyridon; Voulgaris, Spyridon; Kyritsis, Athanasios P.; Fotopoulos, Andreas D.
References1. Cornelius JF, Langen KJ, Stoffels G, Hänggi D, Sabel M, Steiger HJ. PET imaging of meningioma in clinical practice: review of literature and future directions [published online ahead of print October 11, 2011]. Neurosurgery. doi: 10.1227/NEU.0b013e31823bcd87.2. Alexiou GA, Goussia A, Kyritsis AP, et al.. Influence of glioma’s multidrug resistance phenotype on (99m) Tc-tetrofosmin uptake. Mol Imaging Biol. 2011;13(2):348–351.3. Fotopoulos AD, Alexiou GA, Goussia A, et al.. (99m)Tc-tetrofosmin brain SPECT in the assessment of meningiomas: correlation with histological grade and proliferation index. J Neurooncol. 2008;89(2):225–230.4. Alexiou GA, Vartholomatos G, Tsiouris S, et al.. Evaluation of meningioma aggressiveness by (99m)Tc-tetrofosmin SPECT. Clin Neurol Neurosurg. 2008;110(7):645–648.