PET-CT is a combination of cross-sectional anatomic information provided by CT and the metabolic information provided by positron emission tomography (PET).
PET is most commonly performed with 2-[F-18]fluoro-2-deoxy-D-glucose (FDG). Fluorine-18 (F-18) is an unstable radioisotope and has a half-life of approximately 110 minutes. More recently, radiopharmaceuticals such as gallium-68 prostate-specific membrane antigen have been developed and approved for use in PET.
The indications for F-18 fluorodeoxyglucose (FDG) PET-CT imaging include:
staging of cancer which potentially can be treated radically (e.g. small cell lung cancer) 4
establish baseline staging before commencing treatment (e.g. GIST)
evaluation of an indeterminate lesion (solitary pulmonary nodule) 4,5
assessing response to therapy 3
evaluation of suspected disease recurrence, relapse and/or residual disease (e.g. lymphoma, testicular seminoma) 4
to guide a biopsy (e.g. pleural biopsy for mesothelioma)
differentiate between radiation-induced necrosis and tumor recurrence
PET-CT can also be used as a problem-solving tool, for example:
occult primary lesion (e.g. non-metastatic manifestation of neoplastic disease)
evaluation of suspected recurrence in patients with equivocal conventional imaging 4
evaluation of residual disease in patients with treated differentiated thyroid carcinoma and treated medullary thyroid carcinoma with negative/equivocal conventional imaging 4
prior to radical nodal resection in patients with metastatic melanoma
suspected malignant transformation in plexiform neurofibromata (neurofibromatosis type 1)
differentiate between radiation-induced necrosis and tumor recurrence (e.g. primary CNS malignancy)
Timing of PET scans is of particular importance for insulin-dependent diabetic patients, as administration of exogenous insulin can decrease the image quality of certain PET scans (e.g. 18-F FDG PET). Blood sugar levels of up to 13mmol/L are accepted at some centers, where patients are then hydrated with oral or intravenous fluids. If short-acting insulin is administered, scans may have to be delayed by up to 4 hours.
Funding
It is important for referring doctors to be aware that certain criteria exist for patients to satisfy criteria for a Medicare-funded PET scan
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In Australia, Medicare-rebatable PET scans exist only for a number of certain medical conditions that need to meet specific criteria
Example - a patient must have biopsy-confirmed adenocarcinoma of the prostate with at least PSA 10-20mg/mL or Gleason score of 7 or ISUP grade group 2 or 3, or Stage T2b to meet criteria of a Medicare-funded PMSA PET. A high PI-RADS alone does not meet criteria for a funded scan.
Other PET scans such as cardiac sarcoid are unfunded
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