Revised estimates of electron absorbed fractions and radionuclide S-values in trabecular bone

Abstract

The field of nuclear medicine has reached advanced stages in the use of radiopharmaceuticals for the treatment and diagnosis of innumerable maladies. However, along with the use of nuclear medicine come responsibilities inherently associated with the use of radioactive material. It is necessary to be able to calculate doses in the trabecular bone region accurately and consistently. The accurate assessment of patient dose will allow physicians to better predict the amounts of radioactivity needed for specific diagnostic and therapeutic applications. Additionally, improved calculational techniques for bone dosimetry will decrease the likelihood of overadministrations and will allow for reliable predictions of side-effects to patients. The dosimetry of this region is therefore a very important, and unfortunately complicated, area associated with the field of nuclear medicine. A new dosimetric trabecular bone model has been developed and incorporated into a Monte Carlo radiation transport code to determine electron absorbed fractions in red bone marrow and the endosteal tissue which is contained in trabecular bone. The model is based on measured omnidirectional chord length distributions through trabeculae and marrow cavities in nine skeletal locations. Absorbed fractions were calculated for the two target regions, and then estimated from these results for all other skeletal regions thought to contain red marrow. These absorbed fractions were then used to calculate S-values for a variety of beta-emitting radionuclides at each of 15 skeletal locations thought to contain red bone marrow. Absorbed fractions and S-values were calculated for sources in the marrow, on the bone surface, and in the bone volume. Comparisons were made between the new absorbed fractions and those published in ICRP Publication 30, as well as between the new S-values and those determined from the MIRDOSE2 software.