A new type of radioactive wire source.

Abstract

For interstitial radiotherapy there is a marked tendency toward the replacement of radioactive needles by radioactive wires (most commonly 182Ta and 192Ir). The wires have the advantages of flexibility, malleability, and safe fixing in the tissues. In addition, there is a possibility for afterloading (3, 5, 6, 8, 12, 13). The disadvantages inherent in the use of radioactive wire are: (a) The large diameter of the guides and plastic tubes leads to a considerable tissue injury during implantation. (b) The lack of wires overloaded at one or both ends necessitates the crossing of the implant ends, while needles without this disadvantage (dumbbell and Indian club needles) are already in use (1, 4, 10, 11). (c) When hairpins are employed (8, 14), the dose of the points is unevenly distributed (2). In our department we tried to fabricate a linear radioactive source which combines the advantages of the needles overloaded at one or both ends with those of the radioactive wire. We constructed linear sources of wires with a double linear activity in one or both ends. This relationship, according to the data from the literature as verified by our experience, is most favorable for radioactive needles (4, 11). Into the cavity of a No. 10 surgical silk thread 30–40 cm long, a nonradioactive wire is inserted as a guide. This guide is 1 cm longer and 0.1–0.2 mm larger in diameter than the combined linear radioactive wire source in preparation. That end of the thread in which the guide is inserted is submerged for a few minutes in a 30 per cent solution of perchlorvinyl resin. After the thread is taken out of the solution, the acetone evaporates and the resin solidifies. The guide is then removed, and a tract has been created into which the radioactive wire can be easily introduced. In our practice, we employ mainly 182Ta wire with a diameter of 0.2 mm and a linear activity of 1.2 mCi/cm or 2.4 mCi/cm at the overloaded ends. A reliable fixing of the radioactive wire introduced into the thread is assured by a new soaking in the perchlorvinyl resin solution. Before this procedure, the restricting button is put in place. The diameter of the source, elaborated in this way, is approximately 0.8 mm (Fig. 1). A one- or two-sided doubling of the linear activity may be effected by bending one or both ends or by adding in one or both ends supplementary wires 1 cm long, with the same linear activity at the middle portion (Fig. 2). A regular radioactive wire can also be introduced into the tract in case the radioactive source is to be employed according to Paterson and Parker's rules (7). Hairpins with double-loaded points can be prepared in a similar manner. The whole procedure is carried out behind a protective screen. The manipulation of the radioactive substances takes only a few seconds, the radiation dose to the hands thus being minimal. The radioactive source impregnated in perchlorvinyl resin is, from a chemical point of view, absolutely nontoxic for the tissues.