New estimation of electron and photon internal dose coefficients for new adult female computational phantom using DoseCalcs

Abstract

Internal radiation dosimetry is critical in nuclear medicine procedures involving radiopharmaceuticals as it evaluates the risks and benefits of diagnostic and therapeutic applications. In this context, radiological protection quantities, including absorbed dose and effective dose, are derived from the specific absorbed fraction (SAF), a fundamental dose coefficient. The SAF quantifies the fraction of energy deposited in a target region per unit mass relative to the energy emitted from a specified source region.

Updating the SAF dataset using the latest mesh-type computational phantoms is strongly recommended. Comparing these values with SAFs from earlier voxel-based phantoms helps identify target$\leftarrow$source combinations with variations in internal dosimetry coefficients, reflecting the anatomical improvements in mesh-type phantoms.

Simulations using the DoseCalcs platform were conducted for electron and photon transport at eight energies (10 keV to 2 MeV), employing the adult female mesh-type phantom from ICRP Publication 145. Subsequently, SAFs were calculated for twenty-four distinct source regions and compared with those derived by OpenDose using the voxel-based model.

The results showed that SAFs calculated with mesh-type and voxel-based phantoms are similar, with minor differences observed for both photons and electrons. Notable variations were observed for photons in the spleen$\leftarrow$liver combination and for electrons at low energy, particularly in the pancreas$\leftarrow$liver and liver$\leftarrow$pancreas combinations. These differences highlight the impact of anatomical improvements in mesh-type phantoms. These differences arise from improved internal structures, particularly for adjacent organs/tissues, due to differences in contact surface geometry. The mesh-type model uses smooth surfaces, while the voxel-based model employs stair-based surfaces.