Radiation-induced lung toxicity predictors: Retrospective analysis of 90 patients treated with stereotactic body radiation therapy for stage I non-small-cell lung carcinoma.

BACKGROUND: The main complication after hypofractionated radiotherapy for lung carcinoma is radiation-induced lung toxicity, which can be divided into radiation pneumonitis (acute toxicity, occurring within 6 months) and lung fibrosis (late toxicity, occurring after 6 months). The literature describes several predictive factors related to the patient, to the tumor (volume, central location), to the dosimetry and to biological factors.

MATERIALS AND METHODS: This study is a retrospective analysis of 90 patients treated with stereotactic body irradiation for stage I non-small-cell lung carcinoma between December 2010 and May 2015.

RESULTS: Radiation pneumonitis was observed in 61.5% of the patients who were mainly asymptomatic (34%). Chronic obstructive pulmonary disease was not predictive of radiation pneumonitis, whereas active smoking was protective. Centrally located tumors were not more likely to result in this complication if the radiation schedule utilized adapted fractionation. In our study, no predictive factor was identified. Whereas the mean lung dose was a predictive factor in 3D radiotherapy, the lung volume irradiated at high doses seemed to be involved in the pathogenesis after hypofractionated radiotherapy.

CONCLUSION: The discovery of predictive factors for radiation pneumonitis is difficult due to the rarity of this complication, especially with an 8×7.5Gy schedule. Radiation pneumonitis seems to be correlated with the volume irradiated at high doses, which is in contrast to the known knowledge about the organs in parallel. This finding leads us to raise the hypothesis that vessel damage, organs in series, occurring during hypofractionated radiotherapy could be responsible for this toxicity.