We created volumetric-modulated arc therapy (VMAT) plans for portal vein tumor thrombus (PVTT) in hepatocellular carcinoma, and compared the results with those from three-dimensional conformal radiotherapy (3D-CRT) and rotational conformal radiotherapy (R-CRT) plans. CT scan data from 10 consecutive patients with PVTT treated with 3D-CRT between January 2008 and January 2010 were utilized in the analysis. We analyzed the dosimetric properties of the plans for the 10 patients using the three different techniques with three different isocenter doses of 50, 56 and 60 Gy in 2-Gy fractions. The D95, Dmean, homogeneity index and conformity index were compared for the planning target volume (PTV). The Dmean, V20 and V30 were also compared for normal livers. The monitor units (MUs) and the treatment time were also evaluated. The normal liver V30 for VMAT was significantly less than that for 3D-CRT for the prescribed doses of 56 and 60 Gy (P < 0.05). It was also found that the normal liver V30 resulting from 3D-CRT was prohibitively increased when the prescribed dose was increased in two steps. For PTV D95, we found no significant differences between the three techniques for the 50- and 56-Gy prescriptions, or between VMAT and the other techniques for the 60-Gy prescription. The differences in the MUs and treatment times were not statistically significant between VMAT and 3D-CRT. We have demonstrated that VMAT may be a more advantageous technique for dose escalation reaching 60 Gy in the treatment of PVTT due to the reduced normal liver V30.
Keywords: hepatocellular carcinoma; portal vein tumor thrombus; three-dimensional conformal radiotherapy; volumetric-modulated arc therapy.