The idea of using X rays in the treatment of disease arose from the recognition of the injurious effects which followed the prolonged application of the rays for diagnostic purposes. It fell to the lot of many early workers with X rays to notice the production of an inflammation of the skin, or a falling out of the hair over parts which had been subjected to X rays, and Leopold Freund, of Vienna, has stated that his first attempts to utilize X rays in treatment were made in 1896 to cure a hairy mole and were prompted by what he had read of such occurrences. A definite action of the rays upon the skin having been observed, their employment in the treatment of skin diseases followed as a natural corollary. Amongst the earliest investigators of the possible therapeutic effects of X rays the names of Schiff, Freund, Kienböck, Holtzknecht, Sjögren and Stenbeck may be mentioned. In Great Britain Sir Malcolm Morris, E. Dore and J. H. Sequeira were amongst the earliest investigators.
For operating successfully with an agent capable of producing decidedly harmful effects when given in large doses it is necessary to have some method of measurement, and the need for this quickly became apparent when X rays were used for treatment. The results of X-ray photography had already shown that the tubes employed were capable of emitting radiations of very varying powers of penetration, and that the tubes were by no means constant in this respect; and the question whether highly penetrating rays or rays of feeble penetration were to be preferred for therapeutic use became the subject of much discussion. It is now recognized that the rays which act upon the tissues are those which are absorbed by the tissues, and consequently the softer or less penetrating rays are now regarded as those to be used in treatment. So too the problem of measuring the quantity of rays emitted by a tube during a given time began to call for a solution, if that were in any way possible. In 1901 Benoist designed an apparatus by which the quality of the rays emitted by a tube at any moment could be accurately determined, and in 1902 Holtzknecht brought out the first quantitative device. It was called a chromoradiometer, and it enabled the dose administered to a patient to be observed, and recorded for future guidance. Holtzknecht also drew up a scale of units by means of which the indications of his apparatus could be interpreted. The units of Holtzknecht are still used to express the dosage of X rays, though his apparatus has been superseded. Holtzknecht's method of measurement consisted in observing the change of colour in certain pastilles when exposed to X rays, and his apparatus consisted of a scale of tints, and a number of pastilles of a yellow tint which acquired a green colour during exposure. The composition of these was kept a secret, but analysis revealed in them the presence of potassium sulphate combined with celluloid or gelatine. The pastilles were laid upon the surface under treatment, and their change of colour was compared at intervals with the scale of standard tints.
It was next thought that under suitable conditions the measurement of the current passing through the X-ray tube might serve as a guide to the quantity of X rays emitted by the tube, but, although this is the case to a certain extent, the method of quantity measurement which is now employed almost universally in X-ray treatment is that devised by Sabouraud and Noiré, and used with signal success by them in an enormous number of cases of ringworm, in which disease measurement of dose is of the most critical importance, for the following reason. The cure of ringworm by X rays requires that all the hair of the affected region shall be caused to fall out, but, nevertheless, it is necessary for obvious reasons that the hair should grow again after the disease has disappeared. Now if the dose of X rays be insufficient the hair does not come out and no cure results, while if the dose be too great the hair comes out but does not grow again; and the margin of safety is quite a narrow one. The method of Sabouraud and Noiré which has proved itself reliable for such critical measurements of dosage as are required for ringworm treatment, has to-day the universal acceptance of all X-ray workers for other forms of X-ray treatment, although the use of their pastilles has certain disadvantages.
Sabouraud's pastilles consist of small disks of platinocyanide of barium. This chemical compound has a bright yellow-green colour when freshly prepared, and changes through gradations of yellow to a brown colour when exposed to X rays. The pastilles are supplied in a book with which a permanent tint of colour is supplied, to indicate the colour change in the pastille which corresponds with a quantity of X rays equal to the maximum dose which the healthy skin will stand without inflammatory consequences. This is often spoken of as a “pastille dose.” As the amount of irradiation needed to produce the change of colour is considerable, the salt is fixed, during the treatment, at a point half-way between the source of the rays and the skin surface under treatment. During an exposure the chemical salt, in the form of a small disk of the material on cardboard, is adjusted in the required position by means of a pastille holder, and it is examined at intervals during the course of the exposure, until it has reached the required tint. When in the holder the pastille must be protected from light, and should have a piece of metal as a backing, if its indications are to be accurate.
In X-ray treatment some protection of the surrounding healthy parts is usually necessary. With this object various methods of shielding have been devised, either by coverings of the patient by impermeable materials, or by enclosing the tube in an impermeable box. Both methods are used, but tube-boxes are the most convenient, and most instrument makers now supply these boxes with suitable windows or openings of different sizes for the passage of the pencil of rays which is to fall upon the part under treatment.
The effect of the rays on healthy tissues is in the main a destructive one, but some of the cells of the tissues are more sensitive to the rays than are others; and this permits of a selective effect being obtained, with the destruction of some cells and not of the whole tissue. Young cells, and actively growing cells, are the most susceptible, and for this reason it is possible to influence the glands of the skin and the papillae of the hairs with a dose which will not destroy the skin itself. The art of successful working with X rays is based upon a careful adjustment of the dose so as to secure a selective destruction of the morbid elements, and to avoid wholesale damage to the part treated. The effects of excessive doses of X rays is to produce an inflammation which may result in painful sores which obstinately refuse to heal for many weeks or months. A quantity up to double that of the usual maximum or pastille dose may be employed in urgent cases without risk of any serious inflammation, but anything over this is to be avoided most carefully. In the treatment of ringworm the exact pastille dose must not be exceeded, for after a dose of about one and a half pastilles the fall of the hair is likely to be followed by permanent baldness.
In X-ray treatment it is customary to make use of moderate currents, and to bring the X-ray tube in its tube-holder and box into position so that the pencil of rays may fall upon the part to be treated. The distance of the skin surface from the centre of the tube must be known, and the pastille arranged in place accordingly. Fifteen centimetres is a usual distance, and at this distance a tube working with a current of a milliampere should give the full therapeutic dose or “pastille dose” in about 15 minutes. In general X-ray treatment it is quite usual at the present time to proceed by the method of full doses at rather long intervals. From the experience obtained by Sabouraud in numerous cases of ringworm it has been found that a full dose must not be repeated until a month has elapsed. So too in the treatment of rodent ulcer full doses at long intervals are now thought better than smaller doses repeated more often, and such doses are more easily measured by the Sabouraud pastille, which records large doses more simply than small ones, in which the slighter changes of tint are not easy to distinguish.
A great amount of work has been done with X rays for the treatment of cancer, but it is now recognized that the X rays
