title: Evaluation of residual patient position variation for spinal radiosurgery using the Novalis image guided system.
abstract: OBJECTIVE
  The Novalis system has been demonstrated to achieve accurate target localization on anthropomorphic phantoms. However, other factors, such as rotational deviation, patient intrafraction motion, and image fusion uncertainty due to patient body deformation, could contribute additional position uncertainty for actual patients. This study evaluates such position uncertainty for spinal radiosurgery patients.
  
  
  METHODS
  Fifty-two consecutive spinal radiosurgery patients were included in the study. Rotational deviation was evaluated from 6-deg of freedom (6D) fusion results for all patients. The combined uncertainty of patient motion and image fusion was determined from fusion results of additional kV x-ray images acquired before, during, and after treatment for 25 of the 52 patients. The uncertainty of image fusion was also evaluated by performing 6D fusion ten different times with various regions of interest in the images selected for fusion. This was performed for two patients with L3 and T2 lesions, respectively, for comparison.
  
  
  RESULTS
  The mean rotational deviation was 0.7 +/- 1.8, 0.7 +/- 1.5, and 0.7 +/- 1.6 deg along the yaw, roll, and pitch directions, respectively. The combined uncertainty from patient motion and image fusion was 0.1 +/- 0.9, 0.2 +/- 1.2, and 0.2 +/- 1.0 mm in the anteroposterior (AP), longitudinal, and lateral directions, respectively. The uncertainty (standard deviation) due to image fusion was less than 0.28 mm in any direction for the L3 lesion and 0.8 mm in the AP direction for the T2 lesion.
  
  
  CONCLUSIONS
  Overall position uncertainty for spinal radiosurgery patients has been evaluated. Rotational deviation and patient motion were the main factors contributed to position uncertainty for actual patient treatment.
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, Michigan 48202, USA. jjin1@hfhs.org
authors.forename: Jian-Yue
authors.initials: JY
authors.lastname: Jin
authors.forename: Samuel
authors.initials: S
authors.lastname: Ryu
authors.forename: Jack
authors.initials: J
authors.lastname: Rock
authors.forename: Kathleen
authors.initials: K
authors.lastname: Faber
authors.forename: Qing
authors.initials: Q
authors.lastname: Chen
authors.forename: Munther
authors.initials: M
authors.lastname: Ajlouni
authors.forename: Benjamin
authors.initials: B
authors.lastname: Movsas
mesh_terms: D019583:Dose Fractionation, Radiation; D006801:Humans; D009068:Movement; D016634:Radiosurgery / Q000379:methods*; D012189:Retrospective Studies; D012399:Rotation; D013131:Spine / Q000601:surgery*; D025321:Surgery, Computer-Assisted / Q000379:methods*; D035501:Uncertainty