Prog Med Phys.  2015 Sep;26(3):143-152. 10.14316/pmp.2015.26.3.143.

Analysis on the Positional Accuracy of the Non-orthogonal Two-pair kV Imaging Systems for Real-time Tumor Tracking Using XCAT

• Jeong H
• Kim Y
• Oh O
• Lee S
• Jeon H
• Lee SW

• KMID: 2069477
• DOI: http://doi.org/10.14316/pmp.2015.26.3.143

Abstract

In this study, we aim to design the architecture of the kV imaging system for tumor tracking in the dual-head gantry system and analyze its accuracy by simulations. We established mathematical formulas and algorithms to track the tumor position with the two-pair kV imaging systems when they are in the non-orthogonal positions. The algorithms have been designed in the homogeneous coordinate framework and the position of the source and the detector coordinates are used to estimate the tumor position. 4D XCAT (4D extended cardiac-torso) software was used in the simulation to identify the influence of the angle between the two-pair kV imaging systems and the resolution of the detectors to the accuracy in the position estimation. A metal marker fiducial has been inserted in a numerical human phantom of XCAT and the kV projections were acquired at various angles and resolutions using CT projection software of the XCAT. As a result, a positional accuracy of less than about 1mm was achieved when the resolution of the detector is higher than 1.5 mm/pixel and the angle between the kV imaging systems is approximately between 90degrees and 50degrees. When the resolution is lower than 1.5 mm/pixel, the positional errors were higher than 1mm and the error fluctuation by the angles was greater. The resolution of the detector was critical in the positional accuracy for the tumor tracking and determines the range for the acceptable angle range between the kV imaging systems. Also, we found that the positional accuracy analysis method using XCAT developed in this study is highly useful and will be a invaluable tool for further refined design of the kV imaging systems for tumor tracking systems.

Keyword

Tumor tracking; Resolution; kV imaging; XCAT; Radiation therapy

MeSH Terms

Humans

Figure

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  Fig. 1. A schematic of the dual-head gantry radiation therapy system. In this system, the dual meta-voltage (MV) accelerators are mounted on the gantry for therapeutic purpose and the kilo-voltage (kV) imaging systems are used for tumor tracking. The motion range of the kV imaging system is limited in the dual-head gantry design.

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  Fig. 2. Geometry of the two-pair kV imaging system for tumor tracking.

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  Fig. 3. Simulation procedure for the tumor tracking in this study.

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  Fig. 4. Projection images of the human phantom using XCAT. The projections shown here are at each 10o interval for each kV imaging system.

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  Fig. 5. Three-dimensional distance errors of the metal marker fiducials along the x, y, z axis for the corresponding angular intervals between two kV imaging systems. (a) Estimation errors for the markers on the x-axis, (b), y-axis, and (c) z-axis.

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  Fig. 6. The metal fiducial marker at (−31.25, −62.5, 93.75) in the lung and its positional estimation in each x, y, z direction for the given angular intervals between the two kV imaging system.

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  Fig. 7. Position estimation error in each x, y, z direction and the three dimensional distance error of the fiducial at (−31.25, −62.5, 93.75) in the lung with respect to the angular intervals between the two kV imaging systems.

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  Fig. 8. Influence of the detector resolution on the positional estimation of the fiducial at (−31.25, −62.5, 93.75) in the lung for different angular intervals between the two kV imaging systems.

Reference

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