| Question 1: Can hybrid MRI radiotherapy systems perform irradiation and MRI simultaneously? |
| Reference: | 1. MRI quality control for low-field MR-IGRT systems: Lessons learned.
Michael Gach H, Curcuru AN, Wittland EJ, Maraghechi B, Cai B, Mutic S, Green OL. J Appl Clin Med Phys. 2019 Oct;20(10):53-66. doi: 10.1002/acm2.12713.
2. MRI B (0) homogeneity and geometric distortion with continuous linac gantry rotation on an Elekta Unity MR-linac. Jackson S, Glitzner M, Tijssen RHN, Raaymakers BW. Phys Med Biol. 2019 Jun 10;64(12):12NT01. doi: 10.1088/1361-6560/ab231a. |
| Choice A: | No, they operate in an intermittent mode, the magnetic interference degenerates MRI to a non-usable image quality. |
| Choice B: | Not in general, the radiofrequency interference prohibits simultaneous irradiation and MR imaging for linac based systems. Cobalt MRI systems do allow simultaneous MRI and irradiation |
| Choice C: | Yes, the design of these systems is such to prevent magnetic and radiofrequency interference for simultaneous operation. |
| Choice D: | Yes, the hybrid systems are only capable of photon irradiation and photons are not affected by either radiofrequency or magnetic fields. |
| Question 2: How would you compensate for the impact of magnetic field on the dose distribution from hybrid MRI radiotherapy systems? |
| Reference: | 1. Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength. Raaijmakers AJ, Raaymakers BW, Lagendijk JJ. Phys Med Biol. 2008 Feb 21;53(4):909-23. doi: 10.1088/0031-9155/53/4/006
2. Patient dosimetry for hybrid MRI-radiotherapy systems. Kirkby C, Stanescu T, Rathee S, Carlone M, Murray B, Fallone BG. Med Phys. 2008 Mar;35(3):1019-27. doi: 10.1118/1.2839104 |
| Choice A: | Via calibration of the dosimetry equipment. The dosimetry equipment for measuring the dose distributions will be affected by the magnetic, not the dose distribution itself as this is the result from a photon irradiation. An additional correction factor for the dosimetry equipment readings will suffice. |
| Choice B: | By taking the impact of the magnetic field on the dose distribution into account in the inverse optimization for treatment planning. |
| Choice C: | By changing the patient position from feet-head to head-feet on alternate fractions, this will result in a cumulative zero impact from the Lorentz force on the secondary electrons over the course of treatment. |
| Choice D: | By intermittent irradiation and MR imaging and using the time interval between MRI excitation and receive pulses. |
| Question 3: Is MRI fast enough for tracking breathing related anatomical changes during radiation delivery? |
| Reference: | 1. Delivery of magnetic resonance-guided single-fraction stereotactic lung radiotherapy. Finazzi T, van Sörnsen de Koste JR, Palacios MA, Spoelstra FOB, Slotman BJ, Haasbeek CJA, Senan S. Phys Imaging Radiat Oncol. 2020 May 20;14:17-23. doi: 10.1016/j.phro.2020.05.002
2. Delivered dose quantification in prostate radiotherapy using online 3D cine imaging and treatment log files on a combined 1.5T magnetic resonance imaging and linear accelerator system. Kontaxis C, de Muinck Keizer DM, Kerkmeijer LGW, Willigenburg T, den Hartogh MD, van der Voort van Zyp JRN, de Groot-van Breugel EN, Hes J, Raaymakers BW, Lagendijk JJW, de Boer HCJ. Phys Imaging Radiat Oncol. 2020 Jul 13;15:23-29. doi: 10.1016/j.phro.2020.06.005 |
| Choice A: | Yes, MRI can provide 1D, 2D or 3D data at virtually arbitrary refresh rates, however there is a trade-off between image quality and speed. Typically, prior information and/or motion modelling helps to increase the imaging frequency |
| Choice B: | Yes, but only via 1D or 2D images, 3D data sets cannot be generated for tracking breathing related motion. |
| Choice C: | No, although MR imaging can acquire fast enough data for this purpose, the compromises on MRI receive chain for the hybrid MRI radiotherapy systems do limit the image frequency to approximately 1 MRI data set per minute. |
| Choice D: | No, MR imaging can be performed sufficiently fast, also for hybrid MRI radiotherapy systems, but the image reconstruction is done retrospectively, so it cannot be used for tracking during treatment. |
| Question 4: In which orientation should an ion chamber be placed when performing absolute dose calibration to minimize the magnitude of the kB correction factor? Assume the magnetic field is perpendicular to the photon beam. |
| Reference: | Monte Carlo study of ionization chamber magnetic field correction factors as a function of angle and beam quality. Malkov VN, Rogers DWO. Med. Phys. 2018 Feb;45(2):908-925.doi: 10.1002/mp.12716. Epub 2018 Jan 5. https://pubmed.ncbi.nlm.nih.gov/29218730/ |
| Choice A: | Parallel with the magnetic field |
| Choice B: | Perpendicular to the magnetic field |
| Choice C: | Diagonal to the magnetic field |
| Choice D: | kB is not dependent on chamber orientation |
| Question 5: What are the adaptive workflows that exist on the Elekta Unity? |
| Reference: | Analysis of patient-specific quality assurance for Elekta Unity adaptive plans using statistical process control methodology. Strand S, Boczkowski A, Smith B, Snyder JE, Hyer DE, Yaddanapudi S, Dunkerley DAP, St-Aubin, J. J Appl Clin Med Phys. 2021 Apr;22(4):99-107.doi: 10.1002/acm2.13219. Epub 2021 Mar 23. https://pubmed.ncbi.nlm.nih.gov/33756059/ |
| Choice A: | Adapt to overcome / Adapt to shape |
| Choice B: | Minor adaption / Major adaption |
| Choice C: | Adapt to position / Adapt to overcome |
| Choice D: | Adapt to position / Adapt to shape |
| Question 6: Both the ViewRay MRIdian and Elekta Unity are currently able to deliver which of the following intensity modulated treatment types? |
| Reference: | 1. Commissioning and performance evaluation of RadCalc for the Elekta unity MRI-linac. Graves SA, Snyder JE, Boczkowski A, St-Aubin J, Wang D, Yaddanapudi S, Hyer DE. J Appl Clin Med Phys. 2019 Dec;20(12):54-62. doi: 10.1002/acm2.12760. Epub 2019 Nov
13. https://pubmed.ncbi.nlm.nih.gov/31722133/
2. Technical design and concept of a 0.35 T MR-Linac. Kluter S. Clin Transl. Radiat Oncol 2019 Sep; 18: 98–101. doi: 10.1016/j.ctro.2019.04.007 |
| Choice A: | VMAT |
| Choice B: | Sliding window IMRT |
| Choice C: | Step and shoot IMRT |
| Choice D: | Dynamic conformal arc |
| Question 7: Compared to X-ray based IGRT, the main advantage of MR-IGRT lies in its ability to adapt daily treatments for |
| Reference: | Comparison of onboard low-field magnetic resonance imaging versus onboard computed tomography for anatomy visualization in radiotherapy. Noel CE, Parikh PJ, Spencer CR, Green OL, Hu Y, Mutic S, Olsen JR. Acta Oncol 2015;54(9):1474-82. doi: 10.3109/0284186X.2015.1062541. Epub 2015 Jul 24. |
| Choice A: | Tumor motion caused by respiration |
| Choice B: | Patient setup errors |
| Choice C: | Missing accessories: bolus, compensators, compression devices etc. |
| Choice D: | Anatomical changes in PTV/OAR due to tumor shrinkage, organ filling, soft tissue deformation etc |
| Question 8: Compared to X-ray based IGRT, the main disadvantage(s) of MR-IGRT are: |
| Reference: | MRI quality control for low-field MR-IGRT systems: Lessons learned. Gach H, Curcuru AN, Wittland EJ, Maraghechi B, Cai B, Mutic S, Green OL. J Appl Clin Med Phys. 2019 Oct;20(10):53-66. doi: 10.1002/acm2.12713. |
| Choice A: | 2d planar MR image vs 3d volumetric image available with CBCT |
| Choice B: | Spatial distortions induced by gradient nonlinearities and magnetic field inhomogeneities |
| Choice C: | Missing electron density information for radiation dose calculations |
| Choice D: | Inability to visualize and track PTV and OARs during patient treatments. |
| Question 9: Compared to conventional non-adaptive treatments, which of the following steps is a significant contributor to the overall treatment time in the adaptive work-flow of MRgART: |
| Reference: | Time Analysis of Online Adaptive Magnetic Resonancee Guided Radiation Therapy Workflow According to Anatomical Sites. Güngör G,_Serbez I, Temur B, Gür G, Kayalõlar N, Mustafayev TZ, Korkmaz L, Aydõn G, Yapõcõ B, Atalar B, Özyar E. Practical Radiation Oncology®(2021)11, e11ee21. https://doi.org/10.1016/j.prro.2020.07.003 |
| Choice A: | Patient Setup |
| Choice B: | Imaging scans and deformable image registration |
| Choice C: | Image segmentation/contouring |
| Choice D: | Treatment plan optimization and online QA |
| Question 10: MR guided adaptive radiation therapy (MRgART) is ideally suited for which of the following treatment sites? |
| Reference: | Phase I trial of stereotactic MR-guided online adaptive radiation therapy (SMART) for the treatment of oligometastatic or unresectable primary malignancies of the abdomen. Henke L, Kashani R, Robinson C, Curcuru A, DeWees T, Bradley J, Green O, Michalski J, Mutic S, Parikh P, Olsen J. Radiotherapy and Oncology, Volume 126, Issue 3, March 2018, Pages 519-526. https://doi.org/10.1016/j.radonc.2017.11.032 |
| Choice A: | CNS Brain |
| Choice B: | bHead & Neck |
| Choice C: | Upper abdomen |
| Choice D: | Spine |
