Biomedical Engineering Reference
In-Depth Information
DyLB3-10 glass. In this instance, the larger size of the glass microspheres
compared to colloidal particles is believed to be an advantage in reducing
the leakage of radioactivity from the joint. Another promising feature is
that the glass microspheres become embedded and immobilized in the
synovial lining fairly rapidly such that they do not cause any detectable
amount of physical or mechanical damage to the joint tissue. It is
also clear that therapeutic doses of radiation can be delivered by a
few milligrams of neutron activated, radioactive glass microspheres.
On the other hand, a more uniform dispersion and distribution of
the microspheres throughout the synovial lining is desirable to achieve
improved therapeutic results.
13.9 SUMMARY
An expanding number of investigations have shown that glass micro-
spheres are effective as
in situ
radiation delivery vehicles for treating
diseases such as cancer and rheumatoid arthritis. The versatility of glass
is an important advantage to its use in medicine [30] since its properties
can be varied over a wide range and tailored to a particular application
by simple changes in its chemical composition. Glass microspheres can
range from bio-inert to bioactive, from almost completely insoluble to
biodegradable in the body. Similarly, the radiation emitted by glass
microspheres can be tailored for a particular organ by using a glass that
contains one or more neutron activatable elements (e.g. REs) that emit
the optimum radiation for the organ being treated. The manufacturing
of glass microspheres is much easier when the microsphere is made
radioactive by neutron activation of the desired radioisotope as the last
step in the manufacturing process.
One major and unique advantage of using radioactive glass micro-
spheres to irradiate diseased organs in
situ
is that very large doses of
beta radiation can be safely delivered to a patient in this way, with
minimum damage to healthy tissue. Patients with primary liver cancer
are routinely receiving a calculated whole liver dose of up to 150Gy,
with no major side effects. Some patients have received multiple doses
of 150Gy and there are a few documented cases where localized regions
of HCC tumors have received from 1000 to 8000Gy with no adverse
side effects. One reason why such large doses can be used is that the
radioactive glass microspheres are preferentially deposited in the tumor
as opposed to the healthy tissue at ratios from 10 : 1 to 40 : 1. Another
important factor is that the shorter-range, more localized beta radiation
