18P Precision radiotherapy for centrally located non-small cell lung cancer (NSCLC)

Abstract

Molecular analysis of lung tissue toxicity can be performed using radiotherapy dose volumetric parameters (DVP). Minimizing the percentage of volume of bilateral lung parenchyma (exclude tumor) receiving dose more than 20Gy (V20) and 5Gy (V5) and minimizing the mean lung dose (MLD) was proven to be effective to reduce the incidence of radiation induced pneumonitis (RP). We aimed at analyze the lung tissue toxicity between volumetric-modulated arc therapy (VMAT) with single-planar beam arrangement (SP-VMAT), and VMAT with dual-planar beam arrangement (DP-VMAT) based on DVP. A retrospective study was conducted for 17 patients who were treated for stage III centrally located non-small cell lung cancer. Identical CT and structure data set were used to plan SP-VMAT, and DP-VMAT, with prescription to give 60Gy to PTV in 30 fractions. Radiotherapy thoracic DVP to planned target volume (PTV) (including Dmax, Dmean, Dmin, D98% (Gy), D95% (Gy), D50% (Gy), and D2% (Gy)) and DVP to both lungs excluding tumor (V20, V10, V5, and Dmean) were retrieved from SP-VMAT and DP-VMAT. Non parametric paired-T test were used for data analysis. There was no significant difference between all DVP to PTV in both SP-VMAT and DP-VMAT plans, suggesting both SP-VMAT and DP-VMAT plans were clinically acceptable. For DVP to both lungs (excluding tumor), the V5 of SP-VMAT (67.95% ± 14.65) was significantly lower than that of DP-VMAT 71.41 ± 11.83, p=0.006). For ipsilateral lung, Dmean, V10, V5 of SP-VMAT was 24.46Gy ± 5.55, 63.48% ± 14.88 and 71.98% ± 16.18 respectively, which were significantly lower than that of DP-VMAT 25.63Gy ± 5.03, 69.8%±11.73 and 79.73%±11.8. The SP-VMAT in this study showed more favorable DVP in both lungs and ipsilateral lung for centrally located NSCLC. The features of dose distribution can be applied in precision medicine in oncology.