The stability of mechanical calibration for a kV cone beam computed tomography system integrated with linear accelerator

Michael B. Sharpe, Douglas J. Moseley, Thomas G. Purdie, Mohammad Islam, Jeffrey H. Siewerdsen, David A. Jaffray

Research output: Contribution to journalArticlepeer-review

124 Scopus citations


The geometric accuracy and precision of an image-guided treatment system were assessed. Image guidance is performed using an x-ray volume imaging (XVI) system integrated with a linear accelerator and treatment planning system. Using an amorphous silicon detector and x-ray tube, volumetric computed tomography images are reconstructed from kilovoltage radiographs by filtered backprojection. Image fusion and assessment of geometric targeting are supported by the treatment planning system. To assess the limiting accuracy and precision of image-guided treatment delivery, a rigid spherical target embedded in an opaque phantom was subjected to 21 treatment sessions over a three-month period. For each session, a volumetric data set was acquired and loaded directly into an active treatment planning session. Image fusion was used to ascertain the couch correction required to position the target at the prescribed iso-center. Corrections were validated independently using megavoltage electronic portal imaging to record the target position with respect to symmetric treatment beam apertures. An initial calibration cycle followed by repeated image-guidance sessions demonstrated the XVI system could be used to relocate an unambiguous object to within less than 1 mm of the prescribed location. Treatment could then proceed within the mechanical accuracy and precision of the delivery system. The calibration procedure maintained excellent spatial resolution and delivery precision over the duration of this study, while the linear accelerator was in routine clinical use. Based on these results, the mechanical accuracy and precision of the system are ideal for supporting high-precision localization and treatment of soft-tissue targets.

Original languageEnglish (US)
Pages (from-to)136-144
Number of pages9
JournalMedical physics
Issue number1
StatePublished - Jan 2006
Externally publishedYes


  • Computed tomography
  • Cone-beam
  • Image-guidance
  • Radiation therapy

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


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