Acceptance procedure for the linear accelerator component of the 1.5 T MRI‐linac

Woodings, S.; Vries, J.H.W. De; Kok, J G M; Hackett, S.; Asselen, Bram van; Bluemink, J.J.; Zijp, H M van; Soest, T L van; Roberts, David A.; Lagendijk, J J W; Raaymakers, B W; Wolthaus, J.

doi:10.1002/acm2.13068

Cited by 23 publications

(28 citation statements)

References 31 publications

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“…Obviously, visual inspection cannot be used to det ermine the absolute gantry angle; however, it is useful for determining if set positions are within the tolerance specified by Roberts et al [3] (± 0.3°). Note that the mor e recent publication of Woodings et al [5] suggests a specification of < 0.2° for gantry angle, which cannot be achieved with visual inspection. For all projections at the 30.0° intervals, the actual gantry angle appeared to match the set position within 0.3°, further highlighting the accuracy of the gantry rotation system.…”

Section: Discussionmentioning

confidence: 98%

“…Additionally, the process could be improved by imaging with the 3.5 cm longitudinal offset removed and confirming alignment of diametrically opposed ballbearings along the Y-axis on MVI images. An absolute gantry angle offset may also be able to be determined from the offset of ballbearing centres from the lateral pixel centre on the panel; however, correct rotational alignment of the MVI would need to be confirmed, such as that discussed by Woodings et al [5].…”

Section: Discussionmentioning

confidence: 99%

“…The design of the Unity system has been comprehensively discussed by other investigators [1][2][3][4][5], and the reader is referred to these works for further information. In short, the Elekta Unity MRL is a combination of a modified Philips Ingenia 1.5 T MRI, with a split-coil superconducting magnet and a straight-through linear accelerator.…”

Section: Introductionmentioning

confidence: 99%

“…Acceptance, commissioning and continuous QA tests, tolerances and frequencies have been described by other authors [3][4][5][6]. However, as the Unity has only recently been clinically introduced, the scope of such work is limited.…”

Section: Introductionmentioning

confidence: 99%

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Commissioning measurements on an Elekta Unity MR-Linac

et al. 2022

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Magnetic resonance-guided radiotherapy technology is relatively new and commissioning publications, quality assurance (QA) protocols and commercial products are limited. This work provides guidance for implementation measurements that may be performed on the Elekta Unity MR-Linac (Elekta, Stockholm, Sweden). Adaptations of vendor supplied phantoms facilitated determination of gantry angle accuracy and linac isocentre, whereas in-house developed phantoms were used for end-to-end testing and anterior coil attenuation measurements. Third-party devices were used for measuring beam quality, reference dosimetry and during treatment plan commissioning; however, due to several challenges, variations on standard techniques were required. Gantry angle accuracy was within 0.1°, confirmed with pixel intensity profiles, and MV isocentre diameter was < 0.5 mm. Anterior coil attenuation was approximately 0.6%. Beam quality as determined by TPR20,10 was 0.705 ± 0.001, in agreement with treatment planning system (TPS) calculations, and gamma comparison against the TPS for a 22.0 × 22.0 cm2 field was above 95.0% (2.0%, 2.0 mm). Machine output was 1.000 ± 0.002 Gy per 100 MU, depth 5.0 cm. During treatment plan commissioning, sub-standard results indicated issues with machine behaviour. Once rectified, gamma comparisons were above 95.0% (2.0%, 2.0 mm). Centres which may not have access to specialized equipment can use in-house developed phantoms, or adapt those supplied by the vendor, to perform commissioning work and confirm operation of the MRL within published tolerances. The plan QA techniques used in this work can highlight issues with machine behaviour when appropriate gamma criteria are set.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Commissioning measurements on an Elekta Unity MR-Linac

et al. 2022

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“…The workflows presented are specific to a single institution but can provide a useful foundation for any center building a new program through the presentation of case studies and discussion of clinical rationale. It is not the purpose of this work to discuss commissioning of a MRgART program; for that discussion, readers are referred to other works [ 8 , 9 , 10 , 11 , 12 , 13 ].…”

Section: Introductionmentioning

confidence: 99%

Clinical Implementational and Site-Specific Workflows for a 1.5T MR-Linac

Dunkerley

Hyer

Snyder

et al. 2022

JCM

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MR-guided adaptive radiotherapy (MRgART) provides opportunities to benefit patients through enhanced use of advanced imaging during treatment for many patients with various cancer treatment sites. This novel technology presents many new challenges which vary based on anatomic treatment location, technique, and potential changes of both tumor and normal tissue during treatment. When introducing new treatment sites, considerations regarding appropriate patient selection, treatment planning, immobilization, and plan-adaption criteria must be thoroughly explored to ensure adequate treatments are performed. This paper presents an institution’s experience in developing a MRgART program for a 1.5T MR-linac for the first 234 patients. The paper suggests practical treatment workflows and considerations for treating with MRgART at different anatomical sites, including imaging guidelines, patient immobilization, adaptive workflows, and utilization of bolus.

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Longitudinal assessment of quality assurance measurements in a 1.5 T MR‐linac: Part II—Magnetic resonance imaging

Subashi

Dresner

Tyagi

2022

J Applied Clin Med Phys

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To describe and report longitudinal quality assurance (QA) measurements for the magnetic resonance imaging (MRI) component of the Elekta Unity MR-linac during the first year of clinical use in our institution. Materials and methods:The performance of the MRI component of Unity was evaluated with daily, weekly, monthly, and annual QA testing. The measurements monitor image uniformity, signal-to-noise ratio (SNR), resolution/detectability, slice position/thickness, linearity, central frequency, and geometric accuracy. In anticipation of routine use of quantitative imaging (qMRI), we characterize B0/B1 uniformity and the bias/reproducibility of longitudinal/transverse relaxation times (T1/T2) and apparent diffusion coefficient (ADC). Tolerance levels for QA measurements of qMRI biomarkers are derived from weekly monitoring of T1, T2, and ADC. Results: The 1-year assessment of QA measurements shows that daily variations in each MR quality metric are well below the threshold for failure. Routine testing procedures can reproducibly identify machine issues. The longitudinal three-dimensional (3D) geometric analysis reveals that the maximum distortion in a diameter of spherical volume (DSV) of 20, 30, 40, and 50 cm is 0.4, 0.6, 1.0, and 3.1 mm, respectively. The main source of distortion is gradient nonlinearity. Maximum peak-to-peak B0 inhomogeneity is 3.05 ppm, with gantry induced B0 inhomogeneities an order of magnitude smaller. The average deviation from the nominal B1 is within 2%, with minimal dependence on gantry angle. Mean ADC, T1, and T2 values are measured with high reproducibility. The median coefficient of variation for ADC, T1, and T2 is 1.3%, 1.1%, and 0.5%, respectively. The median bias for ADC, T1, and T2 is −0.8%, −0.1%, and 3.9%, respectively. Conclusion:The MRI component of Unity operates within the guidelines and recommendations for scanner performance and stability. Our findings support the recently published guidance in establishing clinically acceptable tolerance levels for image quality. Highly reproducible qMRI measurements are feasible in Unity.

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Acceptance procedure for the linear accelerator component of the 1.5 T MRI‐linac

Abstract: This is an open access article under the terms of the Creat ive Commo ns Attri bution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 23 publications

References 31 publications

Commissioning measurements on an Elekta Unity MR-Linac

Commissioning measurements on an Elekta Unity MR-Linac

Clinical Implementational and Site-Specific Workflows for a 1.5T MR-Linac

Longitudinal assessment of quality assurance measurements in a 1.5 T MR‐linac: Part II—Magnetic resonance imaging

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