Dosage distributions from hairpins of radioactive tantalum wire.

Abstract

A Technique of implantation of the bladder with radioactive tantalum wire (half-life 111 days; β rays, 0·53 MeV; γ rays, 1·12 and 1·22 MeV) has been described by Wallace, Stapleton and Turner (1952). For clinical use wire of diameter either 0·2 or 0·4 mm is sheathed in platinum 0·1 mm thick which absorbs the β emission. Standard “hairpins” are now supplied by A.E.R.E., Harwell. They consist of 12·5 cm lengths bent to the shape shown in Fig. 1. An implant may consist of a single hairpin or two or more placed side by side, with a 1 cm gap between their adjacent prongs. Such an arrangement of active material deviates from that existing in an “ideal” radium implant in three ways: 1. The effective linear activity is uneven around the periphery owing to the increased concentration of material at the loop of the hairpin. 2. The intermediate lines of an implant consisting of more than one hairpin are of the same linear activity as the periphery, i.e. not two-thirds strength as required in an ideal arrangement of radium. 3. Although the open end of the implant may be crossed by bending over the ends of the hairpins after implantation, this procedure has the disadvantage of making the hairpins more difficult to remove. The final implant therefore usually has one uncrossed end.