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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.