Comparison of VMAT and IMRT plans for SBRT treatment of multiple liver metastases using a single isocenter

To perform a comparison of the plan quality between volumetric modulated arc therapy (VMAT) and intensity modulated radiotherapy (IMRT) for multiple liver metastases using single-isocenter stereotactic body radiotherapy (SBRT).

Twenty-one patients who developed two or three adjacent liver metastases were included. For every patient, both VMAT and IMRT plans were replanned respectively for SBRT treatment. Dosimetric parameters, including the mean dose for the planning target volume, conformity index (CI), homogeneity index (HI) and gradient index (GI), were evaluated. Normal tissue sparing was also investigated. Finally, the total delivered monitor units (MUs) for both groups of treatment plans during irradiation were measured and compared.

Both groups of treatment plans satisfied normal tissue tolerance and produced clinically accepted dose distributions. The VMAT plans provided higher values of HI and GI as well as similar CI values in comparison with the IMRT plans. In addition, the VMAT plans obtained ultimately a improved mean dose to the target and a reduced dose to the organs at risk. However, there were no statistically significant differences in the V7Gy and D700cc of healthy liver, the mean dose and V15Gy of the ipsilateral kidney, the mean dose to the stomach, and the maximum dose to the heart between the two groups. Finally, the VMAT plans showed fewer MUs than the IMRT plans.

The plan quality of single-isocenter VMAT plans is superior to that of IMRT plans for the SBRT treatment of multiple metastatic liver tumors from the perspective of pure physical parameters.