Robustness quantification methods comparison in volumetric modulated arc therapy to treat head and neck cancer

Abstract

Background To compare plan robustness of volumetric-modulated arc therapy (VMAT) with intensity-modulated radiation therapy (IMRT) and to compare the effectiveness of 3 plan robustness quantification methods. Methods VMAT and IMRT plans were created for 9 head and neck cancer patients. For each plan, 6 new perturbed dose distributions were computed using ±3mm setup deviations along each of the 3 orientations. Worst-case analysis (WCA), dose-volume histogram (DVH) band (DVHB), and root-mean-square-dose (RMSD) volume histogram (RVH) were used to quantify plan robustness. In WCA a shaded area in the DVH plot bounded by the DVHs from the lowest and highest dose per voxel was displayed. In DVHB we displayed the envelope of all DVHs in band graphs of all the 7 dose distributions. RVH represents the relative volume on the vertical axis and the RMSD on the horizontal axis. The width from the first two methods at different target DVH indices (such as D95% and D5%) and the area under the RVH curves (AUC) for the target were used to indicate plan robustness. Results were compared using Wilcoxon signed-rank test. Results DVHB showed that the width at D95% of IMRT was larger than that of VMAT (unit Gy) [1.59 vs 1.18] and the width at D5% of IMRT was comparable to that of VMAT [0.59 vs 0.54]. WCA showed similar results between IMRT and VMAT plans [D95%: 3.28 vs 3.00; D5%: 1.68 vs 1.95]. RVH showed the AUC of IMRT was comparable to that of VMAT [1.13 vs 1.15]. No statistical significance was found in plan robustness between IMRT and VMAT. Conclusions VMAT is comparable to IMRT in terms of plan robustness. For the 3 quantification methods, WCA and DVHB are DVH-parameter dependent whereas RVH captures the overall effect of uncertainties.

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