No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Impact of the MLC on the MRI field distortion of a prototype MRI-linac
1. C. Plathow, M. Schoebinger, C. Fink, H. Hof, J. Debus, H. Meinzer, and H. Kauczor, “Quantification of lung tumor volume and rotation at 3D dynamic parallel MR imaging with view sharing: Preliminary results,” Radiology 240(2), 537–545 (2006).
2. Y. Suh, S. Dieterich, B. Cho, and P. Keall, “An analysis of thoracic and abdominal tumour motion for stereotactic body radiotherapy patients,” Phys. Med. Biol. 53(13), 3623–3639 (2008).
3. A. Sawant, K. Pauly, M. Alley, S. Vasanawala, B. Loo, S. Joshi, J. Hinkle, and P. Keall, “Real-time MRI for soft-tissue-based IGRT of moving and deforming lung tumors,” Med. Phys. 37, 3424 (2010).
4. T. Bortfeld, K. Jokivarsi, M. Goitein, J. Kung, and S. B. Jiang, “Effects of intra-fraction motion on IMRT dose delivery: Statistical analysis and simulation,” Phys. Med. Biol. 47(13), 2203–2220 (2002).
5. D. Verellen, M. De Ridder, N. Linthout, K. Tournel, G. Soete, and G. Storme, “Innovations in image-guided radiotherapy,” Nat. Rev. Cancer 7(12), 949–960 (2007).
7. B. Raaymakers, J. Lagendijk, J. Overweg, J. Kok, A. Raaijmakers, E. Kerkhof, R. van der Put, I. Meijsing, S. Crijns, and F. Benedosso, “Integrating a 1.5 T MRI scanner with a 6 MV accelerator: Proof of concept,” Phys. Med. Biol. 54(12), N229–N237 (2009).
8. B. Fallone, M. Carlone, B. Murray, S. Rathee, T. Stanescu, S. Steciw, K. Wachowicz, and C. Kirkby, “Development of a Linac-MRI system for real-time ART,” Med. Phys. 34, 2547 (2007).
9. J. Dempsey, D. Benoit, J. Fitzsimmons, A. Haghighat, J. Li, D. Low, S. Mutic, J. Palta, H. Romeijn, and G. Sjoden, “A device for realtime 3D image-guided IMRT,” Int. J. Radiat. Oncol., Biol., Phys., Suppl. 63, S202–S202 (2005).
10. D. Constantin, R. Fahrig, and P. Keall, “A study of the effect of in-line and perpendicular magnetic fields on beam characteristics of electron guns in medical linear accelerators,” Med. Phys. 38(7), 4174–4185 (2011).
11. J. St. Aubin, S. Steciw, C. Kirkby, and B. G. Fallone, “An integrated 6 MV linear accelerator model from electron gun to dose in a water tank,” Med. Phys. 37, 2279–2288 (2010).
12. J. St. Aubin, S. Steciw, and B. G. Fallone, “Waveguide detuning caused by transverse magnetic fields on a simulated in-line 6 MV linac,” Med. Phys. 37, 4751–4754 (2010).
13. J. Yun, J. Aubin, S. Rathee, and B. Fallone, “Brushed permanent magnet DC MLC motor operation in an external magnetic field,” Med. Phys. 37, 2131–2134 (2010).
14. D. Santos, J. S. Aubin, B. Fallone, and S. Steciw, “Magnetic shielding investigation for a 6 MV in-line linac within the parallel configuration of a linac-MR system,” Med. Phys. 39, 788–797 (2012).
15. J. St. Aubin, S. Steciw, and B. G. Fallone, “Magnetic decoupling of the linac in a low field biplanar linac-MR system,” Med. Phys. 37, 4755–4761 (2010).
16. B. Fallone, B. Murray, S. Rathee, T. Stanescu, S. Steciw, S. Vidakovic, E. Blosser, and D. Tymofichuk, “First MR images obtained during megavoltage photon irradiation from a prototype integrated linac-MR system,” Med. Phys. 36, 2084–2088 (2009).
18. B. Burke, A. Ghila, B. Fallone, and S. Rathee, “Radiation induced current in the RF coils of integrated linac-MR systems: The effect of buildup and magnetic field,” Med. Phys. 39, 5004–5014 (2012).
19. S. Crijns, B. Raaymakers, and J. Lagendijk, “Proof of concept of MRI-guided tracked radiation delivery: Tracking one-dimensional motion,” Phys. Med. Biol. 57(23), 7863–7872 (2012).
20. J. Yun, K. Wachowicz, M. Mackenzie, S. Rathee, D. Robinson, and B. Fallone, “First demonstration of intrafractional tumor-tracked irradiation using 2D phantom MR images on a prototype linac-MR,” Med. Phys. 40, 051718 (12pp.) (2013).
21. J. M. Galvin, “The multileaf collimator: A complete guide,” in Proceedings of the AAPM Annual Meeting, Nashville, Tennessee, 1999.
22. J. R. Brauer, What Every Engineer Should Know about Finite Elem Anal 2e (CRC, Xi'an, China, 1993), Vol. 31.
23. Y. Shahbazi, K. Niayesh, and H. Mohseni, “Finite element method analysis of performance of inductive saturable-core fault current limiter,” in 2011 1st International Conference on Electric Power Equipment-Switching Technology (ICEPE-ST), 2011 (IEEE, CRC Handbook of Chemistry & Physics, Taylor and Francis Group, LLC, 2011), pp. 352–355.
25. A. Raaijmakers, B. Raaymakers, and J. Lagendijk, “Magnetic-field-induced dose effects in MR-guided radiotherapy systems: Dependence on the magnetic field strength,” Phys. Med. Biol. 53(4), 909–923 (2008).
Article metrics loading...
To cope with intrafraction tumor motion, integrated MRI-linac systems for real-time image guidance are currently under development. The multileaf collimator (MLC) is a key component in every state-of-the-art radiotherapy treatment system, allowing for accurate field shaping and tumor tracking. This work quantifies the magnetic impact of a widely used MLC on the MRI field homogeneity for such a modality.
The finite element method was employed to model a MRI-linac assembly comprised of a split-bore MRI magnet and the key ferromagnetic components of a Varian Millennium 120 MLC, namely, the leaves and motors. Full 3D magnetic field maps of the system were generated. From these field maps, the peak-to-peak distortion within the MRI imaging volume was evaluated over a diameter sphere volume (DSV) around the isocenter and compared to a maximum preshim inhomogeneity of . Five parametric studies were performed: (1) The source-to-isocenter distance (SID) was varied from 100 to , to span the range of a compact system to that with lower magnetic coupling. (2) The MLC model was changed from leaves only to leaves with motors, to determine the contribution to the total distortion caused by MLC leaves and motors separately. (3) The system was configured in the inline or perpendicular orientation, i.e., the linac treatment beam was oriented parallel or perpendicular to the magnetic field direction. (4) The treatment field size was varied from 0 × 0 to , to span the range of clinical treatment fields. (5) The coil currents were scaled linearly to produce magnetic field strengths B 0 of 0.5, 1.0, and , to estimate how the MLC impact changes with B 0.
(1) The MLC-induced MRI field distortion fell continuously with increasing SID. (2) MLC leaves and motors were found to contribute to the distortion in approximately equal measure. (3) Due to faster falloff of the fringe field, the field distortion was generally smaller in the perpendicular beam orientation. The peak-to-peak DSV distortion was below at (perpendicular) and (inline) for the design. (4) The simulation of different treatment fields was identified to cause dynamic changes in the field distribution. However, the estimated residual distortion was below geometric distortion at (perpendicular) and (inline) for a frequency-encoding gradient. (5) Due to magnetic saturation of the MLC materials, the field distortion remained constant at .
This work shows that the MRI field distortions caused by the MLC cannot be ignored and must be thoroughly investigated for any MRI-linac system. The numeric distortion values obtained for our magnet may vary for other magnet designs with substantially different fringe fields, however the concept of modest increases in the SID to reduce the distortion to a shimmable level is generally applicable.
Full text loading...
Most read this month