Current status of PET imaging in neuro-oncology

Abstract

Over the past decades, a variety of PET tracers have been used for the evaluation of patients with brain tumors. For clinical routine, the most important clinical indications for PET imaging in patients with brain tumors are the identification of neoplastic tissue including the delineation of tumor extent for the further diagnostic and therapeutic management (ie, biopsy, resection, or radiotherapy planning), the assessment of response to a certain anticancer therapy including its (predictive) effect on the patients' outcome and the differentiation of treatment-related changes (eg, pseudoprogression and radiation necrosis) from tumor progression at follow-up. To serve medical professionals of all disciplines involved in the diagnosis and care of patients with brain tumors, this review summarizes the value of PET imaging for the latter-mentioned 3 clinically relevant indications in patients with glioma, meningioma, and brain metastases.

Keywords: DOTATATE; DOTATOC; FDG; FDOPA; FET; FLT; MRI; positron emission tomography.

Fig. 1

A 70-year-old patient with an anaplastic astrocytoma. Contrast-enhanced MRI 31 months after radiation therapy suggests tumor progression. In contrast, O-(2-[¹⁸F]-fluoroethyl)-l-tyrosine (FET) PET shows only slight metabolic activity, and the time–activity curve shows a constantly increasing FET uptake, consistent with treatment-related changes. After a stereotactic biopsy, histological examination yielded signs of radiation-induced necrosis (hematoxylin and eosin staining, original magnification ×200; scale bar, 50 mm). Brain parenchyma shows reactive changes and blood vessels with thickened hyalinized walls (arrows; hematoxylin and eosin staining, original magnification ×100; scale bar, 1000 mm; reproduced from Galldiks et al., with permission from Oxford University Press).

Fig. 2

Postoperative contrast-enhanced MRI and DOTATATE PET/CT of a 32-year-old patient after resection of a World Health Organization grade I meningioma show residual tumor located at the left internal carotid artery and at tumor at the tip of the left orbit (A and D). Surprisingly, 2 additional meningiomas were also visible on the DOTATATE PET/CT (E and F), without corresponding contrast enhancement on MRI (B and, C) (reproduced from Galldiks et al., with permission from Oxford University Press).

Fig. 3

A 45-year-old female patient with a brain metastasis secondary to a v-Raf murine sarcoma viral oncogene homolog B (BRAF)-mutated malignant melanoma treated with dabrafenib and trametinib. Comparison of contrast-enhanced MR and O-(2-[¹⁸F]-fluoroethyl)-l-tyrosine (FET) PET images at baseline (left column) and follow-up 8 weeks later (right column). At follow-up, a clear decrease of the tumor/brain ratios (–35%) is observed, whereas the MRI shows no significant change of both the contrast enhancement and FLAIR signal defined as stable disease according to RANO criteria for brain metastases. The metabolic response was associated with an overall survival of 9 months after treatment initiation (reproduced from Galldiks et al., with permission from Oxford University Press).