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Seed Localization in MR-Assisted CT-Based LDR Post-Implant Plan

T Kim

T Kim1*, D Lee1 , B Lewis1 , P Kapoor1 , R Datsang1 , S Kim1 , N Mead2 , M Schutzer1 , D Moghanaki1 , (1) Virginia Commonwealth University, Richmond, VA, (2) McGuire VAMC, Richmond, VA


WE-RAM2-GePD-JT-4 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Joint Imaging-Therapy ePoster Theater

Purpose: Seed localization is essential in low dose rate (LDR) prostate post-implant planning. Seed localization on CT images is a competent approach because radioactive seeds are distinct from tissues with high intensity on CT images. However, indistinct anatomy of a prostate on CT images may induce inaccurate dose evaluation. In this study, we investigated MR imaging technique to assist CT-based post-implant planning. The purpose of this study is to improve the prostate delineation, while keeping seed localization capability.

Methods: 10 patients underwent post-implant CT and MR imaging on the same day of LDR prostate implant procedures. 8 of 10 patients were scanned with a 3T GE MRI and 2 patients with a 1.5T Siemens MRI. A total of 64 scan series were reviewed and compared with CT images in prostate delineation and seed localization. In comparison, clinical MR protocols included T2-weighted fast recovery fast spin echo (FRFSE), LAVA, T1-weighted fast spin echo (FSE), T1-weighted fast spoiled gradient echo (FSPGR) with the 3T GE MRI and SPACE, T1-weighted Flash, T2-weighted turbo spin echo (TSE) with the 1.5T Siemens MRI.

Results: The radioactive seeds created void signals on the images which were utilized for seed localization. Differentiating T2 properties, axial T2-weighted FRFSE in the 3T GE MRI provided better anatomical information of prostate for delineation compared to T1-weighted images, while void signal of the seeds was preserved for seed localization. With the 1.5T Siemens MRI, T2-weighted TSE provided decent image quality for seed localization in addition to prostate delineation. In seed localization, sagittal prostate images assisted to find a series of the seeds.

Conclusion: Seed localization in MR-assisted CT-based post-implant planning was achieved. A pair of orthogonal T2-weighted FRFSE and T2-weighted TSE were suggested for prostate delineation and seed localization. A further study of auto-segmented seed-based CT-MR image registration is ongoing.

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