Abstract
Intrathecal (IT) administration is of growing interest for drug delivery and its utility is being increasingly investigated through imaging. In this work, the three-dimensional (3D) Voxel-Based Internal Dosimetry Application (VIDA) and 4D Extended Cardiac Torso Phantom (XCAT) were extended to provide radiation safety estimates specific to intrathecal administration. Methods: The 3D VIDA dosimetry application Monte Carlo simulation was run using a modified XCAT phantom with additional and edited cerebrospinal fluid (CSF) regions to produce voxel-level absorbed dose per unit cumulated activity maps for nine selected source regions. Simulation validation was performed to compare dose estimates for common organs in a pre-existing dosimetry tool (OLINDA-EXM). Dynamic planar scintigraphy data were acquired in six healthy subjects using dose volumes of 5 or 15mL (N = 3 each) of 185 MBq (5mCi) of Technetium-99m (99mTc)-DTPA. Radiation absorbed dose was estimated for each subject using the IT-specific dosimetry application. Results: Simulation results were within 6% of OLINDA estimates for common organs. Absorbed dose estimates were highest (0.3-0.8 mGy/MBq) in the lumbar CSF space. Whole body effective dose estimate of 0.003 mSv/MBq were observed. A dose volume dependency was observed with a 15mL dose volume resulting in lower absorbed dose estimates for several intrathecal and non-intrathecal regions. Conclusion: The IT-specific VIDA implementation enables tailored dosimetry estimation for regions most relevant in IT administration. Absorbed doses are highly localized to CSF and spinal regions and should be taken into consideration when designing intrathecal imaging studies. A potentially interesting relationship was observed between absorbed dose and administered dose volume which merits further investigation.
- Copyright © 2017 by the Society of Nuclear Medicine and Molecular Imaging, Inc.