Pulmonary injury and tumor response after stereotactic body radiotherapy (SBRT): results of a serial follow-up CT study.

PURPOSE: To evaluate the CT morphological pattern of tumor response and pulmonary injury after stereotactic body radiotherapy (SBRT) for early stage non-small lung cancer (NSCLC) and pulmonary metastases. MATERIALS AND METHODS: Seventy patients (lesions n=86) with pulmonary metastases (n=48) or primary early stage NSCLC (n=38) were analyzed. Patients were treated with hypofractionated SBRT (three to eight fractions with a single dose between 6 and 12.5 Gy; n=56) or with radiosurgery (26 Gy; n=30). The pattern and sequence of pulmonary injury and of tumor response was evaluated in 346 follow-up CT studies, 4.9 on average. RESULTS: Symptomatic pneumonitis was observed in 10% after a median interval of 5 months. No pulmonary reaction was observed in most patients 6 weeks after treatment; spotted-streaky condensations were characteristic between 3 months and 6 months. Dense consolidation and retraction started after 9 months and the fibrotic remodelling process continued for years. Ten targets relapsed after a median of 7 months. At 12 months complete response was seen in 43% and the differentiation of residual tumor from pulmonary reaction was not possible in 33%. CONCLUSIONS: A typical sequence of pulmonary reactions was observed without differences between hypofractionated treatment and radiosurgery. Onset of pneumonitis was later compared to conventionally fractionated radiotherapy.