Keywords:
Performed at one institution, Experimental, Retrospective, Image registration, Computer Applications-General, CT, Lung
Authors:
S. Maehira1, T. Hiroki1, Y. Fujita2, K. Usui2, E. Kunieda1; 1Kanagawa/JP, 2Tokyo/JP
DOI:
10.26044/ecr2020/C-07928
Methods and materials
Patients
Ten left-sided post lumpectomy patients who underwent free-breathing (FB) CT, abdominal deep inspiration breath-hold (AB) CT, and thoracic deep inspiration breath-hold (TB) CT for breast-conserving radiation therapy were as retrospectively evaluated. The coaching session for using abdominal breathing and thoracic breathing properly was carried out before the CT scan and lasted about 10 minutes. All patients were positioned on a supine breast board with arms extended above their head in supports.
Anatomic characteristics (edge measurements)
To investigate anatomic characteristics between ABCT and TBCT, lung volume, intrathoracic and abdominal anterior-posterior (AP) and left-right (LR) distance at the nipple and 12th thoracic Vertebra level, and craniocaudal (CC) distance from lung apex to heart apex were measured. Additionally, the lung expansion rate was calculated from the measured distance. The two-tailed Wilcoxon signed-rank test was conducted to evaluate the difference in anatomic characteristics. P-values less than 0.05 were considered statistically significant.
Quantitative evaluation of lung motion using DIR
1. Deformable image registration
The workflow of quantitative evaluation using DIR is shown in Fig. 3. The open-source image registration framework Plastimatch (www.plastimatch.org) was used to deform from FBCT to ABCT and TBCT. It is a free and image registration tool that provides the option for applying several registration algorithms and control parameters in single or multistage. It permits the optimization of specific parameters for more precise and customized registration. In this study, the B-Spline algorithm was utilized for DIR, which optimized the deformation over 3 stages using the mean squared error metric. DIR results were verified using visual assessment and image overlays.
2. Deformation quantification
The deformation vector field (DVF) generated from deforming from FBCT to ABCT and TBCT was analyzed to quantify lung motion and deformation. The DVF is a single map aggregating the individual vectors and specifies the coordinate transformation between the two datasets. For data conversion and analysis, MATLAB was used. The DVFs belonging to the lung were resolved into 3 components [DVFRL (right-left), DVFAP (anterior-posterior), and DVFSI (superior-inferior)]. To elucidate the deformation characteristics of each breathing maneuver, boxplots of the lung deformation magnitudes were derived for each patient along each cardinal axis. The directionalities of the deformations are as follows: left, anterior, and inferior are positive, whereas right, posterior, and superior are negative.