Schreiber Eric C, Chang Sha X
Department of Radiation Oncology, University of North Carolina, Chapel Hill, North Carolina 27599, USA.
Med Phys. 2012 Aug;39(8):4669-78. doi: 10.1118/1.4728220.
Microbeam radiation therapy (MRT) is an experimental radiotherapy technique that has shown potent antitumor effects with minimal damage to normal tissue in animal studies. This unique form of radiation is currently only produced in a few large synchrotron accelerator research facilities in the world. To promote widespread translational research on this promising treatment technology we have proposed and are in the initial development stages of a compact MRT system that is based on carbon nanotube field emission x-ray technology. We report on a Monte Carlo based feasibility study of the compact MRT system design.
Monte Carlo calculations were performed using EGSnrc-based codes. The proposed small animal research MRT device design includes carbon nanotube cathodes shaped to match the corresponding MRT collimator apertures, a common reflection anode with filter, and a MRT collimator. Each collimator aperture is sized to deliver a beam width ranging from 30 to 200 μm at 18.6 cm source-to-axis distance. Design parameters studied with Monte Carlo include electron energy, cathode design, anode angle, filtration, and collimator design. Calculations were performed for single and multibeam configurations.
Increasing the energy from 100 kVp to 160 kVp increased the photon fluence through the collimator by a factor of 1.7. Both energies produced a largely uniform fluence along the long dimension of the microbeam, with 5% decreases in intensity near the edges. The isocentric dose rate for 160 kVp was calculated to be 700 Gy∕min∕A in the center of a 3 cm diameter target. Scatter contributions resulting from collimator size were found to produce only small (<7%) changes in the dose rate for field widths greater than 50 μm. Dose vs depth was weakly dependent on filtration material. The peak-to-valley ratio varied from 10 to 100 as the separation between adjacent microbeams varies from 150 to 1000 μm.
Monte Carlo simulations demonstrate that the proposed compact MRT system design is capable of delivering a sufficient dose rate and peak-to-valley ratio for small animal MRT studies.
微束放射治疗（MRT）是一种实验性放射治疗技术，在动物研究中已显示出强大的抗肿瘤作用，同时对正常组织的损伤最小。这种独特的放射形式目前仅在世界上少数几个大型同步加速器研究设施中产生。为了促进对这种有前景的治疗技术进行广泛的转化研究，我们提出并正在对基于碳纳米管场发射X射线技术的紧凑型MRT系统进行初步开发。我们报告了基于蒙特卡罗方法的紧凑型MRT系统设计可行性研究。
使用基于EGSnrc的代码进行蒙特卡罗计算。所提出的小动物研究用MRT装置设计包括形状与相应MRT准直器孔径匹配的碳纳米管阴极、带有滤波器的公共反射阳极以及一个MRT准直器。每个准直器孔径的尺寸设计为在源轴距18.6 cm处提供范围从30至200μm的束宽。用蒙特卡罗方法研究的设计参数包括电子能量、阴极设计、阳极角度、过滤以及准直器设计。对单束和多束配置进行了计算。
将能量从100 kVp增加到160 kVp，使通过准直器的光子注量增加了1.7倍。两种能量在微束的长轴方向上产生的注量基本均匀，边缘处强度降低5%。计算得出，在直径3 cm的靶中心，160 kVp的等中心剂量率为700 Gy∕min∕A。发现准直器尺寸产生的散射贡献对于宽度大于50μm的射野，仅使剂量率产生小的（<7%）变化。剂量与深度的关系对过滤材料的依赖性较弱。随着相邻微束之间的间距从150μm变化到1000μm，峰谷比从10变化到100。
蒙特卡罗模拟表明，所提出的紧凑型MRT系统设计能够为小动物MRT研究提供足够的剂量率和峰谷比。
