A machine vision system with CCD cameras for patient positioning in radiotherapy: a preliminary report.
OBJECTIVE
To determine positioning accuracy of a machine vision system in radiotherapy.


METHODS
The machine vision system was composed of 640 x 480 pixel CCD cameras and computerized control systems. For image acquisition, the phantom was set up for the reference position and a single CCD camera was positioned 1.5 m from the isocenter. The image data of the fiducial marker with 1.5 mm lead pellet on the lateral surface of the phantom was captured onto the CCD, and then the position of the marker was accurately calculated. The phantom was moved 0.25, 0.50, 0.75, 1.00, 2.00, and 3.00 mm from the reference position, using a micrometer head. The position of the fiducial marker was analyzed using a kilo-voltage fluoroscopic imaging system and a machine vision system.


RESULTS
Using fluoroscopic images, the discrepancy between the actual movement of the phantom by micrometer heads and the measurement was found to be 0.12 +/- 0.05 mm (mean +/- standard deviation). In contrast, the detection of the movement by the machine vision system coincided with the discrepancy of 0.0067 +/- 0.0048 mm.


CONCLUSIONS
This study suggests that the machine vision system can be used to measure small changes in patient position with a resolution of less than 0.1 mm.
Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University.
Tadamasa
T
Yoshitake
Katsumasa
K
Nakamura
Yoshiyuki
Y
Shioyama
Tomonari
T
Sasaki
Saiji
S
Ohga
Toshihiro
T
Yamaguchi
Takashi
T
Toba
Shigeo
S
Anai
Hiromi
H
Terashima
Hiroshi
H
Honda
D006257:Head; D006801:Humans; D019047:Phantoms, Imaging; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods; D013813:Therapy, Computer-Assisted