Neuro-Oncology Single-Photon Emission CT: A Current Overview

There is increasing need for noninvasive biomarkers for glioma treatment-response evaluation and for distinguishing tumor progression and recurrence from treatment-related changes. Here, SPECT, particularly ²⁰¹Tl SPECT, plays an important role. SPECT takes advantage of glioma cellular make-up. Specifically, Na⁺/K⁺ pump expression, mitochondrial attenuation, and amino acid transporter expression are probed with ²⁰¹Tl, ^99mTc-MIBI, and ¹²³IMT radiotracers respectively. ²⁰¹Tl can be used to distinguish brain tumors and nontumors and to determine brain tumor type and grade gliomas. However, it is especially valuable in the detection of tumor recurrence in patients treated with radiation therapy for supratentorial glioma. Similarly, ^99mTc-MIBI can be used to distinguish recurrence from treatment residua. ^99mTc-TF is comparable with ^99mTc-MIBI, and both may allow clear identification of tumor boundaries. ¹²³IMT appears to be superior to ^99mTc-MIBI in determining tumor recurrence and is particularly promising in detecting LGG recurrence. Additionally, ¹²³IMT shows promise in treatment planning where there is a survival advantage. LGGs frequently express somatostatin receptors; however, because radiolabeled somatostatin analogs do not cross the BBB and because LGGs frequently do not disturb the BBB, somatostatin-receptor imaging is limited in glioma imaging. Among the non-natural amino acid class, ¹²³IPA is not preferable to the more established ¹²³IMT. In summary, most international experience by using SPECT is with ²⁰¹Tl; however, other radiotracers are used with good effect in some clinics.