Pediatric PET Imaging of Pediatric Brain Tumors Gets a Boost with Easier-to-Manufacture Imaging Agent

The study investigators presented their findings at the Society of Nuclear Medicine and Molecular Imaging’s 2013 60th annual meeting, held June 8–12, 2013, in Vancouver (BC, Canada). Brain cancer imaging is frequently conducted with traditional MRI scanning, but there are some restrictions to this imaging technique. This type of cancer accounts for approximately 80% of all invasive brain tumors and develops in the brain’s glial cells that protect and maintain a state of neural equilibrium.

Traditional MRI can, at times, over- or underestimate the extent of these tumors and the precise shape of their outlying margins. An application of molecular imaging called positron emission tomography (PET), which provides data about physiologic processes instead of structures of the brain, can be performed with a range of imaging agents that bind to specific cellular systems to image gliomas. Two of the main kinds of brain imaging agents used for this objective provide information about either glucose metabolism of cells or the cellular metabolism of amino acids, the essential components of proteins utilized by tissues, in particular, rapidly growing so-called neoplastic tumors.

Amino-acid PET imaging has been shown to be better for detection of neoplastic tissue and treatment monitoring in cases of brain cancer than glucose imaging. Typically, the brain requires more glucose than the body’s other tissues and organs, making brain scans “noisier” and less defined than other regions because of this increase in overall cellular metabolism, whereas areas of increased amino acid activity show up clearly on scans as a visual “hot spot.” This study focuses on a specific amino acid imaging agent, O-(2-[18F]-fluoroethyl)-L-tyrosine (F-18 FET), and its diagnostic value for imaging pediatric gliomas when traditional MRI cannot make out a well-defined image of disease.

“Cancer of the brain and spinal cord are common in children and young adults, and caring for this particular group can be challenging because choice of treatment depends on specific information about the tumor. Tumors in younger patients show a greater variety in both type and size, and in many cases the tumors are located near critical brain structures that prohibit surgical removal,” said Veronika Dunkl, MD, a research scientist at the Institute of Neuroscience and Medicine, Forschungszentrum Jülich (Jülich, Germany). “In patients with brain tumors, contrast-enhanced structural MRI is currently the diagnostic method of choice. However, in youths with newly diagnosed cerebral lesions thought to be brain tumors, MRI’s ability to identify neoplastic tissue or tumor progression and recurrence after treatment is limited. F-18 FET is complementary and can potentially improve diagnosis and treatment of pediatric brain tumors.”

Pediatric brain imaging with PET and F-18 FET can be used not only to evaluate extent of tumors but also to help clinicians prepare for biopsy, surgery, and radiation therapies and monitor response to therapy and recurrence of tumors after completion of a treatment cycle.

F-18 FET is also distinctive from other amino acid PET agents because the generation of the drug can be centrally located and distributed by a radiopharmacy, whereas other amino acid-based PET agents must be manufactured by an on-site cyclotron—a huge particle accelerator that barrages particles with a target used to radiolabel the agent’s molecular compound. For F-18 FET, the amino acid tyrosine allows brain cells to signal each other. The greater logistical simplicity of F-18 FET is due to its radioactive half-life of approximately 110 minutes, whereas many other isotopes have a half-life of just approximately 20 minutes and must be administered for patient imaging almost instantly.

For this study, 15 young patients suspected of glioma cerebral cancer via MRI screening underwent PET imaging with the guidance of F-18 FET. This molecular imaging technique was found to be highly effective, about 87%, for identifying and differentiating brain lesions in children and young adults. The method was able to target 11 out of 12 brain lesions accurately as tumors and two out of three as a nontumorous growth. Repeated PET imaging (17 scans) for seven more pediatric patients provided significant information about cancer progression or remission. F-18 FET imaging was able to detect residual tumor and tumor progression in five out of six scans, and in 11 scans in which the tumor had been destroyed, for a 94% rate of accuracy.

“Results of the present study may improve the clinical management of this vulnerable patient population significantly, especially when a decision for further treatment is difficult or impossible on the basis of conventional MRI alone,” said Dr. Dunkl.

The US National Cancer Institute (Rockville, MD, USA) estimates that brain cancers are among the most common cancers in child populations. Incidence of pediatric brain tumors is approximately 3.2 cases per 100,000 people.

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Institute of Neuroscience and Medicine, Forschungszentrum Jülich