Glasses for Radiotherapy - Bio-Glasses: An Introduction - page 218

m in diameter, of the
lithium silicate glass (LS-Y) listed in Table 13.2 and containing radioac-
tive 90 Y (half-life of 64.2 hours) were injected into the stifle joint of 16
NewZealandWhite rabbits that had been treated with antigens to induce
arthritis in the stifle joint being treated. After neutron activation of the
glass microspheres to produce 90 Y, the microspheres were suspended in
a sterile saline solution containing 1% hyaluronate and injected into the
desired stifle joint. The mean dose injected for low-activity microspheres,
50

In another study [29], microspheres, 5-15 μ

μ Ci/mg, and high-activity microspheres, 500 μ Ci/mg, was 158 and

351 Ci, respectively.

Leakage of the radioactivity from the joint one week after injection,
as determined from the activity of nine organs and excreta, varied from
a low of 0.28% to a high of 0.82% of the injected dose over seven
animals. These values are comparable to the 0.1% Y that was leached
from this glass after being in saline solution, 37 ◦ C, for six weeks. This
amount of leakage is much less than that reported for other materials
now in use. It should be noted that the small amounts of tritium formed
from the 6 Li in these glasses during neutron activation could be avoided
by using a glass that contains only non-activatable 7 Li.
Histological examination of the whole joint collected at one week after
injection showed that clusters of 5-10 microspheres were embedded
50-100

μ

m deep in the synovial lining, similar to what was observed
when DyLB3-10 glass microspheres were injected into the stifle joint of
rats [9]. These results indicate that the glass microspheres, which number
from 400 000 to 3-5 million depending upon their diameter and the
dose being administered, do not remain suspended in the synovial fluid,
but instead become embedded in the synovial tissue after some unknown
period of time, less than one week, where they remain. After three weeks,
the microspheres were enveloped by cells and the average diameter of
the microspheres had not changed.
After one week in vivo , some of the microspheres were surrounded
by a halo suggestive of slow degradation. The diameter of the treated
joints, which was used as a measure of joint inflammation, remained
constant within experimental error. A partial explanation for the lack of
improvement may be the non-uniform distribution of the microspheres
in the synovial lining, which could permit the disease to progress in
those parts of the joint where microspheres were absent.
The overall results of these two studies indicate that biodegradable
glass microspheres are candidates for radiation synovectomy purposes.
In both studies, the release or leakage of radiation from the joint was
less than 1% and within tolerable limits even for the rapidly degrading

μ