Volume 2

Radiography and radio-therapeutics / by Robert Knox.

  • Knox, Robert, 1868-1928
Date:
1917-1918
Catalogue details

Licence: In copyright

Credit: Radiography and radio-therapeutics / by Robert Knox. Source: Wellcome Collection.

    52/260 (page 416)
    The most convenient mercury interrupter is probably a mercury jet interrupter. There are several which are all equally good. It should be possible to control the speed ; a resistance should, therefore, be added for the control of the interrupter. Another resistance is necessary to regulate the amount of current passing through the primary. Figs. 338 and 339 represent convenient arrangements of apparatus for therapeutic work. The coil, spintermeter, valve tube, and milliam- peremeter are placed on the top of an upright cabinet. The leads from the secondary may be carried to a pair of insulated high-tension steel cables, from which the current is carried by means of spring cables to the terminals of the tube. On a suitable switchboard, the regulating devices are conveniently arranged. A mercury jet break is mounted on the base of the cabinet, while above it, if desired, a dipper break with an automatic tachymeter may be added to the outfit, this latter instrument being useful when it is necessary to record accurately the number of interruptions in a given exposure. It cannot, however, be relied on as an absolute measure of the dose ; other methods must always be used as well, in order to get a check observation. The Rhythmeur Interrupter.—This is a useful addition to the thera¬ peutic outfit; it is very valuable for the deep treatment of tumours, when heavy currents require to be passed through hard tubes. It is a mechanical device by means of which the current is automatically cut off for a fixed period of time, varying from one to four or more seconds. This allows the tube time to cool between the periods of activity. On the Use of Valve Tubes.—This has been fully entered into in the radiographic section, but a brief reminder of the methods of connecting up the valve tubes will be useful here. Eigs. 333 and 334 illustrate two methods of connecting the tubes. Sometimes, when a considerable amount of reverse current is present it may be necessary to put two or more valve tubes in a circuit. They can then be arranged on both negative and positive poles. The tube used in X-ray therapy should be under the complete control of the operator. Any type of tube may be used, but it is important to have such control of it that the type of ray best suited to a particular case may be produced. It is not sufficient simply to turn on a switch with any tube and give a few minutes’ exposure to the rays. That method sufficed in the days when little was known of the technique of X-ray treatment, but now we must be able so to manipulate the apparatus that results may be obtained with a degree of certainty. The elaboration of the installation has been a gradual process, brought about by the requirements of individual workers as experience has widened; in consequence, at the present time we are still far removed from a standardisation of apparatus, tubes, and dosage. Before uniform results can be turned out this standardisation must become an established fact. It has been the aim of the writer to reduce, so far as is possible, all the installations under his care to a uniform standard.