4i6 



NATURE 



[April i, 1922 



may be small. With a light atom the amount of 

 scattered radiation is almost always large. 



The problems of scattering have come to the fore 

 recently in radiology in connection with deep therapy. 

 The human body is made up chiefly of carbon, hydrogen, 

 and oxygen — all light atoms — and its ability to scatter 

 X-rays in the adjacent air has long been familiar to 

 radiologists, especially in screening work. But the 

 extent of the scattering within the body itself is just 

 as marked, and this is the case whether the rays are of 

 medium or high penetration. It has been established 

 by Dessauer and others, from measurements made on 

 specified areas at various depths within the tissue, that 

 from 60 to 80 per cent, of the effectiveness of highly 

 penetrating rays is due to scattered rays which originally 

 were not directed at the area in question. 



The subject of protection has recently excited a 

 great deal of attention by reason of a series of casualties 

 to prominent radiologists. The various radiological 

 societies and institutions in London co-operated in 

 1921 in the formation of a representative Committee, 

 which was asked to go into the whole question and draw 

 up recommendations for the guidance of all concerned. 

 It was agreed that the question of the protection of the 

 operator was the sole issue ; the existing measures had 

 proved to be adequate so far as the patient was con- 

 cerned. The word " protection " was to be interpreted 

 in a wide sense. 



The Protection Committee was fortunate in securing 

 Sir Humphry Rolleston as Chairman and, under his 

 eminent leadership, has already drawn up two memor- 

 anda. They need not be referred to in detail here, 

 but they have already been widely acted upon, and 

 there is little doubt that presently the bogey of X-ray 

 dangers will have been laid. In years to come this 

 country will be entitled to congratulate itself on having 

 given a lead to the world in this matter. 



The Committee has laid down certain standards of 

 protection against X- and y-rays, which are expressed 

 very simply in terms of the equivalent thickness of 

 sheet lead. These thicknesses were based on available 

 experimental data; for example, the X-rays from a 

 tube excited by about 180,000 volts are cut down over 

 10,000 times by 3 mm. of lead, and over i milHon times 

 by 10 mm. of lead. The choice of the actual protective 

 material may, of course, be determined by insulating, 

 electrostatic, or other considerations, but its thickness 

 should be such as to provide protection equivalent to 

 the amount of lead specified. 



The Committee sought and secured the co-operation 

 of the National Physical Laboratory, both in investi- 

 gatory work and irx the question of the inspection of 

 existing X-ray departments in hospitals and other in- 

 stitutions. The N.P.L. has already inspected a number 

 of X-ray departments throughout the country, and it 

 may be said at once that, if the conditions which ob- 

 tained there may be regarded as typical, the Protection 

 Committee needs no justification in its labours. The 

 Committee has adopted the common-sense principle 

 that, wherever possible, the tube box or enclosure 

 should form a complete shield in all directions, allowing 

 only the minimum aperture for the work in hand. Few 

 installations subscribe to this very reasonable demand. 



In some cases the scattered radiation in different parts 

 of the X-ray rooms proved to be so excessive as to 

 prohibit examination by electroscope, and observa- 

 tions had to be confined to noting the comparative 

 ease with which the bones of the hand could l^e seen 

 on a screen as it was carried round the room. 



It is established that ventilation is of prime import- 

 ance but, unfortunately, the radiological departments 

 are generally situated in the basement. Ventilation 

 difficulties are multiplied tenfold in consequence and, 

 further, the rooms are largely shut off from the bene- 

 ficent effects of sunshine. In the majority of cases 

 the high-tension system consists of stretched over-head 

 small gauge wires, connected by spring tapes, or spirally 

 wound fine wires to the various apparatus. The 

 resulting brush discharge produces ozone in abund- 

 ance, and, as extractor fans are rarely fitted, the un- 

 fortunate operator gets the full benefit. The Pro- 

 tection Committee has recommended the use of smooth 

 tubes or rods or heavily insulated wires with the object 

 of abolishing the evils of brush discharge. It suggests 

 the employment of commodious rooms with ample head 

 room, especially in the case of deep therapy outfits 

 where the exciting voltages are in the region of 200,000. 

 Another danger is here indicated ; more than one 

 fatality has been occasioned by accidental discharge 

 to an operator working in a small room with slack or 

 looped high-tension wires. 



Generous recognition should be paid to the X-ray 

 manufacturers of this country for the way they are 

 beginning to co-operate with the Committee. The 

 British X-ray manufacturers, divided as they are, are 

 mostly carrying on under great difficulties at the present 

 time. Yet, despite their difficulties, almost all of 

 them have taken steps to obtain from the National 

 Physical Laboratory test figures for the various pro- 

 tective materials which they are incorporating into 

 existing and new installations. Such measurements 

 are rapidly and inexpensively carried out by the 

 Laboratory, and no radiologist need deny himself the 

 security which the N.P.L. certificate affords. The 

 Laboratory experience amply confirms the necessity 

 for such tests. For example, lead glass has been tested 

 — of which only 5 mm. were required to give the pro- 

 tection of I mm. of lead. For other samples of glass 

 as much as 10 mm. were required. The corresponding 

 figures for lead rubber show variations between 1-7 

 mm. and 4 mm. as the equivalent of i mm. of lead. 

 Thus, with either protective material a manufacturer 

 can easily be 100 per cent, out in his reckoning if he 

 employs uncertified material. He owes it to himself 

 and his customers to take no such risks. 



Two noteworthy steps, pregnant with promise for 

 the future of radiology, were taken in the establish- 

 ment of the Diploma in Radiology and the formation 

 of the Society of Radiographers. Here again this 

 country has taken the lead. And when some day 

 we get an Institute of Radiology, with which Mac- 

 kenzie-Davidson's name should be associated in some 

 way, a further great step will have been taken to assist 

 radiology in this country to take the proud position 

 among the sciences to which its important and bene- 

 ficent activities entitle it. 



NO, 2735, VOL. 109] 



