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

Purpose: To evaluate dosimetric factors predictive for radiation-induced pneumonitis (RP) after pulmonary stereotactic body radiotherapy (SBRT). Materials and methods: A 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 alpha/beta ratio of 3 Gy for RP. Dose-volume parameters and incidences of RP >= grade II SWOG were fitted using NTCP models. Results: Eleven 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 (V-2.5-V-50) were correlated with incidences of RP with a continuous decrease of the goodness of fit for higher doses. Conclusions: The MLD and V-2.5-V-50 of the ipsilateral lung were correlated with incidences of RP after pulmonary SBRT. (C) 2010 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 97 (2010) 65-70