28.02.2013 Views

autologous blood and marrow transplantation - Blog Science ...

autologous blood and marrow transplantation - Blog Science ...

autologous blood and marrow transplantation - Blog Science ...

SHOW MORE
SHOW LESS

Create successful ePaper yourself

Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.

686 Chapter 14: Radioimmunotherapy<br />

activity in <strong>marrow</strong> is inferred by measuring the activity in circulating <strong>blood</strong> at<br />

various times after administering a radiolabeled compound <strong>and</strong> correcting for red<br />

cell hematocrit. Siegel et al. 6<br />

recommended 7) that the <strong>marrow</strong> specific activity is<br />

0.2 to 0.4 times that of the <strong>blood</strong>, 2) that the clearance of activity from circulating<br />

<strong>blood</strong> is equal to the clearance of activity from red <strong>marrow</strong>, <strong>and</strong> 3) that the distribution<br />

of activity in <strong>marrow</strong> is uniform. A time-activity curve is constructed <strong>and</strong> a<br />

residence time for <strong>marrow</strong> is determined from the integral of the area under the timeactivity<br />

curve. Marrow becomes a separate tissue from the remainder body tissue.<br />

The dose to <strong>marrow</strong> is then calculated using the conventional MIRD approach.<br />

Direct-assessment method. The assumption behind this method is that activity<br />

in <strong>marrow</strong> can be measured <strong>and</strong> quantified. This method is preferred because it<br />

provides the most accurate dose assessment. Marrow activity may be determined<br />

by direct counting of activity in <strong>marrow</strong> of a vertebral body or the sacrum, 7<br />

or by<br />

counting a <strong>marrow</strong> biopsy specimen. 8<br />

These samples are assumed to contain a<br />

known fraction of total-body red <strong>marrow</strong>. Figure 1 shows a time-activity curve for<br />

red <strong>marrow</strong> obtained by direct measurements of activity in the right or left<br />

time post-injection, hr<br />

Figure 1. Time-activity curve for a radionuclide in <strong>marrow</strong> of a patient, determined by direct<br />

measurement (planar imaging). The amount of <strong>marrow</strong> in the patient is not known, but the<br />

curve may be normalized by measuring the activity per gram of <strong>marrow</strong> in a biopsy specimen<br />

from the same patient.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!