Abstract
We developed a four‐dimensional volumetric modulated arc therapy (4D VMAT) planning technique for moving targets using a direct aperture deformation (DAD) method and investigated its feasibility for clinical use. A 3D VMAT plan was generated on a reference phase of a 4D CT dataset. The plan was composed of a set of control points including the beam angle, MLC apertures and weights. To generate the 4D VMAT plan, these control points were assigned to the closest respiratory phases using the temporal information of the gantry angle and respiratory curve. Then, a DAD algorithm was used to deform the beam apertures at each control point to the corresponding phase to compensate for the tumor motion and shape changes. Plans for a phantom and five lung cases were included in this study to evaluate the proposed technique. Dosimetric comparisons were performed between 4D and 3D VMAT plans. Plan verification was implemented by delivering the 4D VMAT plans on a moving QUASAR™ phantom driven with patient‐specific respiratory curves. The phantom study showed that the 4D VMAT plan generated with the DAD method was comparable to the ideal 3D VMAT plan. DVH comparisons indicated that the planning target volume (PTV) coverages and minimum doses were nearly invariant, and no significant difference in lung dosimetry was observed. Patient studies revealed that the GTV coverage was nearly the same; although the PTV coverage dropped from 98.8% to 94.7%, and the mean dose decreased from 64.3 to 63.8 Gy on average. For the verification measurements, the average gamma index pass rate was 98.6% and 96.5% for phantom 3D and 4D VMAT plans with 3%/3 mm criteria. For patient plans, the average gamma pass rate was 96.5% (range 94.5–98.5%) and 95.2% (range 94.1–96.1%) for 3D and 4D VMAT plans. The proposed 4D VMAT planning technique using the DAD method is feasible to incorporate the intra‐fraction organ motion and shape change into a 4D VMAT planning. It has great potential to provide high plan quality and delivery efficiency for moving targets.
Highlights
Volumetric Modulated Arc Therapy (VMAT) is delivered through synchronized variation in the gantry angle, dose rate, and multi-leaf collimator (MLC) leaf positions.[1]
Studies have shown that VMAT can provide high delivery efficiency without compromising plan quality compared to static beam IMRT.[2,3,4,5]
We propose a 4D VMAT planning technique by applying a direct aperture deformation algorithm to a 3D VMAT plan
Summary
Volumetric Modulated Arc Therapy (VMAT) is delivered through synchronized variation in the gantry angle, dose rate, and multi-leaf collimator (MLC) leaf positions.[1]. The compilation of data in the American Association of Physicists in Medicine (AAPM) Task Group Report 767 revealed that out of 22 lung tumor patients, 12 patients had tumor motion from 3 to 22 mm (mean 8 Æ 4 mm) in the Superior–Inferior direction. In such a situation, the delivered dose distribution could be different from the original planned dose distribution if the intra-fraction tumor and organs-at-risk motions were not taken into account properly.[7,8,9]
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