Abstract: A radiation source wire member for radiotherapy indwelling in cancer-affected part of the body comprises an indwelling tip end portion having a radiation source of rhodium coil wire partially converted to 103Pd, and a filament connected to the indwelling portion, the filament having such a length that at least a rear end portion thereof is exposed outside the body after indwelling in the cancer-affected part. An apparatus for delivering the radiation source wire member to the cancer-affected part of the body has a catheter structure comprising (a) an outer tube having an inner diameter permitting the indwelling portion to pass through without resistance, and (b) an inner tube received in the outer tube movably back and forth therein and having an inner diameter not permitting the indwelling portion to pass through but permitting the filament to pass through without resistance.