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Deformable Registration of Uterus and Upper Vagina Wall Using Gaussian Mixture Model (GMM) Plus Finite Element Model (FEM) and Dose Gradient-Based Evaluation for Supporting GYN HDR Brachytherapy Dose Accumulation

X Wu1*, A Thomas2 , J Williamson3 , D Yang4 , (1) Washington University in Saint Louis, Saint Louis, MO, (2) Washington University School of Medicine, Saint Louis, MO, (3) Washington University, Richmond, VA, (4) Washington University in St Louis, St Louis, MO


(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 221CD

Purpose: We developed a novel GMM-FEM deformable registration approach for uterus and upper vagina wall to support adaptive treatment planning and dose accumulation.

Methods: Proton density weighted MRIs and dose volumes were obtained for 8 GYN HDR patients. Surfaces of uterus and upper vagina wall were manually segmented in MRIs. Structures were aligned at the uterus center and then registered using the GMM-FEM (surface + volume) deformable image registration (DIR) method. Registration errors were computed as the surface distance of registered surfaces. Dose gradients were computed and applied to compute the DIR error tolerances.

Results: Before DIR, all MRIs and dose volumes were aligned in the common physical coordinate system and resampled to 1 mm voxel density. Surface meshes were smoothed to ~7000 nodes to improve computation efficiency. GMM-FEM DIR takes ~40 s. Average surface registration errors were ~4 mm which was more accurate than the alignment alone (surface registration error =~ 6 mm). Dose gradient based DIR error tolerance varies from 0.5mm in the high dose region (close to the HDR applicator) to over 30mm in the low dose region (away from the HDR applicator). Since dose gradient is greater close to the applicator, DIR error tolerance is lower and DIR errors are usually above the tolerance. However, dose accumulation errors are clinically accepted in the regions close to the application due to high dose values. DIR accuracy is generally acceptable in the low dose regions (away from the applicator).

Conclusion: The procedure using GMM-FEM for DIR and dose gradient for DIR evaluation is practical to support dose accumulation for GYN HDR adaptive planning.


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