Feasibility Study of Robotics-based Patient Immobilization Device for Real-time Motion Compensation

Hyekyun Chung; Seungryong Cho; Byungchul Cho

doi:10.14316/pmp.2016.27.3.117

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Chung, Cho, and Cho: Feasibility Study of Robotics-based Patient Immobilization Device for Real-time Motion Compensation

Original Article

Progress in Medical Physics 2016;27(3):117-124.

Published online: 19 September 2016

DOI: https://doi.org/10.14316/pmp.2016.27.3.117

Feasibility Study of Robotics-based Patient Immobilization Device for Real-time Motion Compensation

Hyekyun Chung^∗,^†, Seungryong Cho^∗, Byungchul Cho^†,

^∗Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology, Daejeon Korea

^†Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

Correspondence: Byungchul Cho (cho.byungchul@gmail.com, bcho@amc.seoul.kr) Tel: 82-2-3010-4437, Fax: 82-2-3010-6950

Received 31 August 201619 September 2016 Accepted 20 September 2016

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Intrafractional motion of patients, such as respiratory motion during radiation treatment, is an important issue in image-guided radiotherapy. The accuracy of the radiation treatment decreases as the motion range increases. We developed a control system for a robotic patient immobilization system that enables to reduce the range of tumor motion by compensating the tumor motion. Fusion technology, combining robotics and mechatronics, was developed and applied in this study. First, a small-sized prototype was established for use with an industrial miniature robot. The patient immobilization system consisted of an optical tracking system, a robotic couch, a robot controller, and a control program for managing the system components. A multi speed and position control mechanism with three degrees of freedom was designed. The parameters for operating the control system, such as the coordinate transformation parameters and calibration parameters, were measured and evaluated for a prototype device. After developing the control system using the prototype device, a feasibility test on a full-scale patient immobilization system was performed, using a large industrial robot and couch. The performances of both the prototype device and the realistic device were evaluated using a respiratory motion phantom, for several patterns of respiratory motion. For all patterns of motion, the root mean squared error of the corresponding detected motion trajectories were reduced by more than 40%. The proposed system improves the accuracy of the radiation dose delivered to the target and reduces the unwanted irradiation of normal tissue.

Keywords: Robotics, Mechatronics, Patient immobilizer, Respiratory motion, SBRT

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Fig. 1

(a) Prototype of the patient immobilization system consisting of a robotic arm, a couch, a robot controller, an optical tracker, and a camera. (b) Schematic of the motion compensation system.

Fig. 2

Real-scale patient immobilization system for evaluating the motion compensation performance with respect to the respiration-associated motion.

Fig. 3

(a) Screenshot of the in-house motion detection and control program running on the system control PC. (b) Algorithm flow chart of the developed motion compensation system. P_c(t_i) and P_p(t_i) are 3D positions of the marker on the couch and the marker on the motion phantom at time t_i. R is the coordinate transformation matrix, from the optical tracker system of coordinates to the robot system of coordinates.

Fig. 4

3D position data measured by the optical tracker, for markers attached to the motion phantom and couch. The typical-slow respiratory motion pattern was considered here. (a) Results obtained for the prototype system. (b) Results obtained for the real-scale system. The motion compensation was initiated about halfway into the measurement period.

Table 1.

Mechanical specifications and limitations of the two robot manipulators used in this study.

			HA006A-04	HS160L
Payload			6 kg	160 kg
Max. reach			1,425 mm	3,036 mm
Degree of freedom			6 Axes	6 Axes
Max. motion range	S	Swivel	±172^o	±180^o
	H	For/Backward	＋180^o∼−78^o	＋180^o∼−65^o
	V	Up/Downward	＋180^o∼−82^o	＋230^o∼−135^o
	R2	Rotation 2	±180^o	±360^o
	B	Bending	±135^o	±130^o
	R1	Rotation 1	±360^o	±360^o
Max. speed	S	Swivel	230^o/s	95^o/s
	H	For/Backward	230^o/s	95^o/s
	V	Up/Downward	230^o/s	95^o/s
	R2	Rotation 2	430^o/s	150^o/s
	B	Bending	430^o/s	145^o/s
	R1	Rotation 1	640^o/s	220^o/s
	R2	Rotation 2	1.2 kgf.m	105 kgf.m
	B	Bending	1.0 kgf.m	105 kgf.m
	R1	Rotation 1	0.6 kgf.m	50 kgf.m
Repeatability			±0.04 mm	±0.15 mm
Approximate weight			150 kg	985 kg
Max. rated power			4.4 kVA	8 kVA
Controller model			Hi5a	Hi5a

Table 2.

Calibration errors between the input positions to the robot and the measured positions.

Point number	Error (mm)
1	0.07
2	0.10
3	0.08
4	0.07
5	0.10
6	0.08
7	0.10
8	0.06
Average	0.08

Table 3.

Input position data provided to the robot and the measured positions in the robotic coordinate system.

Point number		Robot input positions		Converted measurement positions
Point number	X (mm)	Y (mm)	Z (mm)	X (mm)	Y (mm)	Z (mm)
1	310	0	870	310.10	0.12	870.08
2	410	0	870	410.07	−0.03	869.85
3	360	200	870	359.96	199.61	869.95
4	410	200	970	409.94	199.66	969.96
5	310	−200	870	310.09	−199.62	870.08
6	410	−200	870	409.92	−199.82	869.92
7	410	−200	970	410.05	−199.85	970.04
8	410	0	970	409.87	−0.08	970.12

Table 4.

3D RMSEs, before and after applying the motion compensation, and the reduction ratios of the 3D RMSEs for seven motion patterns measured using the small-scale prototype device.

Motion pattern	3D RMSE	3D RMSE	Error reduction
Motion pattern	3D RMSE	(Compensated)	ratio (%)
Typical	4.01 mm	1.52 mm	62.2
Typical-fast	4.48 mm	2.30 mm	48.7
Typical-slow	4.70 mm	0.51 mm	89.1
Irregular	3.06 mm	1.35 mm	55.9
Drift-artifact	3.27 mm	1.46 mm	55.4
Cardiac-artifact	2.25 mm	1.24 mm	44.9
Jitter-artifact	3.26 mm	1.50 mm	54.1

Table 5.

3D RMSEs, before and after applying the motion compensation, and the reduction ratios of the 3D RMSEs for three motion patterns measured using the real-scale device.

Motion pattern	3D RMSE	3D RMSE (Compensated)	Error reduction ratio (%)
Typical	5.63 mm	2.95 mm	47.7
Typical-slow	6.54 mm	1.77 mm	72.9
Irregular	3.94 mm	2.35 mm	40.4

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