The future of image-guided radiotherapy will be MR guided.

Advances in image-guided radiotherapy (RT) have allowed for dose escalation and more precise radiation treatment delivery. Each decade brings new imaging technologies to help improve RT patient setup. Currently, the most frequently used method of three-dimensional pre-treatment image verification is performed with cone beam CT. However, more recent developments have provided RT with the ability to have on-board MRI coupled to the teleradiotherapy unit. This latest tool for treating cancer is known as MR-guided RT. Several varieties of these units have been designed and installed in centres across the globe. Their prevalence, history, advantages and disadvantages are discussed in this review article. In preparation for the next generation of image-guided RT, this review also covers where MR-guided RT might be heading in the near future.

[1]  Fridtjof Nüsslin,et al.  Individualized radiotherapy by combining high-end irradiation and magnetic resonance imaging , 2016, Strahlentherapie und Onkologie.

[2]  B. Fallone,et al.  The rotating biplanar linac-magnetic resonance imaging system. , 2014, Seminars in radiation oncology.

[3]  Naishadh A Shah,et al.  Magnetic Resonance Spectroscopy as an Imaging Tool for Cancer: A Review of the Literature , 2006, The Journal of the American Osteopathic Association.

[4]  A N T J Kotte,et al.  Integrating a MRI scanner with a 6 MV radiotherapy accelerator: dose deposition in a transverse magnetic field. , 2004, Physics in medicine and biology.

[5]  J. Chavaudra,et al.  [Definition of volumes in external radiotherapy: ICRU reports 50 and 62]. , 2001, Cancer radiotherapie : journal de la Societe francaise de radiotherapie oncologique.

[6]  Peter Smeets,et al.  Clinical implementation of intensity-modulated arc therapy (IMAT) for rectal cancer. , 2004, International journal of radiation oncology, biology, physics.

[7]  Peter Balter,et al.  Stereotactic ablative radiotherapy versus lobectomy for operable stage I non-small-cell lung cancer: a pooled analysis of two randomised trials. , 2015, The Lancet. Oncology.

[8]  C. Ménard,et al.  Prostate delineation using CT and MRI for radiotherapy patients with bilateral hip prostheses. , 2009, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[9]  Christian Kirisits,et al.  Advancements in brachytherapy. , 2017, Advanced drug delivery reviews.

[10]  H. Poptani,et al.  Characterization of intracranial mass lesions with in vivo proton MR spectroscopy. , 1995, AJNR. American journal of neuroradiology.

[11]  Paul Keall,et al.  Quantifying the accuracy of the tumor motion and area as a function of acceleration factor for the simulation of the dynamic keyhole magnetic resonance imaging method. , 2016, Medical physics.

[12]  Slobodan Devic,et al.  MRI simulation for radiotherapy treatment planning. , 2012, Medical physics.

[13]  P. Keall,et al.  A novel electron gun for inline MRI-linac configurations. , 2014, Medical physics.

[14]  Melanie Traughber,et al.  Evaluating organ delineation, dose calculation and daily localization in an open-MRI simulation workflow for prostate cancer patients , 2015, Radiation Oncology.

[15]  S. Nour,et al.  The Potential Role of Magnetic Resonance Spectroscopy in Image-Guided Radiotherapy , 2014, Front. Oncol..

[16]  Jan J W Lagendijk,et al.  MR guidance in radiotherapy , 2014, Physics in medicine and biology.

[17]  D P Dearnaley,et al.  Distortion-corrected T2 weighted MRI: a novel approach to prostate radiotherapy planning. , 2007, The British journal of radiology.

[18]  Fang-Fang Yin,et al.  Task Group 142 report: quality assurance of medical accelerators. , 2009, Medical physics.

[19]  V. Khoo,et al.  The utility of multimodality imaging with CT and MRI in defining rectal tumour volumes for radiotherapy treatment planning: a pilot study , 2010, Journal of medical imaging and radiation oncology.

[20]  Improved target volume definition for precision radiotherapy planning of meningiomas by correlation of CT and dynamic, Gd-DTPA-enhanced FLASH MR imaging. , 1994, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[21]  B W Raaymakers,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 , 2007, Physics in medicine and biology.

[22]  L. Martí-Bonmatí,et al.  MRS as endogenous molecular imaging for brain and prostate tumors: FP6 project "eTUMOR". , 2006, Advances in experimental medicine and biology.

[23]  M. Halliwell,et al.  Magnetic resonance imaging appearances in the postoperative breast: the clinical target volume-tumor and its relationship to the chest wall. , 2008, International journal of radiation oncology, biology, physics.

[24]  B W Raaymakers,et al.  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 , 2005, Physics in medicine and biology.

[25]  J. Lagendijk,et al.  The development of the MRI linac system for online MRI‐guided radiotherapy: a clinical update , 2016, Journal of internal medicine.

[26]  Anil Sethi,et al.  Influence of MRI on target volume delineation and IMRT planning in nasopharyngeal carcinoma. , 2003, International journal of radiation oncology, biology, physics.

[27]  E. Kouwenhoven,et al.  Magnetic resonance imaging- versus computed tomography-based target volume delineation of the glandular breast tissue (clinical target volume breast) in breast-conserving therapy: an exploratory study. , 2011, International journal of radiation oncology, biology, physics.

[28]  Thomas Bortfeld,et al.  An analytical solution to proton Bragg peak deflection in a magnetic field , 2012, Physics in medicine and biology.

[29]  J G M Kok,et al.  Integrating a 1.5 T MRI scanner with a 6 MV accelerator: proof of concept , 2009, Physics in medicine and biology.

[30]  Jan-Jakob Sonke,et al.  Magnetic resonance-guided adaptive radiotherapy: a solution to the future. , 2014, Seminars in radiation oncology.

[31]  Steffen Ringgaard,et al.  Three-dimensional liver motion tracking using real-time two-dimensional MRI. , 2014, Medical physics.

[32]  Felix Breuer,et al.  Simultaneous multislice (SMS) imaging techniques , 2015, Magnetic resonance in medicine.

[33]  Olivier Salvado,et al.  A magnetic resonance imaging‐based workflow for planning radiation therapy for prostate cancer , 2011, The Medical journal of Australia.

[34]  B. O'neill,et al.  MR vs CT imaging: low rectal cancer tumour delineation for three-dimensional conformal radiotherapy. , 2009, The British journal of radiology.

[35]  Arend Heerschap,et al.  Customizable, multi-functional fluorocarbon nanoparticles for quantitative in vivo imaging using 19F MRI and optical imaging. , 2010, Biomaterials.

[36]  Ping Xia,et al.  A population-based atlas and clinical target volume for the head-and-neck lymph nodes. , 2004, International journal of radiation oncology, biology, physics.

[37]  Tomas Kron,et al.  Magnetic resonance imaging for adaptive cobalt tomotherapy: A proposal , 2006, Journal of medical physics.

[38]  H. Paganetti,et al.  Dosimetric feasibility of real-time MRI-guided proton therapy. , 2014, Medical physics.

[39]  Sasa Mutic,et al.  Characterization of the onboard imaging unit for the first clinical magnetic resonance image guided radiation therapy system. , 2015, Medical physics.

[40]  B. Fallone,et al.  First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system. , 2009, Medical physics.

[41]  Savannah C Partridge,et al.  Are Qualitative Assessments of Background Parenchymal Enhancement, Amount of Fibroglandular Tissue on MR Images, and Mammographic Density Associated with Breast Cancer Risk? , 2015, Radiology.

[42]  Christian Kirisits,et al.  Image guided adaptive brachytherapy with combined intracavitary and interstitial technique improves the therapeutic ratio in locally advanced cervical cancer: Analysis from the retroEMBRACE study. , 2016, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[43]  David A Jaffray,et al.  A facility for magnetic resonance-guided radiation therapy. , 2014, Seminars in radiation oncology.

[44]  U. Flögel,et al.  Technical Advance: Monitoring the trafficking of neutrophil granulocytes and monocytes during the course of tissue inflammation by noninvasive 19F MRI , 2014, Journal of leukocyte biology.

[45]  K. Jingu,et al.  MRI findings of radiation-induced myocardial damage in patients with oesophageal cancer. , 2014, Clinical radiology.

[46]  M. Alley,et al.  MRI guidance for accelerated partial breast irradiation in prone position: imaging protocol design and evaluation. , 2009, International journal of radiation oncology, biology, physics.

[47]  D A Jaffray,et al.  Development of a geometrically accurate imaging protocol at 3 Tesla MRI for stereotactic radiosurgery treatment planning , 2010, Physics in medicine and biology.

[48]  Christian Kirisits,et al.  Image guided brachytherapy in locally advanced cervical cancer: Improved pelvic control and survival in RetroEMBRACE, a multicenter cohort study. , 2016, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[49]  A. Kishan,et al.  A treatment planning comparison between modulated tri-cobalt-60 teletherapy and linear accelerator-based stereotactic body radiotherapy for central early-stage non-small cell lung cancer. , 2016, Medical dosimetry : official journal of the American Association of Medical Dosimetrists.

[50]  Eric S Paulson,et al.  Consensus opinion on MRI simulation for external beam radiation treatment planning. , 2016, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[51]  J. Bulte,et al.  Fluorine (19F) MRS and MRI in biomedicine , 2011, NMR in biomedicine.

[52]  Maria A Schmidt,et al.  Radiotherapy planning using MRI , 2015, Physics in medicine and biology.

[53]  Rebecca Fahrig,et al.  Performance of a clinical gridded electron gun in magnetic fields: Implications for MRI-linac therapy. , 2016, Medical physics.

[54]  C. Kirisits,et al.  Image Guided Adaptive Brachytherapy in cervix cancer: A new paradigm changing clinical practice and outcome. , 2016, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[55]  Stuart Crozier,et al.  The Australian magnetic resonance imaging-linac program. , 2014, Seminars in radiation oncology.

[56]  B W Raaymakers,et al.  Feasibility of MRI guided proton therapy: magnetic field dose effects , 2008, Physics in medicine and biology.

[57]  A W Beavis,et al.  Radiotherapy treatment planning of brain tumours using MRI alone. , 1998, The British journal of radiology.

[58]  M. Pitkänen,et al.  Performance of dose calculation algorithms from three generations in lung SBRT: comparison with full Monte Carlo‐based dose distributions , 2014, Journal of applied clinical medical physics.

[59]  Sasa Mutic,et al.  Quality of Intensity Modulated Radiation Therapy Treatment Plans Using a ⁶⁰Co Magnetic Resonance Image Guidance Radiation Therapy System. , 2015, International journal of radiation oncology, biology, physics.

[60]  Jan J W Lagendijk,et al.  The magnetic resonance imaging-linac system. , 2014, Seminars in radiation oncology.

[61]  Jan J W Lagendijk,et al.  MRI/linac integration. , 2008, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[62]  Charis Kontaxis,et al.  Dosimetric feasibility of intensity modulated proton therapy in a transverse magnetic field of 1.5 T , 2015, Physics in medicine and biology.

[63]  D Verellen,et al.  An overview of volumetric imaging technologies and their quality assurance for IGRT , 2008, Acta oncologica.

[64]  Joe Y. Chang,et al.  Can stereotactic ablative radiotherapy in early stage lung cancers produce comparable success as surgery? , 2013, Thoracic surgery clinics.

[65]  R. Velthuizen,et al.  Brain tumor target volume determination for radiation treatment planning through automated MRI segmentation. , 2004, International journal of radiation oncology, biology, physics.

[66]  C. Catton,et al.  Magnetic resonance imaging (MRI) for localization of the prostatic apex: comparison to computed tomography (CT) and urethrography. , 1998, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[67]  P. Harari,et al.  Gadoxetate for direct tumor therapy and tracking with real-time MRI-guided stereotactic body radiation therapy of the liver. , 2016, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[68]  Mika Kapanen,et al.  T1/T2*-weighted MRI provides clinically relevant pseudo-CT density data for the pelvic bones in MRI-only based radiotherapy treatment planning , 2013, Acta oncologica.

[69]  J. Chavaudra,et al.  Définition des volumes en radiothérapie externe : rapports ICRU 50 et 62 , 2001 .

[70]  Sasa Mutic,et al.  The ViewRay system: magnetic resonance-guided and controlled radiotherapy. , 2014, Seminars in radiation oncology.

[71]  Minsong Cao,et al.  Longitudinal diffusion MRI for treatment response assessment: Preliminary experience using an MRI-guided tri-cobalt 60 radiotherapy system. , 2016, Medical physics.

[72]  Lei Dong,et al.  Point/Counterpoint. IGRT has limited clinical value due to lack of accurate tumor delineation. , 2013, Medical physics.

[73]  C. Njeh,et al.  Tumor delineation: The weakest link in the search for accuracy in radiotherapy , 2008, Journal of medical physics.

[74]  Performance of a cylindrical diode array for use in a 1.5 T MR-linac. , 2016, Physics in medicine and biology.

[75]  P. Choyke,et al.  Diffusion-weighted magnetic resonance imaging as a cancer biomarker: consensus and recommendations. , 2009, Neoplasia.

[76]  Dirk Verellen,et al.  Innovations in image-guided radiotherapy , 2008, Nature Reviews Cancer.

[77]  Shayan Guhaniyogi,et al.  Interleaved diffusion‐weighted improved by adaptive partial‐Fourier and multiband multiplexed sensitivity‐encoding reconstruction , 2015, Magnetic resonance in medicine.

[78]  Satyapal Rathee,et al.  First demonstration of intrafractional tumor-tracked irradiation using 2D phantom MR images on a prototype linac-MR. , 2013, Medical physics.

[79]  H. Shiomi,et al.  Evaluation of potential internal target volume of liver tumors using cine-MRI. , 2014, Medical physics.

[80]  A. Luna,et al.  Clinical Imaging of Tumor Metabolism with ¹H Magnetic Resonance Spectroscopy. , 2016, Magnetic resonance imaging clinics of North America.

[81]  H. Kooy,et al.  Impact of Spot Size and Beam-Shaping Devices on the Treatment Plan Quality for Pencil Beam Scanning Proton Therapy. , 2016, International journal of radiation oncology, biology, physics.

[82]  Richard Pötter,et al.  The impact of sectional imaging on dose escalation in endocavitary HDR-brachytherapy of cervical cancer: results of a prospective comparative trial. , 2003, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[83]  Joe Y. Chang,et al.  Lobectomy, sublobar resection, and stereotactic ablative radiotherapy for early-stage non-small cell lung cancers in the elderly. , 2014, JAMA surgery.

[84]  M. Barton,et al.  The Potential for an Enhanced Role for MRI in Radiation-therapy Treatment Planning , 2013, Technology in cancer research & treatment.

[85]  B. Kavanagh,et al.  Improved survival with stereotactic ablative radiotherapy (SABR) over lobectomy for early stage non-small cell lung cancer (NSCLC): addressing the fallout of disruptive randomized data. , 2015, Annals of translational medicine.