Part 2: Dynamic mixed beam radiotherapy (<scp>DYMBER</scp>): Photon dynamic trajectories combined with modulated electron beams

Mueller, Silvan; Manser, Peter; Volken, W.; Frei, D.; Kueng, R; Herrmann, Evelyn; Eliçin, Olgun; Aebersold, Daniel M.; Stampanoni, Marco; Fix, M.K.

doi:10.1002/mp.13085

Cited by 20 publications

(39 citation statements)

References 56 publications

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“…By delivering MERT plans with a standard photon MLC, the potential arises for seamless mixed electron–photon delivery without interrupting treatment delivery between modality changes. Indeed, mixed‐beam electron–photon radiotherapy (MBRT) plans have been shown to offer additional degrees of freedom to influence the trade‐off between normal tissue dose and target coverage …”

Section: Introductionmentioning

confidence: 99%

Robust mixed electron–photon radiation therapy optimization

2019

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Purpose Mixed beam electron–photon radiation therapy (MBRT) is an emerging technique that has the potential to reduce dose to normal tissue while improving target coverage for cancer sites with superficial tumors. Advances in optimization algorithms and robotic linear accelerators have made the creation and delivery of complex MBRT plans realistic without the need for special additional collimators, devices, or resetup of the patient. However, no study has been performed on the robustness of MBRT dose distributions to patient setup errors. Intensity‐modulated delivery of other charged particles such as protons have been shown to require robust planning techniques to maintain adequate target coverage under positioning errors. We therefore assess the sensitivity of MBRT treatment plans to positioning uncertainties when created under the traditional planning target volume (PTV)‐based planning paradigm and present a novel optimization model for the creation of robust MBRT plans. Methods The column generation method was applied to robust MBRT treatment planning by deriving the pricing problem for stochastic and “worst case” minimax optimization models, two common formulations of robustness. Robust treatment plans were created for two patient cases representative of the cancer sites which stand to benefit from MBRT: soft tissue sarcoma (STS) irradiation and chest wall irradiation with deep‐seated internal mammary, axillary, and supraclavicular nodes (CW‐N). For both patient cases, beamlet dose distributions for electrons and photons were generated for positioning shifts in six directions, ±5mm(xfalse^,yfalse^,zfalse^) in addition to a nominal unshifted scenario, for a total of seven sets of beamlets. Robust plans were created by specifying dose coverage constraints to the clinical target volume (CTV), as opposed to the PTV. Comparisons were performed against traditional PTV‐based plans created with a single set of unshifted beamlets. Results The dose distributions of traditional PTV‐based MBRT plans showed significant degradation in target coverage homogeneity when patient positioning errors were considered. For both cancer sites, cold spots below 95% and hot spots above 108% of the prescription dose appeared within the CTV when shifting the patient by 5 mm, corresponding to the margin added to the CTV to form the PTV. In contrast, CTV‐based robust plans created with the new optimization model maintained target coverage within the 95%–108% limits, for all positioning errors. Conclusion The quality of MBRT treatment plans created using a traditional PTV‐based optimization model was highly sensitive to patient positioning errors. For both patient cases, positioning errors resulted in perturbations to the nominal dose distributions which would have rendered PTV‐based plans clinically unacceptable. In contrast, CTV‐based robust plans were able to maintain adequate target coverage under all positioning error scenarios considered. We therefore conclude that to ensure the fidelity of the dose distribution delivered to the pat...

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Section: Introductionmentioning

confidence: 99%

Robust mixed electron–photon radiation therapy optimization

2019

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“…The second method, on the other hand, would involve a complete delivery of one photon beam energy followed by energy switch and a complete the delivery of second photon beam energy, resulting in a two‐arc plan with the requirement of energy switch only once. Since it can take up to 20 s to switch beam energy on a Varian TrueBeam linear accelerator, the latter method would be practical for the delivery scheme of a MP – VMAT plan. Therefore, the treatment time of MP – VMAT could be little longer due to energy switch requirement in comparison to SE – VMAT.…”

Section: Discussionmentioning

confidence: 99%

“…Improvements in treatment plan quality have been achieved by utilizing additional degrees of freedom during treatment planning. This includes the use of mixed (photon and electron) beam radiotherapy for VMAT and IMRT . While one study generated mixed photon‐electron treatment plans for coplanar IMRT beams, the other study combined photon dynamic trajectories and step and shoot electron apertures to improve the quality of VMAT plans .…”

Section: Introductionmentioning

confidence: 99%

“…This includes the use of mixed (photon and electron) beam radiotherapy for VMAT and IMRT . While one study generated mixed photon‐electron treatment plans for coplanar IMRT beams, the other study combined photon dynamic trajectories and step and shoot electron apertures to improve the quality of VMAT plans . In 4π radiation therapy, the couch rotation has also been utilized to allow noncoplanar beam setups to further improve the plan quality .…”

Section: Introductionmentioning

confidence: 99%

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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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“…[1][2][3][4][5][6] Creation of optimized trajectories via multi-dimensional solution spaces generated from clinical and geometric considerations have successfully guided the position of radiotherapy axes in several recent publications. [3][4][5][6][7][8][9][10][11][12][13] Dynamic trajectory methods have recently been implemented using ray tracing and graph search algorithms, 9 fractional organs-at-risk (OAR)/planning target volume (PTV) overlap maps and navigation algorithms in both photon and photon-electron modulated modalities, 10,12 and direct aperture optimization fluence-based optimization methods. 13 Many of these solutions have shown significance in OAR sparing, however, they cannot currently be calculated or delivered in clinical systems.…”

Section: Introductionmentioning

confidence: 99%

Toward the combined optimization of dynamic axes (CODA) for stereotactic radiotherapy and radiosurgery using fixed couch trajectories

et al. 2019

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Purpose To develop a novel system for patient‐specific combined optimization of couch, collimator, and gantry angles for use in volumetric modulated arc therapy (VMAT) treatment planning. The system was designed to produce highly compact dose distributions by extensively sampling the 4π space. Automated fixed couch trajectory planning was used to reduce normal tissue doses by avoiding beams‐eye‐view (BEV) overlap with organs‐at‐risk (OARs) and improve monitor unit (MU) efficiency through collimator angle optimization. Methods By merging distinct BEV objective functions used to optimize the couch rotation angle and collimator angle, a three‐dimensional (3D) cost space (the CODA cube) was constructed with axes of gantry, couch, and collimator rotation angles. At each voxel in this CODA cube, the cost of implementing this combination of axes positions in fixed couch trajectories was quantified. The CODA cube was sampled and explored using a modified constrained Bellman‐Ford algorithm to suggest low‐cost fixed candidate arcs on each plane of the space, from which 10‐arcs are chosen throughout the 3D space using a k‐means clustering algorithm. These fixed couch trajectories were then imported into the Eclipse treatment planning system (v.11) and inverse‐optimized according to clinical standards. Eight artificial cranial targets were contoured in a test‐patient anatomy, and seven treatment plans were generated from combinations of three and four targets. The CODA cube optimized plans were compared to standard 4‐arc VMAT plans for cranial stereotactic radiotherapy/surgery that were optimized for the same sets of targets; maximum dose to each OAR, V12Gy to normal brain, conformity, and total MUs were compared. Both planning methods were inverse‐optimized with identical dosimetric objectives. Results CODA plans resulted in a reduction in maximum dose to OARs of 20.6% (P < 0.01), with maximum brainstem dose decreased by 2.63 Gy (P = 0.031) on average when compared to the standard arc arrangement. The mean reduction in total MU was 8.6% (P = 0.156), the mean increase in the inverse of the van’t Riet conformation number was 0.1%, (P = 0.67) and the mean decrease in normal brain tissue receiving 12 Gy or higher was 3.9% (P = 0.16), when compared to the standard VMAT arc configuration (n = 7). Conclusions The optimization of couch, collimator, and gantry angles simultaneously using a 3D optimization space achieved improvement on multiple clinical metrics when compared to the standard VMAT arc configuration. A statistically significant sparing to OAR maximum doses was seen. Combining these optimizations may yield superior results to independent optimization.

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Part 2: Dynamic mixed beam radiotherapy (DYMBER): Photon dynamic trajectories combined with modulated electron beams

Abstract: A treatment technique for DYMBER has been successfully developed and verified for its deliverability. The dosimetric superiority of DYMBER over DTRT and VMAT indicates utilizing increased DoF to be the key to improve brain and head and neck radiation treatments in future.

Cited by 20 publications

References 56 publications

Robust mixed electron–photon radiation therapy optimization

Robust mixed electron–photon radiation therapy optimization

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

Toward the combined optimization of dynamic axes (CODA) for stereotactic radiotherapy and radiosurgery using fixed couch trajectories

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