Monte Carlo single-cell dosimetry of I-131, I-125 and I-123 for targeted radioimmunotherapy of B-cell lymphoma

Abstract

Purpose: To study the dosimetric characteristics of a non-internalizing and an internalizing monoclonal antibody (MAb) labeled with ¹³¹I, ¹²⁵I or ¹²³I, which targets a typical lymphoma B-cell. Materials and methods: Using our hybrid Monte Carlo (MC) code which combines detailed- and condensed-history electron track simulation we carry out transport calculations of Auger and beta electrons for different intracellular distributions of radioactivity. Results: Assuming permanent retention of the MAb in cells, ¹²⁵I gave the highest absorbed dose and ¹²³I the highest absorbed dose rate. Under the more realistic scenario of biologic excretion from the cells, ¹²³I resulted in the highest absorbed dose and absorbed dose rate. Conclusion: The present dosimetric analysis shows that biological half-life, subcellular localization, and the proper account of low-energy electrons is critical in assessing the energy deposition inside the targeted cells from the three iodide radioisotopes examined. From a dosimetric point of view and under the present approximations ¹²³I might be superior to the other two radioiodides in the treatment of microscopic disease in B-cell lymphoma patients.

Keywords::

• Auger electron
• Monte Carlo
• cellular dosimetry
• targeted radiotherapy