Three-Dimensional Dosimetry for Radiation Safety Estimates from Intrathecal Administration

Area of Science:

• Medical Imaging and Dosimetry
• Radiopharmaceutical Therapy and Nuclear Medicine

Background:

• Intrathecal administration is gaining traction for drug delivery, necessitating precise radiation safety evaluations.
• Current dosimetry tools require adaptation for the unique anatomical and physiological considerations of intrathecal delivery.

Purpose of the Study:

• To extend the 3-dimensional Voxel-Based Internal Dosimetry Application (VIDA) and 4D Extended Cardiac Torso Phantom (XCAT) for intrathecal administration.
• To provide specific radiation safety estimates for intrathecal drug delivery and imaging studies.

Main Methods:

• A modified XCAT phantom was used with Monte Carlo simulations in VIDA to generate voxel-level absorbed dose maps.
• Simulation results were validated against the OLINDA/EXM dosimetry tool.
• Absorbed dose was estimated in 6 healthy subjects receiving ^99mTc-diethylenetriaminepentaacetic acid via intrathecal administration.

Main Results:

• Simulation estimates closely aligned with OLINDA/EXM for common organs (within 6%).
• Highest absorbed doses were observed in the lumbar cerebrospinal fluid (CSF) space (0.3-0.8 mGy/MBq).
• A whole-body effective dose of 0.003 mSv/MBq was calculated, with lower doses noted for larger administered volumes (15 mL).

Conclusions:

• The adapted VIDA implementation offers tailored dosimetry for intrathecal administration.
• Radiation exposure is primarily localized to CSF and spinal regions.
• The relationship between administered volume and absorbed dose warrants further investigation for optimizing intrathecal therapies.