Analysis of reproducibility and field size using gating system in 4D computed tomography

Abstract

Differences exist in each reproduced image since the scan types are different for the images acquired by axial, helical and cine scanning in accordance with computed tomography. This study was aimed to examine reproducibility using drive phantom in order to identify how accurately each scan type of computed tomography describes the movement of table. This study evaluated gating-based four-dimensional (4D)-computed tomography treatment planning by a comparison with common three-dimensional (3D)-computed tomography treatment planning and examining the change in treatment field size. The study used a self-manufactured drive phantom and a respiration gated drive motor to reproduce movements in the upward/downward direction and in the top/bottom direction. Following this, breathing-induced movement was applied to the self-manufactured model phantom and images were taken by Axial, Helical and cine scanning according to each computed tomography scan type. Reproducibility of the model and volume reflecting the movement was compared and analysed for accuracy using the RPT equipment. The scanning conditions according to each computed tomography scan type were set equally as follows: tube voltage 120 kV, tube current 200 mA, slice thickness and gap between slices 2·5 mm, inter scan delay 1·3, and pitch 1. The 3D-computed tomography and gating-based 4D-computed tomography images were obtained from patients who had undergone radiation treatment for chest and abdomen tumours in the oncology department. From the study results, the total volume of the marker was 88·2 cm³ and when a 3 cm shift in the top/bottom direction and a 0·3 cm shift in the upward/downward direction were taken into account, the total volume was 184·3 cm³. Total volumes by different computed tomography scan types were 135 cm³ for axial scanning, 164·9 cm³ for helical scanning and 181·7 cm³ for cine scanning. Regarding the presentation of reproducibility for movement, the cine scan type depicted the marker as closely as possible. The treatment field size was smaller in volume in the case of 4D-computed tomography treatment planning.

Keywords:

• 4D-CT
• Scan type
• Reproducibility
• Field size

Acknowledgement

This work was supported by the 2013 Inje University research grant.