Zhang Guoliang, Zhang Zhengzhao, Gao Wenchao, Quan Hong
School of Physics and Technology, Wuhan University, 430072, China.
Cancer Radiation Therapy Center, Fifth Medical Center of Chinese PLA General Hospital, 100039, China.
Phys Med. 2023 Mar;107:102539. doi: 10.1016/j.ejmp.2023.102539. Epub 2023 Feb 16.
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).
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.
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 × 10 electrons/s and ∼9.375 × 10 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).
The study systematically investigated the currently known FLASH parameters for VHEE radiotherapy and successfully established a benchmark reference for its FLASH dose rate performance.
超高能电子（VHEE）可弥补低能电子治疗深度不足的问题，同时在光子和质子之间提供中等剂量学优势。将FLASH与VHEE相结合，针对计划质量、剂量率分布（在靶区和危及器官中）以及治疗总时长（束流开启时间），对不同能量进行了定量比较。
在两个患者病例（头部和肺部）中，我们通过蒙特卡洛模拟和基于靶区的优化算法，利用扫描笔形束创建治疗计划。使用Geant4模拟VHEE笔形束，其半高宽（FWHM）定义的尺寸为0.3 - 5毫米。在x和y方向具有高斯分布的单能束（ISOURC = 19）用作电子源。使用大规模非线性求解器（IPOPT）计算最佳光斑权重。优化后，针对治疗计划质量、剂量率分布（在靶区和危及器官中）以及总束流持续时间，对不同能量进行了定量比较。
对于头部病例（80 MeV、100 MeV和120 MeV）和肺部病例（100 MeV、120 MeV和140 MeV），要使靶区体积的> 90%达到高于40 Gy/s的平均剂量率（DADR），最小束流强度需要达到约2.5×10电子/秒和约9.375×10电子/秒。在此束流强度下（分次剂量：10 Gy），头部病例的总照射时间为5258.75毫秒（80 MeV）、5149.75毫秒（100 MeV）和4976.75毫秒（120 MeV），包括扫描时间872.75毫秒。对于肺部病例，该数字分别为1034.25毫秒（100 MeV）、981.55毫秒（120 MeV）和928.15毫秒（140 MeV），包括扫描时间298.75毫秒。能量较高的计划在靶区和危及器官中的剂量率始终更高，因此所需的束流开启时间更短。
本研究系统地研究了当前已知的VHEE放射治疗的FLASH参数，并成功建立了其FLASH剂量率性能的基准参考。
