Modeling radiation pneumonitis of pulmonary stereotactic body radiotherapy: The impact of a local dose–effect relationship for lung perfusion loss

Abstract Purpose To investigate if a local dose–effect (LDE) relationship for perfusion loss improves the NTCP model fit for SBRT induced radiation pneumonitis (RP) compared to conventional LDEs. Methods and materials Multi-institutional data of 1015 patients treated with SBRT were analyzed. Dose distributions were converted to NTD with α/β  = 3 Gy. The Lyman–Kutcher–Burman NTCP model was fitted to the incidence grade ≥2 RP by maximum likelihood estimation with mean lung dose (MLD), equivalent uniform doses (EUD) using three LDE functions (power-law (EUD power ), logistic with 2 free parameters (EUD log-free ) and logistic with fixed parameters describing local perfusion loss (EUD Perfusion )) and volume above a threshold dose (V x ). Models were compared with the Akaike weights (Aw) derived from the Akaike information criteria (AIC). Results The median time to grade ≥2 RP was 4.2 months and plateaued after 17 months at 5.4%. A strong dose–effect relationship for RP incidence was observed. The EUD Perfusion based NTCP model had the lowest AIC. The Aw were 0.53, 0.19, 0.11, 0.11, 0.05 for the EUD Perfusion , V x , MLD, EUD log-free and EUD power LDEs respectively. Conclusion A LDE for perfusion loss provided modest improvement in NTCP model fit for SBRT induced radiation pneumonitis.