Updating internal dose coefficients of radiation therapy alpha-emitting radionuclides, Ac-225, At-211, Bi-213, Th-227, and Ra-223 for new reference male and female phantoms using DoseCalcs

Purpose:

Radiopharmaceuticals, particularly alpha-emitting radionuclides, have garnered significant attention for their potential in targeted cancer therapy because they can deliver lethal doses of radiation over a short range. Therefore, accurately estimating the absorbed dose within the body is critical for optimizing treatment effectiveness and ensuring patient safety. While internal dosimetry coefficients of alpha-emitting radionuclides, including Ac-225, At-211, Bi-213, Th-227, and Ra-223, and their progeny, are already available, they have not yet been computed for the latest generations of phantoms.

Methods:

In this context, we performed Monte Carlo simulations using DoseCalcs code with ICRP Publication 145 new mesh-type phantoms to calculate the S-values of these radionuclides-emitted radiation from different source organs/tissues in adult male and female models.

Results:

The self-irradiation S-values for these radionuclides were significantly elevated, as were the cross-irradiation S-values for contents-to-wall cases. When comparing the S-values calculated in mesh-type phantoms with those derived from OpenDose in voxelized phantoms, the values were generally consistent for most source-to-target cases with ratios around 1. However, ratios between 3–5 were noted for UBW$\leftarrow$UBCs, StW$\leftarrow$Liver and StW$\leftarrow$Brain, and ratios around 2 for UBW$\leftarrow$Liver and Gonads$\leftarrow$Brain. This was especially evident in cases involving walls as target and/or separated by large distances. These differences were attributed to refined wall modeling, smooth organ interfaces, and modified cortical bone densities, leading to improved microscopic energy-deposition estimates.

Conclusion:

Our study provides a comprehensive, updated dataset of S-values of alpha-emitting radionuclides in the mesh-type phantoms; hence, they could be used for comparison and adult-patient dose estimation.