FDG-PET / CT in Oncology

F-18 fluorodeoxyglucose (FDG) PET / CT is the dominant molecular imaging exam in oncology. FDG — a glucose analog — concentrates in metabolically active cells including most malignancies, and its 511 keV annihilation photons are detected by the PET ring. Combined with the CT for anatomic correlation and attenuation correction. The largest volume PET indication globally; the foundation oncology-imaging workflow that PET / CT installed-base economics depend on.

Clinical indications

Staging + restaging — lymphoma, lung cancer, head-and-neck cancer, melanoma, colorectal, esophageal, cervical, many others.
Treatment response — mid-treatment assessment, post-treatment residual disease, Deauville scoring (lymphoma).
Recurrence detection — rising tumor markers, indeterminate CT findings.
Radiotherapy planning — biological target volume (BTV) definition for IMRT / SBRT planning.
Dementia / neuro PET — FDG pattern analysis (separate protocol — neuro-PET).
Infection / inflammation — vasculitis, fever-of-unknown-origin in selected workups.

Workflow

Patient prep — NPO 4–6 hours, glucose < 200 mg/dL at injection.
Injection — ~10 mCi F-18 FDG IV.
Uptake — 60 min in a quiet shielded uptake room.
CT — low-dose CT for attenuation correction + anatomic localization (sometimes diagnostic-quality contrast CT).
PET acquisition — 6–8 bed positions skull base to mid-thigh, 2–3 min per bed (digital SiPM platforms shorter).
Reconstruction — ToF + iterative (Q.Clear on GE, TrueX / OptisoHD on Siemens, AI-DR / equivalents).
Read + report — SUV-max measurements, staging, comparison to priors, Deauville for lymphoma.

Typical systems

GE Discovery 690 — PMT-LYSO, ToF, large refurb base.
GE Discovery MI — digital, SiPM, current generation.
Siemens Biograph mCT — PMT-LSO, large refurb base.
Siemens Biograph Vision — digital SiPM.
Siemens Biograph Vision.X — current top-tier.
Philips Vereos — digital SiPM.
Philips Gemini TF — PMT-LYSO predecessor.

Throughput reality

Scanner throughput rarely limits real-world PET volume. Limits are:

Tracer delivery timing — F-18 half-life is 110 min; daily morning delivery scheduled to the scan day.
Uptake room count — patients occupy uptake rooms for 60+ min; 2 rooms ≈ 12–15 patients / day, 3 rooms ≈ 16–20.
Injection cadence — one injection per 10–15 min during the morning.

Digital SiPM PET / CT shortens scanner time per patient meaningfully but does not address the upstream bottlenecks.

Equipment considerations that bite

Detector technology generation (PMT vs SiPM) is the largest refurb price-determining variable. PMT-era LSO / LYSO PET is value-tier; SiPM digital is current.
ToF timing tier — 178 ps (Vision.X) → 215 ps (Vision) → 375 ps (Discovery MI) → 500 ps (Discovery 690 / mCT). Small-lesion conspicuity scales with timing.
Axial FOV — 16 cm (legacy) vs 25 cm (TrueV) vs 194 cm (uEXPLORER total-body) shapes scan time and dose.
Reconstruction software tier — Q.Clear, TrueX / HD·PET / UltraHD·PET (LSO era), OptisoHD (Vision era) are licensed; confirm in writing on refurb deals.
Radiopharmacy contract — PET delivery cadence and contracted backup pharmacy are operationally critical.

Dose + regulatory

Patient dose ~7–15 mSv (CT + PET combined). Staff dose ALARA — shielded injection, pre-injection room, uptake rooms, control area. NRC or Agreement-State byproduct license required. RSO + Authorized User credentialing mandatory.

Operational reality

PET / CT is a program, not a scan. Tracer delivery, hot lab, RSO, AU credentialing, uptake rooms, and reading workflow all run as a coordinated program.
Theranostic adjuncts — Lu-177 PSMA, Lu-177 DOTATATE follow-up imaging is a growing share, often using the same PET / CT platform with adjusted protocols.
Reimbursement — coverage per indication is settled but per-payer variability exists; oncology programs structure FDG-PET workflows around payer rules.