Biological and dosimetric characterisation of spatially fractionated proton minibeams
Biological and dosimetric characterisation of spatially fractionated proton minibeams
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DOI：
10.1088/1361-6560/aa950c
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发表时间：
2017-12-21
影响因子：
3.5
通讯作者：
Sandison, George
中科院分区：
文献类型：
--
作者：
Meyer, Juergen;Stewart, Robert D.;Sandison, George
质子束的生物有效性随深度、光斑大小和距束中心轴的横向距离而变化。这项工作的目的是将质子相对生物学效应（RBE）和等效均匀剂量（EUD）的考虑到宽束和高度调制的质子微束的比较。本文提出了一种小动物质子束线的蒙特卡罗模型。剂量和可变RBE是在能量范围（30-109 MeV）的每体素基础上计算的。对于开放光束，光束入口处的RBE值范围为1.02-1.04，布拉格峰（BP）为1.3 - 1.6，BP远端为1.4 - 2.0。对于50 MeV质子束，设计用于在BP峰值深度处产生均匀剂量的微型束准直器对深度处的开放束RBE值的影响最小。RBE的变化观察到的表面附近时，准直器被放置与被照射的物体齐平，由于更高的中子的贡献来自质子与准直器的相互作用。对于质子微束，相对平均RBE加权入射剂量（RWD）比物理平均剂量低25%。观察到EUD与馏分大小的强烈依赖性。对于20戈伊剂量，EUD变化很大，这取决于细胞的放射敏感性。对于放射敏感细胞，平均剂量的差异高达50%，平均RWD的差异高达40%，EUD倾向于谷剂量而不是平均剂量。对于空间分割质子微束的均匀剂量的比较研究，建议将来自每体素RWD分布的EUD用于生殖细胞存活和相关终点的生物学评估。
The biological effectiveness of proton beams varies with depth, spot size and lateral distance from the beam central axis. The aim of this work is to incorporate proton relative biological effectiveness (RBE) and equivalent uniform dose (EUD) considerations into comparisons of broad beam and highly modulated proton minibeams. A Monte Carlo model of a small animal proton beamline is presented. Dose and variable RBE is calculated on a per-voxel basis for a range of energies (30-109 MeV). For an open beam, the RBE values at the beam entrance ranged from 1.02-1.04, at the Bragg peak (BP) from 1.3 to 1.6, and at the distal end of the BP from 1.4 to 2.0. For a 50 MeV proton beam, a minibeam collimator designed to produce uniform dose at the depth of the BP peak, had minimal impact on the open beam RBE values at depth. RBE changes were observed near the surface when the collimator was placed flush with the irradiated object, due to a higher neutron contribution derived from proton interactions with the collimator. For proton minibeams, the relative mean RBE weighted entrance dose (RWD) was similar to 25% lower than the physical mean dose. A strong dependency of the EUD with fraction size was observed. For 20 Gy fractions, the EUD varied widely depending on the radiosensitivity of the cells. For radiosensitive cells, the difference was up to similar to 50% in mean dose and similar to 40% in mean RWD and the EUD trended towards the valley dose rather than the mean dose. For comparative studies of uniform dose with spatially fractionated proton minibeams, EUD derived from a per-voxel RWD distribution is recommended for biological assessments of reproductive cell survival and related endpoints.