Position. Aside from placing radium or radon directly in
contact with the lesion, one may use distance application in order to afford a
more homogeneous depth distribution of the energy, or the radioactive
substances may be implanted in the diseased tissues—which is known as
interstitial therapy.
The factor of
distance in the technique of radium application is of great importance. When
radium is used, it might seem to one giving the matter only casual thought that
the tiny differences in distance between the radium and the tissues, amounting
usually to a few millimeters, would not be very significant. Assuming the rays
as coming from a point source (which of course they do not), the falling off in
intensity of the radiation with distance takes place in accordance with what is
known as the law of inverse squares.
Interstitial
therapy is the insertion of radium or radon preparations into the diseased
tissues. The salt is used in needles, and the radon is used in similar
containers or in smaller ones called seeds.
Most radium
needles are constructed of platinum iridium with wall thickness varying from
0.3 to 0.8 mm., with 0.5 mm. generally preferred, which filtration takes out
all beta rays. With 0.5 mm. platinum filtration dosage can be estimated in
roentgens.
The needles
are implanted 1 cm. apart underneath and at the margins of the neoplasm,
surgical asepsis and local or block anesthesia being used. The needles are
implanted not so much in the tumor itself as at the extending borders. A
puncture wound is made with a fine pointed scalpel to facilitate the insertion of
the needle. The eyelet of the needle is threaded
The method of interstitial therapy with gold implants possesses the advantages of simplicity and prolonged exposure, but almost 9 per cent of the transmitted radiation consists of beta rays and accurate distribution is difficult to achieve.
Because of the possibility of carrying infection deeper into the healthy tissue, implants should not be inserted through an ulcerating surface. Otherwise the inflammatory reaction may be enhanced and marked sloughing may take place.
Frequently the gold implants are put in the healthy tissue at or near infiltrating edge of the growth, for the radiation should be equally and thoroughly distributed in the actively growing periphery of the neoplasm, as well as in the central portion. The dosage is influenced by the shape of the tumor, the cross-fire usually being greater for spherical masses. Prior to the implantation of radon, it may be desirable to use external radiation for a purpose similar to that of preoperative radiation and to reenforce the dosage of the implants effectively.
Gold implants are sterilized by boiling and embedded by the use of small trocars, surgical cleanliness always being observed. After implants are inserted, a radiograph may be taken to make sure that they are correctly placed, both in regard to the lesion and in regard to one another.
The method of interstitial therapy with gold implants possesses the advantages of simplicity and prolonged exposure, but almost 9 per cent of the transmitted radiation consists of beta rays and accurate distribution is difficult to achieve.
Because of the possibility of carrying infection deeper into the healthy tissue, implants should not be inserted through an ulcerating surface. Otherwise the inflammatory reaction may be enhanced and marked sloughing may take place.
Frequently the gold implants are put in the healthy tissue at or near infiltrating edge of the growth, for the radiation should be equally and thoroughly distributed in the actively growing periphery of the neoplasm, as well as in the central portion. The dosage is influenced by the shape of the tumor, the cross-fire usually being greater for spherical masses. Prior to the implantation of radon, it may be desirable to use external radiation for a purpose similar to that of preoperative radiation and to reenforce the dosage of the implants effectively.
Gold implants are sterilized by boiling and embedded by the use of small trocars, surgical cleanliness always being observed. After implants are inserted, a radiograph may be taken to make sure that they are correctly placed, both in regard to the lesion and in regard to one another.