Biomedical Engineering Reference
In-Depth Information
radiation emitted by the RE radioisotope, and the ability to form these
radioisotopes by neutron activation are all desirable features of these
RE-containing glasses.
An oxide glass is a versatile material for the
in situ
delivery of
therapeutic amounts of beta or gamma radiation. As we have seen
in Chapter 2, by simple changes in the chemical composition, a glass
can range from being bio-inert, to bioactive, to biodegradable in the
body. During the melting process, most neutron activatable elements of
interest, such as those in Table 13.1, easily dissolve in large amounts
in the melt and become a strongly bonded, inherent part of the glass.
As such, the radioisotope is confined to the glass, which minimizes, and
in most cases prevents, the leakage of radiation from the target organ.
In fact, borosilicate glasses are used to immobilize radioactive isotopes
in nuclear waste. Glass can be made into several convenient shapes
over a wide range in size, as shown by the microspheres and 1mm
diameter rods in Figure 13.1. In short, the versatility of glass is such
that it is possible to design a biocompatible glass for a specific purpose
and tailored to a particular target organ in terms of the radioisotope
that it contains (type of radiation and half-life), its biodegradability
(or lack thereof), and its shape and size. Glass compositions can be
tailored as to whether they are degradable or not, depending on the need
and application.
Figure 13.1
Examples of (a) rods and (b) microspheres made from rare earth
aluminosilicate glasses for use as
in situ
radiation delivery systems (brachytherapy).
The 1mm diameter rods in (a) and the glass microspheres in (b) have a nominal
composition of 46.8wt% Sm
2
O
3
, 18.2wt% Al
2
O
3
, and 35.0wt% SiO
2
,and
55wt% Y
2
O
3
,20wt%Al
2
O
3
, and 25wt% SiO
2
, respectively. The white bar in (b)
is 10
μ
m.
