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PET/CT in lung cancer and the pulmonary nodule
In NSCLC, FDG PET/CT is a mandatory staging study for every patient intended for radical treatment, because it finds unexpected metastases and guides sampling of mediastinal nodes — but a PET-positive node is not enough to deny surgery without tissue confirmation.
Why it matters in the exam
The exam asks about the pulmonary nodule: a solid nodule of 8 mm or more with intermediate probability of malignancy is the classic indication for PET, and a high SUV raises the probability (Herder model). A nodule smaller than 8 mm or a ground-glass nodule may be falsely negative, as may adenocarcinoma in situ and carcinoid. Granulomas, tuberculosis and fungal infection are the common false positives — in endemic areas specificity is lower.
In staging, PET/CT replaces bone scintigraphy and changes the stage in about a quarter of patients. A mediastinal node that is PET-positive requires confirmation by EBUS or mediastinoscopy before surgery is abandoned, because inflammation causes false positives. A negative mediastinum on PET in a peripheral tumour smaller than 3 cm allows invasive sampling to be skipped; in a central tumour, a large tumour or a PET-positive N1 node, sampling is still done. Brain metastases require MRI, because the brain takes up FDG physiologically.
In radiotherapy planning PET defines the target volume and separates tumour from atelectasis. After radiation (including SBRT) radiation pneumonitis takes up FDG for months; linear uptake within the radiation field fits inflammation, while focal, growing uptake raises suspicion of recurrence. In small cell lung cancer (SCLC) PET helps separate limited from extensive disease. An FDG-avid adrenal mass in a patient with NSCLC needs confirmation before a solitary metastasis is declared.
Key points
- PET/CT is mandatory in NSCLC staging before radical treatment.
- Solid nodule 8 mm or more — indication for PET.
- Positive mediastinal node — confirm with EBUS.
- Brain — MRI, not PET.
- After radiation — linear uptake is inflammation.
Summary table
| Situation | Role of PET/CT | Pitfall |
|---|---|---|
| Solid nodule 8 mm or more | Estimating the probability of malignancy | Granulomas and infection |
| Nodule under 8 mm or ground glass | Not recommended | False negative |
| Staging before radical treatment | Mandatory; replaces bone scintigraphy | Positive node — confirm with EBUS |
| Brain | Not suitable | Brain MRI |
| After radiation | Separating inflammation from recurrence | Wait about 3 months |
A free exam question
לפניך בדיקת PET/CT של מטופל עם סרטן ריאה מסוג NSCLC ב RUL לאחר סיום הטיפול במחלה . איזה מבין התיאורים הבאים הוא המתאים ביותר לתגובה של המטופל? Progressive (the question as examined, in Hebrew)
- א. disease תחת הטיפול Pseudoprogressio
- ב. n של הגידול תחת טיפול אימונולוגי
- ג. פנאומוניטיס תחת טיפול ביולוגי
- ד. שינויים דלקתיים בריאה בתגובה לטיפול קרינתי מסוג SBRT
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Sources
- NCCN Guidelines: Non-Small Cell Lung Cancer, 2025 — Pretreatment evaluation and mediastinal staging
- ESMO Clinical Practice Guidelines: Early and Locally Advanced Non-Small-Cell Lung Cancer, 2017 — Staging with PET-CT and invasive mediastinal staging
- British Thoracic Society Guidelines for the Investigation and Management of Pulmonary Nodules, 2015 — PET-CT and the Herder model
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.