Abstract
Purpose In this study we report the first clinical results of monitoring the prostate movement during a VMAT radiation through the use of MIR system (Motion Intrafraction Review, Varian Medical Systems). This method allows using a kV irradiation during treatment delivery and verifying real-time internal displacement volumes. Materials and methods Seven patients with prostatic carcinoma were treated using RapidArc technique on a TrueBeam Novalis accelerator. Before the simulation, three gold markers were implanted in the prostate and a hyaluronic acid injection was performed to remove the anterior wall of the rectum. Each patient received an MRI acquisition in radiotherapy position and a fusion was performed with CT simulation in order to improve the quality of the irradiated volume definition. Algorithm PRO3 (version V 10.0.28) was used for the preparation of the treatment plan on the Eclipse console and two arcs were delivered with a 600 MU/ min dose rate. A schema 20 * 3.1 Gy equivalent to 84 Gy with 5 fractions per week was used. The irradiation was delivered in gated mode required to operate MIR on TrueBeam version 1.6. During the treatment, kV images were automatically acquired at each exhale. The actual position of the markers was directly compared with their expected position represented by a green circle on the acquired image. Results The treatment time was 16 ± 6 min. The number of kV images acquired during irradiation was 26 ± 15 with a maximum of 64. After retrospective analysis, the average deviation of the markers in the superior-inferior direction was 0.29 [0–1.4] mm. The anterior- posterior and lateral offsets are difficult to analyze retrospectively because markers are not visible on all the images. However, a live correction of the fiducials positions has been applied only for two sessions out of 120. Conclusion Verification by kV imaging of intrafraction prostate motion is now possible simultaneously with the delivery of treatment. This online tracking will certainly reduce the PTV margins for hypofractionated treatment with strong dose per fraction. The MIR system available on the TrueBeam will allow in version 2.0 to get rid of the respiratory cycle by producing an image on a request related to the number of seconds, the number of UM or the gantry position.
Published Version
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