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1.中国科学院上海应用物理研究所 嘉定园区 上海 201800
2.中国科学院大学 北京 100049
3.上海艾普强粒子设备有限公司 上海 201800
[ "贾亚军,男,1990年出生,2014年毕业于四川大学,现为硕士研究生,现从事质子治疗扫描照射的研究", "JIA Yajun, male, born in 1990, graduated from Sichuan University in 2014, master student, focusing on scanning irradiation in proton therapy" ]
蒲越虎,E-mail:puyuehu@sinap.ac.cn PU Yuehu, E-mail: puyuehu@sinap.ac.cn
收稿日期:2016-06-13,
修回日期:2016-07-26,
纸质出版日期:2016-09
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贾亚军, 李永江, 张潇, 等. 质子治疗中点扫描照射技术的仿真模拟[J]. 核技术, 2016,39(9):090202
Yajun JIA, Yongjiang LI, Xiao ZHANG, et al. Simulation of spot scanning in proton therapy[J]. Nuclear techniques, 2016, 39(9): 090202
贾亚军, 李永江, 张潇, 等. 质子治疗中点扫描照射技术的仿真模拟[J]. 核技术, 2016,39(9):090202 DOI: 10.11889/j.0253-3219.2016.hjs.39.090202.
Yajun JIA, Yongjiang LI, Xiao ZHANG, et al. Simulation of spot scanning in proton therapy[J]. Nuclear techniques, 2016, 39(9): 090202 DOI: 10.11889/j.0253-3219.2016.hjs.39.090202.
粒子治疗是癌症治疗的有效手段之一,受到越来越多的关注。简述了质子治疗中的治疗系统和点扫描照射技术。利用开发的扫描照射的仿真程序,参照中国科学院上海应用物理研究所正在研制的国产首台质子治疗装置的技术指标,模拟点扫描对固定靶区和运动靶区的照射,以及加速器关断延迟对剂量分布的影响,得到在给定体积靶区照射时的总照射时间和剂量率等信息。固定靶区照射时,得到适形的剂量分布;考虑加速器关断延迟时,剂量分布与计划剂量差异较大。门控技术显著改善受呼吸运动影响的靶区的照射效果。模拟结果为正在研制的装置和将来的临床应用提供必要的参考。
Background:
2
Particle beam therapy has been proved to be an effective and important method for treating cancer patients.There are more than 60 particle beam treatment centers in the world according to recent statistics.At Shanghai Institute of Applied Physics(SINAP)
the first domestic prototype of a proton treatment system based on synchrotron accelerator is being developed.In order to optimize the system design for future development and estimate the performances of the prototype therapy machine using advanced active beam scanning techniques
a sophisticated simulation tool is needed.
Purpose:
2
The primary goal is to develop a computer code which can simulate the irradiation process for treating typical static and moving targets by using beam scanning technique.Using the developed code
detailed case studies will be performed to gain insights of the impacts of various machine parameters on the final dose distributions.
Methods:
2
The simulation code is composed of three major parts
namely the data preparation
irradiation action simulation
and weighted superposition of the dose contributions from all tens of thousands of scanned beam spots.The data preparation includes reading accelerator beam and scanning parameters
generating 3-dimensional(3D)energy-normalized Bragg curve
allocating scanning beam spots inside the target volume
preparing relative beam weights of each scanning beam spot and computing the absolute particle number to be irradiated to each beam spot.Then scanning irradiation is simulated by a spot-wise time integration of the beam spills mocking the function of a beam dose monitor taking the respiratory gating and all the time delays encountered in the scanning system into account.Multi-threading parallel computing is used to speed up the simulation process.
Results:
2
Using the developed simulation code
irradiation processes with discrete spot scanning technique of a static and another moving rectangular target inside a water phantom are successfully simulated.With assumed parameters including scanning speeds
beam current time structure
beam shutoff time delay
scanning spot pitches
prescribed dose
homogeneous 3D dose distributions conformal to the target volume can be obtained.The simulation also shows that beam shutoff time on the order of 200 μs can significantly spoil the dose distribution due to larger delivered number of particles to each beam spot as compared with the planned values unless the beam current from the accelerator is kept sufficiently low.The code shows that in irradiation of a moving target
both the beam gating method and careful selection of faster scanning direction are very effective methods to reduce the interplay effects caused by the motions of the scanning beam and the target.Dose rate and total irradiation time of treating a given target under realistic beam and scanning parameters are easily obtained.Using an 8 core Intel i7-4790 CPU PC
the simulation takes typically 1.5 h for the studied cases.
Conclusions:
2
A useful simulation code is successfully developed and used to study scanning irradiation of static as well as moving targets.Impact of beam switching-off response time and beam intensity on the 3D dose distribution is quantitatively clarified.These results will be considered in works aiming at optimizing the design parameters of new proton therapy systems.It is also shown that respiratory gating technique can effectively mitigate the influence of target motion and distinctly improves the dose distribution.Future research will focus on refining the simulation models and introducing GPU based parallel computing to shorten the time needed for carrying out the simulations.
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