SU-E-U-08: Presentation of a New Intrafractional Prostate Monitoring Method with Ultrasound Image Guidance During Radiotherapy Treatment

Abstract

Purpose: Clinical presentation of a new intrafractional ultrasound image guidance (USIG) prostate monitoring/tracking method. Methods: Clarity ultrasound system has recently released a new feature to monitor/track intrafractional prostate motion using a trans-perineal image acquisition position. After initial localization and image guidance correction, the ultrasound probe remains fixed in the sagittal-plane, trans-perineal imaging position via a couch-mounted arm-support system. The software then enters a live monitoring mode, where the scanning ultrasound probe continuously acquires fanned sagittal images for tracking of during-treatment prostate position. Compared to other tracking technologies (e.g. RF implanted beacon tracking, or real-time fluoro monitoring), the ultrasound system has the unique advantages of live 3D image display, without invasive procedure or imaging radiation dose. We present our initial experience using this monitoring feature for 8 patients and 218 treatment sessions. Results: The monitoring software functioned as expected during treatment with consistent reporting of prostate deviation from isocenter location, and notification of instances where positional error exceeded our tolerance of 3 mm for 5 second. Comparisons of prostate tracking data streams obtained from Clarity USIG with data streams obtained in our clinic from Calypso RF tracking of a similar patient population show similarity of recorded motion information for both methods. Average during-treatment prostate motion for both tracking methods was on the order of 1–2 mm in 3 cardinal directions, with roughly 5% of instances where motion exceeded 3 mm, 5 second tolerance level. When Monitoring reported that tolerance was exceeded we confirmed this by performing redundant, static imaging Alignment, with confirmation that target position had, indeed, changed as reported. Conclusion: The newly released trans-perineal ultrasound Monitoring approach was confirmed to function well clinically, and to report accurate intrafractional monitoring data. Acquired motion streams were consistent with our Calypso monitoring experience obtained on a similar patient population in our own clinic.