Dose distribution to spinal structures from intrathecally administered yttrium-90

Area of Science:

• Nuclear Medicine
• Medical Physics
• Radiotherapy

Background:

• Intrathecal administration of Iodine-131 ((131)I)-radiolabeled monoclonal antibodies has been used for cerebrospinal fluid (CSF) malignancies.
• The use of pure beta-emitters is hypothesized to spare more healthy tissue compared to Iodine-131.

Purpose of the Study:

• To quantitatively compare the radiation dose distribution of Yttrium-90 ((90)Y) to (131)I within the CSF space and surrounding spinal structures.
• To evaluate the potential of (90)Y as a replacement for (131)I in intrathecal cancer therapy.

Main Methods:

• Construction of a 3D digital phantom of the thoracic spine using Visible Human Project data.
• Modeling of radiation distribution for (90)Y and (131)I using Monte Carlo N-particle (MCNP4C) simulations.
• Convolution of CSF compartment images with radiation distribution to determine tissue dosimetry.

Main Results:

• (90)Y radiation distribution is predicted to be largely confined within the vertebral foramen.
• (90)Y demonstrates potential for improved dose distribution to the subarachnoid space and spinal cord surface compared to (131)I.
• The study provides quantitative data supporting the use of (90)Y in CNS malignancy treatment.

Conclusions:

• (90)Y is a potentially suitable radionuclide for intrathecal treatment of central nervous system (CNS) malignancies when conjugated to monoclonal antibodies.
• Using (90)Y may offer favorable dose improvements to the subarachnoid space and spinal cord surface over (131)I.
• This radionuclide offers a promising alternative for targeted radiotherapy in CNS cancers.