title: Distance-to-agreement investigation of Tomotherapy's bony anatomy-based autoregistration and planning target volume contour-based optimization.
abstract: OBJECTIVE
  To compare Tomotherapy's megavoltage computed tomography bony anatomy autoregistration with the best achievable registration, assuming no deformation and perfect knowledge of planning target volume (PTV) location.
  
  
  METHODS
  Distance-to-agreement (DTA) of the PTV was determined by applying a rigid-body shift to the PTV region of interest of the prostate from its reference position, assuming no deformations. Planning target volume region of interest of the prostate was extracted from the patient archives. The reference position was set by the 6 degrees of freedom (dof)-x, y, z, roll, pitch, and yaw-optimization results from the previous study at this institution. The DTA and the compensating parameters were calculated by the shift of the PTV from the reference 6-dof to the 4-dof-x, y, z, and roll-optimization. In this study, the effectiveness of Tomotherapy's 4-dof bony anatomy-based autoregistration was compared with the idealized 4-dof PTV contour-based optimization.
  
  
  RESULTS
  The maximum DTA (maxDTA) of the bony anatomy-based autoregistration was 3.2 ± 1.9 mm, with the maximum value of 8.0 mm. The maxDTA of the contour-based optimization was 1.8 ± 1.3 mm, with the maximum value of 5.7 mm. Comparison of Pearson correlation of the compensating parameters between the 2 4-dof optimization algorithms shows that there is a small but statistically significant correlation in y and z (0.236 and 0.300, respectively), whereas there is very weak correlation in x and roll (0.062 and 0.025, respectively).
  
  
  CONCLUSIONS
  We find that there is an average improvement of approximately 1 mm in terms of maxDTA on the PTV going from 4-dof bony anatomy-based autoregistration to the 4-dof contour-based optimization. Pearson correlation analysis of the 2 4-dof optimizations suggests that uncertainties due to deformation and inadequate resolution account for much of the compensating parameters, but pitch variation also makes a statistically significant contribution.
authors: Division of Radiation Oncology, City of Hope National Medical Center, Duarte, California, USA. ssuh@coh.org
authors: Steve
authors: S
authors: Suh
authors: Timothy E
authors: TE
authors: Schultheiss
mesh_terms: D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000592:standards*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D050397:Radiotherapy, Intensity-Modulated / Q000295:instrumentation / Q000592:standards*; D036542:Tomography, Spiral Computed / Q000295:instrumentation / Q000379:methods / Q000592:standards*