Ground glass and consolidation 1–6 months after thoracic radiotherapy, conforming to the treatment field rather than to anatomical lobes; fibrosis follows with volume loss and traction bronchiectasis — a new mass within it is recurrence until proven otherwise.
Orient first
- Stereotactic body radiotherapy (SBRT) produces focal mass-like consolidation that evolves over years.
- Recurrence: enlarging opacity after 12 months, bulging margins, loss of air bronchograms, filling-in of the fibrosis.
- Immunotherapy pneumonitis is not confined to the field.
Acquire the study
- CT chest with contrast; compare with the radiotherapy plan (dose contour) where available and with all prior studies.
The manoeuvre
- Axial lung window: opacity margins — sharp straight edges crossing fissures along the field.
- Timing relative to treatment completion in months.
- Late phase: volume loss, traction bronchiectasis, air bronchograms.
- Compare with prior studies: enlargement after 12 months, bulging margin, loss of air bronchograms (recurrence features).
- Opacities outside the field: infection, immunotherapy pneumonitis.
What confirms it
- Field-conforming change in the expected time window after radiotherapy.
What licenses you to exclude it
- Opacity outside the treated field is not radiation pneumonitis.
The classic misread
- Calling SBRT consolidation recurrence at 6 months.
- Missing recurrence within established fibrosis.