Brain tumors

Abstract

This review addresses the specific contributions of nuclear medicine techniques, and especially positron emission tomography (PET), for diagnosis and management of brain tumors. (18)F-Fluorodeoxyglucose PET has particular strengths in predicting prognosis and differentiating cerebral lymphoma from nonmalignant lesions. Amino acid tracers including (11)C-methionine, (18)F-fluoroethyltyrosine, and (18)F-L-3,4-dihydroxyphenylalanine provide high sensitivity, which is most useful for detecting recurrent or residual gliomas, including most low-grade gliomas. They also play an increasing role for planning and monitoring of therapy. (18)F-fluorothymidine can only be used in tumors with absent or broken blood-brain barrier and has potential for tumor grading and monitoring of therapy. Ligands for somatostatin receptors are of particular interest in pituitary adenomas and meningiomas. Tracers to image neovascularization, hypoxia, and phospholipid synthesis are under investigation for potential clinical use. All methods provide the maximum of information when used with image registration and fusion display with contrast-enhanced magnetic resonance imaging scans. Integration of PET and magnetic resonance imaging with stereotactic neuronavigation systems allows the targeting of stereotactic biopsies to obtain a more accurate histologic diagnosis and better planning of conformal and stereotactic radiotherapy.

Figure 1

Left: Positron emission tomography (PET) scan with abnormality involving the right frontal lobe. Middle: Contrast magnetic resonance imaging (MRI) scan shows enhancement in the right frontal lobe. Right: There is a focal area of increased fluorodeoxyglucose (FDG) uptake involving the right frontal lobe consistent with a high-grade transformation and recurrence of tumor in the right frontal lobe 8 years after initial diagnosis and therapy. (Color version of figure is available online.)

Figure 2

Anaplastic astrocytoma, World Health Organization (WHO) grade III. (A) Multiple voxel spectra coregistered with postcontrast T1-weighted MRI. (B) Map of Cho/Cr demonstrates a focus of signal intensity in the right frontal lobe. Magnetic resonance spectroscopic imaging (MRSI) signal intensity is presented on a rainbow color scale where blue green is normal background and bright red corresponds to greatly elevated signal intensity. (C) Spectral analysis of the voxel demonstrating maximal Cho/Cr ratio. (D) T1-weighted MRI (postcontrast) demonstrating enhancing lesion in the right frontal lobe. (E) FDG-PET scan shows a focus of increased tracer activity greater than white matter in the right frontal lobe. (F) FDG-PET image coregistered with postcontrast T1-weighted MRI Reprinted with permission from Imani et al.

Figure 3

Oligoastrocytoma, WHO grade II: T1-weighted MRI after application of Gd-DTPA (A) shows no contrast enhancement. T2-weighted MRI scan (B) shows widespread abnormalities. (C) O-(2-¹⁸F-fluoroethyl)-l-tyrosine (¹⁸FFET-PET) identifies metabolically active areas within the tumor and indicates an optimal site for biopsy.

Figure 4

Inhomogeneous anaplastic astrocytoma, WHO grade III: T1-weighted MRI after application of Gd-DTPA (A) shows no contrast enhancement. T2-weighted MRI scan (B) shows widespread abnormalities. (C) ¹⁸F-FET-PET identifies a hot spot in the posterior part that cannot be identified on MRI. Biopsy in this area yielded an anaplastic astrocytoma, WHO grade III.

Figure 5

Glioblastoma (WHO grade IV) pretreated by surgery and radiochemotherapy. T1-weighted MRI after application of Gd-DTPA (A) and T2-weighted MRI (B) are ambiguous. (C) ¹⁸F-FET PET identifies pathologic tracer accumulation, which was confirmed as tumor recurrence. (Color version of figure is available online.)

Figure 6

Composite images of frames summed between 50 and 60 minutes. The patient was a 37-year-old woman with a glioblastoma multiforme in the left insular and temporal opercular regions, who was treated with irinotecan and bevacizumab in 2-week cycles. Representative transaxial slices of the tumor are shown. All images are scaled to the same maximum concentration in Bq/mL. The initial ¹⁸F-FLT uptake is high at baseline (left), drops after 2 weeks of therapy (middle), and remains similar after 6 weeks (right); the respective standardized uptake values (SUV75%) were 1.154, 1.075, and 1.076. Progression-free survival and overall survival were found to be 304 days and 460 days, respectively. (Color version of figure is available online.)