Natural rhenium is composed of two isotopes (185Re and 187Re) that form β-emitting
186Re and 188Re radioisotopes respectively, upon neutron activation. The nuclear and
dosimetric properties of the rhenium radioisotopes are comparable to those of 90Y, but
they have imageable γ-photons and 188Re is easily available from a 188W/188Regenerator
system.
Like the rhenium radioisotopes, 166Ho emits β-particles and photons. It has a
physical half-life of 26.8h resulting in a high dose rate. Its cross section is comparable
with rhenium, but 165Ho has a natural abundance of 100% and thus only one
radioisotope, 166Ho, is formed by neutron bombardment. Taking these characteristics
into consideration, 166Ho is therefore an attractive candidate for use in future
treatments.
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