目的:高能电子(VHEE)可以弥补低能电子的处理深度不足,同时在光子和质子之间提供中等剂量优势。结合FLASH和VHEE,对不同能量进行了定量比较,关于计划质量,剂量率分布(在PTV和OAR中),和治疗的总持续时间(开束时间)。
方法:在2例患者(头部和肺部)中,我们通过蒙特卡罗模拟和基于PTV的优化算法,利用扫描笔形波束创建了治疗计划。Geant4用于模拟VHEE笔形光束,尺寸为0.3-5mm,由半峰全宽(FWHM)定义。在x和y方向(ISOURC=19)上具有高斯分布的单能束用作电子源。使用大规模非线性求解器(IPOPT)来计算最佳点权重。优化后,对治疗计划质量进行了不同能量之间的定量比较,剂量率分布(在PTV和OAR中),和总光束持续时间。
结果:对于头部(80MeV,100MeV,和120MeV)和肺部病例(100MeV,120MeV,和140MeV),最小束强度需要为2.5×1011电子/s和9.375×1011电子/s,以允许>90%体积的PTV达到高于40Gy/s的平均剂量率(DADR)。在此光束强度下(部分剂量:10Gy),头部外壳的总辐照时间为5258.75ms(80MeV),5149.75ms(100MeV),4976.75ms(120MeV),包括扫描时间872.75ms。对于肺部病例,这个数字是1034.25ms(100MeV),981.55ms(120MeV),和928.15ms(140MeV),包括扫描时间298.75ms。更高能量的计划总是以更高的剂量率(在PTV和OAR两者中)执行,并且由此花费更少的递送时间(射束开启时间)。
结论:该研究系统地研究了目前已知的VHEE放疗的FLASH参数,并成功地为其FLASH剂量率性能建立了基准参考。
OBJECTIVE: Very high-energy electron (
VHEE) can make up the insufficient treatment depth of the low-energy electron while offering an intermediate dosimetric advantage between photon and proton. Combining FLASH with
VHEE, a quantitative comparison between different energies was made, with regard to plan quality, dose rate distribution (both in PTV and OAR), and total duration of treatment (beam-on time).
METHODS: In two patient cases (head and lung), we created the treatment plans utilizing the scanning pencil beam via the Monte Carlo simulation and a PTV-based optimization algorithm. Geant4 was used to simulate
VHEE pencil beams and sizes of 0.3-5 mm defined by the full width at half maximum (FWHM). Monoenergetic beams with Gaussian distribution in x and y directions (ISOURC = 19) were used as the source of electrons. A large-scale non-linear solver (IPOPT) was used to calculate the optimal spot weights. After optimization, a quantitative comparison between different energies was made regarding treatment plan quality, dose rate distribution (both in PTV and OAR), and total beam duration.
RESULTS: For head (80 MeV, 100 MeV, and 120 MeV) and lung cases (100 MeV, 120 MeV, and 140 MeV), the minimum beam intensity needs to be ∼2.5 × 1011 electrons/s and ∼9.375 × 1011 electrons/s to allow > 90 % volume of PTV reaching the average dose rate (DADR) higher than 40 Gy/s. At this beam intensity (fraction dose: 10 Gy), the overall irradiation time for the head case is 5258.75 ms (80 MeV), 5149.75 ms (100 MeV), and 4976.75 ms (120 MeV), including scanning time 872.75 ms. For lung cases, this number is 1034.25 ms (100 MeV), 981.55 ms (120 MeV), and 928.15 ms (140 MeV), including scanning time 298.75 ms. The plan of higher energy always performs with a higher dose rate (both in PTV and OAR) and thereby costs less delivery time (beam-on time).
CONCLUSIONS: The study systematically investigated the currently known FLASH parameters for
VHEE radiotherapy and successfully established a benchmark reference for its FLASH dose rate performance.