Feasibility study of dual energy radiographic imaging for target localization in radiotherapy for lung tumors.

Jie Huo,Xianfeng Zhu,Ping Wang,Gang Wang,Xin-Hua Hu,Xuemin Wang,Yuanming Feng,Yang Dong,Zhiyong Yuan,Masaru Katoh

doi:10.1371/journal.pone.0108823

Abstract

PurposeDual-energy (DE) radiographic imaging improves tissue discrimination by separating soft from hard tissues in the acquired images. This study was to establish a mathematic model of DE imaging based on intrinsic properties of tissues and quantitatively evaluate the feasibility of applying the DE imaging technique to tumor localization in radiotherapy.MethodsWe investigated the dependence of DE image quality on the radiological equivalent path length (EPL) of tissues with two phantoms using a stereoscopic x-ray imaging unit. 10 lung cancer patients who underwent radiotherapy each with gold markers implanted in the tumor were enrolled in the study approved by the hospital's Ethics Committee. The displacements of the centroids of the delineated gross tumor volumes (GTVs) in the digitally reconstructed radiograph (DRR) and in the bone-canceled DE image were compared with the averaged displacements of the centroids of gold markers to evaluate the feasibility of using DE imaging for tumor localization.ResultsThe results of the phantom study indicated that the contrast-to-noise ratio (CNR) was linearly dependent on the difference of EPL and a mathematical model was established. The objects and backgrounds corresponding to ΔEPL less than 0.08 are visually indistinguishable in the bone-canceled DE image. The analysis of patient data showed that the tumor contrast in the bone-canceled images was improved significantly as compared with that in the original radiographic images and the accuracy of tumor localization using the DE imaging technique was comparable with that of using fiducial makers.ConclusionIt is feasible to apply the technique for tumor localization in radiotherapy.

Highlights

As a method for tissue discrimination, dual energy (DE) imaging has been shown to be of good performance in thoracic [1], cardiac [2] and mammographic [3] imaging applications
The projection of three dimensional (3D) structures into a two dimensional (2D) image can result in obscuration of the structure of interest such as a lung nodule by overlying structures such as the ribs, which has been identified as a major limiting factor in the detection of lung nodules in radiographs [5]
The evaluation yielded a very high R2 value (0.99), which means that the contrast-to-noise ratio (CNR) in bone-canceled image as a function of DEPL can be expressed by Eq (9)

Summary

Introduction

As a method for tissue discrimination, dual energy (DE) imaging has been shown to be of good performance in thoracic [1], cardiac [2] and mammographic [3] imaging applications. Planar kilovoltage (kV) imaging plays an important role in image guidance in radiation therapy (RT) systems, such as CyberKnife (Accuray, Inc., Sunnyvale, CA), ExacTrac (Brainlab AG, Feldkirchen, Germany) and others. It operates by acquiring two radiographs of the patient’s anatomy in the treatment room at two different beam angles in real-time and comparing them with pre-generated digitally reconstructed radiographs (DRRs) from the computed tomography (CT) image data used in the RT planning. The projection of three dimensional (3D) structures into a two dimensional (2D) image can result in obscuration of the structure of interest such as a lung nodule by overlying structures such as the ribs, which has been identified as a major limiting factor in the detection of lung nodules in radiographs [5]

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