Abstract

PURPOSE
To develop and evaluate accurate and objective on-line patient setup based on a novel semiautomatic technique in which three-dimensional marker trajectories were estimated from two-dimensional cone-beam computed tomography (CBCT) projections.
METHODS AND MATERIALS
Seven treatment courses of stereotactic body radiotherapy for liver tumors were delivered in 21 fractions in total to 6 patients by a linear accelerator. Each patient had two to three gold markers implanted close to the tumors. Before treatment, a CBCT scan with approximately 675 two-dimensional projections was acquired during a full gantry rotation. The marker positions were segmented in each projection. From this, the three-dimensional marker trajectories were estimated using a probability based method. The required couch shifts for patient setup were calculated from the mean marker positions along the trajectories. A motion phantom moving with known tumor trajectories was used to examine the accuracy of the method. Trajectory-based setup was retrospectively used off-line for the first five treatment courses (15 fractions) and on-line for the last two treatment courses (6 fractions). Automatic marker segmentation was compared with manual segmentation. The trajectory-based setup was compared with setup based on conventional CBCT guidance on the markers (first 15 fractions).
RESULTS
Phantom measurements showed that trajectory-based estimation of the mean marker position was accurate within 0.3 mm. The on-line trajectory-based patient setup was performed within approximately 5 minutes. The automatic marker segmentation agreed with manual segmentation within 0.36 ± 0.50 pixels (mean ± SD; pixel size, 0.26 mm in isocenter). The accuracy of conventional volumetric CBCT guidance was compromised by motion smearing (≤21 mm) that induced an absolute three-dimensional setup error of 1.6 ± 0.9 mm (maximum, 3.2) relative to trajectory-based setup.
CONCLUSIONS
The first on-line clinical use of trajectory estimation from CBCT projections for precise setup in stereotactic body radiotherapy was demonstrated. Uncertainty in the conventional CBCT-based setup procedure was eliminated with the new method.

Links

Publisher Full Text

Authors

Worm ES, Høyer M, Fledelius W, Nielsen JE, Larsen LP, Poulsen PR

Institution

Department of Oncology, Aarhus University Hospital, Aarhus, Denmark. esbeworm@rm.dk

Source

International journal of radiation oncology, biology, physics 83:1 2012 May 1 pg e145-51

MeSH

Bile Duct Neoplasms
Bile Ducts, Intrahepatic
Breast Neoplasms
Cholangiocarcinoma
Colorectal Neoplasms
Cone-Beam Computed Tomography
Dose Fractionation
Female
Fiducial Markers
Gold
Humans
Imaging, Three-Dimensional
Liver Neoplasms
Male
Middle Aged
Movement
Phantoms, Imaging
Radiosurgery
Radiotherapy Planning, Computer-Assisted
Respiration

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22516384