Ipsilateral lung dose as a correlative measure for radiation pneumonitis in patients treated with definitive concurrent radiochemotherapy

Objective: Mean lung dose (MLD) and percent of total lung (TL) volume that receive a dose greater than 20 Gy (V-20) have been the most validated parameters in the prediction of radiation pneumonitis (RP). However, these parameters present mean values of TL parenchyma and predict the right and the left lung as a unique functional organ unit, not take into account the difference in function and dose density between the lungs. Furthermore, there have been very limited data evaluating ipsilateral lung dosimetric constraints in addition to TL parameters to predict RP in non-small cell lung cancer (NSCLC) patients treated with radiochemotherapy (RCT). Methods: Between 2010 and 2017, clinical-radiological findings of NSCLC patients treated with RCT were evaluated in terms of RP, retrospectively. MLD, V-20, and V-30 values of ipsilateral lung were assessed from dose-volume histogram and registered. The primary endpoint was to assess the relation between ipsilateral lung dose constraints and RP risk. Results: There were 75 patients. There was >= Grade 2 RP in 33 cases (%44). In univariate analysis, ipsilateral MLD, ipsilateral V-20, ipsilateral V-30,V- and TL V-30 were found to be significant. Ipsilateral MLD and PTV were found to be the independent risk factors for RP. Cutoff values for RP risk were determined as 18Gy, 35%, and 28% for ipsilateral MLD, ipsilateral V-20, and ipsilateral V-30, respectively. Predictive values for ipsilateral MLD and ipsilateral V-20 were higher than TL. Conclusions: In NSCLC patients treated with RCT, MLD, V-20, and V-30 values of ipsilateral lung parameters might increase the predictability of RP risk in addition to TL parameters. Advances in Knowledge: Cutoff values for RP risk were determined as 18Gy, 35%, and 28% for ipsilateral MLD, ipsilateral V-20, and ipsilateral V-30, respectively. Predictive values for ipsilateral MLD and ipsilateral V-20 were higher than TL.