使用带背散射屏蔽的电子射野影像装置开发和测试改进的剂量测定系统。

Development and testing of an improved dosimetry system using a backscatter shielded electronic portal imaging device.

机构信息

School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, New South Wales, Australia.

出版信息

Med Phys. 2012 May;39(5):2839-47. doi: 10.1118/1.4709602.

DOI:10.1118/1.4709602

PMID:22559656

Abstract

PURPOSE

To investigate the properties of a modified backscatter shielded electronic portal imaging device (BSS-EPID) and to develop a dose model to convert BSS-EPID images to dose in water as part of an improved system for dosimetry using EPIDs.

METHODS

The effectiveness of the shielding of the BSS-EPID was studied by comparing images measured with the BSS-EPID mounted on the support arm to images measured with the BSS-EPID removed from the support arm. A dose model was developed and optimized to reconstruct dose in water at different depths from measured BSS-EPID images. The accuracy of the dose model was studied using BSS-EPID images of 28 IMRT fields to reconstruct dose in water at depths of 2, 5, 10, and 20 cm and comparing to measured dose in water from a two-dimensional diode array at the same depths. The ability of the BSS-EPID system to operate independently of detector position was demonstrated by comparing the dose reconstruction of a 10 × 10 cm(2) field using different detector offsets to that measured by a two-dimensional diode array.

RESULTS

The shielding of the BSS-EPID was found to be effective, with more than 99% of pixels showing less than 0.5% change due to the presence of the support arm and at most a 0.2% effect on the central axis for 2 × 2 cm(2) fields to fully open 30 × 40 cm(2) images. The dose model was shown to accurately reconstruct measurements of dose in water using BSS-EPID images with average γ pass rates (2%, 2 mm criteria) of 92.5%, 98.7%, 97.4%, and 97.2% at depths of 2, 5, 10, and 20 cm, respectively, when compared to two-dimensional diode array measurements. When using 3%, 3 mm γ criteria, the average pass rate was greater than 97% at all depths. Reconstructed dose in water for a 10 × 10 cm(2) field measured with detector offsets as large as 10 cm agreed with each other and two-dimensional diode array measurements within 0.9%.

CONCLUSIONS

The modified BSS-EPID and associated dose model provide an improved system for dosimetry measurements using EPIDs. Several important limitations of the current hardware and software are addressed by this system.

摘要

目的

研究一种改良型背散射屏蔽电子射野影像装置（BSS-EPID）的特性，并开发一种剂量模型，以便将 BSS-EPID 图像转换为水中的剂量，作为 EPID 剂量测量系统的改进。

方法

通过比较安装在支撑臂上的 BSS-EPID 测量的图像和从支撑臂上移除的 BSS-EPID 测量的图像，研究 BSS-EPID 的屏蔽效果。开发并优化了一种剂量模型，以便从测量的 BSS-EPID 图像中重建不同深度的水中剂量。使用 28 个调强放射治疗场的 BSS-EPID 图像，研究剂量模型的准确性，以重建 2、5、10 和 20 cm 深度的水中剂量，并与二维二极管阵列在相同深度测量的水中剂量进行比较。通过比较不同探测器偏移量对 10×10 cm² 射野的剂量重建与二维二极管阵列的测量结果，证明 BSS-EPID 系统能够独立于探测器位置运行。

结果

发现 BSS-EPID 的屏蔽效果非常有效，超过 99%的像素由于支撑臂的存在而显示出小于 0.5%的变化，对于 2×2 cm² 射野，中央轴的最大影响为 0.2%，可完全打开 30×40 cm² 的图像。剂量模型能够准确地重建 BSS-EPID 图像测量的水中剂量，当与二维二极管阵列的测量结果相比时，在 2、5、10 和 20 cm 的深度处，平均 γ 通过率（2%，2 mm 标准）分别为 92.5%、98.7%、97.4%和 97.2%。当使用 3%、3 mm γ 标准时，所有深度的平均通过率均大于 97%。对于最大偏移量为 10 cm 的探测器测量的 10×10 cm² 射野的重建水中剂量，与彼此以及二维二极管阵列的测量结果在 0.9%以内一致。