In this paper we investigate the dosimetric effects target inhomogeneities on VHEE (Very High Energy Electron) beam dose profiles. Dose profile sensitivity to high and low density ($0.001-2.2\mathrm{g}/{\mathrm{cm}}^3$) embedded media in water was measured for 156 MeV VHEE beams. To the knowledge of the authors, this is the first systematic experiment on dose penetration in inhomogeneous targets at this high energy electron beams. The results of the dosimetry experiments were compared with simulation results acquired with the TOPAS/GEANT4 Monte Carlo codes and were compared with the sensitivity of photon and proton beams.

Dosimetry experiments with VHEE beams at 156 MeV were performed by embedding various density inserts in a cuboid $30\times 30\times 10$ cm³ water phantom. This setup was then irradiated with a narrow ($\sigma =1.2$ mm) Gaussian VHEE beams. Transverse dose profiles were recorded at various depths within the water phantom using radosensitive EBT-XD Gafchromic films. Simulations were performed using the TOPAS user wrap for the GEANT4 Monte Carlo toolkit with the measured beam and target geometry parameters from the CLEAR facility and compared with sensitivity of photon and protons beams to inhomogeneities in water phantoms.

Less than 8% dose deviation was shown for all measured dose data across all recorded depths (0–20 cm). Monte Carlo simulations within the whole water phantom volume showed a 15% dose deviation. Simulation studies indicated that using proton and photon beams within a therapeutic energy range in MC simulations of this experimental setup resulted in dose change in the central plane up to 100% and 74% of the dose maximum in the central plane respectively.

The dosimetry results of these experiments and TOPAS/GEANT4 simulations compare well. Dose profiles of VHEE beams were found to be relatively insensitive ($<15\%$ dose difference across the central plane) to embedded high and low density geometries compared to simulation results with therapeutic proton beams (up to 100% of dose maximum in the plane). Therefore, VHEE is robust to anatomical changes and has the potential to be a reliable mode of radiotherapy for treating tumors in highly inhomogeneous and mobile regions such as the lung.

在本文中，我们研究了剂量效应对VHEE（超高能电子）束剂量分布的不均匀性的影响。剂量分布对高密度和低密度的敏感性（$0.001--2.2\mathrm{G}/{\mathrm{厘米}}^3$）测量了156 MeV VHEE光束在水中的嵌入介质。据作者所知，这是在高能电子束下非均匀靶中剂量穿透的第一个系统性实验。将剂量学实验的结果与使用TOPAS / GEANT4蒙特卡罗编码获得的模拟结果进行比较，并与光子和质子束的灵敏度进行比较。

通过在长方体中嵌入各种密度插入物来进行156 MeV的VHEE光束的剂量学实验 $30\times 30\times 10$ 厘米³水幻影。然后以窄幅（$\sigma =1.2$ mm）高斯VHEE光束。使用灵敏的EBT-XD Gafchromic胶片在水模内的各个深度记录横向剂量分布。使用TOPAS用户包装进行GEANT4蒙特卡洛工具包的仿真，使用CLEAR设施中测得的光束和目标几何参数，并与光子和质子束对水体模型中不均匀性的敏感性进行了比较。

在所有记录的深度（0-20厘米）内，所有测得的剂量数据均显示小于8％的剂量偏差。在整个水体模型体积内的蒙特卡罗模拟显示剂量偏差为15％。模拟研究表明，在此实验装置的MC模拟中，在治疗能量范围内使用质子束和光子束会导致中心平面中的剂量变化分别达到中心平面中最大剂量的100％和74％。

这些实验的剂量测定结果与TOPAS / GEANT4模拟的结果相吻合。发现VHEE光束的剂量分布相对不敏感（$<15％$与使用治疗性质子束的模拟结果（高达平面中最大剂量的100％）相比，嵌入式高密度和低密度几何形状的剂量差异更大。因此，VHEE对解剖学变化具有鲁棒性，并且有可能成为放射疗法的可靠模式，用于治疗高度异质性和活动性区域（如肺）的肿瘤。