Design and simulation of a short, variable‐energy 4 to 10 MV S‐band linear accelerator waveguide
Design and simulation of a short, variable‐energy 4 to 10 MV S‐band linear accelerator waveguide
复制标题
短、可变能量 4 至 10 MV S 波段线性加速器波导的设计和仿真
DOI：
--
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
S. Steciw
中科院分区：
文献类型：
--
作者：
D. Baillie;G. Fallone;S. Steciw
目的对先前设计的10 mV短直线加速器波导进行改造，使其能够产生4-10 mV的任何能量。改进后的波导被设计成替代作者目前的直线加速器-磁共振成像仪(Linac-MR)中使用的6 MV波导。方法以本课题组设计的短路10 mV直线加速器为起点，将端口移至第四腔，去掉向第一耦合腔的移位，在第一耦合腔中增加一个调谐圆柱体。每个腔都使用有限元方法(FEM)模拟以在所需的频率下共振。有限元模拟被用来确定不同调谐柱面深度下的射频场分布，而电子轨迹则被用来计算所需的射频功率水平和调谐柱面深度，以产生4、6、8和10 mV光子束的电子能量分布。然后用蒙特卡罗模拟比较了瓦里安直线加速器的深度剂量分布与已公布的电子束特性所产生的剂量分布。结果对于每个期望的光子能量，电子束能量均在靶区平均能量的0.5%以内，最大剂量深度在1.5 mm以内，10 cm深度与20 cm深度的剂量比在1%以内。结论模拟了一种新的27.5 cm直线加速器波导设计，可以在4~10 mV范围内产生任何光子能量，但耦合端口的设计和10 mV电子束电流增加的影响仍有待研究。对于4、6和10 mV的特定情况，该直线加速器产生的深度剂量分布与已公布的瓦里安直线加速器光谱所产生的剂量分布相似。
Purpose To modify a previously designed, short, 10 MV linac waveguide, so that it can produce any energy from 4 to 10 MV. The modified waveguide is designed to be a drop‐in replacement for the 6 MV waveguide used in the author's current linear accelerator‐magnetic resonance imager (Linac‐MR). Methods Using our group's previously designed short 10 MV linac as a starting point, the port was moved to the fourth cavity, the shift to the first coupling cavity was removed and a tuning cylinder added to the first coupling cavity. Each cavity was retuned using finite element method (FEM) simulations to resonate at the desired frequency. FEM simulations were used to determine the RF field distributions for various tuning cylinder depths, and electron trajectories were computed using a particle‐in‐cell model to determine the required RF power level and tuning cylinder depth to produce electron energy distributions for 4, 6, 8, and 10 MV photon beams. Monte Carlo simulations were then used to compare the depth dose profiles with those produced by published electron beam characteristics for Varian linacs. Results For each desired photon energy, the electron beam energy was within 0.5% of the target mean energy, the depth of maximum dose was within 1.5 mm of that produced by the Varian linac, and the ratio of dose at 10 cm depth to 20 cm depth was within 1%. Conclusions A new 27.5 cm linear accelerator waveguide design capable of producing any photon energy between 4 and 10 MV has been simulated, however coupling port design and the implications of increased electron beam current at 10 MV remain to be investigated. For the specific cases of 4, 6, and 10 MV, this linac produces depth dose profiles similar to those produced by published spectra for Varian linacs.