401862
—
April 1954
me
CALCULATION OF RADIOACTIVE IODINE BETA RADIAMLIONOS
DOSE TO THE BONE MARROW
By James S. Ropertson, M.D., Ph.D., and Joun T. Gopwin, M.D.
Medical Physics and Pathology Divisions of the Medical Department, Brookhaven National Laboratory,
Upton, Long Island, New York
(Accepted for publication September, 1953)
HEN doses of 1!I of the order of 100 me or
more are administered, as is sometimes done
in the treatment of thyroid carcinoma, the assoctated
irradiation of the hematopoietic tissues is the most
important factor limiting the dose which the patient
can tolerate. The radiation delivered to the bone
marrow is usually estimated by assuming that the
dose of radiation delivered to the bone marrow is
individuals with their age, health and nutritional
status and in a given individual there are variations
from bone to bone and even from point to point in
the same bone.
The areas obtained in measurements made in
twelve selected fields were: 19-4, 18-4, 17-2, 16-4,
15-8, 9-9, 9.2, 8-8, 8-0, 6-7, 5-1 and 4-0 per cent of
the area of the field. The meanforthis series is 11-6
equal to that delivered to the blood (Rall, Foster,
per cent. It is not areas, however, but volumes
Yalow and Siegel, 1952; Marinelli and Hill, 1950),
the method of Marinelli, Quimby and Hine (1948)
being used to calculate the dose delivered to the
blood. This method includes the assumption that
absorption. It is easily shown that the relative areas
represent the relative volumes. As a first approximation we shall assume that the orientation of the
trabeculae is random. Consider a block of unit
released and the energy absorbed in a unit volume
two phases with the fraction, f*, of its volume in
Robbins, Lazerson, Farr and Rawson, 1953; Seidlin,
for the B-particle contribution to the dose the energy
of a given tissue are equal. Although the hematopoietic portion of the bone marrowis a soft tissue,
the tissue regarded anatomically as the bone marrow
is characterised by the presence of interspersed bony
trabeculae which absorb someof the energy released
in the soft tissue. Therefore, the assumptions involved in the soft-tissue method of dose calculation
are not strictly valid for bone marrow. An estimate
of the energy absorbed in the bony trabeculae is
which are significant in determining radiation
height and width having its contents distributed in
phase II as illustrated in Fig. 1. A section through
A
PHASE I —
PHASE I ——
derived in the presentarticle.
A major requirementin establishing the required
estimate is a value for the relative volume of the
marrow occupied by bony trabeculae. This part of
the problem was approached by measuring the bony
areas of representative portions of normal appearing
marrow from ribs and vertebrae obtained routinely
at autopsy from adult patients dying of various
9~270=2
and eosin. Photomicrographs of one or more fields
this block parallel to face AB has the fraction, f, of
diseases.* Sections were stained with haematoxylin
from each of the several bone sections were made on
45 in. Ektachrome film at low-power magnifica-
COL 2 i ae
tion. An effort was made to select representative
fields with average distributions of trabeculae and
marrow. The area occupied by the bony trabeculae
was obtained by planimetry. It is apparent that any
figure so obtained for the trabecular area must be
regarded as an approximation only, because the
structure and composition of bone varies among
* Dr. Henry L. Jaffe kindly supplied several of the bone
sections used in this study.
its area in phase II. Of the sections parallel to face
ACor to BC, a portion (1—f) will have none of their
areas in phase II, while those in the remaining
portion, f, will have f of their areas in phase II, so
the average area for these sections is also f*. For
other orientations of sections the averaging effect
may not be so obvious, but since the sums of the
areas multiplied by the thicknesses of the sections
gives the volumes involved, for uniformly thin
sections the average percentage area of phase II
represents the percentage volume of phase II.
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