Dose–response relationship for radiation-induced pneumonitis after pulmonary stereotactic body radiotherapy

PurposeTo evaluate dosimetric factors predictive for radiation-induced pneumonitis (RP) after pulmonary stereotactic body radiotherapy (SBRT).Materials and methodsA retrospective analysis was performed based on 59 consecutive patients treated with cone-beam CT-based image-guided SBRT for primary NSCLC (n = 21) or pulmonary metastases (n = 54). The majority of patients were treated with radiosurgery of 26 Gy to 80% (n = 29) or three fractions of 12.5 Gy to 65% (n = 40). To correct for different single fraction doses, local doses were converted to 2 Gy equivalent normalized total doses (NTDs) using α/β ratio of 3 Gy for RP. Dose–volume parameters and incidences of RP ⩾ grade II SWOG were fitted using NTCP models.ResultsEleven patients developed RP grade II. With an average MLD of 10.3 ± 5.6 Gy to the ipsilateral lung, a significant dose–response relationship was observed: the MLD was 12.5 ± 4.3 Gy and 9.9 ± 5.8 Gy for patients with and without development of RP, respectively. Additionally, volumes of the lung exposed to minimum doses between 2.5 and 50 Gy (V2.5–V50) were correlated with incidences of RP with a continuous decrease of the goodness of fit for higher doses.ConclusionsThe MLD and V2.5–V50 of the ipsilateral lung were correlated with incidences of RP after pulmonary SBRT.