Abstract
BackgroundEmerging hypofractionated prostate radiotherapy regimens require solutions for accurate target tracking during beam delivery. The goal of this study is to evaluate the performance of the Clarity ultrasound monitoring system for prostate motion tracking.MethodsFive prostate patients underwent continuous perineum ultrasound imaging during their daily treatments. Initial absolute 3D positions of fiducials implanted in the prostate were estimated from the KV images. Fiducial positions in MV images acquired during beam delivery were compared with predicted positions based on Clarity 3D tracking. The uncertainty in the comparison results was evaluated in a phantom validation study.ResultsContinuous real-time ultrasound motion tracking was recorded in 5 patients and 167 fractions for overall of 39.7 h. Phantom validation of the proposed procedure demonstrated that predicted and observed fiducial positions agree within 1.1 mm. In patients agreement between predicted and actual fiducial positions varied between 1.3 mm and 3.3 mm. On average ultrasound tracking reduced the maximum localization error in patients by 20% on average. With the motion corrected, the duration prostate beyond 1 mm from its initial treatment position can be reduced from 37 to 22% of the total treatment time.ConclusionReal-time ultrasound tracking reduces uncertainty in prostate position due to intra-fractional motion.Trial registrationIRB Protocol #27372. Date of registration of trial: 12/17/2013.
Highlights
Emerging hypofractionated prostate radiotherapy regimens require solutions for accurate target tracking during beam delivery
The prostate contours were set as an image guidance volume with minor adaptions to better represent edges in the ultrasound images
A 3D shift vector was calculated by the Clarity® system so that the spatial relation between the treatment isocenter and the prostate center reflected in the guidance ultrasound image matched the intended spatial relation captured in the reference ultrasound image
Summary
Emerging hypofractionated prostate radiotherapy regimens require solutions for accurate target tracking during beam delivery. Hypofractionated prostate treatment is contingent on having the technical means to deliver treatments with minimum risk of mis-targeting. Various type of fiducials are usually implanted and tracked via x-ray images or electromagnetic signals, but this method is invasive and the fiducials could migrate over the time [1]. Hypofractionated prostate treatment’s wide adoption is contingent on providing solutions for accurate tracking during beam delivery when accurate targeting is most critical. Ultrasound, as a non-invasive, real-time and inexpensive modality for imaging soft tissue, can be a powerful tool for guidance of radiation treatment and minimizing the risk of mis-targeting. It is possible to use the imaging modality for both simulation and treatment with no additional imaging dose [3].
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