A positioning QA procedure for 2D/2D (kV/MV) and 3D/3D (CT/CBCT) image matching for radiotherapy patient setup.
Abstract
A positioning QA procedure for Varian's 2D/2D (kV/MV) and 3D/3D (planCT/CBCT) matching
was developed. The procedure was to check: (1) the coincidence of on-board imager
(OBI), portal imager (PI), and cone beam CT (CBCT)'s isocenters (digital graticules)
to a linac's isocenter (to a pre-specified accuracy); (2) that the positioning difference
detected by 2D/2D (kV/MV) and 3D/3D(planCT/CBCT) matching can be reliably transferred
to couch motion. A cube phantom with a 2 mm metal ball (bb) at the center was used.
The bb was used to define the isocenter. Two additional bbs were placed on two phantom
surfaces in order to define a spatial location of 1.5 cm anterior, 1.5 cm inferior,
and 1.5 cm right from the isocenter. An axial scan of the phantom was acquired from
a multislice CT simulator. The phantom was set at the linac's isocenter (lasers);
either AP MV/R Lat kV images or CBCT images were taken for 2D/2D or 3D/3D matching,
respectively. For 2D/2D, the accuracy of each device's isocenter was obtained by checking
the distance between the central bb and the digital graticule. Then the central bb
in orthogonal DRRs was manually moved to overlay to the off-axis bbs in kV/MV images.
For 3D/3D, CBCT was first matched to planCT to check the isocenter difference between
the two CTs. Manual shifts were then made by moving CBCT such that the point defined
by the two off-axis bbs overlay to the central bb in planCT. (PlanCT can not be moved
in the current version of OBI1.4.) The manual shifts were then applied to remotely
move the couch. The room laser was used to check the accuracy of the couch movement.
For Trilogy (or Ix-21) linacs, the coincidence of imager and linac's isocenter was
better than 1 mm (or 1.5 mm). The couch shift accuracy was better than 2 mm.
Type
Journal articleSubject
HumansImaging, Three-Dimensional
Radiotherapy Planning, Computer-Assisted
Lasers
Phantoms, Imaging
Computer Simulation
Image Processing, Computer-Assisted
Cone-Beam Computed Tomography
Patient Positioning
Permalink
https://hdl.handle.net/10161/19392Published Version (Please cite this version)
10.1120/jacmp.v10i4.2954Publication Info
Guan, Huaiqun; Hammoud, Rabih; & Yin, Fang-Fang (2009). A positioning QA procedure for 2D/2D (kV/MV) and 3D/3D (CT/CBCT) image matching for
radiotherapy patient setup. Journal of applied clinical medical physics, 10(4). pp. 2954. 10.1120/jacmp.v10i4.2954. Retrieved from https://hdl.handle.net/10161/19392.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Show full item recordScholars@Duke
Fang-Fang Yin
Gustavo S. Montana Distinguished Professor of Radiation Oncology
Stereotactic radiosurgery, Stereotactic body radiation therapy, treatment planning
optimization, knowledge guided radiation therapy, intensity-modulated radiation therapy,
image-guided radiation therapy, oncological imaging and informatics

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