Electron beam collimation with a photon MLC for standard electron treatments

Mueller, Silvan; Fix, M.K.; Henzen, Dominik; Frei, D.; Frauchiger, D.; Loessl, K.; Stampanoni, Marco; Manser, Peter

doi:10.1088/1361-6560/aa9fb6

Cited by 21 publications

(34 citation statements)

References 42 publications

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“…It is noteworthy, that the output of the electron beams must be well predicted for the whole utilized SSD range of 70–82.5 cm. Even though the utilized electron beam model is commissioned using measurements collected only at one SSD of 70 cm, MC simulations are still capable to accurately predict dose distributions for other SSDs . A further important deliverability aspect of DYMBER is the plan robustness associated to patient movements and body variations.…”

Section: Discussionmentioning

confidence: 99%

“…Even though the utilized electron beam model is commissioned using measurements collected only at one SSD of 70 cm, MC simulations are still capable to accurately predict dose distributions for other SSDs. 35,49,50 A further important deliverability aspect of DYMBER is the plan robustness associated to patient movements and body variations. This is not yet studied and thus, robustness needs to be investigated in future studies and solutions to improve the robustness like robust optimization are desirable to be used for DYMBER.…”

Section: Discussionmentioning

confidence: 99%

“…For pMLC collimated electron beams, it is suggested to use a reduced source-to-surface distance (SSD) to yield a shorter penumbra, because of reduced particle inair scatter. 17,34,35 Therefore, the isocenter position is chosen such that the SSD is as short as possible, but still large enough to avoid collisions between the gantry and the patient and table. The resulting SSD is typically in the range of 70-82.5 cm.…”

Section: A Treatment Planning Processmentioning

confidence: 99%

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

et al. 2018

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: A Treatment Planning Processmentioning

confidence: 99%

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

et al. 2018

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“…These issues were addressed in recent studies by demonstrating the viability of delivering modulated electron radiation therapy (MERT) with a photon multileaf collimator (MLC) to eliminate the accessory requirements (applicators, cut‐outs, electron‐specific MLC) of traditional electron RT . 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.…”

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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“…Modulation of the electron fields may improve the dose conformity 3 and has been extensively investigated using the photon multi‐leaf collimator (MLC) 4, 5, 6 or a dedicated electron MLC 7, 8. Nevertheless, the use of static electron fields remains common 9 and collimation is typically performed using aperture cut‐outs placed in the electron applicator at a small distance from the patient's skin 10…”

Section: Introductionmentioning

confidence: 99%

Production of patient‐specific electron beam aperture cut‐outs using a low‐cost, multi‐purpose 3D printer

Michiels

Mangelschots

Roover

et al. 2018

J Applied Clin Med Phys

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Electron beam collimators for non‐standard field sizes and shapes are typically fabricated using Styrofoam molds to cast the aperture cut‐out. These molds are often produced using a dedicated foam cutter, which may be expensive and only serves a single purpose. An increasing number of radiotherapy departments, however, has a 3D printer on‐site, to create a wide range of custom‐made treatment auxiliaries, such as bolus and dosimetry phantoms. The 3D printer can also be used to produce patient‐specific aperture cut‐outs, as elaborated in this note. Open‐source programming language was used to automatically generate the mold's shape in a generic digital file format readable by 3D printer software. The geometric mold model has the patient's identification number integrated and is to be mounted on a uniquely fitting, reusable positioning device, which can be 3D printed as well. This assembly likewise fits uniquely onto the applicator tray, ensuring correct and error‐free alignment of the mold during casting of the aperture. For dosimetric verification, two aperture cut‐outs were cast, one using a conventionally cut Styrofoam mold and one using a 3D printed mold. Using these cut‐outs, the clinical plan was delivered onto a phantom, for which the transversal dose distributions were measured at 2 cm depth using radiochromic film and compared using gamma‐index analysis. An agreement score of 99.9% between the measured 2D dose distributions was found in the (10%–80%) dose region, using 1% (local) dose‐difference and 1.0 mm distance‐to‐agreement acceptance criteria. The workflow using 3D printing has been clinically implemented and is in routine use at the author's institute for all patient‐specific electron beam aperture cut‐outs. It allows for a standardized, cost‐effective, and operator‐friendly workflow without the need for dedicated equipment. In addition, it offers possibilities to increase safety and quality of the process including patient identification and methods for accurate mold alignment.

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Electron beam collimation with a photon MLC for standard electron treatments

Cited by 21 publications

References 42 publications

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

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

Robust mixed electron–photon radiation therapy optimization

Production of patient‐specific electron beam aperture cut‐outs using a low‐cost, multi‐purpose 3D printer

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