Optically guided patient positioning techniques.
Optical tracking determines an object's position by measuring light either emitted or reflected from the object. The hallmark of optical tracking systems is their high spatial resolution and measurement in real time; such systems can resolve the position of a point source within a fraction of a millimeter and report at a rate of 10 Hz or faster. Several systems have been developed for radiation therapy, all of which track infrared markers attached to the patient's external surface. The positions of the optical markers relative to the target volume, together with the desired marker positions relative to treatment isocenter, are determined during computed tomography simulation. In the treatment room, the real marker positions are measured relative to isocenter; rigid-body mathematics then determine marker displacements from their desired positions and hence target displacement from isocenter. Real-time feedback allows one to correct the patient's position. The first systems were used for intracranial stereotaxis radiotherapy; rigid arrays of optical markers were attached to the patient via a biteplate linkage. Subsequent systems for extracranial radiotherapy tracked external markers to determine patient position and/or gate the radiation beam based on patient motion. Lastly, optical tracking has been integrated with ultrasound or stereoscopic x-ray imaging to determine the position of internal anatomy targets relative to isocenter.
Meeks
Sanford L
SL
Department of Radiation Oncology, M.D. Anderson Cancer Center Orlando, FL 32806, USA. smeeks@orhs.org
Tomé
Wolfgang A
WA
Willoughby
Tywla R
TR
Kupelian
Patrick A
PA
Wagner
Thomas H
TH
Buatti
John M
JM
Bova
Francis J
FJ
D006801:Humans; D008433:Mathematics; D009369:Neoplasms / Q000532:radiotherapy*; D055095:Optics and Photonics / Q000295:instrumentation*; D011187:Posture; D015641:Radiography, Interventional; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D011881:Radiotherapy, Computer-Assisted / Q000295:instrumentation*; D013238:Stereotaxic Techniques; D014057:Tomography, X-Ray Computed; D018084:Ultrasonography, Interventional