Purpose: To commission the program of using MR-Linac (Unity™) MR images for gynecological HDR brachytherapy, including optimizing and assessing MR image quality and workflow development.
Methods: Imaging analysis including geometric QA was performed using the Magphan™ RT phantom on newly developed scan protocols (T2-, T1-weighted images) for HDR treatment planning on the Unity. Venezia™ applicator reconstruction accuracy using Unity MR images was assessed using an MRI-HDR QA phantom of ground beef and banana with MR-line saline markers inserted in the catheters for the MR images. Applicator reconstruction on CT images of MR-HDR QA phantom with x-ray markers inserted served as the ground truth. A dry run of the developed workflow, including patient-transfer using a Zephyr™ table, MRI scans with a healthy volunteer, considerations for anesthesia equipment, and data-transfer between the MR-Linac console and treatment planning system (TPS) (Oncentra Brachy™) was performed. Data transfer between the TPS and the afterloader (Flexitron™) was performed using a plan created with the phantom images.
Results: MR imaging analysis results were within acceptable ranges and a max distortion magnitude of 0.96 mm and 1.36 mm was calculated on the T1- and T2-weighted images respectively over a 350 mm diameter spherical volume. The reconstruction uncertainties for the Venezia applicator’s tandem and two lunar-ovoids on the MR images were measured within ICRU 89 tolerance (2 mm). Treatment planning and delivery using the MR-HDR QA phantom was performed without issues. Vital monitoring and HDR equipment performed as expected throughout the full dry-run scan. MRI data from the MR-Linac console was required to initially be sent to Velocity™ and then exported to Oncentra due to DICOM compatibility issues.
Conclusion: The MR-Linac (Unity) MR image based gynecological HDR program was successfully developed through MR image commissioning for planning and dry-runs with a phantom and a healthy volunteer.
Brachytherapy, MRI, Image-guided Therapy
IM/TH- MRI in Radiation Therapy: MRI guidance - Brachytherapy