AbstractID: 6984 Title: Three-Dimensional Ultrasound Image Guided Patient Positioning Based on
Stereotactic 2D-Ultrasound Imaging
We have recently introduced a technique of patient positioning for high-precision
radiation therapy using a 3D-ultrasound (3DUS) probe. This system was extended to use
any 2D-ultrasound (2DUS) probe to acquire the 3DUS images. It consists of a method of
calibrating and registering the 2DUS image position to the room isocenter, an acquisition
of stereotactic 3DUS images with a 2DUS probe, a registration of the 3DUS image to a
previously acquired CT/MR scan, and a displacement of the target to the room isocenter.
The 2DUS probe position is tracked using a CCD camera focused on IRLEDs
attached to the probe. The probe calibration procedure determines the 2DUS image
position based on the probe tracking (stability ~0.2mm and ~0.5degrees). The 3DUS
image is acquired by placing the 2DUS probe in a rocking cradle (reproducing the fan
motion of 3DUS transducer), and by recording the 2DUS video image and its room
position. CT/MR contours of the target and adjacent structures are then overlaid on the
3DUS image to register it to the previously acquired CT/MR scan. Finally, the target is
moved to isocenter by optically tracking the patient. Accuracy of this positioning system
was measured to be on average AP=1.4mm, Lat=.6mm, Ax=0.4mm (target depth
between 3-11cm, showing a small degradation over the 3DUS probe based technique
(AP=0.2mm, Lat=.9mm, Ax=0.6mm).
A system for high-precision patient positioning has been developed and tested,
providing real-time tracking of the patient anatomy with displacement of the target along
six degrees of freedom.
Research performed in collaboration with Zmed