autologous blood and marrow transplantation - Blog Science ...

Fisher 687
acetabulum. The curve is normalized to percent administered activity per gram
(%ID/g) with measurement of a marrow biopsy specimen from the same patient.
The area under the curve provides the residence time for a marrow dose
calculation.
RESULTS
Marrow absorbed doses should be estimated individually for each patient who
receives an internal administration of a therapeutic radiopharmaceutical. The
variation in patient-specific parameters dictates that each dose assessment be
customized or tailored to each patient. Results will depend on the method, model,
and assumptions used in the dose calculation.
DISCUSSION
Many factors influence the calculated absorbed dose to red marrow from an
internally administered radionuclide. The three approaches described above apply
to different sets of starting assumptions. Additionally, the models on which the
calculations are based may be subject to change from time to time, leading to
differences in calculated results. Direct measurements of marrow radioactivity in
vivo are also subject to normal statistical counting errors and measurement
uncertainties. And finally, the dose-related response of patients to high marrow
doses from protracted, low-dose-rate irradiation is highly variable.
Choice of appropriate S value
The mean dose per unit cumulated activity (or S value) for each source organ
and target organ pair has been calculated for more than 120 different radionuclides
and for more than 10 different anthropomorphic models of the human representing
different ages, sizes, and sexes. Since the S value accounts for transport of radiation
as well as the physical structure of marrow tissue, the derivation of S values is
complicated. As scientists revise their model representations of bone marrow
structure and composition and refine their physics calculations for a broad
spectrum of radiation emissions and energies, they obtain new sets of tabulated 5
values to choose from. Three major sets of marrow S values are in common use,
and each will result in a different marrow dose result:
MIRD-11/MIRDOSE1 (1975). The first comprehensive tabulation of S values
was completed by the MIRD committee 9
in 1975. The basis for the marrow 5
values was prior work by Spiers, 10-12
who measured chord-length distribution in
skeletal trabeculae and marrow cavities and calculated the energy deposited by