Positron Emission Tomography


Positron Emission Tomography (PET) is an imaging modality used in the field of neurology and oncology and in some cases used in conjunction with magnetic resonance imaging (MRI).  PET is used to define the radiotherapeutic target volume of a tumour or the extent of disease before surgically removing a tissue structure or organ from the human body.  PET also assists to establish a prognostic value about the patients’ overall cancer outcome, regardless of therapy through molecular imaging. For example, the PET radiotracer, fluorine-18 labelled fluoroethyltyrosine (18F-FET) has been shown to predict prognosis of improved target delineation to assess treatment response.  A recent study using 18F-FET-PET and T1 weighted image MRI was used to predict the effectiveness in treatment following chemoradiation therapy of glioblastoma patients. The radiotracer, fluorodopa F-18 (fluoro-deoxyphenylalanine 18F-DOPA) is used to provide additional clinical information which may be validated by histopathology. Another target for brain tumour imaging is the translocator protein (TSPO).  This protein is overexpressed in glioblastoma patients and clinical investigations have shown a link to the neuro-inflammatory component by observing a TSPO PET signal. Positron Emission Tomography is also used in the evaluation of head and neck cancers such as nasopharyngeal carcinomas, squamous cell cancer and salivary tumours. Furthermore, the hybrid PET and computed tomography (CT) scanner are able to provide an insight into the status of nodal metastases of the tumour and tissue metabolism.  PET/CT is used to enables contouring for chemotherapy and radiotherapy in radiation treatment planning. Lung cancer occurs in 80-90% of patients with non-small cell lung cancer (NSCLC). PET imaging with 18F-FDG (fluorodeoxyglucose) is used for staging patients with NSCLC.  In another diagnostic investigation, PET/CT PSMA (prostate-specific membrane antigen) ligands labelled with gallium-68 or fluorine-18 is used in prostate cancer screening programmes because it provides an excellent target-to-background ratio which leads to a better detection rate. PSMA is highly specific for prostatic tumoral tissue.