Glasses for Radiotherapy - Bio-Glasses: An Introduction - page 217

(half-life 2.3 hours), verified that very little of the radioactive 165 Dy was
released during the degradation of this borate glass in SSF. After being
immersed in the SSF for 7.2 hours (or three half-lives for 165 Dy), which
corresponds to the decay of 87.5% of the initial activity, less than 0.1%
of the 165 Dy initially present in the microspheres was detected in the
SSF. These results for the DyLB3-10 glass indicate that leakage of the
radioactivity during the degradation of the microspheres should be of
minimal concern.
Similarly encouraging results were obtained from in vivo experiments
[9] in which 1mg of non-radioactive DyLB3-10 microspheres, from 5 to
15 m in diameter, were injected in the stifle joint of a rat. The typical

appearance of the remnants of DyLB3-10 microspheres after being in the
rat stifle joint for 14 days is shown in Figure 13.4. While degradation of
the microspheres clearly occurred, the diameter of the remnants is close to
that of the original microspheres. Energy-dispersive X-ray spectroscopy
(EDS) analysis of several remnants showed that they consisted primarily
of dysprosium along with phosphorus and calcium from reaction with
the body or synovial fluids. Most likely, this dysprosium phosphate-
rich material was formed as the glass microsphere degraded such that
the dysprosium reacted with the body fluids, which is the source of
Ca and P.
Histological examination of the stifle joints revealed that the glass
microspheres were embedded within the synovial membrane [9, 10].
No microspheres were found in the articular cartilage and there was
no evidence of mechanical damage to joint tissue. Typically, clus-
ters of microspheres were observed dispersed throughout the synovial
membrane. Tissue response was mild and no serious inflammation
was observed. The only foreign-body response observed consisted of
macrophage/giant cell formation and the proliferation of fibrous tissue
around the agglomerated microspheres. This is normal for anything
implanted that is biocompatible but not bioactive.
Based on the in vitro and in vivo results, the DyLB3-10 borate
glass microspheres were considered good candidates for radiation syn-
ovectomy [9]. The microspheres degraded in vivo at an acceptable
rate and the leakage of radioactivity from the joint was quite small,
0.1-0.2%, which is much less than the materials now being used for
radiation synovectomy in Europe. Other than mild inflammation, there
was no physical or histological damage to the tissue within a joint. The
DyLB3-10 glass microspheres were easily neutron activated: 1 hour at a
neutron flux of 8

μ

10 13 cm − 2 s − 1 yielded a specific activity of 165 Dy of
220 Ci/g, which should be adequate for most synovectomy treatments.

×