Biomedical Engineering Reference
In-Depth Information
In general, either external beam or in situ radiation sources are
used to irradiate diseased sites in the body. One of the most important
advantages of in situ irradiation is that a weaker, shorter-range radiation
can often be used and targeted to the specific tumor, and, consequently,
damage to adjacent, healthy tissue is minimized. This means that larger
doses of radiation can be safely used, which translates into a higher
probability of destroying the malignant tumors.
From a theoretical standpoint, a wide range of radioisotopes emitting
beta, gamma, or alpha radiation can be chemically incorporated into
glass particles. Oxide glasses containing rare earth (RE) radioisotopes
have been of great interest because the chemical and physical properties
of these glasses, coupled with the properties of the RE radioisotopes,
make them well suited for in vivo radiation therapy [4, 5].
Data for those RE glasses of general interest, and which are primarily
beta emitters, are summarized in Table 13.1. Their high RE content,
the half-life of the radioisotope, the range in soft tissue of the beta
Table 13.1 Selected properties a for rare earth (RE) aluminosilicate glasses and
data for rare earth radioisotopes formed by neutron activation.
Property
Y 2 O 3
Sm 2 O 3
Ho 2 O 3
Dy 2 O 3
RE 2 O 3 content (wt%)
35-55
32-64
36-69
47-65
Density (gm/cm 3 )
2.80-3.89
3.31-4.65
3.39-5.55
4.07-4.99
Transformation
temperature, T g ( C)
885-895
780-820
860-878
856-874
Dilatometric softening
point, T d ( C)
935-945
815-875
898-912
882-910
Thermal expansion
coefficient,
α
31-70
51-75
41-60
52-66
10 -7 / C)
(
×
10 -9
10 -9
10 -9
10 -9
Dissolution rate
(gm/cm 2 min) in
deionized water
at 37 C
1
×
1.6-30
×
0.5-3
×
<
1
×
90 Y
153 Sm
166 Ho
165 Dy
Radioisotope
Half-life (hours)
64
46.3
26.8
2.3
Range in tissue (mm)
average
2.5
0.8
2
1.4
maximum
10.3
3.1
8.5
5.7
Maximum activity b
(Ci/g)
2.4
61
63
230
a The lowest-highest values for a given property are shown.
b Per gram of radioactive nuclide in REAS glass, neutron flux of 10 13 neutron/cm 2 s.
 
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