Optimization approaches to volumetric modulated arc therapy planning

Unkelbach, Jan; Bortfeld, Thomas; Craft, David; Alber, M.; Bangert, Mark; Bokrantz, Rasmus; Chen, Danny; Li, Ruijiang; Li, Xing; Men, Chunhua; Nill, Simeon; Papp, Dávid; Romeijn, Edwin; Salari, Ehsan

doi:10.1118/1.4908224

Cited by 66 publications

(115 citation statements)

References 63 publications

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“…One advantage of sliding window VMAT is the technique’s capability to faithfully reproduce optimized fluence maps. Leaf traversal across the entire width of the target for each arc sector can, however, be time consuming, which makes the sliding window technique a relatively time‐consuming form of delivery . We have shown that the delivery time for sliding window VMAT can be considerably reduced if the collimator angle is chosen with care.…”

Section: Discussionmentioning

confidence: 99%

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

2019

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Purpose To provide a method for optimizing the multileaf collimator angle trajectory in volumetric modulated arc therapy (VMAT) in order to make VMAT delivery and planning more efficient. Methods Static fluence maps are optimized at a 10‐degree spacing around the patient. Sliding window delivery time of each of these fields is computed for a large set of possible collimator orientations. An optimal trajectory, which selects a collimator angle for each field and assures that the collimator angles do not differ excessively between adjacent fields, is computed by solving a network flow model of a shortest path problem. Results For four clinical cases (two brains, an anal, and a spine), we demonstrate time reductions from 6% to 32% (average: 24%) for the optimal static angle vs the worst static angle. Further reductions from 3% to 17% (average 9%) are achievable when dynamic collimator trajectories are allowed. Conclusions Dynamic collimator trajectories, which can be computed with an efficient linear programming formulation, can improve the efficiency of VMAT delivery.

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Section: Discussionmentioning

confidence: 99%

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

2019

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“…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.…”

Section: Introductionmentioning

confidence: 70%

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

et al. 2019

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Purpose Despite the availability of multiple energy photon beams on clinical linear accelerators, volumetric modulated arc therapy (VMAT) optimization is currently limited to a single photon beam. The purpose of this work was to present a proof‐of‐principle study on an algorithm for simultaneous optimization of mixed photon beams for VMAT (MP – VMAT), utilizing an additional photon energy as an additional degree of freedom. Methods The MP – VMAT optimization algorithm is presented as a two‐step heuristic approach. First, a convex linear programming problem is solved for simultaneous optimization of nonuniform dual energy intensity maps (DEIMs) for an angular resolution of 36 equi‐spaced beam segments. Subsequently, for a given gantry speed schedule, the second step aims to best replicate each DEIM by dispersing MP – VMAT apertures along with their corresponding intensities over their respective beam segment. This constitutes a nonlinear problem, which is linearized using McCormick relaxation. The final large‐scale mixed integer linear programming (MILP) dispersion model ensures a contiguous and smooth transition of multileaf collimators (MLCs) from one beam segment to the next. To demonstrate the proof‐of‐principle, we first compared the quality of dose volume histograms (DVHs) of MP – VMAT to the ones calculated from 36 DEIMs following the step 1 of MP – VMAT model. Additionally, the MLCs motion violations were evaluated for the complete 360° gantry rotation for gantry speeds ranging from 1 to 6° per second. The quality of MP – VMAT plans were also compared to conventional single energy VMAT plans via DVH, homogeneity index (HI), and conformity number (CN) for two prostate cases. Results The MP – VMAT model resulted in a successful convergence of DVHs relative to the ones from DEIMs with HI and CN of 0.05 and 0.9, respectively, for 1 and 2° per second gantry speed schedules. In replicating the DEIMs, the MILP dispersion model was able to achieve optimality for almost all segments at 1° per second and for majority of segments at 2° per second. Although, DVHs quality was slightly inferior for 3° per second gantry speed, the target conformity of 0.9 and heterogeneity of 0.08 were achievable even for the suboptimal solutions. No violations of the MLC constraints were observed throughout the complete 360 degree arc rotation for any gantry speed schedule, thereby confirming MILP dispersion model. For the two prostate cases, the results showed MP – VMAT's ability to achieve substantial dose reduction in rectum and bladder while yielding similar target coverage compared to single energy VMAT. Bladder volume was mostly spared in low‐to‐intermediate dose region. Rectal volume sparing (3 % to 12 %) was observed in the intermediate (from 25 to 50 Gy) dose region. Conclusion We demonstrate the first formalism of a large‐scale simultaneous optimization of mixed photon energy beams for VMAT. Dosimetric comparison of MP – VMAT to single energy VMAT demonstrated potential advantages of using mixed photon energy beams for prostat...

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“…We consider IMRT plans consisting of 19 equispaced coplanar beams, which approximates the best coplanar rotation therapy plan, which could be delivered with tomotherapy or VMAT [17]. We use a beamlet resolution of 5×5 mm.…”

Section: Methodsmentioning

confidence: 99%

Spatiotemporal fractionation schemes for liver stereotactic body radiotherapy

Unkelbach

Papp

Gaddy

et al. 2017

Radiotherapy and Oncology

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Background and Purpose Dose prescription in stereotactic body radiotherapy (SBRT) for liver tumors is often limited by the mean liver dose. We explore the concept of spatiotemporal fractionation as an approach to facilitate further dose escalation in liver SBRT. Materials and Methods Spatiotemporal fractionation schemes aim at partial hypofractionation in the tumor along with near-uniform fractionation in normal tissues. This is achieved by delivering distinct dose distributions in different fractions, which are designed such that each fraction delivers a high single fraction dose to complementary parts of the tumor while creating a similar dose bath in the surrounding noninvolved liver. Thereby, higher biologically effective doses (BED) can be delivered to the tumor without increasing the mean BED in the liver. Planning of such treatments is performed by simultaneously optimizing multiple dose distributions based on their cumulative BED. We study this concept for five liver cancer patients with different tumor geometries. Results Spatiotemporal fractionation presents a method of increasing the ratio of prescribed tumor BED to mean BED in the noninvolved liver by approximately 10–20%, compared to conventional SBRT using identical fractions. Conclusions Spatiotemporal fractionation may reduce the risk of liver toxicity or facilitate dose escalation in liver SBRT in circumstances where the mean dose to the non-involved liver is the prescription-limiting factor.

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Optimization approaches to volumetric modulated arc therapy planning

Cited by 66 publications

References 63 publications

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

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

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

Spatiotemporal fractionation schemes for liver stereotactic body radiotherapy

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