Technical Note: Experimental results from a prototype high‐field inline MRI‐linac

Liney, Gary; Dong, Bin; Begg, Jarrad; Vial, P; Zhang, K; Lee, F; Walker, Amy; Rai, Roshika; Causer, Trent; Alnaghy, Saree; Oborn, Bradley M; Holloway, Lois; Metcalfe, Peter E; Bartoň, Michael; Crozier, Stuart; Keall, Paul J.

doi:10.1118/1.4961395

Cited by 45 publications

(72 citation statements)

References 17 publications

(12 reference statements)

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“…14 Finally, there is a 1 T split-bore magnet research system under development at the Ingham Institute in Sydney Australia. 15,16 This system is the world's first high-field strength inline system with an air-core MRI. At present, at least 30 publications are related to this program.…”

Section: B Current State Of the Art In Mrxtmentioning

confidence: 99%

Future of medical physics: Real‐time MRI‐guided proton therapy

et al. 2017

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With the recent clinical implementation of real-time MRI-guided x-ray beam therapy (MRXT), attention is turning to the concept of combining real-time MRI guidance with proton beam therapy; MRIguided proton beam therapy (MRPT). MRI guidance for proton beam therapy is expected to offer a compelling improvement to the current treatment workflow which is warranted arguably more than for x-ray beam therapy. This argument is born out of the fact that proton therapy toxicity outcomes are similar to that of the most advanced IMRT treatments, despite being a fundamentally superior particle for cancer treatment. In this Future of Medical Physics article, we describe the various software and hardware aspects of potential MRPT systems and the corresponding treatment workflow. Significant software developments, particularly focused around adaptive MRI-based planning will be required. The magnetic interaction between the MRI and the proton beamline components will be a key area of focus. For example, the modeling and potential redesign of a magnetically compatible gantry to allow for beam delivery from multiple angles towards a patient located within the bore of an MRI scanner. Further to this, the accuracy of pencil beam scanning and beam monitoring in the presence of an MRI fringe field will require modeling, testing, and potential further development to ensure that the highly targeted radiotherapy is maintained. Looking forward we envisage a clear and accelerated path for hardware development, leveraging from lessons learnt from MRXT development. Within few years, simple prototype systems will likely exist, and in a decade, we could envisage coupled systems with integrated gantries. Such milestones will be key in the development of a more efficient, more accurate, and more successful form of proton beam therapy for many common cancer sites.

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Section: B Current State Of the Art In Mrxtmentioning

confidence: 99%

Future of medical physics: Real‐time MRI‐guided proton therapy

et al. 2017

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“…Hence, combining MRI with a linear accelerator (MRI‐linac), provides a more accurate treatment and therefore the potential for improvement of patient outcomes. In a MRI‐linac, the magnetic field lines can be either in‐line with (longitudinal orientation), or perpendicular to (transverse orientation) the radiation beam.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: Penumbral width trimming in solid lung dose profiles for 0.9 and 1.5 T MRI‐Linac prototypes

et al. 2017

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Purpose: Longitudinal magnetic fields narrow beam penumbra and tighten lateral spread of secondary electrons in air cavities, including lung tissue. Gafchromic â EBT3 film was used to investigate differences between penumbra in solid water and solid lung, without a magnetic field (0 T) and with two field strengths (0.9 and 1.5 T). Methods: The first prototype of the Australian MRI-linac consisted of a 1.5 T Siemens Sonata MRI and Varian industrial linatron (nominal 4 MV). The second prototype replaced the Sonata with a 1.0 T Agilent split-bore magnet. Measurements were completed at 0.9 T to maintain the same source-to-surface distance between set-ups. Gammex-rmi â solid water with 50 mm of CIRS solid lung inserted as a lung cavity was positioned inside each magnet. This was compared to the same set-up with solid water only, where film measurements were completed at solid water equivalent depths corresponding to entrance interface/mid/exit interface positions of solid lung from the first set-up. Multileaf collimator (MLC)-defined field sizes were set to 3 9 3 cm 2 and 10 9 10 cm 2 . The 80%-20% penumbral width was determined. Results: Under 1.5 T conditions, penumbra narrowing occurred up to 4.4 AE 0.1 mm compared to 0 T. As expected, the effect was less for 0.9 T, which resulted in a maximum narrowing of 2.5 AE 0.1 mm. Exit profile penumbra were more affected than entrance penumbra by up to 2.6 AE 0.2 mm. The 1.5 T field brought the solid water and lung penumbral widths more into alignment by a maximum difference of 0.4 AE 0.1 mm. Conclusions:The trimming of penumbral widths due to magnetic fields in solid water and lung was demonstrated and compared to 0 T. The 0.9 and 1.5 T field trimmed the penumbra by up to 2.5 AE 0.1 mm and 4.4 AE 0.1 mm respectively.

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“…Since electron contamination increases with field size, the relative shift in dmax between with and without a B-field is greater for field sizes smaller than 10 × 10 cm 2 and less for larger fields. The opposite may be true with inline MR-linac configurations where the beam and B-field are parallel, as the confining effect of the B-field on contaminant electrons in this configuration enhances the surface dose and changes the PDD relative to the case without a B-field [16]. Figure 2 shows lateral dose profiles with and without the B-field at a depth of 10 cm for a 10 × 10 cm 2 field size.…”

Section: Pdd and Dose Profilesmentioning

confidence: 98%

Dosimetry in the presence of strong magnetic fields

O'Brien

Schupp

Pencea

et al. 2017

J. Phys.: Conf. Ser.

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Abstract. Magnetic resonance imaging-guided radiotherapy (MRIgRT) is an emerging technology that requires the use of radiation fields in the presence of magnetic (B) fields. In the presence of B-fields the Lorentz force influences the trajectories of the secondary electrons, which in turn affects both the dose distribution in water and the dose-response of ionization chambers and several other detectors. Thus, dosimetry in the presence of a B-field requires understanding both the B-field effects on the dose distribution and the response of detectors. In this paper we present measured data to show effects of the B-field on the dose distributions, response of ionization chambers, and presence of air-gaps surrounding the sensitive volume of the detector.

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Technical Note: Experimental results from a prototype high‐field inline MRI‐linac

Abstract: A proof-of-concept high-field MRI-linac has been built and experimentally characterized. This system has allowed us to establish the efficacy of a high field inline MRI-linac and study a number of the technical challenges and solutions.

Cited by 45 publications

References 17 publications

Future of medical physics: Real‐time MRI‐guided proton therapy

Future of medical physics: Real‐time MRI‐guided proton therapy

Technical Note: Penumbral width trimming in solid lung dose profiles for 0.9 and 1.5 T MRI‐Linac prototypes

Dosimetry in the presence of strong magnetic fields

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