Lung dosimetry in a linac‐MRI radiotherapy unit with a longitudinal magnetic field

Kirkby, Charles; Murray, B.; Rathee, S; Fallone, B. G.

doi:10.1118/1.3475942

Cited by 83 publications

(97 citation statements)

References 19 publications

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“…There is recent interest to exploit real-time magnetic resonance imaging (MRI) during treatments to monitor and compensate for intrafractional tumor motion. This interest in magnetic resonance imagingguided radiation therapy (MRIgRT) has led several groups to develop or propose prototype systems combining linear accelerators (Linac) [1][2][3][4] or teletherapy-like systems with magnetic resonance (MR) scanners. 5,6 ViewRay™ (Oakwood Vollage, OH) has developed a MRI-guided teletherapy unit utilizing cobalt-60 source, 5 which is currently being used to treat patients at multiple locations in the U.S.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulations of patient dose perturbations in rotational‐type radiotherapy due to a transverse magnetic field: A tomotherapy investigation

et al. 2015

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Purpose: Several groups are exploring the integration of magnetic resonance (MR) image guidance with radiotherapy to reduce tumor position uncertainty during photon radiotherapy. The therapeutic gain from reducing tumor position uncertainty using intrafraction MR imaging during radiotherapy could be partially offset if the negative effects of magnetic field-induced dose perturbations are not appreciated or accounted for. The authors hypothesize that a more rotationally symmetric modality such as helical tomotherapy will permit a systematic mediation of these dose perturbations. This investigation offers a unique look at the dose perturbations due to homogeneous transverse magnetic field during the delivery of Tomotherapy ® Treatment System plans under varying degrees of rotational beamlet symmetry. Methods: The authors accurately reproduced treatment plan beamlet and patient configurations using the Monte Carlo code 4. This code has a thoroughly benchmarked electromagnetic particle transport physics package well-suited for the radiotherapy energy regime. The three approved clinical treatment plans for this study were for a prostate, head and neck, and lung treatment. The dose heterogeneity index metric was used to quantify the effect of the dose perturbations to the target volumes.Results: The authors demonstrate the ability to reproduce the clinical dose-volume histograms (DVH) to within 4% dose agreement at each DVH point for the target volumes and most planning structures, and therefore, are able to confidently examine the effects of transverse magnetic fields on the plans. The authors investigated field strengths of 0.35, 0.7, 1, 1.5, and 3 T. Changes to the dose heterogeneity index of 0.1% were seen in the prostate and head and neck case, reflecting negligible dose perturbations to the target volumes, a change from 5.5% to 20.1% was observed with the lung case. Conclusions: This study demonstrated that the effect of external magnetic fields can be mitigated by exploiting a more rotationally symmetric treatment modality. C 2015 American Association of Physicists in Medicine. [http://dx

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Section: Introductionmentioning

confidence: 99%

Monte Carlo simulations of patient dose perturbations in rotational‐type radiotherapy due to a transverse magnetic field: A tomotherapy investigation

et al. 2015

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“…Hence, treatment planning with the magnetic field considered is necessary, which has also been suggested previously by other studies. [28][29][30][31][32][33] The most distinct feature differentiating our conceptual system from the existing MRI-LINAC systems is its smaller FoV. As opposed to integrating a full body MRI scanner with a LINAC, we propose using a new MRI design that has a small (∼15 cm diameter) FoV.…”

Section: Dosimetric Impacts Of the Magnetic Fieldmentioning

confidence: 99%

New concept on an integrated interior magnetic resonance imaging and medical linear accelerator system for radiation therapy

Jia

Tian

et al. 2017

J. Med. Imag

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Abstract. Image guidance plays a critical role in radiotherapy. Currently, cone-beam computed tomography (CBCT) is routinely used in clinics for this purpose. While this modality can provide an attenuation image for therapeutic planning, low soft-tissue contrast affects the delineation of anatomical and pathological features. Efforts have recently been devoted to several MRI linear accelerator (LINAC) projects that lead to the successful combination of a full diagnostic MRI scanner with a radiotherapy machine. We present a new concept for the development of the MRI-LINAC system. Instead of combining a full MRI scanner with the LINAC platform, we propose using an interior MRI (iMRI) approach to image a specific region of interest (RoI) containing the radiation treatment target. While the conventional CBCT component still delivers a global image of the patient's anatomy, the iMRI offers local imaging of high soft-tissue contrast for tumor delineation. We describe a top-level system design for the integration of an iMRI component into an existing LINAC platform. We performed numerical analyses of the magnetic field for the iMRI to show potentially acceptable field properties in a spherical RoI with a diameter of 15 cm. This field could be shielded to a sufficiently low level around the LINAC region to avoid electromagnetic interference. Furthermore, we investigate the dosimetric impacts of this integration on the radiotherapy beam.

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“…These dose perturbations can be minimized in MRI-guided radiation therapy systems which orient the radiation beam parallel to the direction of the MRI's magnetic field. 14 Monte Carlo simulations have demonstrated that for systems with a strong transverse magnetic field, irradiation of lung tissue surrounded by a higher density material will produce a dose increase at the high-to-low-density interface and a dose decrease at the low-to-high-density interface. 9,15 In previous studies, investigators simulated the irradiation of a human lung phantom with a 6 MV beam in the presence of a 1.5 T magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Technical Note: A Monte Carlo study of magnetic‐field‐induced radiation dose effects in mice

et al. 2015

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Purpose: Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. Methods: Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV , 2 MV, and 1.25 MeV ) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. Results: In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. Conclusions: The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac. C 2015 American Association of Physicists in Medicine. [http://dx

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Lung dosimetry in a linac‐MRI radiotherapy unit with a longitudinal magnetic field

Cited by 83 publications

References 19 publications

Monte Carlo simulations of patient dose perturbations in rotational‐type radiotherapy due to a transverse magnetic field: A tomotherapy investigation

Monte Carlo simulations of patient dose perturbations in rotational‐type radiotherapy due to a transverse magnetic field: A tomotherapy investigation

New concept on an integrated interior magnetic resonance imaging and medical linear accelerator system for radiation therapy

Technical Note: A Monte Carlo study of magnetic‐field‐induced radiation dose effects in mice

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