Prediction of radiation-induced changes in the lung after stereotactic body radiation therapy of non–small-cell lung cancer

Purpose: To estimate the risk of radiation-induced changes in the lung before single-dose treatment (stereotactic body radiation therapy [SBRT]) of lung cancer, the quantitative dose-response and volume–response relations must be known. Methods and Materials: A total of 64 patients treated for non–small-cell lung cancer with single doses of 20–30 Gy were classified according to the occurrence or nonoccurrence of perifocal changes in the lung detected by CT. Patients without toxic events in the lung were required to have ≥6 months of follow-up. The mean dose (Dmean ) in the ipsilateral lung and the volume receiving >7 or 10 Gy (V7 and V10 , respectively) were used to calculate the dose-response and volume–response curves. The predictive value of additional variables was also investigated. Results: Of the 64 patients, 83% exhibited the selected endpoint. The tolerance values at a 50% probability of toxic events were 1.2 ± 0.7 Gy for the Dmean and 5.8 ± 3.0% and 3.1 ± 2.0% for V7 and V10 , respectively. A nonsignificant shift to higher doses was seen for the dose–response curve for the upper compared with the lower part of the lung. Conclusion: The Dmean , V7 , and V10 can be used to predict the risk of lung toxicity after SBRT treatment of non–small-cell lung cancer. Because of the lack of patients with low prescribed doses, however, the related uncertainty of this prediction is still relatively large. The Dmean , V7 , and V10 are equally well suited. The additional investigated variables did not provide significant advantages. The lower part of the lung appears to be more radiosensitive than the upper.