Differences and radiation pneumonitis prediction of lung dosimetric parameters based on three normal lung definitions in 3DCRT treatment planning

Abstract

Objective To compare lung dose-volume histogram (DVH) parameters based on commonly used normal lung definitions,i.e.,lungs-gross tumor volume (GTV),lungs-clinical target volume (CTV),and lungs-planning target volume (PTV),in three-dimensional conformal radiotherapy (3 DCRT) and to determine to what extent they differ in predicting radiation pneumonitis (RP).Methods A total of 147 non-small cell lung cancer patients treated with concurrent chemotherapy and 3DCRT from 2006 to 2010 were collected.RP was diagnosed according to RTOG criteria.Lung DVHs were generated with exclusion of GTV,CTV,or PTV.Independent-samples t test was used to compare DVH parameters based on different normal lung definitions,and the predictive values of these parameters for RP were evaluated with the receiver operating characteristic (ROC) curve.Results There were significant differences in minimum lethal dose (MLD) between lungs-GTV and lungs-CTV/lungs-PTV ((1.16 ± 0.96) Gy vs.(3.45 ± 1.43) Gy).The biggest difference in MLD for the same patient based on different definitions was 8.73 Gy.MLD based on lungs-GTV had a better predictive value for grades ≥2 and ≥3 RP than MLD based on lungs-CTV and lungs-PTV,with larger areas under the ROC curve (lungs-GTV ∶ area =0.614,P=0.024;area =0.678,P=0.056;lungs-CTV∶area =0.556,P=0.269;area =0.602,P=0.226 ; lungs-PTV ∶ area =0.551,P =0.317 ; area =0.616,P =0.167).We drew a similar conclusion when analyzing lung V5-V50.Conclusions There are significant differences between DVH parameters based on various normal lung definitions,which cannot be neglected in the clinical setting.DVH parameters based on lungs-GTV may be the most accurate in predicting RP. Key words: Carcinoma, non-small cell lung/radiotherapy; Radiotherapy, three-dimensional conformal ; Radiation pneumonitis ; Dosimetry