Chemical properties

Er-165 is a radiolanthanide, usually in trivalent state. The ionic radius of Er³⁺ is 89 pm, i.e. just 3% larger than Lu³⁺, which explains that chelators suitable for Lu-177 can be directly employed for Er-165 too, in particular DOTA.

Nuclear properties

Er-165 decays by electron capture decay with a half-life of 10.36 hours to stable Ho-165.

Er-165 emits no gamma-rays, but X-rays, notably K_α at ≈47 keV (59.4(9) %) and K_β at ≈54 keV (14.3(19) %). These energies make Er-165 suitable for SPECT-imaging.

The mean photon energy per decay is 37 keV and the mean electron energy emitted per decay is 5 keV . Most electrons are short-range Auger electrons with <1 µm and <26 µm respectively. Er-165 has therefore been proposed as therapeutic Auger electron emitter .

Production

Er-165 is produced by proton irradiation of natural Ho carbonate targets at Hevesy Laboratory at DTU. A Ho/Er separation is performed by ion exchange chromatography.

Distribution

Activity will be shipped from the PRISMAP facility Hevesy Laboratory (DTU, Risø, Denmark) to the users in form of Er³⁺ solution.

Examples of use

• Preclinical imaging with Er-165 has been reported .
• Er-165-EDTMP as bone seeker has been tested preclinically .
• A Gd³⁺/Er-165 cocktail was used to assess the Zn²⁺ dependent MRI response .