Clinical Experience and Feasibility of Using 2D-kV Image Online Intervention in the Ultrafractionated Stereotactic Radiation Treatment of Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> This study reports the clinical experience and feasibility of using 2D-kV image system with online intervention in the ultra-fractionated stereotactic radiation treatment of prostate cancer. <h3>Materials/Methods</h3> 15 low/intermediate risk prostate patients, all with three transperineally implanted fiducial markers, received 40 Gy in 5 fractions to a PTV with margins of 3 mm posteriorly and 5 mm in other directions with online 2D-kV image tracking and manual beam interruption strategy with a 2 mm-threshold. A total of 180 kV paired setup images and 1272 intraoperative radiotherapy (IORT) 2D-kV images were analyzed to evaluate the setup deviation and intra-treatment target deviation. Elapsed time at different timestamps of different treatment, target deviation from planning position at different timestamps, and prostate motion during treatment, were calculated against beam interruption to evaluate their correlation. A subset of data from 22 fractions were re-evaluated to check the differences between using planning position and using pre-treatment setup position as reference. Margins based on the derived system and random errors were calculated to evaluate the feasibility of the workflow in ensuring prostate coverage during treatment. <h3>Results</h3> 50 out of 75 fractions were found to require interruption. Interruption had a strong correlation with prostate motion along longitudinal direction and had moderate correlations with prostate motion along vertical direction and prostate's prior-treatment setup along vertical direction. Using pre-treatment position as reference for IORT monitoring, the magnitude of motion deviation from reference position was reduced by 0.3 mm at vertical direction and 0.4 mm at lateral and longitudinal directions. The 3D margin calculated was 3.7 mm, 4.6 mm, 5.0 mm at lateral, vertical, longitudinal directions, respectively. <h3>Conclusion</h3> It is feasible to use a 2D-kV online IORT monitoring system with a proper intervention scheme to perform ultra-fractionated stereotactic radiation treatment for prostate cancer. High quality and safe delivery can be achieved by minimizing the elapsed time between setup image and the start of treatment beam-on, increasing the imaging frequency, and shortening the treatment time.