Nuclear Techniques ›› 2016, Vol. 39 ›› Issue (9): 90202-090202.

• LOW ENERGY ACCELERATOR, RAY AND APPLICATIONS •

### Simulation of spot scanning in proton therapy

JIA Yajun1,2, LI Yongjiang3, ZHANG Xiao3, MA Xiaoying3, WU Chao1,2, LYU Ming3, PU Yuehu1,3

1. 1. Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China;
3. Shanghai APTRON Particle Equipment Corporation, Shanghai 201800, China
• Received:2016-06-13 Revised:2016-07-26 Online:2016-09-10 Published:2016-09-09
• Supported by:

Supported by Independent Innovation and Development of High-tech Industry Project of Shanghai(No.Y439022061)

Abstract:

Background: 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: 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: 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: 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: 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.

CLC Number:

• TL99