Addendum to MIRD Pamphlet No. 28

TO THE EDITOR: The journal has recently published MIRD pamphlet no. 28, parts 1 and 2, which describe and provide validation for the nuclear medicine software code MIRDcalc, part of the MIRDsoft.org series of freely accessible software for the field of nuclear medicine (1,2). We wish this letter to serve as an addendum clarifying an important technical aspect of the work in regard to some of the graphical presentations of the library of phantom computational models used to generate radionuclide S values, which form the computational engine of organ dosimetry in the MIRDcalc code.

In both part 1 and part 2 of MIRD pamphlet no. 28, we reference 4 International Commission on Radiological Protection (ICRP) publications that provide key reference material for MIRDcalc: two regarding computational phantoms and two regarding values of specific absorbed fractions (or SAFs) from which radionuclide S values were computed. The ICRP phantoms used in MIRDcalc data are the ICRP publication 110 reference adult male and adult female voxel phantoms (3) and the ICRP publication 143 reference pediatric male and female phantoms (4). The corresponding ICRP official values of SAFs are included in ICRP publication 133 (for the adult publication 110 phantoms) and in an in-press ICRP publication (for the pediatric publication 143 phantoms) (5,6). Confusion might arise in that ICRP is also in the process of migrating from voxelized reference phantoms to mesh-type reference phantoms. The adult mesh-type reference phantoms, the next generation of the Publication 110 adult voxel phantoms, have been already published in ICRP publication 145, with pediatric mesh-based phantoms to appear in an upcoming ICRP document (3,7,8). We point out, however, that the only official ICRP values of photon, electron, and α-particle SAFs published by ICRP are those derived in the voxelized reference phantoms of publications 110 and 143, along with supplemental stylized models of the respiratory tract and alimentary tract. No updated SAFs have been published by the ICRP for the newer mesh-based reference phantoms.

These details are implicit in the text descriptions in both parts 1 and 2 of MIRD pamphlet no. 28, especially in regard to the references to ICRP publications 110, 133, 143, and the in-press document on pediatric SAFs. However, for graphical purposes—to include Figures 3 and 4 of part 1 and Figure 1 of part 2—we chose to display the ICRP reference phantoms using their mesh-type formats. In this addendum, we wish to clarify that showing the ICRP reference phantoms in their mesh-type formats does not imply that new SAFs were derived for the mesh-type phantoms during the development of the MIRDcalc software. As noted, the original source of the SAFs used for S-value calculation were clearly cited in both parts 1 and 2 of this MIRD pamphlet, and both ICRP documents themselves make clear that the voxel-type reference phantoms were used.

• © 2023 by the Society of Nuclear Medicine and Molecular Imaging.

• Received for publication July 10, 2023.
• Revision received July 17, 2023.