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MRI guided High Dose Rate Gynecological Brachytherapy using an MR-Linac as an MR simulator: A Single Institutional Experience
Journal article   Open access   Peer reviewed

MRI guided High Dose Rate Gynecological Brachytherapy using an MR-Linac as an MR simulator: A Single Institutional Experience

Whitney Massock, Yusung Kim, M. Alex Dresner, Wenqing Sun, Joe Caster, Quentin Adams, Jill Jespersen and Joel St-Aubin
Practical Radiation Oncology, Vol.14(1), pp.70-79
01/2024
DOI: 10.1016/j.prro.2023.08.003
PMID: 37652344
url
https://doi.org/10.1016/j.prro.2023.08.003View
Published (Version of record) Open Access

Abstract

Purpose The goal of this study was to commission the use of an MR-Linac (Unity) for imaging of gynecological HDR brachytherapy. This included optimizing imaging protocols and workflow development. Methods and Materials T1-weighted and T2-weighted HDR imaging protocols were optimized on the Unity for HDR GYN imaging and treatment planning. Phantom measurements using these protocols were performed to determine geometric distortion and to assess reconstruction accuracy of the applicator compared to the ground truth CT image. A treatment plan was created within the treatment planning system that was then delivered to a phantom. New workflows were developed which were tested with a full dry run with a healthy volunteer including patient transfer, anesthesia considerations, and data transfer. Validation of the workflow was completed on one patient who received imaging on both the Unity MRI and on a dedicated 3T MRI simulator. Results Imaging analysis results were favorable with MR-Linac images with a maximum distortion of 0.96 mm and 1.36 mm measurement over a 350 mm diameter spherical volume on the T1- and T2-weighted images respectfully and the maximum effect of the applicator was 0.36 ppm of the main magnetic field. Reconstruction uncertainties of the Venezia applicator's tandem and two lunar-ovoids on the MR-Linac images were within the 2 mm tolerance of ICRU 89. Treatment planning and delivery was performed on the MR-HDR QA phantom without issue. Dry run and healthy volunteer imaging showed adequate performance of both vital monitoring and HDR equipment. For the patient for which both the Unity MRI and 3T images were acquired, 95.78% and 95.80% of the HR-CTV volume received 100% of the dose respectively. Both plans were considered clinically acceptable. Conclusions Unity MR-linac MR images were successfully used in gynecological HDR brachytherapy treatment planning and a usable workflow was established.

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