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中华肿瘤防治杂志 2023年第1期30卷 36-42页

作者：殷培钧虞刚尹勇李振江山东师范大学物理与电子科学学院山东济南250358 山东省肿瘤防治研究院(山东省肿瘤医院)放射物理技术科山东第一医科大学(山东省医学科学院)山东济南250117

目的设计一种利用电子射野影像装置(EPID)实现精确摆位的方法,应用该方法探究mr-linac的配准误差并提出配准质量保证工作流程。方法通过观察EPID图像中钨球位置的方法实现精确摆位,并选择Head模体验证该方法的精度。使用Zeus运动胸廓... 详细信息

目的设计一种利用电子射野影像装置(EPID)实现精确摆位的方法,应用该方法探究mr-linac的配准误差并提出配准质量保证工作流程。方法通过观察EPID图像中钨球位置的方法实现精确摆位,并选择Head模体验证该方法的精度。使用Zeus运动胸廓模体在5种不同运动模式下扫描模拟CT并分别生成参考计划。每组参考计划在模体位置和运动模式不变的情况下扫描治疗前mrI,并分别以脊髓和大体肿瘤体积(GTV)为感兴趣区域(ROI)与模拟CT配准并记录图像对齐的移动距离。在模体位置不变、运动模式改变的情况下扫描治疗前mrI进行配准以考察运动状态对配准误差的影响。对齐距离即配准误差(ΔX、ΔY和ΔZ),误差的正负值代表不同的方向,统计配准误差的大小范围并分析运动状态和ROI选择对误差的影响。结果 Head模体的配准误差为ΔX=1.10 mm,ΔY=1.80 mm,ΔZ=0.30 mm。Zeus模体的配准误差(ΔX,ΔY,ΔZ)最小值分别为-1.00、-1.40和-1.90 mm;最大值分别为0.60、6.30和-1.40 mm。ΔY的标准差最大,为2.36 mm;ΔZ的标准差最小,为0.19 mm。以GTV作为ROI时,所有方向误差的标准差均大于以脊髓作为ROI时的配准结果。mr与CT运动状态相同时的配准误差小于运动不同时的误差。结论基于EPID图像辅助摆位的方法准确可靠,并提出了一种利用运动模体进行mr-linac配准质量控制的工作流程。mr-linac在上下方向的配准误差最不稳定,但总体误差范围是可接受的。

关键词：磁共振引导的放射治疗 mr-linac 配准运动模体质量控制

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Measurement of Electron Return Effect and Skin Dose Reduction by a Bolus in an Anthropomorphic Physical Phantom under a Magnetic Resonance Guided Linear Accelerator (mr-linac) System

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International Journal of Medical Physics, Clinical Engineering and Radiation Oncology 2018年第3期7卷 339-346页

作者： Eun Young Han Zhifei Wen Hannah J. Lee Arnold dela Cruz Paulino Choonsik Lee Department of Radiation Physics The University of Texas MD Anderson Cancer Center Houston TX USA Division of Cancer Epidemiology and Genetics National Cancer Institute National Institutes of Health Rockville USA

Background: Magnetic resonance image-guided radiation therapy (mr-IGRT) promises more precise and effective radiation treatments compared to conventional IGRT by using real-time on-board mr imaging. Under the influence of a magnetic field, however, secondary electrons exiting a surface can be forced in a circular path and re-enter the medium, resulting in dose increase at a beam-exit surface, called the electron return effect (ERE). The purpose of the study is to compare the exit skin dose computed by Monte Carlo dose calculation with measurements using an adult anthropomorphic phantom and to measure the effect of skin dose reduction by adding 1 cm-thick bolus. Method: The plan was compared with measurements using an adult anthropomorphic phantom combined with radiochromic films and thermoluminescent dosimeters. We also measured the skin dose reduction by adding 1 cm-thick bolus on the frontal surface of the phantom. Results: We found that 1 cm-thick bolus reduced the skin dose by up to 20% both in measurements and calculations. The plan was found to overestimate the measured skin dose by about 10% and there was no significant difference in the bolus effect between the breast skin and the skin (without breast attachment) doses. Conclusion: In conclusion, we confirmed the ERE effect on the anthropomorphic phantom under the magnetic field and the exit skin dose reduction by adding a bolus. Skin dose measurements using anthropomorphic phantom may be helpful to evaluate more realistic skin dose and the bolus effect in the magnetic field.

关键词： mr-linac Electron Return Effect Skin Dose

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The effect of the magnetic fields from three different configurations of the mrIgRT systems on the dose deposition from lateral opposing photon beams in a laryngeal geometry–A Monte Carlo study

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Radiation Medicine and Protection 2021年第3期2卷 103-111页

作者： Vivien W.S.Chu Monica W.K.Kan Louis K.Y.Lee Kenneth C.W.Wong Macy Tong Anthony T.C.Chan Department of Clinical Oncology Prince of Wales HospitalHong KongChina Department of Clinical Oncology The Chinese University of Hong KongHong KongChina Medical Center The Chinese University of Hong KongChina State Key Laboratory of Translational Oncology Sir YK Pao Center for CancerDepartment of Clinical OncologyHong Kong Cancer Institute and Prince of Wales HospitalThe Chinese University of Hong KongHong KongChina

Objective:To investigate the impact of different magnetic field strengths and orientations on the dose deposition from lateral opposing photon beams irradiating a laryngeal geometry,with particular attention focused on the dose homogeneity of the area around the air cavity inside the ***:Geant4 simulation toolkit was used to perform Monte Carlo simulations on a phantom resembling the *** energy spectrum of a 6 MV photon beam from a Varian Clinac iX machine was used to provide the source of *** configurations of the Magnetic Resonance Image-Guided Radiation Therapy(mrIgRT)system were simulated:the Fixed Cylindrical(FC)geometry,the Longitudinal Rotating Biplanar(LRBP)geometry,and the Transverse Rotating Biplanar(TRBP)*** magnetic fields of different field strengths were *** relative dose maps and the homogeneity index(HI)were obtained for ***:The LRBP geometry together with a magnetic field strength of 0.5 T produced the most homogeneous dose distribution with a HI of 0.139 for the region of interest around the air cavity,compared with a HI of 0.180 when the magnetic field was *** TRBP geometry,the dose distribution shifted towards the cranial direction,leading to a region of hot spots at the superior edge and a region of cold spots at the inferior edge of the irradiated *** HI around the air cavity was therefore *** addition,strong electron streaming effect(ESE)was *** the FC geometry,hot and cold spots were formed around the air cavity which increased the ***:Out of the three configurations of the mrIgRT systems,the LRBP geometry produced the most clinically beneficial dose distribution in which it provided a higher dose to the treatment area and a boost in dose to the tissue immediately adjacent to the air cavity.

关键词： Monte Carlo mrIgRT mr-linac Magnetic field Air cavity

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