多叶准直器塑形的未展平光子束的蒙特卡罗研究

Monte Carlo Study of Unflattened Photon Beams Shaped by Multileaf Collimator.

作者信息

Kajaria A, Sharma N, Sharma Sh, Pradhan S, Mandal A, Aggarwal L M

机构信息

School of Biomedical Engineering, Indian Institute of Technology (BHU), Varanasi, UP, India.

Department of Radiotherapy and Radiation Medicine, Institute of Medical Science (BHU), Varanasi, UP, India.

出版信息

J Biomed Phys Eng. 2019 Apr 1;9(2):137-150. eCollection 2019 Apr.

PMID:31214519

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC6538911/

Abstract

INTRODUCTION

This study investigates basic dosimetric properties of unflattened 6 MV photon beam shaped by multileaf collimator and compares them with those of flattened beams.

MATERIALS AND METHODS

Monte Carlo simulation model using BEAM code was developed for a 6MV photon beam based on Varian Clinic 600 unique performance linac operated with and without a flattening filter in beam line. Dosimetric features including lateral profiles, central axis depth dose, photon and electron spectra were calculated for flattened and unflattened cases, separately.

RESULTS

An increase in absolute depth dose with a factor of more than 2.4 was observed for unflattened beam which was dependent on depth. PDDs values were found to be lower for unflattened beam for all field sizes. Significant decrease in calculated mlc leakage was observed when the flattening filter was removed from the beam line. The total scatter factor, S was found to show less variation with field sizes for unflattened beam indicating a decrease in head scatter. The beam profiles for unflattened case are found to have lower relative dose value in comparison with flattened beam near the field edge, and it falls off faster with distance.

CONCLUSION

Our study showed that increase in the dose rate and lower peripheral dose could be considered as realistic advantages for unflattened 6MV photon beams.

摘要

引言

本研究调查了由多叶准直器塑形的未 flatten 的 6MV 光子束的基本剂量学特性，并将其与 flatten 束的特性进行比较。

材料与方法

基于瓦里安 Clinac 600 独特性能直线加速器，使用 BEAM 代码开发了蒙特卡罗模拟模型，该直线加速器在束流线上有或没有 flattening 滤波器的情况下运行。分别计算了 flatten 和未 flatten 情况下的剂量学特征，包括横向轮廓、中心轴深度剂量、光子和电子能谱。

结果

观察到未 flatten 束的绝对深度剂量增加了 2.4 倍以上，这取决于深度。对于所有射野尺寸，未 flatten 束的百分深度剂量值较低。当从束流线上移除 flattening 滤波器时，计算出的多叶准直器泄漏显著减少。发现未 flatten 束的总散射因子 S 随射野尺寸的变化较小，表明头部散射减少。与 flatten 束相比，未 flatten 情况下的束轮廓在射野边缘附近的相对剂量值较低，并且随距离下降更快。