RADIOTHERAPY is the treatment of disease by the appli cation of rays of radioactive substances (i.e., Röntgen rays). The discovery of X-rays by Röntgen in the autumn of 1895 marked an advance in the history of science, which, even yet, is not appreciated by the average individual. Röntgen himself realised immediately the value of his discovery to the science of medicine, and communicated it to the Physico-Medical Society of Wurzburg. Since then, if one excepts the years 1914-1918, hardly a month has passed without some innovation.
In 1910 the X-ray tube had varied but little from the original tube used by Röntgen and Crookes, the improvements in focusing and increasing the intensity of the rays being due to the labours of Campbell Swinton and chiefly to Prof. Jackson in 1896; in deed the modern focus tube (gas tube) has not materially changed since then. In this tube, the current is carried across the tube by a certain amount of gas, which is left behind in the process of evacuation. The current, impinging on a tungsten target, under a pressure of anything over 8o,000 volts, results in the production of X-rays, which rays are now known to be electromagnetic impulses of very short wave-length. The only disadvantage of this tube is that individual control of the current and voltage is not absolute owing to fluctuations in the amount of residual gas. Despite this, however, it is largely used and for many pur poses possesses advantages over the Coolidge tube.
The Coolidge Tube.—At a later period Dr. Coolidge of New York discovered that a glowing body emitted electrons, and at once designed a new type of bulb in which the current was car ried across the vacuum by a stream of electrons from a hot tung sten wire. The hotter the wire the greater the current which passed across the bulb. This, of course, solved the problem of separate control of the voltage and the current and thereby the problem of being able to reproduce exact working conditions at any interval. Unfortunately the hope, raised at first by the pro duction of this tube, of obtaining an absolutely homogeneous beam of X-rays, was not realised.
The intensity of the X-rays depends upon the voltage employed to produce it and as the manufacture of high-potential generators (induction coils and step-up transformers) has improved out of all recognition since 1910, we can now produce rays of great in tensity, far greater than are needed for radiographic purposes.
On the photographic side, improvements in technique have been very noticeable, the most noteworthy improvements being the use of intensifying screens to shorten exposures, double-coated films to increase the contrast of the negative and the Potter Bucky diaphragm, the latter an ingenious contrivance for the purpose of cutting out secondary radiations and thereby sharpen ing the resulting picture.
During the years 1914-8 science was more or less subservient to the claims and the necessities of warfare, but even in this limited field X-rays were of enormous help. The localisation of bullets and shrapnel, which by any other means would have been impracticable, if not impossible, was carried out by numbers of experts, and to the energies of these men a host of soldiers prac tically owe their lives.
Employment in Diagnosis.—The past few years have seen great activity in the X-ray world. Improvements in technique previously mentioned have brought the use of X-rays into much greater prominence in the study and the diagnosis of internal diseases (see DIAGNOSIS). Skiagrams of the lungs, which were difficult to make and still more difficult to interpret, are now of the very greatest possible value in the study of diseases of the heart (q.v.) and lungs. It is no exaggeration to say that no diagnosis of disease of either of these organs is complete without an X-ray examination.
This advance is seen in the large hospitals for diseases of the chest ; where formerly only a few hundred examinations were made, now the number amounts to thousands in the year. Whereas the air-filled lungs showed up clearly against the more dense, blood filled heart and solid thoracic walls, the abdominal organs, that is to say the hollow viscera, being all of the same density, were all penetrated equally by X-rays and consequently were not readily differentiated on a plate. For a long time this difficulty appeared to be unsurmountable. Many substances were known to be opaque to X-rays but none of them could be taken with safety. Haudek, of Vienna, made careful experiments with bismuth sulphate mixed with jam and watched its progress through the oesophagus, but completely forgot to look for it in the stomach.