PET/CT Scan - Positron Emission Tomography
A PET/CT scan maps where an injected tracer collects in the body and overlays it on a CT, to stage cancer, judge treatment and find recurrence. In a randomized trial it cut futile lung cancer operations from 38 to 21. We explain FDG and PSMA tracers, preparation, what the scan can miss, the radiation dose, and a two to three day visit.
About This Department
CT shows the shape of the body. PET shows what its cells are doing. One scan combines both, from head to thigh, in about 20 minutes.
A PET/CT scan, positron emission tomography with computed tomography, follows a small dose of a radioactive tracer through the body and lays the picture over a CT scan, so that active disease shows as bright spots on an exact anatomical map. The standard tracer, FDG, is a form of glucose, and most cancers take up far more glucose than normal tissue. In a randomized trial of patients about to have lung cancer surgery, adding PET to the usual tests cut operations that could not help from 41 to 21 percent (van Tinteren and colleagues, Lancet, 2002). In head and neck cancer, PET/CT after chemoradiotherapy replaced routine neck surgery, with 54 operations instead of 221 and no loss of survival (Mehanna and colleagues, New England Journal of Medicine, 2016). This page explains how PET/CT works, the tracers, what it is used for, the evidence in lung cancer, lymphoma and head and neck cancer, its limits, preparation and diabetes, the scan day, radiation, the report, and how patients from abroad arrange a PET/CT scan at Biruni Hospital in Istanbul.
What PET/CT is
| Scan | What it shows | Strength |
|---|---|---|
| CT | Shape, size and density | Fast, detailed anatomy |
| MRI | Soft tissue contrast | Brain, liver, pelvis, spine |
| PET/CT | Metabolic activity on an anatomical map | Whole-body search for active disease |
The tracer
A lymph node of normal size can hold cancer, and an enlarged one can be harmless. PET/CT adds activity to size, and the combination answers questions neither answers alone.
Why sugar
Cancer cells are hungry.
Most tumors burn glucose many times faster than the tissue around them, a pattern first described almost a century ago, and they do so even when oxygen is plentiful, because rapid growth demands the building blocks that glucose provides. FDG exploits that appetite. After injection it spreads through the blood, enters cells through the same transporters as glucose and becomes trapped inside, so an hour later the most active tissues glow brightest on the scan, whether they lie in the chest, the abdomen or a single rib.
Brain, heart and inflamed tissue burn sugar too. That shapes how scans are read.
Tracers and uses
| Tracer | Target | Main use |
|---|---|---|
| F-18 FDG | Glucose metabolism | Most cancers, infection, heart, brain |
| Ga-68 or F-18 PSMA | Prostate-specific membrane antigen | Prostate cancer |
| Ga-68 DOTATATE | Somatostatin receptors | Neuroendocrine tumors |
| Ga-68 FAPI | Cancer-associated fibroblasts | Stomach, pancreas, bile duct cancer |
| F-18 amyloid tracers | Amyloid plaques | Memory disorders |
| F-18 FDG, heart protocol | Living heart muscle | Viability before bypass or stenting |
PET/CT in cancer
| Question | When | Effect on care |
|---|---|---|
| Staging, how far the cancer has spread | At diagnosis | Surgery, radiotherapy or systemic treatment |
| Response to treatment | During or after chemotherapy | Continue, change or stop |
| Recurrence | Rising markers, new symptoms | Finds the site to treat |
| Unknown primary | Metastasis without a known origin | Points to the source |
| Radiotherapy planning | Before treatment | Draws the target more precisely |
A PET/CT earns its place when the answer changes treatment. Routine scans after curative treatment, without symptoms, rarely help.
Lung cancer
Addition of PET to conventional workup prevented unnecessary surgery in one out of five patients with suspected non-small-cell lung cancer (van Tinteren and colleagues, 2002).
| Group | Futile operations | Reason counted as futile |
|---|---|---|
| Standard tests only | 41 percent | Benign disease, unresectable tumor, relapse or death within a year |
| Standard tests plus PET | 21 percent | Same definition |
| Relative reduction | 51 percent | PET found spread that changed the plan |
Lymphoma
| Score | Uptake in lymphoma sites | Meaning |
|---|---|---|
| 1 | None | Complete metabolic response |
| 2 | At or below the chest blood pool | Complete metabolic response |
| 3 | Above blood pool, at or below liver | Usually complete response |
| 4 | Moderately above liver | Residual disease |
| 5 | Markedly above liver or new sites | Residual or progressing disease |
Head and neck cancer
| Measure | PET/CT surveillance | Planned neck dissection |
|---|---|---|
| Two-year survival | 84.9 percent | 81.5 percent |
| Neck dissections | 54 | 221 |
| Quality of life | Similar | Similar |
A scan as a decision tool
Pictures do not treat anyone. Decisions do.
The three trials above share one lesson. In each, PET/CT mattered because a clear rule linked the result to an action, operate or not, add bleomycin or not, dissect the neck or not, and patients gained because they were spared treatment that could not help them.
We ask what a scan will change before we book it.
Limits and false results
| Cause | Where | How we tell it apart |
|---|---|---|
| Infection and inflammation | Lungs, lymph nodes, joints | History, pattern, follow-up scan |
| Recent surgery or radiotherapy | Treated area | Timing, shape |
| Sarcoidosis and tuberculosis | Chest nodes, lungs | Biopsy when decisive |
| Brown fat | Neck, around the spine | Warm room, symmetric pattern |
| Bone marrow stimulation | Whole skeleton | Growth factor injections |
| Normal bowel and muscle activity | Gut, tense muscles | Pattern, CT correlation |
A bright spot is a finding. When the result would change treatment, a biopsy makes the diagnosis.
- Brain metastases are better seen on MRI.
- Low-uptake tumors may need PSMA, DOTATATE or FAPI tracers.
- A high blood sugar lowers tumor uptake and can hide disease.
| Situation | Better choice | Why |
|---|---|---|
| Brain metastases | MRI with contrast | High brain background on FDG |
| Prostate cancer | PSMA PET/CT | Low FDG uptake |
| Well-differentiated neuroendocrine tumor | DOTATATE PET/CT | Receptor-based |
Diabetes and blood sugar
Can I have a PET/CT scan if I have diabetes?
| Blood sugar | Action | Note |
|---|---|---|
| Under 200 mg/dL, 11 mmol/L | Scan goes ahead | Standard |
| Above that level | Correct and wait, or rebook | Uptake reduced |
| Insulin pump | Individual plan | Discuss when booking |
Preparation and the scan day
Fast for six hours before the scan. Plain water is allowed and helps. Avoid strenuous exercise for 24 hours, since working muscles take up FDG.
| Step | Duration | Note |
|---|---|---|
| Registration and blood sugar | 15 minutes | Bring earlier scans |
| Injection | A few seconds | Painless |
| Uptake rest | About 60 minutes | Warm, quiet room |
| Scan | 15 to 25 minutes | Breathe normally |
| After the scan | Leave at once | Eat and drink normally |
| Item | Why | Format |
|---|---|---|
| Earlier CT, MRI or PET | Comparison | Disc or secure link |
| Pathology report | Question to answer | Copy |
| Medicine list | Diabetes and contrast plan | Written list |
Radiation and safety
| Source | Typical effective dose | Note |
|---|---|---|
| FDG tracer | 5 to 7 mSv | Depends on body weight |
| Low-dose CT for PET | 1 to 4 mSv | Localization only |
| Diagnostic contrast CT | 5 to 10 mSv | When detailed anatomy needed |
| Natural background, one year | 2 to 3 mSv | Varies by place |
Children and pregnancy
Children receive weight-adjusted doses. In pregnancy, PET/CT is done only when the result is essential.
Reading the report
Numbers appear in every report.
The standardized uptake value, SUV, compares the tracer in a spot with an even spread through the body, and a higher value points to more active tissue, but it depends on timing, blood sugar and the scanner, so the pattern across the body and the change between scans matter more than any single figure.
Your oncologist reads the report with the whole story.
Results and next steps
Timing
Comparison with earlier scans makes a report far more useful. Please send every previous CT, MRI and PET.
Follow-up scans
Response scans use the same scanner and protocol where possible, so that values can be compared fairly.
For patients from abroad
A PET/CT needs one to two days in Istanbul, the scan on the first day and a consultation with the report on the next. You can fly the same day.
| Day | Step | Note |
|---|---|---|
| Day 1 | Consultation and scan | Fasting from the night or morning before |
| Day 2 | Report and discussion | Tumor board if needed |
| Same or next day | Flight home | No restriction |
One coordinator from the international patients office handles arrangements from the first message through discharge and answers the same WhatsApp number after you return. The office works in English, Arabic, French, Russian, Serbian, Romanian and Spanish and books interpreters for other languages, and it arranges the visa invitation letter, airport transfers, daily transport and accommodation near the hospital. Halal, vegetarian and diabetic meals, a prayer room on site, and a female physician on request wherever the rota allows.
Cost
We quote after reviewing your records, before you travel.
What a quote covers
| Item | Included | Priced separately |
|---|---|---|
| Scan | FDG tracer, PET/CT from skull base to mid-thigh | Whole-body or brain protocol |
| Reporting | Written report with comparison | Tumor board review |
| Consultation | Discussion of the report | Biopsy or further imaging |
References
- van Tinteren H, Hoekstra OS, Smit EF, et al. Effectiveness of positron emission tomography in the preoperative assessment of patients with suspected non-small-cell lung cancer. The PLUS multicentre randomised trial. Lancet. 2002;359(9315):1388-1393.
- Mehanna H, Wong WL, McConkey CC, et al. PET-CT surveillance versus neck dissection in advanced head and neck cancer. N Engl J Med. 2016;374(15):1444-1454.
- Johnson P, Federico M, Kirkwood A, et al. Adapted treatment guided by interim PET-CT scan in advanced Hodgkin's lymphoma. N Engl J Med. 2016;374(25):2419-2429.
Editor's note
Written by the Biruni Hospital medical editorial team. Reviewed by Specialist Dr. Nesrin Aslan İlkmen, Nuclear Medicine.
Medically reviewed by
Specialist Dr. Nesrin Aslan İlkmen
Nuclear Medicine
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