First evaluation of the feasibility of MLC tracking using ultrasound motion estimation.
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Date
2016-08-01Author
Fast, MF
O'Shea, TP
Nill, S
Oelfke, U
Harris, EJ
Type
Journal Article
Metadata
Show full item recordAbstract
PURPOSE: To quantify the performance of the Clarity ultrasound (US) imaging system (Elekta AB, Stockholm, Sweden) for real-time dynamic multileaf collimator (MLC) tracking. METHODS: The Clarity calibration and quality assurance phantom was mounted on a motion platform moving with a periodic sine wave trajectory. The detected position of a 30 mm hypoechogenic sphere within the phantom was continuously reported via Clarity's real-time streaming interface to an in-house tracking and delivery software and subsequently used to adapt the MLC aperture. A portal imager measured MV treatment field/MLC apertures and motion platform positions throughout each experiment to independently quantify system latency and geometric error. Based on the measured range of latency values, a prostate stereotactic body radiation therapy (SBRT) delivery was performed with three realistic motion trajectories. The dosimetric impact of system latency on MLC tracking was directly measured using a 3D dosimeter mounted on the motion platform. RESULTS: For 2D US imaging, the overall system latency, including all delay times from the imaging and delivery chain, ranged from 392 to 424 ms depending on the lateral sector size. For 3D US imaging, the latency ranged from 566 to 1031 ms depending on the elevational sweep. The latency-corrected geometric root-mean squared error was below 0.75 mm (2D US) and below 1.75 mm (3D US). For the prostate SBRT delivery, the impact of a range of system latencies (400-1000 ms) on the MLC tracking performance was minimal in terms of gamma failure rate. CONCLUSIONS: Real-time MLC tracking based on a noninvasive US input is technologically feasible. Current system latencies are higher than those for x-ray imaging systems, but US can provide full volumetric image data and the impact of system latency was measured to be small for a prostate SBRT case when using a US-like motion input.
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http://dx.doi.org/10.1118/1.4955440Collections
Subject
Humans
Prostatic Neoplasms
Ultrasonography
Radiosurgery
Radiotherapy Dosage
Artifacts
Calibration
Feasibility Studies
Equipment Design
Radiometry
Phantoms, Imaging
Motion
Time Factors
Software
Male
Fiducial Markers
Radiotherapy, Image-Guided
Research team
Imaging for Radiotherapy Adaptation
Radiotherapy Physics Modelling
Language
eng
Date accepted
2016-06-25
License start date
2016-08
Citation
Medical physics, 2016, 43 (8), pp. 4628 - ?
Publisher
WILEY