Elsevier

Physica Medica

Volume 65, September 2019, Pages 53-58
Physica Medica

Original paper
Availability of a simplified lung ventilation imaging algorithm based on four-dimensional computed tomography

https://doi.org/10.1016/j.ejmp.2019.08.006Get rights and content

Highlights

  • We propose a simplified algorithm, VIAAVG, which is independent on DIR and requires only AVG CT as input.

  • Accuracy and efficiency are evaluated for 50 patients, which is the largest cohort as far as we know.

  • VIAAVG shows nearly substantial similarity with gold standard, VISPECT, which is higher than other proposed algorithms.

  • VIAAVG takes much less time to compute CTVI than other algorithms proposed before.

  • VIAAVG is more convenient for clinical use, since structures, dose, lung function are all defined on the same AVG CT.

Abstract

Purpose

It is still not conclusive which four-dimensional computed tomography (4DCT)-based ventilation imaging algorithm is most accurate and efficient. In this study, we proposed a simplified algorithm (VIAAVG) which only requires the average computed tomography (AVG CT) as input, and quantitatively compared its accuracy and efficiency with three other popular algorithms.

Material and methods

Fifty patients with lung or esophageal cancer who underwent radiotherapy were enrolled. Single photon emission computed tomography (SPECT) ventilation images (VI-SPECT) and 4DCT were acquired 1–3 days before the first treatment session. The end of exhalation and the end of inhalation CT were registered to derive deformable vector field (DVF) using MIMvista. 4DCT-based ventilation images (CTVI) were first calculated respectively by means of four algorithms (VIAJAC, VIAHU, VIAPRO and VIAAVG). The computation times were compared using paired t-test. The corresponding CTVIs (CTVIJAC, CTVIHU, CTVIPRO and CTVIAVG) and VI-SPECT were segmented into three equal sub-volumes (high, medium and low function lung, respectively) after smoothing and normalization. The Dice Similarity Coefficients (DSCs) were calculated for each sub-volume between each CTVI and VI-SPECT. The average DSCs for high, medium and low function lung in different CTVIs for each patient were compared using paired t-test.

Results

The mean DSCs for CTVIJAC, CTVIHU, CTVIPRO and CTVIAVG were 0.3255, 0.4465, 0.5865 and 0.5958, respectively. The average computation times for CTVIJAC, CTVIHU, CTVIPRO and CTVIAVG were 18.3 s, 24.2 s, 144.8 s and 15.0 s.

Conclusion

VIAAVG is available for clinical use because of its high accuracy, improved efficiency and less input requirement compared to the other algorithms.

Introduction

It is beneficial to utilize pulmonary function images, acquired by single photon emission tomography (SPECT) [1] or positron emission tomography (PET) [2] in radiotherapy. In recent years, four-dimensional computed tomography (4DCT)-based ventilation imaging has become a research hotpot. It can provide functional information in lung without additional dose or monetary cost to the patient, since 4DCT simulation is a clinical routine for thoracic cancer patient in most of radiation oncology clinics. In clinical practice, the 4DCT-based Ventilation Image (CTVI) has been used for assessing the regional function [3] or function changes [4], [5], [6], [7], [8] in lung tissue, predicting radiation pneumonitis [9], [10] and guiding radiotherapy treatment planning [2], [11], [12], [13], [14], [15].

Three ventilation imaging algorithms (VIA) to produce CTVI have been reported. The first VIA (VIAHU) is described by Guerrero et al. [16] which generates static 3D ventilation images based solely on the physical density-change between the exhalation breath-hold and inhalation breath-hold computed tomography (CT) images using deformable image registration (DIR) and the underlying CT density information. The second widely used VIA (VIAJAC) is introduced by Reinhardt et al. [17], which utilizes the Jacobian determinant of the DIR spatial transformation to quantify the regional volume-change of lung volume elements. The third VIA (VIAPRO) is proposed by Kipritidis et al. [18], which estimates the ventilation in terms of the 4D time-averaged regional product of air and tissue densities at each voxel without requiring DIR.

However, the correlations between the CTVIs based on any of above algorithms and the clinical golden standard (99mTc-SPECT [19] or 68Ga-Galligas PET [20]) are highly variable [21], [22], [23], [24]. Many causes have been reported, such as the image quality [25], breathing variations [26], the DIR inaccuracy [27], [28], and the 4DCT sorting method [29]. It still remains unclear which VIA is the most accurate and efficient for clinical use.

Inspired by the study of Kipritidis et al. [18], in this study we propose a simplified VIA (VIAAVG) , which requires only average CT (AVG CT) as input data. Its availability is quantitatively evaluated by comparing the accuracy and efficiency of VIAAVG with those VIAs proposed before (i.e. VIAHU, VIAJAC and VIAPRO) for 50 enrolled patients.

Section snippets

Patients

Fifty thoracic cancer patients (lung or esophageal cancer) were enrolled in this study and underwent radiotherapy in our hospital between 2015 and 2018. 4DCT images were acquired in 4DCT simulation as routine part of radiotherapy prior to the treatment. SPECT ventilation images (VI-SPECT) were also acquired 1–3 days before the first radiotherapy session with the same supine position used in 4DCT simulation. The time interval between 4DCT simulation and VI-SPECT acquisition was less than 3 days

Results

A visual comparison between different ventilation images is illustrates in Fig. 1 for a specific patient in transverse (first row) and coronal (second row) view. The correctness of segmentation algorithm used in this study can be confirmed by comparing the original VI-SPECT (first column) and the segmented VI-SPECT (second column). Generally, segmented CTVIPRO and CTVIAVG are very similar, and showing a high similarity with segmented VI-SPECT. However, the similarity between segmented CTVIJAC,

Discussion

In this study, we propose a simplified algorithm, VIAAVG, inspired by the method proposed by Kipritidis et al. with the aim to reduce input requirement and computation time. In VIAHU and VIAJAC, two phases of 4DCT images (T50 and T00) are required as input data. In VIAPRO, even all phases of 4DCT images are required. In contrast, the simplified algorithm requires only AVG CT to compute CTVIAVG. The availability of this algorithm is evaluated by comparing its accuracy and efficiency with other

Conclusion

The simplified algorithm proposed in this study, VIAAVG, shows a nearly substantial correlation with the commonly used clinic-gold-standard lung functional image (VI-SPECT). Compared with other proposed algorithms, it is a promising modality for the further application of 4DCT-based ventilation imaging in radiation therapy because of less input requirement, improved computation efficiency and independence on DIR.

Acknowledgements

The authors sincerely thank Dr. Li Mei and her team of the Nuclear Medicine Department of Peking TongRen Hospital for their great help in SPECT image acquisitions. This work was supported by the National Natural Science Foundation for Young Scholars of China (Grant No. 81502649) and National Key Projects of Research and Development (Grant No. 2016YFC0904600).

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