Room: Exhibit Hall | Forum 2
Purpose: MRI is the preferred imaging modality for sites typically treated with HDR brachytherapy. However, because it appears as negative contrast, the HDR applicator cannot be localized accurately on MRI. We attempt to determine the utility and longevity of an MRI-positive HDR lumen marker used in performing localization of the HDR applicator during treatment planning.
Methods: Two Orionâ„¢ Positive-Signal HDR MRI Lumen Markers (C4 Imaging) were inserted into a plastic, MR-compatible HDR ring applicator, which was placed in a uniform water phantom. Studies of the phantom were acquired using a 3-T clinical MRI scanner with T1-weighted spin gradient echo and T2-weighted 3D SPACE imaging sequences used for gynecological HDR treatment planning in our clinic. Additional 2D T2-weighted and CISS imaging sequences, as well as CT images, were also acquired for comparison. The markers were received one week after production, and MRI scans were repeated 3 times a week during the one-month FDA-approved lifespan of the marker. The contrast to noise ratio (CNR) compared to background water signal for each study was evaluated.
Results: T1-weighted images had a high CNR, while T2-weighted images showed no apparent signal at the marker location. CISS sequence images showed a low signal compared to the water phantom background. On T1-weighted images, the mean CNR during that time was 5.83 (range 1.88-9.29). The CNR did not noticeably degrade over the period the marker was approved for clinical use.
Conclusion: The HDR MRI-positive marker provides good contrast on T1-weighted images over the one-month lifespan of the marker. Our results show the feasibility of localizing the marker and HDR applicator without using CT images for HDR brachytherapy planning, eliminating the necessity of acquiring CT images for HDR brachytherapy patients and reducing the burden on clinical resources.