Very high energy electron (VHEE) beams have been proposed as an alternative radiotherapy modality to megavoltage photons; they penetrate deeply without significant scattering in inhomogeneous tissue because of their high relativistic inertia. However, the depth dose distribution of a single, collimated VHEE beam is quasi-uniform, which can lead to healthy tissue being overexposed. This can be largely overcome by focusing the VHEE beam to a small spot. Here, we present experiments to demonstrate focusing as a means of concentrating dose into small volumetric elements inside a target. We find good agreement between measured dose distributions and Monte Carlo simulations. Focused radiation beams could be used to precisely target tumours or hypoxic regions of a tumour, which would enhance the efficacy of radiotherapy. The development of new accelerator technologies may provide future compact systems for delivering these focused beams to tumours, a concept that can also be extended to X-rays and hadrons.

已经提出使用超高能电子（VHEE）束作为兆伏光子的替代放射疗法。它们具有很高的相对论惯性，因此可以很深地穿透而不会在不均匀的组织中产生明显的散射。但是，单个准直的VHEE光束的深度剂量分布是准均匀的，这可能导致健康组织曝光过度。通过将VHEE光束聚焦到一个小点可以大大克服这一点。在这里，我们目前的实验来证明聚焦是将剂量集中到靶标内小的体积元素的一种手段。我们发现测得的剂量分布与蒙特卡洛模拟之间有很好的一致性。聚焦的辐射束可用于精确地瞄准肿瘤或肿瘤的低氧区域，这将增强放射疗法的功效。