A compact cartridge (20) for an afterloader (10) includes a housing (21) containing a radioactive source wire, and a dummy test wire each accommodated in a helical groove on the periphery of a wire storage drum (124). The wires are contained in the grooves (125) by low friction bearings such as rollers (140) so that advancement of the wire from the drum is under very low friction conditions. The cartridge is removably inserted in the head (16) of an afterloader apparatus that engages a primary drive system (38), and an emergency retract mechanism (40) mounted in the head. The cartridge also contains an electronics board (123) with software for updating the software in the control electronics for the afterloader.
