Fast approximate delivery of fluence maps for IMRT and VMAT

Abstract

In this article we provide a method to generate the trade-off between delivery time and fluence map matching quality for volumetric modulated arc therapy (VMAT). At the heart of our method lies a mathematical programming model that, for a given duration of delivery, optimizes leaf trajectories and dose rates such that the desired fluence map is reproduced as well as possible. This model was presented for the single map case in a companion paper (Craft and Balvert). The resulting large-scale, non-convex optimization problem was solved using a heuristic approach. The single-map approach cannot directly be applied to the full arc case due to the large increase in model size, the issue of allocating delivery times to each of the arc segments, and the fact that the ending leaf positions for one map will be the starting leaf positions for the next map. In this article the method proposed in Craft and Balvert is extended to solve the full map treatment planning problem. We test our method using a prostate case and a head and neck case, and present the resulting trade-off curves. Analysis of the leaf trajectories reveal that short time plans have larger leaf openings in general than longer delivery time plans. Our method allows one to explore the continuum of possibilities between coarse, large segment plans characteristic of direct aperture approaches and narrow field plans produced by sliding window approaches. Exposing this trade off will allow for an informed choice between plan quality and solution time. Further research is required to speed up the optimization process to make this method clinically implementable.

Technical Note: Improving VMAT delivery efficiency by optimizing the dynamic collimator trajectory

“…Note that pure sliding window delivery is not necessarily the most efficient algorithm for dynamic fluence map delivery . However, it results in a simple equation which estimates the time to deliver a fluence map.…”

Simultaneous optimization of mixed photon energy beams in volumetric modulated arc therapy

“…Therefore, there is a potential to improve the dosimetric quality of a treatment plan by utilizing an additional photon energy beam as an extra degree of freedom through simultaneous optimization process. To our knowledge, this notion has not been reported in any of the previous literatures for VMAT treatment planning.…”

“…A beam segment length of 10° was selected in the first step based on previously published results, which demonstrated that in order to achieve a high‐quality plan the gantry angles should be spaced evenly ≤10° . Current clinical photon beam energies in radiotherapy planning mostly range from 6 to 18 MV.…”

Relaxing leaf‐motion restrictions in dynamic multileaf collimator leaf sequencing

“…To that end, we adopt the approach used in Ref. and define a PWL function of the form as shown in Fig. .…”

“…However, this gives rise to a far more challenging LS problem, which requires the development of new models and efficient solution methods. Craft and Balvert have recently studied the potential benefit of bidirectional leaf trajectories for IMRT and VMAT . In particular, they formulate the LS problem for each MLC row as a nonconvex optimization problem in terms of the left‐ and right‐leaf trajectories and use standard gradient‐descent methods to solve the formulation.…”