Dose–volume thresholds and smoking status for the risk of treatment-related pneumonitis in inoperable non-small cell lung cancer treated with definitive radiotherapy

Abstract Purpose To identify clinical risk factors and dose–volume thresholds for treatment-related pneumonitis (TRP) in patients with non-small cell lung cancer (NSCLC). Methods and materials Data were retrospectively collected from patients with inoperable NSCLC treated with radiotherapy with or without chemotherapy. TRP was graded according to Common Terminology Criteria for Adverse Events, version 3.0, with time to grade ⩾3 TRP calculated from start of radiotherapy. Clinical factors and dose–volume parameters were analyzed for their association with risk of TRP. Results Data from 576 patients (75% with stage III NSCLC) were included in this study. The Kaplan–Meier estimate of the incidence of grade ⩾3 TRP at 12 months was 22%. An analysis of dose–volume parameters identified a threshold dose–volume histogram (DVH) curve defined by V20 ⩽25%, V25 ⩽20%, V35 ⩽15%, and V50 ⩽10%. Patients with lung DVHs satisfying these constraints had only 2% incidence of grade ⩾3 TRP. Smoking status was the only clinical factor that affected the risk of TRP independent of dosimetric factors. Conclusions The risk of TRP varied significantly, depending on radiation dose–volume parameters and patient smoking status. Further studies are needed to identify biological basis of smoking effect and methods to reduce the incidence of TRP.