What Is a Radiotracer — and Which One Will I Be Given?

The radiation dose from a PET tracer is low relative to the clinical value of the information it provides. The radioactive component decays rapidly after injection, and what remains is cleared from your body in urine over the hours that follow. Your oncologist and the imaging team weigh the exposure against the clinical need before ordering any scan — PET scans are not requested routinely. If you have had several scans and are concerned about cumulative exposure, raise it directly with your oncologist rather than deciding to skip a scan on your own.

Fasting keeps your blood glucose low before the FDG injection. When blood glucose is elevated, normal cells throughout your body compete with cancer cells to absorb the tracer, which makes the images less clear and harder to interpret accurately. Your team will give you specific preparation instructions before your appointment. Do not carry over instructions from a previous scan without checking — preparation can vary depending on the tracer being used and your individual medical situation.

Yes, but preparation is different for people with diabetes because managing blood glucose with fasting is more complex. Tell the scan centre about your diabetes in advance rather than on the day of the appointment. The team may adjust the timing of your scan, ask you to manage your medications differently on the morning, or check your blood sugar before deciding whether to proceed. Never stop or change your diabetes medication without guidance from your treating team — your oncologist and the scan centre can coordinate your preparation between them.

After the tracer is injected, your body needs time to absorb it before imaging can begin. The tracer travels through your bloodstream and gradually accumulates in metabolically active areas. You will typically be asked to sit quietly in a separate room during this period. Moving around or feeling very anxious can increase tracer uptake in muscle tissue, which makes the images harder to read accurately. Sitting still and staying calm is genuinely part of how the scan produces useful images — it is not simply waiting.

The tracer is chosen based on your specific cancer type and the clinical question your oncologist is trying to answer at this moment in your treatment. FDG works well for most cancers but does not reliably show prostate cancer in certain situations, and it is not the right tracer for neuroendocrine tumours. A person with prostate cancer may receive a PSMA tracer; someone with a neuroendocrine tumour may receive Ga-68 DOTATATE. The same person can also receive different tracers at different points in their treatment if the question being asked has changed. The tracer reflects the question, not the severity of your situation.

A specialist doctor — a nuclear medicine physician or a radiologist trained in nuclear medicine — reads the PET-CT images and prepares a written report. That report goes to your oncologist, who interprets it alongside your biopsy results, blood tests, symptoms, and everything else they know about your case. The scan and the report alone are not a diagnosis. If the report contains terms you do not understand, ask your oncologist what they mean for your specific situation — the same finding can carry very different significance depending on the clinical context.