Intrafractional Prostate Motion Management with the Clarity Autoscan System

Intrafractional motion of the prostate can be significant, and its management is of particular importance for hypofractionated regimes and stereotactic ablative radiotherapy (SABR). In this paper, we describe the Clarity Autoscan with Monitoring system and its use of non-invasive soft tissue imaging to monitor prostate motion during the course of radiotherapy. The system uses a 4D autoscan ultrasound probe to image the prostate through the acoustic window of the perineum. We discuss this imaging technique, as well as the algorithms used to track the prostate during treatment. We measure the accuracy of the tracking algorithm with a motion phantom and find it to be -0.2 ± 0.2 mm, 0.2 ± 0.4 mm and -0.0 ± 0.2 mm in the A/P, L/R and S/I directions, respectively. Keywords— radiotherapy, prostate, motion management, intrafractional motion, ultrasound.