Abstract：Objective To evaluate the impact of an external magnetic field on the dose distribution and electronic disequilibrium region around a Bebig type 60Co HDR brachytherapy source and to judge the feasibility of applying MRI scanner during brachytherapy.Methods The source model was established based on the Monte Carlo package Geant4 software. The simulated geometries consisted of the 60Co source inside a water phantom of 10.0cm×10.0cm×10.0cm in size. The magnetic field strength of the 0T,1.5T and 3.0T was considered,respectively. The voxels with a size of 0.2 mm, 0.5 mm and 0.5 mm were established along the x-, y-and z-axis. The influence of the magnetic field on the Kerma (kinetic energy released to matter) distribution and dose distribution within the 10.0mm region from the source center was evaluated. Furthermore,the ratio of the Kerma to dose as a function of the distance to the center source was acquired. Results The 1.5T magnetic field exerted no effect on the dose distribution adjacent to 60Co HDR brachytherapy source, whereas3.0T magnetic field caused significant increase in the dose distribution within r<6 mm from the source center. The dose distribution was increased by 40% at r=5.4 mm from the source center. The ratio of Kerma to dose was less than 1 within the region of 1.2 mm<r<6.0 mm, suggesting that 3.0T magnetic field can lead to electronic disequilibrium within a larger region from the source center.Conclusions For Bebig 60Co HDR brachytherapy source,it is safe and reliable to apply1.5T external magnetic field. Nevertheless, 3.0T magnetic field can cause high dose risk. Consequently, safety assessment and verification should be delivered prior to clinical application.
Cui Zhenguo,Chen Jiayi,Yun Weikang et al. The impact of a magnetic field on the dose distribution using the Bebig60Co HDR sources[J]. Chinese Journal of Radiation Oncology, 2020, 29(3): 193-196.
[1] Ballester F. Evaluation of high-energy brachytherapy s-ource electronic disequilibrium and dose from emitted electrons[J]. Med Phys,2009,36(9):4250-4256. DOI:10.1118/1.2962843.
[2] Nath R,Anderson LL,Meli JA,et al. Code of practice for brachytherapy physics:report of the AAPM Radiation Therapy Committee Task Group No.56. American Association of Physicists in Medicine[J]. Med Phys,1999,24(10):1557. DOI:10.1118/1.597966.
[3] Okamoto H,Aikawa A,Wakita A,et al. Dose error from deviation of dwell time and source position for high dose-rate 192Ir in remote afterloading system[J]. J Radiat Res,2014,55(4):780-787. DOI:10.1093/jrr/rru001.
[4] Hendrik DL. A dual-plane co-RASOR technique for accurate and rapid tracking and position verification of an Ir-192 source for single fraction HDR brachytherapy[J]. Phys Med Biol,2013,21(58):DOI:10.1088/0031-9155/58/21/7829.
[5] Bosch MR,Den V,Moman MR,et al. MRI-guided robotic system for transperineal prostate interventions:proof of principle[J]. Phys Med Biol,2010,55(5):N133-140. DOI:10.1088/0031-9155/55/5/N02.
[6] Raaijmakers A,Raaymakers B,Lagendijk J. Magnetic fieldinduced dose effects in MR-guided radiotherapy systems:dependence on the magnetic field strength[J]. Phys Med Biol,2008,4(53):DOI:10.1088/0031-9155/53/4/006.
[7] 吴爱林,吴爱东,朱磊,等.瓦里安高剂量率铱源剂量学参数的蒙特卡罗模拟研究[J]. 中华放射医学与防护杂志,2018,38(11):859-864. DOI:10.3760/cma.j.issn.0254-5098.2018.11.012.
Wu AL,Wu AD,Zhu L,et al. Monte Carlo simulation study of dosimetric parameters of Varian HDR Ir source[J]. Chin J Radiol Med Prot,2018,38(11):859864. DOI:10.3760/cma.j.issn.0254-5098.2018.11.012.
[8] Agostinelli S,Allison J,Amako K,et al. Geant 4—a simulation toolkit[J]. Nucl Inst Meth Phys Res,2003,506(3):250-303. DOI:10.1016/S0168-9002(03)01368-8.
[9] Almansa AS. NuDat 2.0:nuclear structure and decay data on the internet[J]. International Conference on Nuclear Data for Science and Technology,2005,10(1):575. DOI:10.1063/1.1945075.
[10] Ballester F,Hernandez C,Lliso F,et al. Monte Carlo calculation of dose rate distributions around Ir-192 wires[J]. Med Phys,1997,24(8):1221. DOI:10.1118/1.598142.
[11] Cullen D,Chen M,Hubbell J,et al. Tables and graphs of photon-interaction cross sections from 10 eV to 100 GeV. Derived from the LLNL evaluated photon data library (EPDL),Z=1-50(Part A) and Z=51-100(Part B),UCRL-50400,Vol 6 Part A and Part B[J]. Embo J,1989,27(1):188-200. DOI:10.1038/sj.emboj.7601939.
[12] Ballester F,Granero D,Pérez-Calatayud,et al. Monte Car-lo dosimetric study of the BEBIG Co-60 HDR source[J]. Phys Med Biol,2005,50(21):309-316. DOI:10.1088/0031-9155/50/21/N03.
[13] White JR,Wilson JF. Brachytherapy and breast cancer[J].1997,13(3):190-195. DOI:10.1002/(sici)1098-2388(199705/06)13:3<190::aid-ssu6>3.0.co;2-2.
[14] 王先良,袁珂,康胜伟,等.环形施源器重建偏差对宫颈癌患者剂量影响分析[J]. 中华放射肿瘤学杂志,2017,26(3):316-319. DOI:10.3760/cma.j.issn.1004-4221.2017.03.014.
Wang XL,Yuan K,Kang SW. Impacting applicator reconstruction uncertainties on radiation dose in patientswithcervicalcancer[J]. Chin J Radiat Oncol,2017,26(3):316-319. DOI:10.3760/cma.j.issn.1004-4221.2017.03.014.
[15] De Leeuw H,Moerland MA. A dual-plane co-RASOR technique for accurate and rapid tracking and position verification of an Ir-192 source for single fraction HDR brachytherapy[J]. Phys Med Biol,2013,58(21):7829-7839. DOI:10.1088/0031-9155/58/21/7829.
[16] Beld E,Seevinck PR,Lagendijk JJ,et al. Monte Carlo study of the impact of a magnetic field on the dose distribution in MRI-guided HDR brachytherapy using Ir-192[J]. Phys Med Biol,2016,61(18):6791-6807. DOI:10.1088/0031-9155/61/18/6791.
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