Abstract
Imaging plays a critical role in the management of the highly complex and widely diverse central nervous system (CNS) malignancies in providing an accurate diagnosis, treatment planning, response assessment, prognosis, and surveillance. Contrast-enhanced magnetic resonance imaging (MRI) is the primary modality for CNS disease management due to its high contrast resolution, reasonable spatial resolution, and relatively low cost and risk. However, defining tumor response to radiation treatment and chemotherapy by contrast-enhanced MRI is often difficult due to various factors that can influence contrast agent distribution and perfusion, such as edema, necrosis, vascular alterations, and inflammation, leading to pseudoprogression and pseudoresponse assessments. Amino acid positron emission tomography (PET) is emerging as the method of resolving such equivocal lesion interpretations. Amino acid radiotracers can more specifically differentiate true tumor boundaries from equivocal lesions based on their specific and active uptake by the highly metabolic cellular component of CNS tumors. These therapy-induced metabolic changes detected by amino acid PET facilitate early treatment response assessments. Integrating amino acid PET in the management of CNS malignancies to complement MRI will significantly improve early therapy response assessment, treatment planning, and clinical trial design.
Highlights
Malignancies of the central nervous system (CNS) account for an estimated 23,000 cases and over 16,000 deaths each year [1]
Metabolic changes detected by amino acid positron emission tomography (PET) occur in response to therapy sooner than morphological and structural changes providing an earlier response to therapy assessment and prognosis
Metabolic uptake of radiolabeled amino acids is specific to the proliferating cellular component of the tumor, occurs independently of the status of the blood-brain barrier, and excludes non-cellular lesions created by necrosis, edema, and inflammation
Summary
Malignancies of the central nervous system (CNS) account for an estimated 23,000 cases and over 16,000 deaths each year [1]. The most recent 2016 World Health Organization (WHO) Classification of Tumors of the Central Nervous System defines CNS malignancies within four categories (grades I, II, III, and IV) based on molecular parameters and histology [4]. High-grade gliomas (HGG) are classified in grades III and IV and include the most aggressive form, glioblastoma (grade IV), which has a median overall survival of 1.5 years [5]. The complexity and diversity of CNS malignancies necessitate a multifaceted approach to therapy that includes surgery, radiation treatment, chemotherapy and, more recently, immunotherapy. Therapy of CNS tumors entailed surgery and radiotherapy. Improving outcomes relied on radiotherapy dose escalation and responses were measured by overall survival. Imaging became an integral component of every stage of CNS disease management providing information that is critical to staging, formulating preoperative strategies, monitoring therapy response, surveillance, and prognosis
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