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. 2017 Nov;90(1079):20170266.
doi: 10.1259/bjr.20170266. Epub 2017 Oct 9.

A robotic C-arm cone beam CT system for image-guided proton therapy: design and performance

Chiaho Hua  1 , Weiguang Yao  1 , Takao Kidani  2 , Kazuo Tomida  2 , Saori Ozawa  2 , Takenori Nishimura  2 , Tatsuya Fujisawa  2 , Ryousuke Shinagawa  2 , Thomas E Merchant  1
Affiliations

A robotic C-arm cone beam CT system for image-guided proton therapy: design and performance

Chiaho Hua et al. Br J Radiol. 2017 Nov.

Abstract

Objective: A ceiling-mounted robotic C-arm cone beam CT (CBCT) system was developed for use with a 190° proton gantry system and a 6-degree-of-freedom robotic patient positioner. We report on the mechanical design, system accuracy, image quality, image guidance accuracy, imaging dose, workflow, safety and collision-avoidance.

Methods: The robotic CBCT system couples a rotating C-ring to the C-arm concentrically with a kV X-ray tube and a flat-panel imager mounted to the C-ring. CBCT images are acquired with flex correction and maximally 360° rotation for a 53 cm field of view. The system was designed for clinical use with three imaging locations. Anthropomorphic phantoms were imaged to evaluate the image guidance accuracy.

Results: The position accuracy and repeatability of the robotic C-arm was high (<0.5 mm), as measured with a high-accuracy laser tracker. The isocentric accuracy of the C-ring rotation was within 0.7 mm. The coincidence of CBCT imaging and radiation isocentre was better than 1 mm. The average image guidance accuracy was within 1 mm and 1° for the anthropomorphic phantoms tested. Daily volumetric imaging for proton patient positioning was specified for routine clinical practice.

Conclusion: Our novel gantry-independent robotic CBCT system provides high-accuracy volumetric image guidance for proton therapy. Advances in knowledge: Ceiling-mounted robotic CBCT provides a viable option than CT on-rails for partial gantry and fixed-beam proton systems with the added advantage of acquiring images at the treatment isocentre.

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Figures

Figure 1.
Figure 1.
Photographs on the top row show the three imaging positions with the C-arm in place and the head phantom experimental setup. Positions 0 and 1 are 27 cm apart. Lower left photograph illustrates the major components of the CBCT system. Serial photographs with arrows in the lower right figure illustrate the deployment of the robotic C-arm from one of the four parking positions above the nozzle to the imaging position 2. C-arm retraction follows the same path in reverse. CBCT, cone beam CT.
Figure 2.
Figure 2.
Photographs showing the three phantom locations on the table top that were used to test image guidance accuracy at imaging position 2. Location B was at the centre of the 100-cm long calibrated volume of the PPS. Location A and location C were 50 cm superior and 30 cm inferior to location B, respectively. This was designed to test if residual errors after PPS setup correction are larger for objects placed away from the centre of the calibrated volume, which is 100 cm from the wrist flange of the robot.
Figure 3.
Figure 3.
Example CBCT images of the head and pelvis (window width/level = 2000/–200 HU). CBCT, cone beam CT.
See this image and copyright information in PMC

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