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Evaluation of a Time-Resolved Ultrasound System for Prostate Tracking Using a Novel, Multimodality KV-Ultrasound Dynamic Phantom

D Ionascu

D Ionascu1*, R Sandhu1, N Tyagi2, D Yan1, (1) William Beaumont Hospital, Royal Oak, MI, (2) Memorial Sloan-Kettering Cancer Center, New York, NY

SU-E-U-12 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Development of novel multi-modality dynamic phantom and technique designed to evaluate the accuracy of a time-resolved ultrasound device (4D-US), used for localization and motion monitoring of the prostate during hypo-fractionated radiotherapy.

Methods: A modified dynamic thorax phantom was designed using a spherical, ultrasound compatible, prostate phantom. The phantom end of the 90° arm was submerged in a water filled plastic container. A coupling cavity between the ultrasound probe and the container wall was developed. The motion of the dynamic phantom was pre-programmed to test the 4D-US capability to accurately reproduce the input trajectories. The Clarity 4D-US presents two types of scanning modes: a volumetric mode for reference volume acquisition; and an auto-scan mode for real-time monitoring of the target. Using the monitoring mode, the amplitude detected was compared with the input amplitude in order to determine speed-dependent, amplitude under-sampling effects. Using the volumetric mode, the system time lag and manifestation of volumetric distortion due to increase in the phantom speed was determined. The difference between the largest dimension of the detected volume and the reference volume diameter divided by the phantom speed, determined the time lag of the 4D-US system.

Results: In monitoring mode, the system was capable to accurately reproduce a Sup-Inf sinusoidal phantom trajectory with 2cm amplitude and a period of ~15s ( speed~2.7mm/s), showing an increased amplitude under-sampling effect as the motion period was gradually decreased to 4s. In volumetric acquisition mode, the system average time lag, calculated based on the speed induced volumetric distortion, was found to be 0.31s.

Conclusion: We have developed a novel kV-US dynamic phantom to establish the 4D-US scanning system parameters in order to accurately detect prostate motion. The novel phantom can be used in a multi-modality concomitant imaging scheme allowing a direct, on-line comparison of different real-time tracking modalities.

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