Volumetric intensity-modulated Arc (RapidArc) therapy for primary hepatocellular carcinoma: comparison with intensity-modulated radiotherapy and 3-D conformal radiotherapy

Background: To compare the RapidArc plan for primary hepatocellular carcinoma (HCC) with 3-D conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) plans using dosimetric analysis. Methods: Nine patients with unresectable HCC were enrolled in this study. Dosimetric values for RapidArc, IMRT, and 3DCRT were calculated for total doses of 45 similar to 50.4 Gy using 1.8 Gy/day. The parameters included the conformal index (CI), homogeneity index (HI), and hot spot (V(107%)) for the planned target volume (PTV) as well as the monitor units (MUs) for plan efficiency, the mean dose (D(mean)) for the organs at risk (OAR) and the maximal dose at 1% volume (D(1%)) for the spinal cord. The percentage of the normal liver volume receiving >= 40, > 30, > 20, and > 10 Gy (V(40 Gy), V(30 Gy), V(20 Gy), and V(10 Gy)) and the normal tissue complication probability (NTCP) were also evaluated to determine liver toxicity. Results: All three methods achieved comparable homogeneity for the PTV. RapidArc achieved significantly better CI and V(107%) values than IMRT or 3DCRT (p < 0.05). The MUs were significantly lower for RapidArc (323.8 +/- 60.7) and 3DCRT (322.3 +/- 28.6) than for IMRT (1165.4 +/- 170.7) (p < 0.001). IMRT achieved a significantly lower D(mean) of the normal liver than did 3DCRT or RapidArc (p = 0.001). 3DCRT had higher V(40 Gy) and V(30 Gy) values for the normal liver than did RapidArc or IMRT. Although the V(10 Gy) to the normal liver was higher with RapidArc (75.8 +/- 13.1%) than with 3DCRT or IMRT (60.5 +/- 10.2% and 57.2 +/- 10.0%, respectively; p < 0.01), the NTCP did not differ significantly between RapidArc (4.38 +/- 2.69) and IMRT (3.98 +/- 3.00) and both were better than 3DCRT (7.57 +/- 4.36) (p = 0.02). Conclusions: RapidArc provided favorable tumor coverage compared with IMRT or 3DCRT, but RapidArc is not superior to IMRT in terms of liver protection. Further studies are needed to establish treatment outcome differences between the three approaches.