磁场中6MeV X线在不同模体中的剂量学研究北大核心CSCD

目的研究不同强度正交磁场对6MeV X线在均匀水模体和异质性模体中剂量分布的影响。方法采用蒙特卡罗模拟软件Gate 8.2版,研究10cm×10cm射野的X线束分别在0.0、0.5、1.0、1.5、3.0 T磁场条件下,在均匀水模体、水-空气/骨-水层模体以及“自定义肺模型”中的剂量分布情况,分析磁场强度与X线在模体中剂量分布的关系。结果磁场的存在会引起X线在水模体中建成区缩短;中心轴上的最大剂量改变可达56.22%(3.0 T);垂直磁场方向上射野的横向剂量分布向一侧迁移,最大可达43.64%(-44.55%)。在水-气-水模体中,空气层内平均剂量最高可降低57.4%(3.0 T);水-骨-水模体,骨层近端剂量降低16.5%,远端剂量增加22.6%;自定义肺模型中各层内剂量变化与磁场强度呈正相关。结论正交磁场的存在会引起X线在模体中剂量沉积的建成区和射野两侧剂量分布的改变,且这种改变在异质性模体交界面附近更加明显。

Dosimetric study of 6MeV X-ray in different phantoms in a magnetic field

Objective To evaluate the effects of orthogonal magnetic fields on the dose distribution of 6MeV X-ray in a uniform water and heterogeneous phantoms. Methods The Monte Carlo simulation software Gate v8.2 was used to investigate the dose distribution of X-ray beams of different field sizes in a uniform water phantom, water-air/bone-water layer phantom and"custom lung model" in the magnetic field strength of 0.0, 0.5, 1.0, 1.5, 3.0 T, respectively. The relationship between the intensity of magnetic field and the dose distribution of X-rays in the phantoms was analyzed. Results The existence of a magnetic field would cause the X-ray to shorten the built-up area in the water phantom;when the field was 10cm×10cm, the maximum dose on the central axis could change by up to 56.22%(3.0 T). The transverse dose distribution of the radiation field in the direction of the vertical magnetic field shifted to one side by up to 43.64%(-44.55%). The average dose of the air layer in the water-air-water phantom could be reduced by 57.4%(3.0 T). In the water-bone-water phantom, the dose at the proximal end of the bone layer was decreased by 16.5%, whereas the dose at the distal end was increased by 22.6%(1.5 T). The dose change in each layer in the customed lung model was positively correlated with the magnetic field strength. Conclusion The existence of the orthogonal magnetic field will cause the change of X-ray dose distribution on the built-up area and both sides of the radiation field in the phantoms, which is more obvious adjacent to the interface of heterogeneous phantom.