What is a PET scan?
Most of the radiotracers used in Nuclear Medicine emit radiation that can be detected with a gamma camera. Certain radiotracers emit a different type of radiation-positron radiation- that is not adequately detected with gamma cameras. The principle example of a positron emitting radiotracer is Fluorine labelled glucose (FDG) and this is the radiotracer used in most PET scans. The interest in FDG is that this tracer is an exquisite tumour localising radiotracer and is now used routinely in diagnosis, staging and monitoring of many tumours.

When should I order a PET scan?
Most patients have PET scans organised by their oncologist as part of either their initial work up or as part of their continuing assessment. There is now an established role for FDG PET imaging in non-small cell lung cancer, colorectal cancer, esophageal cancer, head and neck cancer, lymphoma, melanoma, sarcoma, ovarian cancer, cervical cancer, brain cancer and thyroid cancer.

What do I tell my patient?
Allow 3 hours.

The patient needs to fast for six hours before the scan. The patient receives an intravenous injection of tracer and then is allowed to rest for 60 minutes prior to the scan starting. The patient is then scanned with the test taking about 30 minutes to perform.

What will the scan tell me?
Focal uptake of FDG is usually due to viable tumour. A negative study is a good sign that the disease is in remission.

What next?
This is predicated on the clinical condition of the individual patient.