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

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 358deg arc was used for PTVs1-3, while three 135deg 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. (author)