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Dosimetric characteristics test of 1.5T magnetic resonance accelerator
Li Minghui, Tian Yuan, Zhang Ke, Men Kuo, Dai Jianrong
Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/ Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
AbstractObjective The Lorentz force produced by magnetic field deflects the paths of secondary electrons. The X-ray beam dosimetry characteristics of the magnetic resonance accelerator (MR-Linac) are different from conventional accelerators. The purpose of this study was to measure and analyze the X-ray beam dosimetry characteristics of 1.5T MR-Linac. Methods In May 2019, our hospital installed a Unity 1.5T MR-Linac and measured it with magnetic field compatible tools. The measurement indexes include:surface dose, maximum dose point depth, beam quality, off-axis dose profile center, beam symmetry, penumbra width, output changes of different gantry angles. Results The average surface dose was 40.48%, and the average maximum dose depth was 1.25cm. The center of the 10cm×10cm beam field was offset by 1.47mm to the x2 side and 0.3mm to the y2 side. The x-axis symmetry was 101.33%, and the penumbra width on both sides was 6.86mm and 7.14mm, respectively. The y-axis symmetry was 100.85%, and the penumbra width on both sides was 5.92mm and 5.95mm, respectively. The maximum deviation of output dose with different gantry angles reached 1.50%. Conclusions The surface dose of MR-Linac tend to be consistent, and the depth of the maximum dose point became shallower. The off-axis in the x-axis direction was shifted to the x2 side, which resulting in worse symmetry and penumbra asymmetry. The output dose at different angles has obvious variation and needs correction.
Corresponding Authors:
Dai Jianrong, dai_jianrong@163.com;Men Kuo,menkuo126@126.com
Cite this article:
Li Minghui,Tian Yuan,Zhang Ke et al. Dosimetric characteristics test of 1.5T magnetic resonance accelerator[J]. Chinese Journal of Radiation Oncology, 2020, 29(11): 963-967.
Li Minghui,Tian Yuan,Zhang Ke et al. Dosimetric characteristics test of 1.5T magnetic resonance accelerator[J]. Chinese Journal of Radiation Oncology, 2020, 29(11): 963-967.
[1] Lagendijk J, Van Vulpen M, Raaymakers B. The development of the MRI linac system for online MRI-guided radiotherapy:a clinical update[J]. J Inter Med, 2016, 280(2):203-208. DOI:10.1111/joim.12516. [2] Lagendijk JJ, Raaymakers BW, Raaijmakers AJ, et al. MRI/linac integration[J]. Radiother Oncol, 2008, 86(1):25-29. DOI:10.1016/j.radonc.2007.10.034. [3] Raaymakers B, Jürgenliemk-Schulz I, Bol G, 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[J]. Phys Med Biol, 2017, 62(23):L41. DOI:10.1088/1361-6560/aa9517. [4] Thess A, Votyakov EV, Kolesnikov Y. Lorentz force velocimetry[J]. Phys Rev Lett, 2006, 96(16):164501. DOI:10.1103/PhysRevLett.96.164501. [5] Hackett SL, van Asselen B, Wolthaus JW, et al. Spiraling contaminant electrons increase doses to surfaces outside the photon beam of an MRI-linac with a perpendicular magnetic field[J]. Phys Med Biol, 2018, 63(9):095001. DOI:10.1088/1361-6560/aaba8f. [6] Oborn B, Kolling S, Metcalfe PE, et al. Electron contamination modeling and reduction in a 1 T open bore inline MRI-linac system[J]. Med Phys, 2014, 41(5):051708. DOI:10.1118/1.4871618. [7] Keyvanloo A, Burke B, Warkentin B, et al. Skin dose in longitudinal and transverse linac-MRIs using Monte Carlo and realistic 3D MRI field models[J]. Med Phys, 2012, 39(10):6509-6521. DOI:10.1118/1.4754657. [8] Ahmad SB, Sarfehnia A, Paudel MR, et al. Evaluation of a commercial MRI Linac based Monte Carlo dose calculation algorithm with geant 4[J]. Med Phys, 2016, 43(2):894-907. DOI:10.1118/1.4939808. [9] Heylen A, Bunting K. Electron drift velocities in a moderate and in a strong crossed magnetic field[J]. Int J Electr Theor Exper, 1969, 27(1):1-12. DOI:10.1080/00207216908900000. [10] Lee H, Alqathami M, Wang J, et al. PO-0800:Fricke-type dosimetry for “real-time” 3D dose measurements using MR-guided RT:a feasibility study[J]. Radiother Oncol, 2016, 119:S377-S378. DOI:10.1016/s0167-8140(16)32050-3. [11] O′Brien D, Roberts D, Ibbott G, et al. Reference dosimetry in magnetic fields:formalism and ionization chamber correction factors[J]. Med Phys, 2016, 43(8Part1):4915-4927. DOI:10.1118/1.4959785. [12] Alnaghy SJ, Begg J, Causer T, et al. Penumbral width trimming in solid lung dose profiles for 0.9 and 1.5 T MRI-Linac prototypes[J]. Med Phys, 2018, 45(1):479-487. DOI:10.1002/mp.13117. [13] Woodings SJ, Bluemink J, De Vries J, et al. Beam characterisation of the 1.5 T MRI-linac[J]. Phys Med Biol, 2018, 63(8):085015. DOI:10.1088/1361-6560/aab566. [14] Keall PJ, Barton M, Crozier S. The Australian magnetic resonance imaging–linac program[J]. Semin Radiat Oncol, 2014, 24(3):203-206. DOI:10.1016/j.semradonc.2014.02.015.
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