Prostate Intra-fraction Motion Monitoring Using an Integrated Linear Accelerator kV Imaging System

Abstract

To assess the outcomes of intra-fraction prostate motion monitoring using an integrated linear accelerator based KV imaging system. Between June 2017 and December 2018, 1516 radiation treatment fractions were delivered to 35 prostate cancer patients. Each patient had 3 gold fiducial markers placed in the prostate prior to initiation of therapy and underwent IMRT treatment planning using an arc therapy technique. A commercially available integrated kV imaging system (capable of 2D and 3D cone beam imaging) with localization software was used for each treatment. Prior to initiation of treatment, a cone beam CT was obtained to align the fiducial markers and assess bladder and rectal filling. Once treatment was initiated, a planar kV image was obtained every 40 degrees in the treatment arc (approximately every 5-7 seconds) and analyzed for fiducial marker position. If the fiducial marker position varied by greater than 3.5mm, the treatment was stopped with less than 1 MU delivered. Fiducial marker position was reassessed with another kV image within 10 seconds and if the markers were still outside of the 3.5mm threshold, the patient was repositioned and treatment resumed. All treatment fractions were delivered successfully without imaging system failure. The average time for a treatment fraction was 9.4 minutes ± 2.7 minutes (6.8 - 28.8 minutes). 672 of the treatments (44.3%) had at least one beam interruption due to fiducial marker variation over 3.5 mm from anticipated location. 171 (11.3%) treatments required at least 2 treatment interruptions, 74 (4.9%) treatments required at least 3 treatment interruptions and 35 (2.3%) treatments required 4 or more interruptions. Patient repositioning was required in 365 (24.1%) treatments. An integrated linear accelerator based kV imaging system can be used to successfully and efficiently to monitor intra-fraction prostate motion.