Magnetic shielding investigation for a 6 MV in-line linac within the parallel configuration of a linac-MR system

Santos, D. M.; Aubin, J St.; Fallone, B. G.; Steciw, S

doi:10.1118/1.3676692

Cited by 21 publications

(23 citation statements)

References 23 publications

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“…25 Without proper RF shielding, the linac interferes with the MRI image signals; as well, there are variable magnetic susceptibility M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 7 effects due to the changing position and state of the linac. 26,27 MRI has no electron density information, so this needs to be addressed by either a bulk density override of the patient anatomy 28 or some other density assignment technique such as atlas-based fusion of a "pseudo CT" to the MRI. 29 Finally, magnet system-level and patient-specific geometric distortions need to be assured to be within acceptable tolerance for radiation treatment planning.…”

Section: Daily In-room Treatment Imagingmentioning

confidence: 99%

Online Adaptive Radiation Therapy

Lim‐Reinders

Keller

Al-Ward

et al. 2017

International Journal of Radiation Oncology*Biology*Physics

152

135

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Section: Daily In-room Treatment Imagingmentioning

confidence: 99%

Online Adaptive Radiation Therapy

Lim‐Reinders

Keller

Al-Ward

et al. 2017

International Journal of Radiation Oncology*Biology*Physics

152

135

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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%

“…8 The second is to place magnetic shielding around the gun such that the field is reduced enough that acceptable gun performance is obtained. 9 Both these approaches were shown to be very effective, however, both have drawbacks. Redesign of the gun optics requires a bespoke gun design for each different field it is to be used in.…”

Section: Introductionmentioning

confidence: 99%

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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“…Thus, currently there are efforts underway to construct a MRI-linac hybrid-machine [26]. In the years past, it was a key challenge bringing the MRI and linac systems together due to interactions between these two devices with compromises in the performance levels [29-31,33,35]. The dutch working group, for example, could solve this problem through active magnetic shielding and smart radiofrequency design in a diagnostic quality closed-bore system [26].…”

Section: Discussionmentioning

confidence: 99%

MR-guidance – a clinical study to evaluate a shuttle- based MR-linac connection to provide MR-guided radiotherapy

et al. 2014

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BackgroundThe purpose of this clinical study is to investigate the clinical feasibility and safety of a shuttle-based MR-linac connection to provide MR-guided radiotherapy.Methods/DesignA total of 40 patients with an indication for a neoadjuvant, adjuvant or definitive radiation treatment will be recruited including tumors of the head and neck region, thorax, upper gastrointestinal tract and pelvic region. All study patients will receive standard therapy, i.e. highly conformal radiation techniques like CT-guided intensity-modulated radiotherapy (IMRT) with or without concomitant chemotherapy or other antitumor medication, and additionally daily short MR scans in treatment position with the same immobilisation equipment used for irradiation for position verification and imaging of the anatomical and functional changes during the course of radiotherapy. For daily position control, skin marks and a stereotactic frame will be used for both imaging modalities. Patient transfer between the MR device and the linear accelerator will be performed with a shuttle system which uses an air-bearing patient platform for both procedures. The daily acquired MR and CT data sets will be digitally registrated, correlated with the planning CT and compared with each other regarding translational and rotational errors. Aim of this clinical study is to establish a shuttle-based approach for realising MR-guided radiotherapy for certain clinical situations. Second objectives are to compare MR-guided radiotherapy with the gold standard of CT image guidance for quality assurance of radiotherapy, to establish an appropiate MR protocol therefore, and to assess the possibility of using MR-based image guidance not only for position verification but also for adaptive strategies in radiotherapy.DiscussionCompared to CT, MRI might offer the advantage of providing IGRT without delivering an additional radiation dose to the patients and the possibility of optimisation of adaptive therapy strategies due to its superior soft tissue contrast. However, up to now, hybrid MR-linac devices are still under construction and not clinically applicable. For the near future, a shuttle-based approach would be a promising alternative for providing MR-guided radiotherapy, so that the present study was initiated to determine feasibility and safety of such an approach. Besides positioning information, daily MR data under treatment offer the possibility to assess tumor regression and functional parameters, with a potential impact not only on adaptive therapy strategies but also on early assessment of treatment response.

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Magnetic shielding investigation for a 6 MV in-line linac within the parallel configuration of a linac-MR system

Cited by 21 publications

References 23 publications

Online Adaptive Radiation Therapy

Online Adaptive Radiation Therapy

A novel electron accelerator for MRI‐Linac radiotherapy

MR-guidance – a clinical study to evaluate a shuttle- based MR-linac connection to provide MR-guided radiotherapy

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