Part II (online exam) – MRI for Radiation Therapy

(Reviewed April 2022)

The following nine topics will be covered in both the Part II and Part III (oral) exams. The approximate weighting of each topic is listed in parentheses. The applicant may find it of benefit to review the Suggested Study Materials.

MR Signal Generation and Manipulation (10%)

  • Spins, magnetic moment, and magnetization
  • Equilibrium magnetization and static magnetic field (B0-field)
  • Flip angle; interaction between magnetization and radiofrequency (RF) magnetic field (B0-field)
  • Larmor equation and resonance
  • Classical and quantum mechanical descriptions of ½ spin system
  • Free induction decay (FID) and T2* relaxation time
  • Spin echo and T2 relaxation time
  • Saturation recovery, inversion recovery, and T1 relaxation time
  • Repetition time (TR), echo time (TE), and inversion time (TI)
  • Bloch equations

Spatial Encoding and Image Formation (10%)

  • Frequency selective and non-selective RF pulses
  • Slice selection
  • Formation of gradient echo
  • Frequency encoding
  • Phase encoding
  • k-Space and its relation to image resolution and field-of-view
  • Fourier-transform-based image reconstruction
  • 2D versus 3D imaging and their applications
  • Radial and non-Cartesian acquisitions

Image Pulse Sequences, Signal-to-Noise Ratio, and Image Contrast (10%)

  • Spin-echo and fast (turbo) spin-echo sequences
  • Essential gradient-echo sequences (including steady-state free precession)
  • Sequence parameters to produce T1-weighted, T2-weighted, proton-density-weighted, diffusion-weighted, BOLD, contrast-enhanced MRI, and fat/water images
  • Steady state free precession (balanced and unbalanced)
  • Signal-to-noise ratio and its relationship with image acquisition parameters
  • Tissue specific contrast for tumor and organ-at-risk delineation
  • Contrast-to-noise ratio and its relationship with image acquisition parameters
  • Image spatial resolution
  • Tissue specific contrast for tumor and OAR delineation or common sequences for RT
  • MRI protocols for radiotherapy planning
    • Optimization and selection of sequences for dose calculation, target delineation, metal artifact reduction, and special procedures such as brachy GYN HDR, prostate seed implant SRS
    • Common sequences for RT
    • Site specific requirements (brain, head and neck, abdomen, cervix, prostate, etc.)
  • Fat saturation methods
  • Motion management for radiation therapy planning
    • Respiratory gating
    • Navigators
    • Tumor tracking
    • Realtime MRI
    • 4D MRI
    • MRI-compatible immobilization devices

Distortion and other Image Artifacts (10%)

  • Image distortion due to B0-field inhomogeneities and magnetic susceptibility effects
  • Image distortion due to magnetic field gradients
  • Strategies to reduced image distortion during image acquisition and/or reconstruction
  • Common artifacts encountered in clinical MR images: recognition and mitigation
    • Truncation artifact
    • Motion/flow artifacts
    • Aliasing artifacts (due to improper FOV or parallel imaging)
    • Chemical shift artifacts
    • Ghosting artifacts
    • Shading (e.g., B1-nonuniformity) artifacts
    • Blurring artifacts
    • Null banding artifacts
    • Susceptibility artifacts from ferrous and non-ferrous material or implants

Physics in Radiation Therapy (20%)

  • Imaging modalities for therapy simulations
  • Treatment localization and verification
  • Photon treatment planning
  • Management of inter- and intra-fraction variations
  • Treatment planning system safety, regulatory compliance, and error prevention
  • Dose implications (e.g., secondary electron return effects, proton perturbations) from magnetic fields
  • Imaging vs. radiation isocenters
  • Treatment modes (Step and shoot/IMRT, sliding window, arc therapy/VMAT)

Image Segmentation and Co-registration and MR-only Treatment Planning Methods (10%)

  • Essential image co-registration algorithms and software (deformable vs. non-deformable registration)
  • MRI-to-CT image co-registration
  • Inter- and intra-scan MRI-to-MRI co-registration
  • Evaluation of co-registration accuracy
  • MRsim, MR-only, and MRgRT workflows
  • Adaptive RT
  • MR-only treatment planning and synthetic CT methods
    • Bulk density overrides
    • Tissue class segmentation
    • Machine-learning approaches
    • Atlas-based conversion

Hardware and Instrumentation (10%)

  • Essential hardware of an MRI scanner
    • Magnet (permanent and superconducting magnets)
    • Gradient subsystem
    • RF transceiver chain, including RF coils
    • Computers and processors
    • Siting including RF and main magnetic field shielding
    • Patient monitoring
    • Requirements for an MR simulator – immobilization and coil configuration
  • Essential hardware of a LINAC
    • Photon/electron medical accelerators (physics and design)
    • Beam characteristics
    • Delivery hardware
    • Equipment QA, including absolute calibration for photon and electron beams
    • Shielding
    • External laser positioning system (ELPS)
  • Essential design considerations of an MRI-LINAC
  • Low-field MRI-LINAC considerations
  • High-field MRI-LINAC considerations
  • Differences and similarities among diagnostic MRI, MRI simulation, and MR-IGRT

Site planning, Commissioning, and Quality Assurance for MRsim and MR-LINAC (10%)

  • Commissioning specifications and tolerances
  • Effects of MR fringe field on LINAC and radiation detector performance
  • Quality Assurance

Safety (10%)

  • Effects of ionizing radiation
  • Effects of static magnetic field (B0) and spatial field gradient
  • Effects of time-varying gradient and dB/dt
  • Effects of radiofrequency irradiation
  • Safety screening considerations and risks for implants and shrapnel
  • Safety of gadolinium-based contrast agents
  • MR safety program administration (level 1 and level 2 personnel; zoning, safety polices, etc.)
  • RT specific safety considerations, including pacemakers, defibrillators, and implants
  • Safety of MR-LINAC QA instruments
  • Weighing risks versus benefits

Suggested Study Materials:

  1. Liney G and van der Heide U. MRI for Radiotherapy: Planning, Delivery, and Response Assessment 1st ed. 2019.
  2. C.K. Glide-Hurst, E.S. Paulson, K. McGee, N. Tyagi, Y. Hu, J. Balter, J. Bayouth, “Task group 284 report: magnetic resonance imaging simulation in radiotherapy: considerations for clinical implementation, optimization, and quality assurance,” Med. Phys. 48, e636-e670 (2021).
  3. AAPM 2021 Summer School on “Modern Applications of MR in Radiation Therapy”. https://w4.aapm.org/meetings/2021SS/
  4. AAPM Scientific Sessions and Symposia on MR for Radiation Therapy. https://www.aapm.org/meetings/default.asp
  5. ISMRM Scientific and Educational Sessions relevant to MR for Radiation Therapy.

References:

1           Glide-Hurst, C.K., Paulson, E.S., McGee, K., Tyagi, N., Hu, Y., Balter, J., Bayouth, J. (2021). Task group 284 report: magnetic resonance imaging simulation in radiotherapy: considerations for clinical implementation, optimization, and quality assurance. Medical Physics, 48, e636-e670. https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.14695

2           Gach, H.M., Green, L., Mackey, S.L., Wittland, E.J., Marko, A., Endicott, S.H., Davis, M.R., Hugo, D., Kim, H., Michalski, J.M. (2022). Implementation of magnetic resonance safety program for radiation oncology. Practical Radiation Oncology, 12, e49-e55. https://www.practicalradonc.org/article/S1879-8500(21)00224-1/fulltext

3           Gach, H.M., Curcuru, A.N., Mutic, S., Kim, T. (2020). B0 field homogeneity recommendations, specifications, and measurement units for MRI in radiation therapy. Medical Physics, 47, 4101-4114.

4           H.M. Gach, A.N. Curcuru, E.J. Wittland, B. Maraghechi, B. Cai, S. Mutic, O.L. Green, “MRI quality control for low-field MR-IGRT systems: Lessons learned,” J. Appl. Clin. Med. Phys. 20, 53-66 (2019).

5           J.M. Cunningham, E.A. Barberi, J. Miller, J.P. Kim, C.K. Glide-Hurst, “Development and evaluation of a novel MR-compatible pelvic end-to-end phantom,” J. Appl. Clin. Med. Phys. 20, 265-275 (2019).

6           C.K. Glide-Hurst, J.P. Kim, D. To, Y. Hu, M. Kadbi, T. Nielsen, I.J. Chetty, “Four dimensional magnetic resonance imaging optimization and implementation for magnetic resonance imaging simulation,” Pract. Radiat. Oncol. 5, 433-442 (2015).

7           C.K. Glide-Hurst, P. Lee, A.D. Yock, J.R. Olsen, M. Cao, F. Siddiqui, W. Parker, A. Doemer, Y. Rong, A.U. Kishan, S.H. Benedict, X.A. Li, B.A. Erickson, J.W. Sohn, Y. Xiao, E. Wuthrick, “Adaptive Radiation Therapy (ART) Strategies and Technical Considerations: A State of the ART Review From NRG Oncology,” Int. J. Radiat. Oncol. Biol. Phys. 109, 1054-1075 (2021).

8           K.P. McGee, N. Tyagi, J.E. Bayouth, M. Cao, B.G. Fallone, C.K. Glide-Hurst, F.L. Goerner, O.L. Green, T. Kim, E.S. Paulson, N.E. Yanasak, E.F. Jackson, J.H. Goodwin, S. Dieterich, D.W. Jordan, G.D. Hugo, M.A. Bernstein, J.M. Balter, K.M. Kanal, J.D. Hazle, N.J. Pelc, “Findings of the AAPM Ad Hoc committee on magnetic resonance imaging in radiation therapy: Unmet needs, opportunities, and recommendations,” Med. Phys. 48, 4523-4531 (2021).

9           S.P. Nejad-Davarani, J.P. Kim, D. Du, C. Glide-Hurst, “Large field of view distortion assessment in a low-field MR-linac,” Med. Phys. 46, 2347-2355 (2019).

10          S.P. Nejad-Davarani, P. Sevak, M. Moncion, K. Garbarino, S. Weiss, J. Kim, L. Schultz, M.A. Elshaikh, S. Renisch, C. Glide-Hurst, “Geometric and dosimetric impact of anatomical changes for MR-only radiation therapy for the prostate,” J. Appl. Clin. Med. Phys.2019).

11          A.M. Owrangi, P.B. Greer, C.K. Glide-Hurst, “MRI-only treatment planning: benefits and challenges,” Phys. Med. Biol. 63, 05TR01 (2018).

12          B.C. Lewis, B. Gu, R. Klett, R. Lotey, O.L. Green, T. Kim, “Characterization of radiotherapy component impact on MR imaging quality for an MRgRT system,” J. Appl. Clin. Med. Phys. 21, 20-26 (2020).

13          W.A. Hall, E.S. Paulson, U.A. van der Heide, C.D. Fuller, B.W. Raaymakers, J.J.W. Lagendijk, X.A. Li, D.A. Jaffray, L.A. Dawson, B. Erickson, M. Verheij, K.J. Harrington, A. Sahgal, P. Lee, P.J. Parikh, M.F. Bassetti, C.G. Robinson, B.D. Minsky, A. Choudhury, R. Tersteeg, C.J. Schultz, M.R.L.A. Consortium, C.T.R.C. the ViewRay, “The transformation of radiation oncology using real-time magnetic resonance guidance: A review,” Eur. J. Cancer 122, 42-52 (2019).

14          C.E. Noel, P.J. Parikh, C.R. Spencer, O.L. Green, Y. Hu, S. Mutic, J.R. Olsen, “Comparison of onboard low-field magnetic resonance imaging versus onboard computed tomography for anatomy visualization in radiotherapy,” Acta Oncol. 54, 1474-1482 (2015).

15          T. Kim, B. Gu, B. Maraghechi, O. Green, B. Lewis, S. Mutic, H.M. Gach, “Characterizing MR imaging isocenter variation in MRgRT,” Biomedical Physics & Engineering Express 6, 1-10 (2020).

16          T. Kim, B. Lewis, R. Lotey, E. Barberi, O. Green, “Clinical experience of MRI4D QUASAR motion phantom for latency measurements in 0.35T MR-LINAC,” J. Appl. Clin. Med. Phys. 22, 128-136 (2021).

17          T. Kim, B.C. Lewis, A. Price, T. Mazur, H.M. Gach, J.C. Park, B. Cai, E. Wittland, L. Henke, H. Kim, S. Mutic, O. Green, “Direct tumor visual feedback during free breathing in 0.35T MRgRT,” J. Appl. Clin. Med. Phys. 21, 241-247 (2020).

18          M. Oliver, W. Ansbacher, W.A. Beckham, “Comparing planning time, delivery time and plan quality for IMRT, RapidArc and Tomotherapy,” J. Appl. Clin. Med. Phys. 10, 117-131 (2009).

19          T. De La Fuente Herman, E. Schnell, J. Young, K. Hildebrand, O. Algan, E. Syzek, T. Herman, S. Ahmad, “Dosimetric comparison between IMRT delivery modes: Step-and-shoot, sliding window, and volumetric modulated arc therapy – for whole pelvis radiation therapy of intermediate-to-high risk prostate adenocarcinoma,” J. Med. Phys. 38, 165-172 (2013).

20          K. Scheffler, S. Lehnhardt, “Principles and applications of balanced SSFP techniques,” Eur. Radiol. 13, 2409-2418 (2003).

21          R.W. Brown, Y.-C.N. Cheng, E.M. Haacke, M.R. Thompson, R. Venkatesan, Magnetic Resonance Imaging: Physical Principles and Sequence Design. (Wiley Blackwell, Hoboken, 2014).

22          W.P. Segars, G. Sturgeon, S. Mendonca, J. Grimes, B.M. Tsui, “4D XCAT phantom for multimodality imaging research,” Med. Phys. 37, 4902-4915 (2010).

23          W.P. Segars, B.M.W. Tsui, “MCAT to XCAT: The evolution of 4-D computerized phantoms for imaging research,” Proceedings of the IEEE 97, 1954-1968 (2009).

24          O.L. Green, L.J. Rankine, B. Cai, A. Curcuru, R. Kashani, V. Rodriguez, H.H. Li, P.J. Parikh, C.G. Robinson, J.R. Olsen, S. Mutic, S.M. Goddu, L. Santanam, “First clinical implementation of real-time, real anatomy tracking and radiation beam control,” Med. Phys. 45, 3728-3740 (2018).

25          E.E. Klein, J. Hanley, J. Bayouth, F.F. Yin, W. Simon, S. Dresser, C. Serago, F. Aguirre, L. Ma, B. Arjomandy, C. Liu, C. Sandin, T. Holmes, A.A.o.P.i.M. Task Group, “Task Group 142 report: quality assurance of medical accelerators,” Med. Phys. 36, 4197-4212 (2009).

26          P. Keall, T. Yamamoto, Y. Suh, “Introduction to 4D motion modeling and 4D radiotherapy,” in 4D Modeling and Estimation of Respiratory Motion for Radiation Therapy, edited by J. Ehrhardt, C. Lorenz (Springer, 2013), pp. 1-16.

27          P.J. Keall, G.S. Mageras, J.M. Balter, R.S. Emery, K.M. Forster, S.B. Jiang, J.M. Kapatoes, D.A. Low, M.J. Murphy, B.R. Murray, C.R. Ramsey, M.B. Van Herk, S.S. Vedam, J.W. Wong, E. Yorke, “The management of respiratory motion in radiation oncology report of AAPM Task Group 76,” Med. Phys. 33, 3874-3900 (2006).

28          S. Crijns, B. Raaymakers, “From static to dynamic 1.5T MRI-linac prototype: impact of gantry position related magnetic field variation on image fidelity,” Phys. Med. Biol. 59, 3241-3247 (2014).

29          M. Glitzner, P.L. Woodhead, P.T.S. Borman, J.J.W. Lagendijk, B.W. Raaymakers, “Technical note: MLC-tracking performance on the Elekta unity MRI-linac,” Phys. Med. Biol. 64, 15NT02 (2019).

30          S. Jackson, M. Glitzner, R.H.N. Tijssen, B.W. Raaymakers, “MRI B0 homogeneity and geometric distortion with continuous linac gantry rotation on an Elekta Unity MR-linac,” Phys. Med. Biol. 64, 12NT01 (2019).

31          J.J. Lagendijk, B.W. Raaymakers, A.J. Raaijmakers, J. Overweg, K.J. Brown, E.M. Kerkhof, R.W. van der Put, B. Hardemark, M. van Vulpen, U.A. van der Heide, “MRI/linac integration,” Radiother. Oncol. 86, 25-29 (2008).

32          J.J. Lagendijk, B.W. Raaymakers, C.A. Van den Berg, M.A. Moerland, M.E. Philippens, M. van Vulpen, “MR guidance in radiotherapy,” Phys. Med. Biol. 59, R349-369 (2014).

33          J.J. Lagendijk, B.W. Raaymakers, M. van Vulpen, “The magnetic resonance imaging-linac system,” Semin. Radiat. Oncol. 24, 207-209 (2014).

34          A.J. Raaijmakers, B.W. Raaymakers, J.J. Lagendijk, “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. 50, 1363-1376 (2005).

35          A.J. Raaijmakers, B.W. Raaymakers, J.J. Lagendijk, “Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength,” Phys. Med. Biol. 53, 909-923 (2008).

36          B.W. Raaymakers, A.J. Raaijmakers, J.J. Lagendijk, “Feasibility of MRI guided proton therapy: magnetic field dose effects,” Phys. Med. Biol. 53, 5615-5622 (2008).

37          R.H.N. Tijssen, S.P.M. Crijns, J.J. Bluemink, S.S. Hacket, J.H.W. DeVries, M.J. Kruiskamp, J.J.W. Philippens, J.J.W. Lagendijk, B.W. Raaymakers, “Comprehensive MRI acceptance testing & commissioning of a 1.5 T MR-Linac: Guidelines and results,” in ESTRO 36 (Vienna, Austria, 2017), pp. OC-0257.

38          S.J. Woodings, J.J. Bluemink, J.H.W. de Vries, Y. Niatsetski, B. van Veelen, J. Schillings, J.G.M. Kok, J.W.H. Wolthaus, S.L. Hackett, B. van Asselen, H.M. van Zijp, S. Pencea, D.A. Roberts, J.J.W. Lagendijk, B.W. Raaymakers, “Beam characterisation of the 1.5 T MRI-linac,” Phys. Med. Biol. 63, 085015 (2018).