Dosimetric differences among volumetric modulated arc radiotherapy (RapidArc) plans based on different target volumes in radiotherapy of hepatocellular carcinoma

摘要

We investigated the dosimetric differences among volumetric-modulated arc radiotherapy (RapidArc, RA) plans designed for various target volumes in hepatocellular carcinoma (HCC). Ten HCC patients underwent 3D-CT scanning at free breathing (FB), 3D-CT at end inspiration hold (EIH) assisted by an Active Breathing Coordinator (ABC), and 4D-CT scanning. Gross tumor volumes (GTVs) were manually contoured on CT images. The individualized internal gross target volume (IGTV1) was obtained from 10 GTVs from 4D-CT images. Tumor individual margins were measured from GTVFB to IGTV1. The IGTV2 was obtained from GTVFB by applying individual margins. Four planning target volumes (PTV1-4) were obtained from IGTV1, IGTV2, GTVFB, and GTVEIH, respectively. An RA plan was designed for each of the PTVs (RA1–4). One 358° arc was used for PTVs1–3, while three 135° arcs were used for PTV₄. It was found that PTV₂ and PTV₃ were larger than PTV₁ and PTV₄. The mean values of PTV₃/PTV₁ and PTV₃/PTV₄ were 2.5 and 1.9, respectively. The individual margins in the X, Y and Z axial directions varied greatly among these patients. There were no significant differences in the conformal index or homogeneity index among the four RA plans. RA₁ and RA₄ significantly reduced the radiation dose of normal liver tissue compared with RA₂ and RA₃ (P < 0.01). There were no significant differences between the radiation doses of the stomach and duodenum. RapidArc combined with 4D-CT or ABC technology is a promising method in radiotherapy of HCC, and accurately targeted the tumor volume while sparing more normal liver tissue.