加速器机载影像系统图像质量量化评价及质量保证阈值设定研究

目的 探讨加速器机载影像(OBI)系统图像质量量化分析方法和图像质量保证警告与行动阈值设定。方法 利用瓦里安EDGE加速器机载影像系统,半扇、全扇模式扫描Catphan604模体,基于Python编程语言自主实现软件分析图像CT值线性、几何线性、层厚、空间分辨率、均匀性和低对比度分辨率。将16个月内16次扫描图像指标定量分析结果归一平均值,计算标准偏差(σ),进行运行图分析,建立图像质量参数的警告与行动阈值。结果 自主编程软件可量化分析半扇、全扇扫描模式OBI系统各项图像指标,低对比度分辨率半扇优于全扇扫描,空间分辨率全扇优于半扇。归一化图像质量参数以1个σ设为警告阈值,2个σ设为行动阈值,且半扇容差水平均小于全扇。结论 自主开发软件可实现图像质量量化评价,建立了影像系统质量保证警告和行动容差,为图像引导放疗规范下图像质量保证提供指导。

A quantitative evaluation on the image-quality parameters and quality assurance thresholds setting of accelerator on-board imaging system

Objective To achieve quantitative analysis of image quality parameters and establish warning and action thresholds for the on-board imaging (OBI) system of linear accelerator. Methods The Catphan604 phantom was repeatedly scanned in the Full-Fan and Half-Fan CBCT scanning modes on a Varian EDGE linear accelerator, and the software based on Python language development in-house was utilized to analyze image quality parameters, such as CT number linearity, geometric consistency, slice thickness, spatial resolution, uniformity and low-contrast resolution. The quantitative analysis results of each image quality parameter obtained from 16 times of scanning within 16 months were normalized to the mean and the standard deviations were recorded. A run chart analysis was created to determine the warnings and action thresholds. Results The software built in-house can quantitatively analyze the image parameters of the two scanning modes of OBI system. The low-contrast resolution of Half-Fan was better than that of Full-Fan, whereas the spatial resolution of Full-Fan was superior to that of Half-Fan. One standard deviation (1σ) was set as the warning threshold and 2 standard deviations (2σ) as the action threshold, respectively. The tolerance level of Half-Fan was smaller than that of Full-Fan. Conclusion Self-developed software enables quantitative analysis of accelerator image quality parameters, establishes warning and action tolerance of quality assurance and provides guidance for image quality assurance under image-guided radiotherapy specification.