FDG PET-CT — Oncology

FDG PET-CT combines the glucose-analogue tracer F-18 FDG with anatomical CT to map tissue glucose metabolism across the body. Malignant cells overexpress GLUT transporters and hexokinase, trapping phosphorylated FDG (FDG-6-phosphate) intracellularly, producing high tumour-to-background contrast. It is central to staging, restaging, response assessment and radiotherapy planning across oncology, with the Deauville 5-point scale used for lymphoma response and PERCIST/EORTC frameworks for quantitative solid-tumour response.

Indications

Staging and restaging of Hodgkin and aggressive non-Hodgkin lymphoma with interim and end-of-treatment Deauville scoring
Staging, restaging and treatment response of solid tumours (lung, head and neck, oesophageal, colorectal, melanoma, cervical)
Characterisation of the indeterminate solitary pulmonary nodule (>8-10 mm)
Detection of recurrence in the setting of rising tumour markers (e.g. CEA, thyroglobulin) with negative conventional imaging
Radiotherapy target-volume delineation and identification of an unknown primary with metastatic presentation

Contraindications & Cautions

Pregnancy is a relative contraindication; defer or justify and minimise dose as FDG crosses the placenta
Breastfeeding: FDG is minimally excreted in milk but close infant contact should be limited for ~12 h owing to external dose from the mother
Uncontrolled hyperglycaemia (blood glucose typically >11 mmol/L / 200 mg/dL) reduces tumour uptake and degrades study quality — reschedule
Recent chemotherapy, granulocyte colony-stimulating factor or radiotherapy cause reactive marrow and inflammatory uptake — allow adequate interval (chemo ~2-3 weeks, radiotherapy ~8-12 weeks)
Inability to lie still or maintain the pre-scan resting/fasting protocol

Patient Preparation

Fast 4-6 hours (water only); withhold food, sugary drinks and IV dextrose to lower serum insulin
Check capillary blood glucose before injection; target <11 mmol/L (200 mg/dL)
Diabetic patients: schedule early, adjust insulin/oral hypoglycaemics per protocol; avoid short-acting insulin close to injection
Rest quietly in a warm room after injection to reduce muscle and brown-fat uptake; avoid talking, chewing and exertion for 24 h prior
Ensure hydration and encourage voiding before imaging to reduce urinary tracer activity

Technique & Parameters

Administer F-18 FDG ~3-4 MBq/kg (2.5-5 MBq/kg) intravenously after confirming glucose and hydration
Uptake (incorporation) phase of ~60 minutes resting supine; standardise the interval to keep SUV reproducible
Acquire integrated PET/CT from skull base to mid-thigh (extend to vertex and lower limbs for melanoma or where indicated)
Low-dose CT for attenuation correction and localisation; add diagnostic contrast-enhanced CT when required
Measure SUVmax/SUVpeak normalised to body weight or lean body mass; record uptake time and glucose for comparison studies

Systematic Review

Confirm injected activity, uptake time and blood glucose — all affect SUV comparability
Review PET, CT and fused images in three planes; correlate every focus with the CT substrate
Assess the primary site, regional nodal stations and common metastatic sites (liver, lung, bone, adrenal)
Recognise physiologic uptake: brain, myocardium, bowel, salivary/vocal, thymus, brown fat, and urinary excretion
Compare with prior studies using matched SUV methodology; grade lymphoma response on the Deauville 5-point scale
Screen the CT for incidental non-FDG-avid findings and radiation-relevant anatomy

Key Findings & Significance

Focal uptake exceeding mediastinal blood pool and liver background suggests viable malignancy
Deauville 1-2 (uptake at or below mediastinum/liver) is a complete metabolic response; Deauville 4-5 (above liver / markedly increased or new lesions) indicates inadequate response or progression
Diffusely increased marrow and splenic uptake follows chemotherapy, G-CSF or anaemia — a reactive, not neoplastic, pattern
Necrotic or mucinous tumours and small (<8-10 mm) or low-grade lesions may be falsely FDG-negative
Inflammatory and infective processes (sarcoidosis, TB, abscess, post-radiation change) are FDG-avid and mimic tumour

Differential Considerations

FDG-avid nodes: metastatic disease, lymphoma, reactive/infective adenopathy, sarcoidosis
Solitary pulmonary nodule uptake: malignancy versus granuloma, infection or organising pneumonia
Diffuse marrow uptake: G-CSF/chemotherapy effect, anaemia, myeloproliferative disease, marrow infiltration
Bowel uptake: physiologic, metformin effect, inflammatory bowel disease, polyp or primary tumour
Focal thyroid incidentaloma uptake: ~30% malignancy risk — recommend ultrasound and correlation

Pearls & Pitfalls

Always record glucose and uptake time on the report — SUV is only comparable between studies with matched technique
Metformin causes intense, often diffuse bowel uptake; a 48-72 h hold aids abdominal assessment when clinically appropriate
Brown-fat uptake (neck, supraclavicular, paraspinal) is reduced by keeping the patient warm and, in some protocols, beta-blockade
Post-treatment inflammation is FDG-avid — wait ~2-3 weeks after chemotherapy and 8-12 weeks after radiotherapy or surgery
Deauville is scored visually against mediastinal blood pool and liver, not by an absolute SUV cut-off

Structured Report

State tracer, injected activity, blood glucose, uptake time and scan extent
Describe the primary lesion with SUVmax, size and CT correlate, then nodal and distant disease by station/organ
For lymphoma give the Deauville score and compare with the baseline/interim study
Summarise metabolic response (complete/partial/stable/progressive) using consistent methodology
Provide TNM or disease extent, flag incidental CT findings, and give clear management recommendations

References

Boellaard R, et al. FDG PET/CT: EANM procedure guidelines for tumour imaging version 2.0. Eur J Nucl Med Mol Imaging 2015
SNMMI Procedure Standard / EANM Practice Guideline for FDG PET/CT (v2.0)
Barrington SF, et al. Lugano Classification / Deauville criteria for response assessment in lymphoma. J Clin Oncol 2014
Wahl RL, et al. From RECIST to PERCIST: evolving considerations for PET response criteria. J Nucl Med 2009
Kapoor V, et al. An introduction to PET-CT imaging. RadioGraphics 2004

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.

FDG PET-CT — Oncology

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References