What are the guidelines for using Fluorodeoxyglucose (FDG) Positron Emission Tomography/Computed Tomography (PET/CT) scans in primary care settings for patients with suspected pulmonary conditions?

FDG-PET/CT Guidelines for Pulmonary Conditions in Primary Care

In primary care, FDG-PET/CT should be ordered for indeterminate solid pulmonary nodules >0.8 cm when the pre-test probability of malignancy is low to moderate (5%-65%), for suspected lung cancer recurrence in patients who are candidates for salvage treatment, and for initial staging of confirmed lung cancer to detect nodal and distant metastases. 1

When to Order FDG-PET/CT

Indeterminate Pulmonary Nodules

• Order FDG-PET/CT for solid nodules >0.8 cm when discovered incidentally and the malignancy risk is uncertain 1
• The Fleischner Society and ACCP guidelines specifically recommend functional imaging with FDG-PET/CT for solid indeterminate nodules ≥0.8 cm when pre-test probability of malignancy is 5%-65% 1
• FDG-PET/CT demonstrates pooled sensitivity and specificity of 88-96% and 77-88% respectively for differentiating benign from malignant nodules 1
• Do not order FDG-PET/CT for nodules <0.8 cm due to limited spatial resolution that reduces accuracy 1

Suspected Lung Cancer Recurrence

• Order FDG-PET/CT when there is clinical suspicion of recurrent disease in patients who are candidates for salvage treatment 1, 2
• FDG-PET/CT shows superior performance with 90% sensitivity and 90% specificity for detecting recurrent lung cancer, compared to 78% sensitivity and 80% specificity for conventional imaging 1
• FDG-PET/CT can rule out recurrence or metastasis in approximately 25% of scans performed for suspected recurrence, avoiding unnecessary interventions 1
• Order FDG-PET/CT to assess focal lesions on chest CT that may represent radiation fibrosis, atelectasis, or other benign conditions, though histopathologic confirmation of FDG-avid lesions remains necessary 1

Initial Staging of Confirmed Lung Cancer

• Order FDG-PET/CT for all patients with newly diagnosed non-small cell lung cancer (NSCLC) to stage mediastinal nodes and detect distant metastases 1
• FDG-PET/CT is superior to CT alone for N and M staging, reducing futile thoracotomies by 17-20% 1
• Integrated FDG-PET/CT demonstrates 83% sensitivity and 92% specificity for mediastinal node metastases 1
• For small cell lung cancer (SCLC), order FDG-PET/CT only if limited-stage disease is suspected; when extensive disease is established, FDG-PET/CT is optional 1

When NOT to Order FDG-PET/CT

Ground-Glass Nodules and Part-Solid Nodules

• Do not order FDG-PET/CT for ground-glass nodules or part-solid nodules with small solid components 1
• These lesions show low metabolic activity regardless of malignancy status, making PET/CT unreliable 1
• Follow-up chest CT is the preferred approach for ground-glass nodules due to their indolent behavior 1
• Low-grade malignancies including bronchioloalveolar carcinoma and carcinoid tumors frequently produce false-negative PET results 3, 4

Routine Surveillance Without Clinical Suspicion

• Do not order FDG-PET/CT for routine surveillance of treated lung cancer in asymptomatic patients without clinical suspicion of recurrence 1, 2
• Evidence for routine surveillance FDG-PET/CT in SCLC is scarce and its utility remains indeterminate 1
• Chest CT with IV contrast is the recommended surveillance modality for asymptomatic patients 1

Inflammatory and Infectious Conditions

• Do not order FDG-PET/CT in regions with high prevalence of endemic infections (tuberculosis, histoplasmosis, coccidioidomycosis) without understanding the high false-positive rate 1
• Specificity drops to 25-61% in endemic regions compared to 77% in non-endemic areas 1
• Active granulomatous infections, sarcoidosis, and rheumatoid nodules cause false-positive FDG uptake 1, 4

Diffuse Lung Disease

• Do not order FDG-PET/CT for evaluation of diffuse lung disease, acute exacerbation of interstitial lung disease, or routine follow-up of confirmed diffuse lung disease 1
• Limited research does not support FDG-PET/CT for these indications 1
• High-resolution CT without contrast is the appropriate imaging modality 1

Critical Timing Considerations

Post-Treatment Imaging

• Wait at least 3 months after completion of treatment before ordering FDG-PET/CT for response assessment 5
• Wait at least 1 month after radiotherapy or surgery to reduce false-positive results from inflammation 6
• For staging purposes, perform FDG-PET/CT within 60 days of planned resection and within 30 days before radiation therapy 1

Important Caveats and Pitfalls

False-Negative Results

• Be aware that certain malignancies show low FDG uptake: carcinoid tumors, adenocarcinomas with predominant ground-glass components, mucinous adenocarcinomas, and bronchioloalveolar carcinoma 1, 3
• Small nodule size (<0.8 cm) is the most common cause of false-negative results 1
• Defective imaging technique can produce false-negative studies 1

False-Positive Results

• Inflammatory and infectious processes are the primary cause of false-positive FDG-PET/CT results 1, 4
• Active tuberculosis, histoplasmosis, coccidioidomycosis, sarcoidosis, and rheumatoid nodules all demonstrate increased FDG uptake 1, 7
• Always correlate PET findings with clinical context and consider biopsy confirmation for FDG-avid lesions 1, 8

Specific Anatomic Sites

• FDG-PET/CT has high accuracy (>90%) for detecting bone metastases, superior to bone scintigraphy 1
• For adrenal nodules, lack of FDG uptake conclusively indicates benign adenoma (94% sensitivity, 82% specificity), obviating further workup 1
• For liver metastases, FDG-PET/CT demonstrates 92-100% accuracy despite heterogeneous physiologic liver activity 1
• FDG-PET/CT cannot evaluate brain metastases; brain MRI with contrast is required for this purpose 1

Essential Referral Information

When ordering FDG-PET/CT from primary care, include 6:

• Complete patient demographics: name, date of birth, medical record number, height, weight 6
• Specific clinical question the PET/CT must answer and how results will change management 6
• Oncological history: known tumor sites, stage of disease, whether initial staging or restaging 6
• Treatment history: type and date of last treatment, current medications 6
• Prior imaging: dates and reports from chest X-rays, CT, MRI, previous PET/CTs with DICOM data when available 6
• Relevant comorbidities: chronic kidney disease, thyroid dysfunction, infectious/inflammatory diseases 6
• Current glucose level, as hyperglycemia reduces FDG uptake accuracy 6