Image guidance Cyberknife

1 image guidance

1.1 6d skull
1.2 xsight
1.3 fiducial
1.4 synchrony

image guidance

the second cyberknife system uses image guidance system. x-ray imaging cameras located on supports around patient allowing instantaneous x-ray images obtained.

6d skull

the original (and still utilized) method called 6d or skull based tracking. x-ray camera images compared library of computer generated images of patient anatomy. digitally reconstructed radiographs (or drr s) , computer algorithm determines motion corrections have given robot because of patient movement. imaging system allows cyberknife deliver radiation accuracy of 0.5mm without using mechanical clamps attached patient s skull. use of image-guided technique referred frameless stereotactic radiosurgery. method referred 6d because corrections made 3 translational motions (x, y , z) , 3 rotational motions. should noted necessary use anatomical or artificial feature orient robot deliver x-ray radiation, since tumor never sufficiently defined (if visible @ all) on x-ray camera images.

6d skull tracking


xsight

additional image guidance methods available spinal tumors , tumors located in lung. tumor located in spine, variant of image guidance called xsight-spine used. major difference here instead of taking images of skull, images of spinal processes used. whereas skull rigid , non-deforming, spinal vertebrae can move relative each other, means image warping algorithms must used correct distortion of x-ray camera images.

a recent enhancement xsight xsight-lung allows tracking of lung tumors without need implant fiducial markers.

fiducial

for soft tissue tumors, method known fiducial tracking can utilized. small metal markers (fiducials) made out of gold bio-compatibility , high density give contrast on x-ray images surgically implanted in patient. carried out interventional radiologist, or neurosurgeon. placement of fiducials critical step if fiducial tracking used. if fiducials far location of tumor, or not sufficiently spread out each other not possible accurately deliver radiation. once these markers have been placed, located on ct scan , image guidance system programmed position. when x-ray camera images taken, location of tumor relative fiducials determined, , radiation can delivered part of body. fiducial tracking not require bony anatomy position radiation. fiducials known migrate , can limit accuracy of treatment if sufficient time not allowed between implantation , treatment fiducials stabilize.

synchrony

cyberknife machine

another technology of image guidance cyberknife system can use called synchrony system or synchrony method. method uses combination of surgically placed internal fiducials (typically small gold markers, visible in x-ray imaging), , light emitting optical fibers (led markers) mounted on patient skin. led markers tracked infrared tracking camera. since tumor moving continuously, continuously image location using x-ray cameras require prohibitive amounts of radiation delivered patient s skin. synchrony system overcomes periodically taking images of internal fiducials, , computing correlation model between motion of external led markers , internal fiducials. time stamps 2 sensors (x-ray , infrared led) needed synchronize 2 data streams, hence name synchrony.

motion prediction used overcome motion latency of robot , latency of image acquisition. before treatment, computer algorithm creates correlation model represents how internal fiducial markers moving compared external markers. during treatment, system continuously infers motion of internal fiducials, , therefore tumor, based on motion of skin markers. correlation model updated @ fixed time steps during treatment. thus, synchrony tracking method makes no assumptions regularity or reproducibility of patient breathing pattern.

to function properly, system requires given correlation model there functional relationship between markers , internal fiducials. external marker placement important, , markers placed on patient abdomen motion reflect internal motion of diaphragm , lungs. method invented in 1998. first patients treated @ cleveland clinic in 2002. synchrony utilized tumors in motion while being treated, such lung tumors , pancreatic tumors.