Seventy-nine consecutive patients with either a planning target volume (PTV) > 100 cm3 (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 (EQD2 Gy) (伪/尾 = 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 猢? 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 cm3. Grade 猢? 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 猢? RP, with excellent discrimination (C-statistic: 0.868).
Contralateral MLD and ITV size are both strong predictors of grade 猢? RP post treatment. Planning constraints should aim to keep contralateral MLD below 3.6 Gy.