PET-CT Scan (FDG PET-CT)

PET-CT combines two scans in one machine. The PET part tracks a small dose of radioactive tracer, most often FDG, a form of glucose, which collects in cells that use a lot of energy, as many cancers do. The CT part provides the anatomical map. Fused together, the images show where in the body abnormal activity is located.

It is used mainly to stage cancer, to look for spread, to check response to treatment and to investigate suspected recurrence. It is not a general cancer screening test for healthy people. Inflammation and infection also light up, some tumours take up little FDG, and deposits smaller than about 5 to 8 mm can be missed.

What PET-CT Scan (FDG PET-CT) shows

FDG PET-CT shows the primary tumour, involved lymph nodes and distant metastases in a single whole-body study, usually from the base of the skull to the mid-thigh. Uptake is measured as a standardised uptake value (SUV). It is particularly valuable in lung cancer, lymphoma (where response is graded with the Deauville score), melanoma, head and neck, oesophageal, cervical and colorectal cancer recurrence, and in searching for an unknown primary tumour. It also helps in fever of unknown origin, vasculitis, sarcoidosis, infected grafts and some dementia assessments. It performs poorly in the brain and urinary tract, where normal uptake is high, and in tumours such as many prostate cancers, well-differentiated neuroendocrine tumours, some kidney cancers and mucinous or lobular types, for which other tracers or scans are preferred.

When PET-CT Scan (FDG PET-CT) is recommended

• Staging of a newly diagnosed cancer where spread would change treatment, for example before lung, oesophageal or major head and neck surgery
• Lymphoma, at diagnosis, mid-treatment and at the end of treatment
• Assessing a solitary lung nodule over about 8 mm
• Rising tumour markers or suspicious symptoms after treatment, with inconclusive CT or MRI
• Planning radiotherapy fields
• Fever, inflammation or infection of unknown source, after standard tests

Limits and situations where another test is better:

• Screening people without symptoms, which produces false alarms and radiation exposure without proven benefit
• Pregnancy, unless essential
• Poorly controlled diabetes with glucose above about 11 mmol/L (200 mg/dL) on the day, which degrades the images
• Within about 2 to 3 weeks of chemotherapy, 6 weeks of surgery or 8 to 12 weeks of radiotherapy, when healing tissues cause misleading uptake
• Prostate and neuroendocrine tumours, which call for PSMA or DOTATATE tracers

How to prepare

• Fast for 4 to 6 hours; plain water is encouraged
• Avoid strenuous exercise for 24 hours and keep warm before the scan, since active muscle and brown fat take up tracer
• Follow a low-carbohydrate meal plan the evening before if instructed
• Diabetics need specific timing of insulin and metformin; ask in advance
• Bring previous scans on disc and reports, plus dates of recent chemotherapy, radiotherapy, surgery and growth factor injections
• Tell staff if you might be pregnant, are breastfeeding or are claustrophobic

What happens during the test

Your blood glucose is checked and the tracer is injected into a vein in the arm. You then rest quietly in a warm room for 45 to 60 minutes without talking, reading or using a phone, so that muscles stay relaxed. You empty your bladder and lie on the scanner table, which moves through a wide ring for 15 to 30 minutes. It is quiet and open compared with MRI. Contrast dye for the CT part is sometimes added. The whole visit takes 2 to 3 hours.

Results and next steps

A nuclear medicine physician and radiologist report the scan, usually within 1 to 2 working days. The report should reach the doctor who is managing your care, since findings are interpreted against your biopsy, history and other imaging. Hot spots often need confirmation by biopsy before they change treatment. Ask for the full image set in DICOM format on disc or by link, as your home team or tumour board will want to review the images and not only the report.

• Test time: 2 to 3 hours in total, 15 to 30 minutes on the scanner
• Results ready: 1 to 2 working days
• Back to everyday activity: None; limit contact with small children for about 6 hours

Safety and risks

• Radiation dose of roughly 10 to 25 mSv depending on the CT protocol, equivalent to several years of natural background
• False positives from infection, inflammation, recent surgery or benign growths
• False negatives with small or slow-growing tumours
• Allergic reaction or kidney strain if iodinated contrast is used
• Bruising at the injection site

Arranging PET-CT Scan (FDG PET-CT) in Türkiye

PET-CT is often done within days in Istanbul, which is one reason patients include it in a second-opinion or treatment-planning visit. It makes sense when requested by an oncologist for a defined question. Avoid close contact with infants and pregnant women for about 6 hours afterwards. If flying within a day or two, carry the scan letter, as airport radiation sensors can be triggered.

Send your previous reports and the question you want answered and a Clinic-Y coordinator replies within 24 hours with suitable teams and written, all-inclusive proposals side by side. Reviewing your case is free.

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