S-values for radium-223 and absorbed doses estimates for ²²³RACL₂ using three computational phantoms

Area of Science:

• Medical Physics
• Nuclear Medicine
• Radiotherapy

Background:

• Radium-223 dichloride (223RaCl2) is an FDA-approved treatment for bone metastases in castration-resistant prostate cancer (CRPC).
• Current activity prescription for 223RaCl2 therapy does not account for organ-at-risk absorbed dose limits, specifically the bone marrow.
• Accurate internal dosimetry is crucial for optimizing radionuclide therapy and ensuring patient safety.

Purpose of the Study:

• To develop a comprehensive set of S-values for Radium-223 and its decay products using validated Monte Carlo simulations.
• To evaluate absorbed doses in bone marrow for 223RaCl2 therapy across different computational models and biodistributions.
• To compare absorbed dose estimations in male computational models of varying body weights.

Main Methods:

• Utilized the GATE Monte Carlo simulation code, validated with the Radioactive Decay Module (RDM).
• Calculated S-values for Radium-223 and its decay chain using male and female XCAT computational phantoms.
• Estimated absorbed doses for 223RaCl2 therapy using three male computational models (standard, Pat1, Pat2) and literature-based biodistributions.

Main Results:

• A comprehensive set of S-values was generated for 30 source and 47 target regions (Male) and 30 source and 42 target regions (Female).
• Absorbed dose evaluations indicated that the Pat2 phantom (highest body weight) consistently received the greatest absorbed dose in the red marrow across all evaluated biodistributions.
• The study successfully compared and validated simulation methods for internal dosimetry of 223RaCl2.

Conclusions:

• The newly calculated S-values will aid in more accurate absorbed dose calculations for Radium-223 therapy.
• Patient-specific dosimetry, considering anatomical variations and biodistribution, is essential for safe and effective Radium-223 treatment.
• Larger body weight phantoms (Pat2) exhibited higher red marrow absorbed doses, highlighting the need for individualized dose assessments.