Radiological changes after stereotactic radiotherapy for stage I lung cancer

Stereotactic body radiation therapy (SBRT) is entering routine clinical use for selected patients with early-stage non-small cell lung cancer. Post-SBRT radiological changes are commonly seen on follow-up computed tomography (CT) imaging and can cause diagnostic dilemmas. The aim of this study is to describe the incidence, radiological severity, and long-term morphology of these changes.

CT scans from patients treated between 2003 and June 2008 were eligible for evaluation if radiological follow-up had been performed at our center for at least 2 years, and there was no definite evidence of local recurrence. Timing, incidence, morphology, and severity of lung changes were determined.

CT scans from 61 patients (68 lesions) with a median follow-up of 2.5 years were evaluated. Within 6 months, 54% of lesions were associated with additional radiological abnormalities, and this figure reached 99% after 36 months. Most changes were scored as mild to moderate, and although the median time to first observation was 17 weeks, 25% appeared ≥ 1 year post-SBRT. In 47% of lesions, the morphology or severity of changes continued to evolve more than 2 years posttreatment.

Mild-moderate radiological changes are common after lung SBRT. Some degree of late change is nearly universal, and it often continues to evolve more than 2 years post-SBRT. Clinicians should be aware of these radiological findings, which need to be distinguished from the uncommon cases of local failure post-SBRT.