Mass scaling of S values for blood-based estimation of red marrow absorbed dose: the quest for an appropriate method

As a first step in performing patient-specific absorbed dose calculations, it may be necessary to scale dose conversion factors (e.g., S values in the MIRD system or dose factors in the RADAR system) by patient organ mass. The absorbed dose to active marrow is of particular interest for radionuclide therapy. When using the blood-based model of red marrow (RM) absorbed dose estimation, there are only 2 S values of concern, representing RM self-dose and cross-dose terms. Linear mass scaling has generally been performed for the self-dose term, whereas the cross-dose term is considered to be mass independent. We will illustrate that each radionuclide may need to have its mass-based correction determined to assess whether the conventionally used linear mass scaling is appropriate and should be applied not only to the self-dose S value but also to the cross-dose term.