FEM design and simulation of a short, 10 MV, S‐band Linac with Monte Carlo dose simulations

Baillie, Devin; Aubin, J St.; Fallone, B. G.; Steciw, S

doi:10.1118/1.4915953

Cited by 6 publications

(26 citation statements)

References 21 publications

(42 reference statements)

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“…16 Note that we calculate normalized emittance instead of the geometric emittance which has been used in previous recent publications in this journal. 3,8,9,18,20,21 This is because the former quantity is a more appropriate and robust metric in instances where the beam energy is changing. 16,22 If it is assumed that the relativistic γ and β distributions are single valued, normalized emittance can be also described as ε N = ε G βγ 16 where ε G is the geometric emittance which has been utilized in other recent publications.…”

Section: D Beam Assessment At the Targetmentioning

confidence: 99%

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A novel electron accelerator for MRI‐Linac radiotherapy

et al. 2016

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Purpose: MRI guided radiotherapy is a rapidly growing field; however, current electron accelerators are not designed to operate in the magnetic fringe fields of MRI scanners. As such, current MRI-Linac systems require magnetic shielding, which can degrade MR image quality and limit system flexibility. The purpose of this work was to develop and test a novel medical electron accelerator concept which is inherently robust to operation within magnetic fields for in-line MRI-Linac systems. Methods: Computational simulations were utilized to model the accelerator, including the thermionic emission process, the electromagnetic fields within the accelerating structure, and resulting particle trajectories through these fields. The spatial and energy characteristics of the electron beam were quantified at the accelerator target and compared to published data for conventional accelerators. The model was then coupled to the fields from a simulated 1 T superconducting magnet and solved for cathode to isocenter distances between 1.0 and 2.4 m; the impact on the electron beam was quantified. Results: For the zero field solution, the average current at the target was 146.3 mA, with a median energy of 5.8 MeV (interquartile spread of 0.1 MeV), and a spot size diameter of 1.5 mm full-widthtenth-maximum. Such an electron beam is suitable for therapy, comparing favorably to published data for conventional systems. The simulated accelerator showed increased robustness to operation in in-line magnetic fields, with a maximum current loss of 3% compared to 85% for a conventional system in the same magnetic fields. Conclusions: Computational simulations suggest that replacing conventional DC electron sources with a RF based source could be used to develop medical electron accelerators which are robust to operation in in-line magnetic fields. This would enable the development of MRI-Linac systems with no magnetic shielding around the Linac and reduce the requirements for optimization of magnetic fringe field, simplify design of the high-field magnet, and increase system flexibility. C 2016 American Association of Physicists in Medicine. [http://dx

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Section: D Beam Assessment At the Targetmentioning

confidence: 99%

“…16,22 If it is assumed that the relativistic γ and β distributions are single valued, normalized emittance can be also described as ε N = ε G βγ 16 where ε G is the geometric emittance which has been utilized in other recent publications. 8,18,20 …”

Section: D Beam Assessment At the Targetmentioning

confidence: 99%

A novel electron accelerator for MRI‐Linac radiotherapy

et al. 2016

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“…Multimode electron accelerators are a current area of research for MRI-linacs. 14,15 Of the major manufactures, Tomotherapy, Cyber-Knife, and Siemens all utilize gridded guns. Varian uses gridded guns on multimode systems, and diode guns on low energy guides.…”

Section: Discussionmentioning

confidence: 99%

“…Although the MRI-linac devices investigated in the published literature to date appear to utilize diode electron guns, [11][12][13] recent publications have focused on the potential of multimode MRI-linac devices to improve achievable dose distributions for deep seated tumors, 14,15 and beam gating using MRI-linacs. 16,17 As such, it is clear that triode electron guns are likely to find useful application in the next generation of MRI-linac systems.…”

Section: Introductionmentioning

confidence: 99%

Performance of a clinical gridded electron gun in magnetic fields: Implications for MRI‐linac therapy

et al. 2016

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Purpose: MRI-linac therapy is a rapidly growing field, and requires that conventional linear accelerators are operated with the fringe field of MRI magnets. One of the most sensitive accelerator components is the electron gun, which serves as the source of the beam. The purpose of this work was to develop a validated finite element model (FEM) model of a clinical triode (or gridded) electron gun, based on accurate geometric and electrical measurements, and to characterize the performance of this gun in magnetic fields. Methods: The geometry of a Varian electron gun was measured using 3D laser scanning and digital calipers. The electric potentials and emission current of these guns were measured directly from six dose matched true beam linacs for the 6X, 10X, and 15X modes of operation. Based on these measurements, a finite element model (FEM) of the gun was developed using the commercial software /. The performance of the FEM model in magnetic fields was characterized using parallel fields ranging from 0 to 200 G in the in-line direction, and 0-35 G in the perpendicular direction.Results: The FEM model matched the average measured emission current to within 5% across all three modes of operation. Different high voltage settings are used for the different modes; the 6X, 10X, and 15X modes have an average high voltage setting of 15, 10, and 11 kV. Due to these differences, different operating modes show different sensitivities in magnetic fields. For in line fields, the first current loss occurs at 40, 20, and 30 G for each mode. This is a much greater sensitivity than has previously been observed. For perpendicular fields, first beam loss occurred at 8, 5, and 5 G and total beam loss at 27, 22, and 20 G. Conclusions: A validated FEM model of a clinical triode electron gun has been developed based on accurate geometric and electrical measurements. Three different operating modes were simulated, with a maximum mean error of 5%. This gun shows greater sensitivity to in-line magnetic fields than previously presented models, and different operating modes show different sensitivity. C 2016 American Association of Physicists in Medicine. [http://dx

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“…The larger length of the waveguide, when positioned parallel to the magnetic fields, (e.g., as in the Alberta linac‐MR system) would limit the immediate use of the system within a conventional radiotherapy treatment vault and would require a larger than typical vault. To address this gap in currently available technology, our group previously designed a short, 10 MV accelerator to be compatible with the Alberta linac‐MR …”

Section: Introductionmentioning

confidence: 99%