title: Patterns of patient movement during frameless image-guided radiosurgery.
abstract: OBJECTIVE
  Image-guided radiosurgery aligns the treatment beam to the target site by using a radiographic imaging system to locate anatomic landmarks associated with the treatment target. Because the procedure is performed without a rigid frame, the precision of dose alignment can be affected by patient movement. Movement is limited by noninvasive restraints and compensated by remeasuring the target position at short intervals throughout treatment and then realigning the beam. Frameless image-guided radiosurgery has been used at our institution to treat 250 cranial, 23 spinal, 9 lung, and 3 pancreas cases involving malignant and benign tumors as well as vascular malformations. We have analyzed the target position records for all of these cases to assess the frequency, magnitude, and case-by-case patterns of patient movement.
  
  
  METHODS
  The position of the treatment site during image-guided radiosurgery was measured at approximately 1-2-min intervals, on average, using orthogonal amorphous silicon X-ray cameras and an image registration process that determined all six degrees of freedom in the target's position. The change in position from one measurement to the next was indicative of patient movement.
  
  
  RESULTS
  The treatment site position along each axis of translation was observed to vary by an average of 0.45 mm for the cranium, 0.53 mm for the cervical spine, 0.53 mm for the lumbar and thoracic spine, 1.06 mm for the lung, and 1.50 mm for the pancreas. Half of all cranial cases showed systematic drifting of the target away from the initial setup position.
  
  
  CONCLUSIONS
  Using noninvasive restraints and supports, short-term movement of the head and spine during image-guided radiosurgery was limited to a radius of 0.8 mm, which satisfies the prevailing standard for radiosurgical dose alignment precision, but maintaining this margin of error throughout a treatment fraction requires regular monitoring of the target site's position.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA. martin@reyes.stanford.edu
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Murphy
authors.forename: Steven D
authors.initials: SD
authors.lastname: Chang
authors.forename: Iris C
authors.initials: IC
authors.lastname: Gibbs
authors.forename: Quynh-Thu
authors.initials: QT
authors.lastname: Le
authors.forename: Jenny
authors.initials: J
authors.lastname: Hai
authors.forename: Daniel
authors.initials: D
authors.lastname: Kim
authors.forename: David P
authors.initials: DP
authors.lastname: Martin
authors.forename: John R
authors.initials: JR
authors.lastname: Adler
mesh_terms: D001932:Brain Neoplasms / Q000601:surgery; D002574:Cervical Vertebrae; D004867:Equipment Design; D019416:Head Movements; D006801:Humans; D007103:Immobilization; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery; D008175:Lung Neoplasms / Q000601:surgery; D009068:Movement; D010190:Pancreatic Neoplasms / Q000601:surgery; D010315:Particle Accelerators; D011187:Posture; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012119:Respiration; D012149:Restraint, Physical / Q000295:instrumentation*; D012371:Robotics; D013125:Spinal Neoplasms / Q000601:surgery; D025321:Surgery, Computer-Assisted