MRI Linac Systems

  • Brendan Whelan
  • Brad Oborn
  • Gary LineyEmail author
  • Paul Keall


This chapter describes magnetic resonance imaging-linear accelerator (MRI-Linac) systems, focusing on the challenges of integrating MRI and linacs that are common to all current and future MRI-Linac systems. The four MRI-Linac systems in existence at the time of writing are reviewed and compared. Predictions of the future of MRI-Linacs and their potential are made.


  1. Acharya S, Fischer-Valuck BW, Kashani R, et al. Online magnetic resonance image guided adaptive radiation therapy: first clinical applications. Int J Radiat Oncol Biol Phys. 2016;94:394–403.PubMedCrossRefPubMedCentralGoogle Scholar
  2. Barton MB, Jacob S, Shafiq J, et al. Estimating the demand for radiotherapy from the evidence: a review of changes from 2003 to 2012. Radiother Oncol. 2014;112:140–4.PubMedCrossRefGoogle Scholar
  3. Bielajew AF. The effect of strong longitudinal magnetic fields on dose deposition from electron and photon beams. Med Phys. 1993;20:1171–9.PubMedCrossRefPubMedCentralGoogle Scholar
  4. Bol G, Hissoiny S, Lagendijk J, et al. Fast online Monte Carlo-based IMRT planning for the MRI linear accelerator. Phys Med Biol. 2012;57:1375.PubMedCrossRefPubMedCentralGoogle Scholar
  5. Bol GH, Lagendijk JJ, Raaymakers BW. Compensating for the impact of non-stationary spherical air cavities on IMRT dose delivery in transverse magnetic fields. Phys Med Biol. 2015;60:755–68.PubMedCrossRefPubMedCentralGoogle Scholar
  6. Burke B, Wachowicz K, Fallone B, et al. Effect of radiation induced current on the quality of MR images in an integrated linac-MR system. Med Phys. 2012;39:6139–47.PubMedCrossRefPubMedCentralGoogle Scholar
  7. Chen Y, Bielajew AF, Litzenberg DW, et al. Magnetic confinement of electron and photon radiotherapy dose: a Monte Carlo simulation with a nonuniform longitudinal magnetic field. Med Phys. 2005;32:3810–8.PubMedCrossRefPubMedCentralGoogle Scholar
  8. Chopra S, Foltz WD, Milosevic MF, et al. Comparing oxygen-sensitive MRI (BOLD R2*) with oxygen electrode measurements: a pilot study in men with prostate cancer. Int J Radiat Biol. 2009;85:805–13.PubMedCrossRefPubMedCentralGoogle Scholar
  9. Constantin DE, Fahrig R, Keall PJ. A study of the effect of in-line and perpendicular magnetic fields on beam characteristics of electron guns in medical linear accelerators. Med Phys. 2011;38:4174–85.PubMedPubMedCentralCrossRefGoogle Scholar
  10. Cuculich PS, Schill MR, Kashani R, et al. Noninvasive cardiac radiation for ablation of ventricular tachycardia. N Engl J Med. 2017;377:2325–36.PubMedPubMedCentralCrossRefGoogle Scholar
  11. Donovan E, Bleakley N, Denholm E, et al. Randomised trial of standard 2D radiotherapy (RT) versus intensity modulated radiotherapy (IMRT) in patients prescribed breast radiotherapy. Radiother Oncol. 2007;82:254–64.PubMedCrossRefPubMedCentralGoogle Scholar
  12. Erridge SC, Seppenwoolde Y, Muller SH, et al. Portal imaging to assess set-up errors, tumor motion and tumor shrinkage during conformal radiotherapy of non-small cell lung cancer. Radiother Oncol. 2003;66:75–85.PubMedCrossRefPubMedCentralGoogle Scholar
  13. Fallone BG. The rotating biplanar linac–magnetic resonance imaging system. Semin Radiat Oncol. 2014;24:200–2.CrossRefGoogle Scholar
  14. Fallone BG, Murray B, Rathee S, et al. First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system. Med Phys. 2009;36:2084–8.PubMedCrossRefPubMedCentralGoogle Scholar
  15. Gargett M, Oborn B, Metcalfe P, et al. Monte Carlo simulation of the dose response of a novel 2D silicon diode array for use in hybrid MRI-LINAC systems. Med Phys. 2015;42:856–65.PubMedCrossRefPubMedCentralGoogle Scholar
  16. Gargett MA, Oborn B, Alnaghy SJ, et al. A high resolution 2d array detector system for small-field MRI-Linac applications. Biomed Phys Eng Express. 2018;4:035041.CrossRefGoogle Scholar
  17. Gibbs P, Liney GP, Pickles MD, et al. Correlation of ADC and T2 measurements with cell density in prostate cancer at 3.0 Tesla. Investig Radiol. 2009;44:572–6.CrossRefGoogle Scholar
  18. Hoogcarspel SJ, Zijlema SE, Tijssen RH, et al. Characterization of the first RF coil dedicated to 1.5 T MR guided radiotherapy. Phys Med Biol. 2018;63:025014.PubMedCrossRefPubMedCentralGoogle Scholar
  19. Ingersoll L, Liebenberg D. The Faraday effect in gases and vapors. I. J Opt Soc Am. 1954;44:566–71.CrossRefGoogle Scholar
  20. Ingersoll L, Liebenberg D. Faraday effect in gases and vapors. II. J Opt Soc Am. 1956;46:538–42.CrossRefGoogle Scholar
  21. Ipsen S, Blanck O, Oborn B, et al. Radiotherapy beyond cancer: target localization in real-time MRI and treatment planning for cardiac radiosurgery. Med Phys. 2014;41:120702.PubMedCrossRefPubMedCentralGoogle Scholar
  22. Karzmark C, Nunan CS, Tanabe E. Medical electron accelerators. New York City, NY: McGraw-Hill; 1993.Google Scholar
  23. Keall PJ, Mageras GS, Balter JM, et al. The management of respiratory motion in radiation oncology report of AAPM Task Group 76. Med Phys. 2006;33:3874–900.PubMedCrossRefPubMedCentralGoogle Scholar
  24. Keall PJ, Barton M, Crozier S. The Australian magnetic resonance imaging–linac program. Semin Radiat Oncol. 2014;24:203–6.CrossRefGoogle Scholar
  25. Kirkby C, Stanescu T, Rathee S, et al. Patient dosimetry for hybrid MRI-radiotherapy systems. Med Phys. 2008;35:1019–27.PubMedCrossRefPubMedCentralGoogle Scholar
  26. Kirkby C, Murray B, Rathee S, et al. Lung dosimetry in a linac-MRI radiotherapy unit with a longitudinal magnetic field. Med Phys. 2010;37:4722–32.PubMedCrossRefPubMedCentralGoogle Scholar
  27. Kolling S, Oborn B, Keall P. Impact of the MLC on the MRI field distortion of a prototype MRI-linac. Med Phys. 2013;40:12705.Google Scholar
  28. Kontaxis C, Bol G, Lagendijk J, et al. A new methodology for inter-and intrafraction plan adaptation for the MR-linac. Phys Med Biol. 2015;60:7485.CrossRefGoogle Scholar
  29. Kontaxis C, Bol G, Stemkens B, et al. Towards fast online intrafraction replanning for free-breathing stereotactic body radiation therapy with the MR-linac. Phys Med Biol. 2017;62:7233.CrossRefGoogle Scholar
  30. Kumar V. Understanding the focusing of charged particle beams in a solenoid magnetic field. Am J Phys. 2009;77:737–41.CrossRefGoogle Scholar
  31. Lagendijk JJ, Raaymakers BW, van Vulpen M. The magnetic resonance imaging–linac system. Semin Radiat Oncol. 2014;24:207–9.CrossRefGoogle Scholar
  32. Lamey M, Burke B, Blosser E, et al. Radio frequency shielding for a linac-MRI system. Phys Med Biol. 2010a;55:995–1006.PubMedCrossRefPubMedCentralGoogle Scholar
  33. Lamey M, Rathee S, Johnson L, et al. Radio frequency noise from the modulator of a linac. IEEE Trans Electromagn Compat. 2010b;52:530–6.CrossRefGoogle Scholar
  34. Latifi K, Oliver J, Baker R, et al. Study of 201 non-small cell lung cancer patients given stereotactic ablative radiation therapy shows local control dependence on dose calculation algorithm. Int J Radiat Oncol Biol Phys. 2014;88:1108–13.PubMedCrossRefPubMedCentralGoogle Scholar
  35. Lee JY, Spratt DE, Liss AL, et al. Vessel-sparing radiation and functional anatomy-based preservation for erectile function after prostate radiotherapy. Lancet Oncol. 2016;17:e198–208.PubMedCrossRefPubMedCentralGoogle Scholar
  36. Liao ZX, Komaki RR, Thames HD Jr, et al. Influence of technologic advances on outcomes in patients with unresectable, locally advanced non-small-cell lung cancer receiving concomitant chemoradiotherapy. Int J Radiat Oncol Biol Phys. 2010;76:775–81.PubMedCrossRefGoogle Scholar
  37. Liney GP, Dong B, Begg J, et al. Technical note: experimental results from a prototype high-field inline MRI-linac. Med Phys. 2016;43:5188–94.PubMedCrossRefPubMedCentralGoogle Scholar
  38. Liney GP, Dong B, Weber E, et al. Imaging performance of a dedicated radiation transparent RF coil on a 1.0 Tesla inline MRI-linac. Phys Med Biol. 2018a;63:135005.CrossRefGoogle Scholar
  39. Liney G, Whelan B, Oborn B, et al. MRI-linear accelerator radiotherapy systems. Clin Oncol. 2018b;30:686–91.PubMedCrossRefPubMedCentralGoogle Scholar
  40. Liu L, Sanchez-Lopez H, Liu F, et al. Flanged-edge transverse gradient coil design for a hybrid LINAC–MRI system. J Magn Reson. 2013;226:70–8.PubMedCrossRefPubMedCentralGoogle Scholar
  41. Low D, Mutic S, Shvartsman S, et al. TU-H-BRA-02: the physics of magnetic field isolation in a novel compact linear accelerator based MRI-guided radiation therapy system. Med Phys. 2016;43:3768.CrossRefGoogle Scholar
  42. Meijsing I, Raaymakers BW, Raaijmakers AJ, et al. Dosimetry for the MRI accelerator: the impact of a magnetic field on the response of a Farmer NE2571 ionization chamber. Phys Med Biol. 2009;54:2993–3002.PubMedCrossRefPubMedCentralGoogle Scholar
  43. Mutic S, Dempsey JF. The ViewRay system: Magnetic resonance-guided and controlled radiotherapy. Semin Radiat Oncol. 2014;24:196–9.CrossRefGoogle Scholar
  44. Nutting CM, Morden JP, Harrington KJ, et al. Parotid-sparing intensity modulated versus conventional radiotherapy in head and neck cancer (PARSPORT): a phase 3 multicentre randomised controlled trial. Lancet Oncol. 2011;12:127–36.PubMedPubMedCentralCrossRefGoogle Scholar
  45. Oborn BM, Metcalfe PE, Butson MJ, et al. High resolution entry and exit Monte Carlo dose calculations from a linear accelerator 6 MV beam under the influence of transverse magnetic fields. Med Phys. 2009;36:3549–59.PubMedCrossRefPubMedCentralGoogle Scholar
  46. Oborn BM, Metcalfe PE, Butson MJ, et al. Monte Carlo characterization of skin doses in 6 MV transverse field MRI-LINAC systems: effect of field size, surface orientation, magnetic field strength, and exit bolus. Med Phys. 2010;37:5208–17.PubMedCrossRefPubMedCentralGoogle Scholar
  47. Oborn B, Metcalfe PE, Butson M, et al. Electron contamination modeling and skin dose in 6 MV longitudinal field MRIgRT: Impact of the MRI and MRI fringe field. Med Phys. 2012;39:874–90.PubMedCrossRefPubMedCentralGoogle Scholar
  48. Oborn B, Kolling S, Metcalfe PE, et al. Electron contamination modeling and reduction in a 1 T open bore inline MRI-linac system. Med Phys. 2014;41:051708.PubMedCrossRefPubMedCentralGoogle Scholar
  49. Oborn BM, Ge Y, Hardcastle N, et al. Dose enhancement in radiotherapy of small lung tumors using inline magnetic fields: a Monte Carlo based planning study. Med Phys. 2016;43:368.PubMedCrossRefPubMedCentralGoogle Scholar
  50. Oborn BM, Gargett MA, Causer TJ, et al. Experimental verification of dose enhancement effects in a lung phantom from inline magnetic fields. Radiother Oncol. 2017;125:433–8.PubMedCrossRefPubMedCentralGoogle Scholar
  51. O’Brien DJ, Roberts DA, Ibbott GS, et al. Reference dosimetry in magnetic fields: formalism and ionization chamber correction factors. Med Phys. 2016;43:4915.PubMedCrossRefPubMedCentralGoogle Scholar
  52. Ogawa S, Lee T-M, Kay AR, et al. Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proc Natl Acad Sci U S A. 1990;87:9868–72.PubMedPubMedCentralCrossRefGoogle Scholar
  53. Overweg J, Raaymakers B, Lagendijk J, et al. System for MRI guided radiotherapy. Proc Int Soc Magn Reson Med. 2009;2009:593.Google Scholar
  54. Paganelli C, Whelan BM, Peroni M, et al. MRI-guidance for motion management in external beam radiotherapy: current status and future challenges. Phys Med Biol. 2018;63:22TR03.PubMedCrossRefPubMedCentralGoogle Scholar
  55. Palma D, Visser O, Lagerwaard FJ, et al. Impact of introducing stereotactic lung radiotherapy for elderly patients with stage I non-small-cell lung cancer: a population-based time-trend analysis. J Clin Oncol. 2010;28:5153–9.PubMedCrossRefPubMedCentralGoogle Scholar
  56. Pignol J-P, Olivotto I, Rakovitch E, et al. A multicenter randomized trial of breast intensity-modulated radiation therapy to reduce acute radiation dermatitis. J Clin Oncol. 2008;26:2085–92.PubMedCrossRefPubMedCentralGoogle Scholar
  57. Raaijmakers AJ, Raaymakers BW, Lagendijk JJ. Integrating a MRI scanner with a 6 MV radiotherapy accelerator: dose increase at tissue-air interfaces in a lateral magnetic field due to returning electrons. Phys Med Biol. 2005;50:1363–76.PubMedCrossRefPubMedCentralGoogle Scholar
  58. Raaijmakers AJ, Hardemark B, Raaymakers BW, et al. Dose optimization for the MRI-accelerator: IMRT in the presence of a magnetic field. Phys Med Biol. 2007a;52:7045–54.PubMedCrossRefPubMedCentralGoogle Scholar
  59. Raaijmakers AJ, Raaymakers BW, Lagendijk JJ. Experimental verification of magnetic field dose effects for the MRI-accelerator. Phys Med Biol. 2007b;52:4283–91.PubMedCrossRefPubMedCentralGoogle Scholar
  60. Raaijmakers AJ, Raaymakers BW, van der Meer S, et al. Integrating a MRI scanner with a 6 MV radiotherapy accelerator: impact of the surface orientation on the entrance and exit dose due to the transverse magnetic field. Phys Med Biol. 2007c;52:929–39.PubMedCrossRefPubMedCentralGoogle Scholar
  61. Raaijmakers AJ, Raaymakers BW, Lagendijk JJ. Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength. Phys Med Biol. 2008;53:909–23.PubMedCrossRefPubMedCentralGoogle Scholar
  62. Raaymakers BW, Raaijmakers AJ, Kotte AN, et al. Integrating a MRI scanner with a 6 MV radiotherapy accelerator: dose deposition in a transverse magnetic field. Phys Med Biol. 2004;49:4109–18.PubMedCrossRefPubMedCentralGoogle Scholar
  63. Raaymakers BW, de Boer JC, Knox C, et al. Integrated megavoltage portal imaging with a 1.5 T MRI linac. Phys Med Biol. 2011;56:N207–14.PubMedCrossRefPubMedCentralGoogle Scholar
  64. Raaymakers BW, Jurgenliemk-Schulz IM, Bol GH, et al. First patients treated with a 1.5 T MRI-Linac: clinical proof of concept of a high-precision, high-field MRI guided radiotherapy treatment. Phys Med Biol. 2017;62:L41–50.PubMedCrossRefPubMedCentralGoogle Scholar
  65. Reynolds M, Fallone BG, Rathee S. Dose response of selected ion chambers in applied homogeneous transverse and longitudinal magnetic fields. Med Phys. 2013;40:042102.PubMedCrossRefPubMedCentralGoogle Scholar
  66. Reynolds M, Fallone BG, Rathee S. Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields. Med Phys. 2014;41:092103.PubMedCrossRefPubMedCentralGoogle Scholar
  67. Reynolds M, Fallone BG, Rathee S. Technical note: response measurement for select radiation detectors in magnetic fields. Med Phys. 2015;42:2837–40.PubMedCrossRefPubMedCentralGoogle Scholar
  68. Rudra S, Jiang N, Rosenberg SA, et al. High dose adaptive MRI guided radiation therapy improves overall survival of inoperable pancreatic cancer. Int J Radiat Oncol Biol Phys. 2017;99:E184.CrossRefGoogle Scholar
  69. Santos D, St Aubin J, Fallone B, et al. Magnetic shielding investigation for a 6 MV in-line linac within the parallel configuration of a linac-MR system. Med Phys. 2012;39:788–97.PubMedCrossRefPubMedCentralGoogle Scholar
  70. Seppenwoolde Y, Shirato H, Kitamura K, et al. Precise and real-time measurement of 3D tumor motion in lung due to breathing and heartbeat, measured during radiotherapy. Int J Radiat Oncol Biol Phys. 2002;53:822–34.PubMedCrossRefPubMedCentralGoogle Scholar
  71. Shih CC. High energy electron radiotherapy in a magnetic field. Med Phys. 1975;2:9–13.PubMedCrossRefPubMedCentralGoogle Scholar
  72. Smit K, Van Asselen B, Kok J, et al. Towards reference dosimetry for the MR-linac: magnetic field correction of the ionization chamber reading. Phys Med Biol. 2013;58:5945.PubMedCrossRefPubMedCentralGoogle Scholar
  73. Spindeldreier CK, Schrenk O, Bakenecker A, et al. Radiation dosimetry in magnetic fields with Farmer-type ionization chambers: determination of magnetic field correction factors for different magnetic field strengths and field orientations. Phys Med Biol. 2017;62:6708–28.PubMedCrossRefPubMedCentralGoogle Scholar
  74. St Aubin J, Santos DM, Steciw S, et al. Effect of longitudinal magnetic fields on a simulated in-line 6 MV linac. Med Phys. 2010a;37:4916–23.Google Scholar
  75. St Aubin J, Steciw S, Fallone B. Effect of transverse magnetic fields on a simulated in-line 6 MV linac. Phys Med Biol. 2010b;55:4861.PubMedCrossRefPubMedCentralGoogle Scholar
  76. St Aubin J, Steciw S, Fallone BG. Magnetic decoupling of the linac in a low field biplanar linac-MR system. Med Phys. 2010c;37:4755–61.Google Scholar
  77. Tadic T, Fallone BG. Design and optimization of superconducting MRI magnet systems with magnetic materials. IEEE Trans Appl Supercond. 2012;22:4400107.CrossRefGoogle Scholar
  78. Tari SY, Wachowicz K, Fallone BG. A non-axial superconducting magnet design for optimized patient access and minimal SAD for use in a Linac-MR hybrid: proof of concept. Phys Med Biol. 2017;62:N147.CrossRefGoogle Scholar
  79. Turnbull LW, Buckley DL, Turnbull LS, et al. Differentiation of prostatic carcinoma and benign prostatic hyperplasia: correlation between dynamic Gd-DTPA-enhanced MR imaging and histopathology. J Magn Reson Imaging. 1999;9:311–6.PubMedCrossRefGoogle Scholar
  80. Wang J, Trovati S, Borchard PM, et al. Thermal limits on MV x-ray production by bremsstrahlung targets in the context of novel linear accelerators. Med Phys. 2017;44:6610–20.PubMedPubMedCentralCrossRefGoogle Scholar
  81. Webb A, Van de Moortele P. The technological future of 7 T MRI hardware. NMR Biomed. 2016;29:1305–15.PubMedCrossRefPubMedCentralGoogle Scholar
  82. Weinhous MS, Nath R, Schulz RJ. Enhancement of electron beam dose distributions by longitudinal magnetic fields: Monte Carlo simulations and magnet system optimization. Med Phys. 1985;12:598–603.PubMedCrossRefPubMedCentralGoogle Scholar
  83. Whelan B, Gierman S, Holloway L, et al. A novel electron accelerator for MRI-linac radiotherapy. Med Phys. 2016a;43:1285–94.PubMedPubMedCentralCrossRefGoogle Scholar
  84. Whelan B, Holloway L, Constantin D, et al. Performance of a clinical gridded electron gun in magnetic fields: implications for MRI-linac therapy. Med Phys. 2016b;43:5903.PubMedPubMedCentralCrossRefGoogle Scholar
  85. Whelan B, Kolling S, Oborn BM, et al. Passive magnetic shielding in MRI-Linac systems. Phys Med Biol. 2018;63:075008.PubMedCrossRefPubMedCentralGoogle Scholar
  86. Whitmire DP, Bernard DL, Peterson MD, et al. Magnetic enhancement of electron dose distribution in a phantom. Med Phys. 1977;4:127–31.PubMedCrossRefPubMedCentralGoogle Scholar
  87. Woodings SJ, Bluemink J, de Vries J, et al. Beam characterisation of the 1.5 T MRI-linac. Phys Med Biol. 2018;63:085015.PubMedCrossRefPubMedCentralGoogle Scholar
  88. Yun J, St Aubin J, Rathee S, et al. Brushed permanent magnet DC MLC motor operation in an external magnetic field. Med Phys. 2010;37:2131–4.PubMedCrossRefPubMedCentralGoogle Scholar
  89. Zelefsky MJ, Kollmeier M, Cox B, et al. Improved clinical outcomes with high-dose image guided radiotherapy compared with non-IGRT for the treatment of clinically localized prostate cancer. Int J Radiat Oncol Biol Phys. 2012;84:125–9.PubMedCrossRefPubMedCentralGoogle Scholar

Copyright information

© Springer Nature Switzerland AG 2019

Authors and Affiliations

  • Brendan Whelan
    • 1
  • Brad Oborn
    • 2
    • 3
  • Gary Liney
    • 4
    Email author
  • Paul Keall
    • 1
  1. 1.ACRF Image X InstituteUniversity of SydneySydneyAustralia
  2. 2.Centre for Medical Radiation PhysicsUniversity of WollongongWollongongAustralia
  3. 3.Illawarra Cancer Care CentreWollongong HospitalWollongongAustralia
  4. 4.Ingham Institute of Applied Medical ResearchLiverpoolAustralia

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