Gholamhossein Izadi Vasafi, Firoozabadi Mohammad Mehdi, Mahdi Ghorbani
Department of Physics, Faculty of Sciences, University of Birjand, Birjand, Iran.
Biomedical Engineering and Medical Physics Department, Faculty of Medicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Rep Pract Oncol Radiother. 2019 Nov-Dec;24(6):660-666. doi: 10.1016/j.rpor.2019.10.002. Epub 2019 Nov 4.
The purpose of this study is to analyse how small variations in the elemental composition of soft tissue lead to differences in dose distributions from a Cf brachytherapy source and to determine the error percentage in using water as a tissue-equivalent material.
Water is normally used as a tissue-equivalent phantom material in radiotherapy dosimetry.
Neutron energy spectra, neutron and gamma-ray dose rate distributions were calculated for a Cf AT source located at the center of a spherical phantom filled with various types of tissue compositions: adipose, brain, muscle, International Commission on Radiation Units and Measurements (ICRU) report No. 44 9-component soft tissue and water, using Monte Carlo simulation.
The obtained results showed differences between total dose rates in various tissues relative to water varying between zero and 4.94%. The contributions of neutron and total gamma ray doses to these differences are, on average, 81% and 19%, respectively. It was found that the dose differences between various soft tissues and water depend not only on the soft tissue composition, but also on the beam type emitted from the Cf source and the distance from the source.
Assuming water as a tissue-equivalent material, although leads to overestimation of dose rate (except in the case of adipose tissue), is acceptable and suitable for use in Cf brachytherapy treatment planning systems based on the recommendation by the ICRU that the uncertainties in dose delivery in radiotherapy should be lower than 5%.
本研究旨在分析软组织元素组成的微小变化如何导致锎近距离放射治疗源剂量分布的差异，并确定使用水作为组织等效材料时的误差百分比。
在放射治疗剂量测定中，水通常用作组织等效体模材料。
使用蒙特卡罗模拟，计算位于充满各种类型组织成分（脂肪、脑、肌肉、国际辐射单位与测量委员会（ICRU）第44号报告中的9成分软组织和水）的球形体模中心的锎锕源的中子能谱、中子和γ射线剂量率分布。
所得结果表明，各种组织相对于水的总剂量率差异在0至4.94%之间。中子剂量和总γ射线剂量对这些差异的贡献平均分别为81%和19%。发现各种软组织与水之间的剂量差异不仅取决于软组织组成，还取决于锎源发射的束流类型和距源的距离。
尽管将水假定为组织等效材料会导致剂量率高估（脂肪组织情况除外），但根据ICRU的建议，即放射治疗中剂量传递的不确定性应低于5%，这是可以接受的，并且适用于锎近距离放射治疗治疗计划系统。
