TY - JOUR
T1 - Implementation of a New Method for Dynamic Multileaf Collimator Tracking of Prostate Motion in Arc Radiotherapy Using a Single kV Imager
AU - Poulsen, Per Rugaard
AU - Cho, Byungchul
AU - Sawant, Amit
AU - Keall, Paul J.
N1 - Funding Information:
This work was partially supported by NCI grant P01CA116602 and Varian Medical Systems .
PY - 2010/3/1
Y1 - 2010/3/1
N2 - Purpose: To implement a method for real-time prostate motion estimation with a single kV imager during arc radiotherapy and to integrate it with dynamic multileaf collimator (DMLC) target tracking. Methods and Materials: An arc field with a circular aperture and 358° gantry rotation was delivered to a motion phantom with a fiducial marker under continuous kV X-ray imaging at 5 Hz, perpendicular to the treatment beam. A pretreatment gantry rotation of 120° in 20 sec with continuous imaging preceded the treatment. During treatment, each kV image was first used together with all previous images to estimate the three-dimensional (3D) target probability density function and then used together with this probability density function to estimate the 3D target position. The MLC aperture was then adapted to the estimated 3D target position. Tracking was performed with five patient-measured prostate trajectories that represented characteristic prostate motion patterns. Two data sets were recorded during tracking: (1) the estimated 3D target positions, for off-line comparison with the actual phantom motion; and (2) continuous portal images, for independent off-line calculation of the 2D tracking error as the positional difference between the marker and the MLC aperture center in each portal image. All experiments were also made with 1- Hz kV imaging. Results: The mean 3D root-mean-square error of the trajectory estimation was 0.6 mm. The mean root-mean-square tracking error was 0.7 mm, both parallel and perpendicular to the MLC. The accuracy degraded slightly for 1- Hz imaging. Conclusions: Single-imager DMLC prostate tracking that allows arbitrary beam modulation during arc radiotherapy was implemented. It has submillimeter accuracy for most prostate motion types.
AB - Purpose: To implement a method for real-time prostate motion estimation with a single kV imager during arc radiotherapy and to integrate it with dynamic multileaf collimator (DMLC) target tracking. Methods and Materials: An arc field with a circular aperture and 358° gantry rotation was delivered to a motion phantom with a fiducial marker under continuous kV X-ray imaging at 5 Hz, perpendicular to the treatment beam. A pretreatment gantry rotation of 120° in 20 sec with continuous imaging preceded the treatment. During treatment, each kV image was first used together with all previous images to estimate the three-dimensional (3D) target probability density function and then used together with this probability density function to estimate the 3D target position. The MLC aperture was then adapted to the estimated 3D target position. Tracking was performed with five patient-measured prostate trajectories that represented characteristic prostate motion patterns. Two data sets were recorded during tracking: (1) the estimated 3D target positions, for off-line comparison with the actual phantom motion; and (2) continuous portal images, for independent off-line calculation of the 2D tracking error as the positional difference between the marker and the MLC aperture center in each portal image. All experiments were also made with 1- Hz kV imaging. Results: The mean 3D root-mean-square error of the trajectory estimation was 0.6 mm. The mean root-mean-square tracking error was 0.7 mm, both parallel and perpendicular to the MLC. The accuracy degraded slightly for 1- Hz imaging. Conclusions: Single-imager DMLC prostate tracking that allows arbitrary beam modulation during arc radiotherapy was implemented. It has submillimeter accuracy for most prostate motion types.
KW - Image-guided radiotherapy
KW - Intrafraction motion
KW - Prostate
KW - Tumor tracking
UR - http://www.scopus.com/inward/record.url?scp=76049122954&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=76049122954&partnerID=8YFLogxK
U2 - 10.1016/j.ijrobp.2009.06.073
DO - 10.1016/j.ijrobp.2009.06.073
M3 - Article
C2 - 19910138
AN - SCOPUS:76049122954
SN - 0360-3016
VL - 76
SP - 914
EP - 923
JO - International Journal of Radiation Oncology Biology Physics
JF - International Journal of Radiation Oncology Biology Physics
IS - 3
ER -