P1.17-20 Excluding PTV From Lung Volume May Better Predict Radiation Pneumonitis For IMRT Treated Lung Cancer Patients

Abstract

Lung dose-volume histogram(DVH) could be calculated from multiple normal lung definitions. These dose differences have a direct impact on lung cancer radiotherapy treatment planning. Earlier study from 3D conformal radiation therapy suggested dose computation from total normal lung excluding gross tumor volume (GTV) may be more accurate than that of excluding planning target volume (PTV). It is unclear which definition should be used to more accurately predict radiation pneumonitis (RP) in lung cancer patients treated with intensity-modulated radiation therapy (IMRT). We aim to determine a superior normal lung volume to more accurately predict symptomatic RP in lung cancer patients treated with IMRT. This is a retrospective study. All patients treated with IMRT with at least 3 months follow-up are eligible. The normal lungs are defined by total lung volume excluding GTV, PTV or directly using the total lung volume. V5, V20, and MLD have been extracted for all three definitions. RP was diagnosed and graded according to the National Cancer Institute’s Common Terminology Criteria for Adverse Events, version 4.03. The primary endpoint was grade 2 or higher RP (RP2). Correlation between RP2 and dose parameters were analyzed by logistic regression. We compared RP prediction performance of each lung volume using area under the receiver operating characteristic curve (AUC). A total of 184 consecutive patients treated between January 2014 and October 2017 were eligible, 26 patients (14%) developed RP2 within 3 months after treatment. Significant dosimetric difference was found between any 2-paired lung volumes (Ps<0.0001). All dose parameters from Lung-PTV method had significant correlation with RP2, with greater AUCs than the other two definitions. The best RP prediction performance was found in Lung-PTV volume MLD (AUC=0.649), which is significantly better than Lung-GTV volume MLD (AUC=0.611, P=0.006). There were significant dosimetric differences from various normal lung definitions. Excluding PTV method may accurately predict acute symptomatic radiation pneumonitis for IMRT treated lung cancer patients.