Prognostic imaging of neuroblastoma

Abstract

Neuroblastoma is the most common extracranial neoplasm in children. It represents about 8 % of childhood malignancies and 90% of those affectedare under the age of 5 years. It is an embryonal tumor and develops mostly in the adrenal medulla. It is metastatic and has a high risk of relapse [1–3]. The treatment of the tumor is dependent on several factors including age, stage, location of the tumor and molecular pathology. Diagnosis is made from blood, urine and tissue samples using different biomarkers, and is completed with in vivo imaging studies. In vivo imaging studies play a central role in selection of the therapeutic approach as well as in following the therapeutic response [4]. They can also be used to obtain prognostic estimates of disease progression. Several radiological imaging modalities are used in the diagnosis of neuroblastoma. Traditionally CT has been the first method of choice. Concerns about the radiation burden in children have resulted in the use of other imaging modalities including MRI and ultrasonography. The information obtained with all these imaging modalities consists of anatomical localization, estimation of the tumor size and detection of metastases based on the contrast in relation to the surrounding tissue. CT imaging is based on x-rays and electron density while MRI isbased onprotondensity, and ultrasonography on the speed of sound in tissue. Although these imaging modalities are the first interventions used for diagnosis, they provide only secondary information on the stage of the malignancy based on the spread of metastases. The INRG (International Neuroblastoma Risk Group) has published guidelines on the imaging and staging of neuroblastic tumors with the aim of optimizing imaging and uniform reporting for staging [5]. Children with an abdominal or pelvic mass should be initially investigated by ultrasonography due to its noninvasive nature and widespread availability. MRI and CT studies are recommended for further evaluation of the primary tumor. Functional imaging with nuclear medicine imaging techniques is gaining importance for staging neuroblastic tumors and for the selection of a personalized therapeutic approach, and even to obtain prognostic estimates of disease progression. Since the presently used methods for making prognostic estimates of the disease are heavily based on semiquantitative analyses of nuclear medicine imaging enhanced with anatomical information obtained by CT or MRI, it is imperative to deeply evaluate which basic technical factors affect nuclear medicine imaging data [2, 6]. The most important factor in nuclear medicine imaging is the biological problem to be investigated (e.g. a biological dysfunction, the presence of tumor,etc.).Thefunctionalbiochemistryoftheproblemunder investigation may allow selection of a biomarker and of a possible detection ligand (drug). A method for the radiosynthesis of the drug then needs to be established and a radioisotopeselected,whichwill indicatethemostappropriate