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A Method for On-The-Fly Resampling of Radionuclide Energy Deposition Kernels for Convolution-Based Voxelwise Dosimetry

S Graves*, D Hyer , R Flynn , J Sunderland , University of Iowa Hospitals and Clinics, Iowa City, IA


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

Room: 301

Purpose: Convolution-based radionuclide dose calculations require energy deposition kernels of appropriate size and resolution. The purpose of this work was to demonstrate a method for efficient and accurate resampling of publicly available energy deposition kernels from the pre-tabulated radial coordinates to the Cartesian image domain.

Methods: Kernels from a previously described library (Graves et al., AAPM, 2018) were sampled onto a Cartesian matrix, consisting of voxels sized smaller than the image data by an integer multiplier (resample factor – rf). The energy contained within the center voxel in this high-resolution matrix was calculated by integrating the radial dose point kernel to a volume equal to the volume of the center voxel. To enforce the requirement that activity is uniformly distributed within a voxel in the image domain, this high-resolution kernel was convolved with a rectangular function equal to the size of an image voxel. The result of this convolution was down-sampled to the target image resolution, and scaled to conserve energy.

Results: Kernel generation (25x25x25 voxels; rf=8) was complete within ~3.2 seconds on a workstation grade CPU in MatLab. With a peak memory allocation of <200 MB, this process appears feasible on standard clinical workstations. Computation time did not depend significantly on voxel-size, and diminishing returns on spatial accuracy were observed for rf > 8. The resulting kernels compared favorably against literature kernels that were generated natively in a Cartesian geometry. For accurate incorporation of photon dose it was found desirable to generate a larger low-resolution photon-only kernel. This two-kernel approach accelerates the subsequent dose calculation, potentially increasing collapsed cone-type calculation speed.

Conclusion: It is feasible to rapidly and accurately compute a custom radionuclide dose kernel from publicly available radial energy deposition kernels. These methods expand calculation flexibility in voxelwise targeted radiopharmaceutical dosimetry.


Nuclear Medicine, Radial Dose Function, Radiation Dosimetry


IM/TH- Radiopharmaceutical therapy: Non I-131 MIRD/analytical dose estimation

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