Evaluation of Non-Rigid Image-Registration Algorithms Using Discrepancy Distance Between Organ Contours

Yuichi Saito ,Akira Nakata ,Kengo Nakata ,Maiya Hori ,Takahiro Nakazawa ,K Fujimoto ,Tadanori Abe ,Masaki Yano ,Kunihiko Tateoka ,Keisuke Shima ,M Hareyama ,Mie Someya ,Koichi Sakata

doi:10.4172/2155-9619.1000307

Yuichi Saito , Akira Nakata + Show 11 more

Open Access

https://doi.org/10.4172/2155-9619.1000307

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Abstract

Purpose: Non-rigid image registration (NIR) is useful for adaptive radiotherapy. However, no method has been established for evaluating the quality of the algorithms used in NIR. To remedy this situation, we demonstrate herein a novel method to evaluate NIR algorithms. Methods: We define the NIR error as the discrepancy distance between (i) the organ contours obtained from computed tomography (CT) images acquired during the treatment period (reference contours) and (ii) the contours obtained from the treatment-planning CT images that are constructed by automated propagation during the treatment period (evaluation contours). However, the continuous positional relationship between the points where the reference contour intersects the evaluation contour is assumed to be maintained. In addition, we adapt the proposed method so that it can be applied to the contours of complex organs such as spherical and tubular organs. To demonstrate this method, we measure the contours of the prostate, right seminal vesicle, left seminal vesicle, urinary bladder, and rectum. The obtained NIR error presented in two-dimensional (2D) discrepancy maps. Results: The 2D discrepancy maps show the difference between the reference and evaluation contours from CT images. The proposed method measures the difference between the contours of spherical and tubular organs and evaluates the NIR error based on the positional relationship between the points constituting the contours. Conclusions: This study accounts for and measures the continuous positional relationship between corresponding points in the contours of complex-shaped spherical and tubular organs with irregularities and evaluates NIR algorithms based on these organ contours.

Highlights

Intensity-modulated radiotherapy (IMRT), which uses a steep dose gradient, can be administered in high doses to target organs and minimizes exposure to the surrounding normal organs [1]
IMRT is planned based on treatment-planning computed tomography images taken before treatment
This method requires the radiation oncologist to manually create the contours of the target and normal organs on the repeat computed tomography (CT) images acquired during the treatment period, which involves considerable time and effort

Summary

Introduction

Intensity-modulated radiotherapy (IMRT), which uses a steep dose gradient, can be administered in high doses to target organs and minimizes exposure to the surrounding normal organs [1]. During the radiotherapy period, a treatment plan based on pCT images does not sufficiently consider the anatomical changes (deformation and displacement) in the target organ and surrounding normal organs. Regarding anatomical changes during the treatment period, Michel et al [4] reported that an appropriate dose can be administered to the target and surrounding normal tissues by using adaptive radiotherapy, in which treatment re-planning is promptly implemented. This method requires the radiation oncologist to manually create the contours of the target and normal organs on the repeat CT (rCT) images acquired during the treatment period, which involves considerable time and effort

Methods

Results

Conclusion