Analysis of the dosimetry differences between peripheral early stage non-small cell lung cancer (NSCLC) treated with SBRT technique

Objective: To explore the dosimetric difference between different radiotherapy technologies in the treatment of early peripheral stage non-small-cell lung cancer (NSCLC). Methods: Four-dimensional computed tomography scans and delineation of target volumes and organs at risk (OARs) were performed in 5 patients pathologically diagnosed with stage T₁/T₂ peripheral NSCLC who were admitted from 2014 to 2015. Target volumes contained gross tumor volume (GTV), internal target volume (ITV), and planning target volume (PTV). ITV was contoured on the maximum intensity projection images. PTV was defined as ITV plus a 5 mm margin. OARs contained the heart, lung, esophagus, and spinal cord. The Monaco 5.0 treatment planning system was used to design three plans. The three-dimensional conformal radiotherapy (3DCRT) plan had 11 fields in the diseased lung covering the PTV plus a 0.2 cm margin. The sliding window intensity-modulated radiotherapy (SW-IMRT) plan had 9 fields in the same areas as the 3DCRT plan. The volumetric modulated arc therapy (VMAT) plan had the gantry rotating 180° around the diseased lung. The evaluation criteria referred to the RTOG 0618 trial. Comparison was made by paired t test. Results: The SW-IMRT plan had a significantly better homogeneity index than the 3DCRT plan (1.03 vs. 1.24, P =0.017). Compared with the VMAT plan, the mean monitor units in the 3DCRT plan was significantly reduced by 24.5%(P = 0.022). The V₃₀ and V₄₀ of the 3DCRT plan were significantly reduced by 29.4% and 28.4%, respectively, compared with the SW-IMRT plan (P = 0.003, 0.006) and 56.7% and 59.7%, respectively, compared with the VMAT plan (P = 0.041, 0.019). Conclusions: 3DCRT may be an appropriate radiotherapy method for early stage NSCLC. (authors)