Glass

Glass

Glass is relatively resistant to radiation-damage, highly insoluble, and non-toxic.
Glass can be easily spheridized in uniform sizes and has minimal radionuclidic
impurities. The manufacturing process is described comprehensively by Ehrhardt and
Day [10]. The yield of microspheres with the desired diameter, 20-30 μm (see below),
is around 15%. Advances in this technology have led to the production of glass
microspheres with practically no leaching [11]. Although the glass spheres have
several advantages, their high density (3.29 g/ml [12]) and their non-biodegradability
are major drawbacks [13,14]. The relatively high density increases the chance of
intravascular settling [15]. These glass microspheres produced under the name
TheraSpheres are the first registered microsphere product for internal radionuclide
therapy, and are used in patients with primary or metastatic tumours. Because of the
lack of γ-emission of 90Y, radioactive rhenium (186Re/188Re) microspheres were also
produced. The general method of manufacture of these spheres was the same as for
the 90Y spheres [2,16].
Brown et al. [17] prepared 166Ho-loaded glass particles (2-5 μm) for direct injection
into tumours of mice, which resulted in an effective modality for deposition of intense
γ-radiation for use in localised internal radionuclide therapy. However, no further
studies were done.
Kawashita et al. [18] suggested the use of phosphorus-rich Y2O3-Al2O3-SiO2-glass
microspheres containing phosphorus ions, which were produced by thermoelectron
bombardment of red phosphorus vapour and implanted into glass, thus resulting in a
high phosphorus content and high chemical durability. After activation by neutron
bombardment the glass contains phosphorus-32 (32P).