Nuclear Techniques ›› 2020, Vol. 43 ›› Issue (1): 10202-010202.doi: 10.11889/j.0253-3219.2020.hjs.43.010202


Fast confirmation of the incident electron energy by simulation for medical linac

Junjie HAN1,Yongdong ZHUANG2,Xiaowei LIU2()   

  1. 1. Department of Radiation Oncology, Guangdong General Hospital, Guangzhou 510080, China
    2. School of Physics, Sun Yat-sen University, Guangzhou 510275, China
  • Received:2019-10-08 Revised:2019-11-27 Online:2020-01-15 Published:2020-01-21
  • Contact: Xiaowei LIU
  • About author:HAN Junjie, male, born in 1991, graduated from Sun Yat-sen University in 2016, focusing on radiotherapy
  • Supported by:
    Joint Fund of National Natural Science Foundation of China(U1832128)

Abstract: Background

Monte Carlo method provides a powerful tool for the simulation of particle transport in radiotherapy, hence can be used for determination of the target energy of the incident electron in medical linac simulation.


This study aims to find a way that can confirm the incident electron energy accurately and quickly, and save time for Monte Carlo linac simulation.


First of all, Monte Carlo program package EGSnrc/BEAMnrc was employed to build up the beam models of Varian 600C, Trilogy and Edge FFF (Flattening Filter Free) model with the same nominal energy of simulation of 6 MV. Then, the dose distributions in different fields (3 cm×3 cm, 10 cm×10 cm, 40 cm×40 cm) using different incident electron energies in water phantom were calculated. Finally simulation results were compared and analyzed to find out a way to ensure the incident electron energy accurately and quickly.


When the incident electron energy varies from 5.5 MeV to 6.5 MeV, percentage depth dose (PDD) is insensitive to the incident electron energy; the off axis ratio (OAR) profiles of 3 cm×3 cm and 10 cm×10 cm are insensitive to the incident electron energies, the OAR profiles of different incident electron energies are almost the same. The OAR profile of 40 cm×40 cm is very sensitive to the incident electron energy. Detailed results at 5 cm underwater show that when the incident electron energy increases by every 0.1 MeV, the average of OAR between the off axis distance from 14.5 cm to 19 cm decreases: 0.82% for Varian 600C 6 MV, 0.98% for Trilogy 6 MV, 0.47% for Edge 6 MV FFF, respectively. Combining the measured OAR profiles of large field (40 cm×40 cm) with the linear relationship between average OAR and the incident electron energy, the incident electron energy can be determined quickly. Compared with the measured values, the PDD and OAR using the fitting energy as input in water phantom, profiles differences are both within 1%.


This proposed method provides a way to ensure the incident electron energy accurately and quickly for medical linac.

Key words: Medical linear accelerator, Incident electron shooting energy, Varian 600C trilogy edge, Monte Carlo simulation

CLC Number: 

  • TL53