Guidelines for PET/CT Scanning in Clinical Practice
PET/CT scanning is indicated for specific clinical scenarios in oncology, with established protocols that vary by indication, but should not be used for routine screening due to limitations in detecting occult primary cancers. 1, 2
Key Indications for PET/CT in Oncology
Lung Cancer
- Diagnosis of malignancy in solitary pulmonary lesions >1 cm that are suspicious on initial imaging (level of evidence: A) 1
- Assessment of locoregional involvement and metastatic screening, particularly for adrenal gland involvement (level of evidence: A) 1
- Differential diagnosis of recurrence versus post-treatment fibrosis (level of evidence: B2) 1
Colorectal Cancer
- Assessment of operability for recurrent disease and metastases 1
- Diagnosis of recurrence in patients with confirmed elevation of serum carcinoembryonic antigen (level of evidence: B2) 1
Other Solid Tumors
- Initial metastatic screening in high-risk melanoma patients (Stage III AJCC) (level of evidence: B2) 1
- Assessment of nodal involvement in cervical cancer patients (level of evidence: B2) 1
- Pretreatment evaluation of nodal and metastatic status in esophageal cancer to complement scans and endoscopic ultrasound (level of evidence: B2) 1
- Suspicion of local or metastatic recurrence in ovarian cancer (level of evidence: C) 1
Occult Primary Cancer
- May be warranted in specific situations such as presence of supraclavicular nodes 1, 2
- Most appropriate for patients with a single site of metastasis when therapy with curative intent is planned 2
Technical Protocols for PET/CT Scanning
Patient Preparation
- Blood glucose levels should be <7 mmol/L (126 mg/dL) preferred, <10 mmol/L (180 mg/dL) acceptable 1
- Interval between FDG injection and image acquisition should be at least 60 min, preferably 90 min 1
- Patient should remain motionless during scanning to avoid motion artifacts 3
CT Component
- Low-dose CT scan for attenuation correction and anatomical correlation is standard 1
- CT acquisition parameters should be chosen to minimize patient exposure while obtaining necessary diagnostic information 1
- CT-AC scan should be performed during tidal or shallow breathing 1
PET Component
- Scoring FDG uptake: qualitative visual grading; if result is unclear, compare with liver background (grading 0–3) 1
- Decay correction must be enabled 1
- Body parts to include: from top of head to at least midthigh, preferably to below the knees 1
Limitations of PET/CT
- Limited accuracy in anatomic localization due to poor accumulation of FDG tracer in certain neoplastic tissues 2
- False-negative results occur in subcentimetric lesions (<1 cm) due to insufficient metabolically active malignant cells 2
- Poor detection of peritoneal disease, especially with lesion sizes <5 mm 2
- Limited sensitivity in detecting early-stage (T1 and T2) tumors 2
- Not recommended for routine screening due to undefined exact role 1, 2
Special Considerations
Brain Imaging
- Patient preparation should be specific for brain scanning 1
- 5-minute acquisition 45-50 minutes after injection with doses of 300-400 MBq 1
- Arms down, head fixed in a head holder 1
Radiation Safety
- Combined PET/CT imparts radiation dose from both modalities, creating unique radiation safety issues 4
- CT scan parameters should be chosen to minimize exposure while maintaining diagnostic quality 1
- Ultra low-dose CT scans with iterative reconstruction methods can reduce radiation exposure 1
Clinical Value and Interpretation
- Side-by-side viewing of PET and CT scans is essential, as in 42.4% of cases, combined viewing is important for correct diagnosis 5
- PET/CT can speed up patient throughput by at least 25% compared to separate PET and CT scans 6
- For therapy monitoring, consistency in patient preparation, image acquisition, and processing between baseline and follow-up scans is crucial 7