Nuclear Techniques ›› 2020, Vol. 43 ›› Issue (9): 90302-090302.

### Monte Carlo simulation of the influence of medical foam on particle dose

Yang XIAO1,2,Qingxian ZHANG1()

1. 1.Chengdu University of Technology, Chengdu 610000, China
2.The Second Affiliated Hospital of Chongqing Medical University, Chongqing 400010, China
• Received:2020-04-05 Revised:2020-05-09 Online:2020-09-15 Published:2020-09-09
• Contact: Qingxian ZHANG E-mail:512598780@qq.com
• About author:XIAO Yang, male, born in 1992, graduated from Chengdu University of Technology in 2016, master student, focusing on accelerator technology

Abstract: Background

At present, styrofoam is widely used in radiotherapy positioning, but there is no relevant report on its impact on accelerator basic dose.

Purpose

This study aims to investigate the effects of different thicknesses of styrofoam on the particles dose of medical electronic linear accelerator flattening filter (FF) and flattening filter free (FFF) , and provide guidance for clinical use.

Methods

The Monte Carlo program EGSnrc was used for modeling and calculation. First of all, the PEGS4 material library and cross-section data were established according to the parameters of the styrofoam provided by the manufacturer, and the BEAMnrc was used to establish accelerator head models of different shooting fields of Varian True Beam series and perform calculations to generate corresponding phase space files. Then, the BEAMdp was employed to analyze the differences in ray energy spectrum and energy fluence generated by different model structures. Finally, the effect of different thickness foams on the fixed field and fixed thickness foams on the field was calculated and analyzed by using Dosexyznrc.

Results

In the presence of styrofoam, the percentage depth dose (PDD) in both FF and FFF modes has a phenomenon of moving forward to varying degrees, resulting in an increase in the surface dose whilst little effect on the quality of the radiation. In the FF mode, the maximum dose deviation at the same depth is ≤2% when the thickness of the foam is ≤5 cm. When the thickness of the form reaches 10 cm, the maximum dose deviation at the same depth increases to 6%, and the PDD0 exceeds 90% in both modes. In both modes, the presence of styrofoam has a greater effect on the off-axis ratio and penumbra of the shot, the smaller the shooting field, the smaller the effect on the particle dose.

Conclusions

When using styrofoam for clinical purposes, try to control the thickness within 5 cm, and FFF mode is recommended for more thicker styrofoam. Styrofoam has little effect on dose of stereotactic radiation therapy.

CLC Number:

• TL53