Before a PET/CT procedure, patients are required to fast for at least 6 hours. The procedure begins with the measurement of the patient's blood sugar level. Once blood sugar is within acceptable limits, a radioactive substance is injected intravenously. The most commonly used substance is F-18 Fluorodeoxyglucose (FDG), which is a sugar molecule bound to the radioactive isotope Fluorine-18. Following the injection, the patient waits for approximately one hour to allow the substance to adequately accumulate in the targeted cancerous tissues. Afterwards, the patient is positioned in the PET/CT scanner for imaging.

Other important substances used in PET/CT besides F-18 FDG include: F-18 NaF for detecting bone metastases; Ga-68 PSMA for investigating the spread of prostate cancer; and Ga-68 DOTA-TATE, used in the investigation of neuroendocrine tumors. Additionally, many less commonly used radiopharmaceuticals are available for specific situations.

PET/CT plays a vital role in the fight against cancer. It is utilized in numerous stages, from the detection of cancerous tissues to treatment planning, from evaluating treatment effectiveness to planning radiotherapy.