Complex sentence: Cobalt-60 tends to be used in teletherapy units while the iridium-192 tends to be used in a different mode of therapy (brachytherapy) where a palladium-coated iridium/palladium alloy wire is made radioactive by neutron activation.
Split into simpler sentences: Cobalt-60 tends to be used in teletherapy units while iridium-192 tends to be used in a different mode of therapy (brachytherapy). The irridium wires for brachythereapy are a palladium-coated iridium/palladium alloy wire made radioactive by neutron activation.