Predictive parameters of symptomatic radiation pneumonitis following stereotactic or hypofractionated radiotherapy delivered using volumetric modulated arcs.

Abstract

To identify dosimetric factors that predict development of radiation pneumonitis (RP) following stereotactic or hypofractionated radiotherapy for lung tumors. Seventy-nine consecutive patients with either a planning target volume (PTV)>100 cm(3) (n=69) or prior pneumonectomy or bi-lobectomy (n=13) were identified. Radiation doses (range: 5-50 Gy, with 5 Gy increments) were converted to equivalent doses (EQD(2 Gy)) (α/β=3). Total lung (TL), ipsilateral (IL) and contralateral lung (CL) volumes minus PTV, receiving 5 Gy (V5) up to 50 Gy (V50) and mean lung dose (MLD) were analyzed. Predictors of grade ≥3 RP (CTCAEv4.03) were identified with concordance-statistics (C-statistic) and p-values used to quantify the performance of the model. Factors found to be significant were entered into a recursive partitioning analysis (RPA). Median PTV was 150 cm(3). Grade ≥3 RP was observed in 8 patients (10%). In univariable analysis, CL-MLD, CL-V5-15, TL-MLD, TL-V5-V10 and ITV size were predictive of RP (p<0.05). In multivariable analysis, contralateral MLD (p=.007) and ITV (p=.063) were the strongest predictors of grade ≥3 RP, with excellent discrimination (C-statistic: 0.868). Contralateral MLD and ITV size are both strong predictors of grade ≥3 RP post treatment. Planning constraints should aim to keep contralateral MLD below 3.6 Gy.