(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Volumetric modulated arc therapy (VMAT), an extension of intensity modulated radiation therapy (IMRT), employs modifications in gantry rotation speed, machine dose rate and multi-leaf collimator motion to deliver a 3D dose distribution in rotational mode while using less treatment time than conventional IMRT. This study compared VMAT to IMRT for patients with liver carcinoma.
Methods: Ten patients with liver carcinoma previously treated with IMRT or VMAT were retrospectively selected for this study. Each patient received a total dose of 54 Gy in 1.8 Gy fractions. For each patient, a multibeam IMRT, or single or double-arc VMAT treatment plan, was generated using Varian’s Eclipse RapidArc treatment planning system with the same CT image sets and optimization constraints used for the corresponding clinical IMRT or VMAT treatment plan. For dosimetry evaluation, the dose-volume histograms (DVH) for planning target volumes (PTV) and organs at risk (spine, kidneys, stomach) were used. For efficiency evaluation, monitor units (MU) and beam on times (BOT) were recorded.
Results: Compared to IMRT, VMAT plans showed significant differences in the homogeneity index [mean 5.9% (IMRT) vs. 3.8% (VMAT) with (p=0.009)] and insignificant differences in both conformality index [mean 1.14 (IMRT) vs. 1.08 (VMAT) with (p=0.257)] and normal tissue sparing [mean spine, L/R kidney and stomach doses of 2.68, 1.18/3.21, and 5.49 Gy (IMRT), vs. 2.55, 1.43/2.68, and 5.13 Gy (VMAT) with (p=0.778, 0.144/0.059, 0.721 respectively)]. VMAT required marginally fewer mean MU and shorter BOT (488 MU, 0.81 minutes) when compared to IMRT (575 MU, 0.96 minutes) with (p=0.380).
Conclusion: For radiation therapy treatment of liver carcinoma, IMRT and VMAT can achieve similar PTV coverage and normal tissue sparing. Treatment time is only marginally shorter with VMAT vs. IMRT, with either technique providing associated benefits (decreased damage from secondary radiation, and treatment delivery uncertainty due to intrafraction tumor motion).
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