1979, British Journal of Radiology, 52, 330

Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents) Treatment of ankylosing spondylitis

REFERENCE SMITH, P. G., DOLL, R., and RADFORD, E. P., 1977. Cancer

mortality among patients with ankylosing spondylitis not given X-ray therapy. British Journal of Radiology. 50, 728-734.

T H E EDITOR—-SIR, In an article published in T H E BRITISH JOURNAL OF RADI-

OLOGY Smith et al. (1977) reviewed the causes of death in a group of patients with ankylosing spondylitis who were not intially treated by X rays and compared them with a larger and not strictly comparable group who had been treated by X rays at about the same time. They concluded that the known increased incidence of malignant tumours, including leukaemia, in patients treated with X rays is due to the treatment rather than to the disease process itself, but drew attention to the possibility that the increase in deaths from malignancies in irradiated patients may be compensated, at least in part, by a reduced number of deaths from other causes when comparison is made with the mortality experience of patients treated in other ways. The question was therefore asked yet again whether treatment by radiotherapy can be justified on the grounds that it offers the possibility of better symptomatic relief than that which follows other forms of treatment and, in particular, the suggestion was made that The British Institute of Radiology should organize a clinical trial to assess the symptomatic improvement accruing from X-ray treatment of patients with ankylosing spondylitis compared with the treatment by non-radiation methods. It was suggested that on the rather unlikely assumption that treatment with X rays reduces mortality rates by 40% compared with other methods of treatment, then it would be necessary to include about 1000 patients in a trial and follow them for ten years to be 90% certain of declaring a difference significant at the 5% level. However, a smaller number of patients would be required if the criterion of effectiveness was the relief of symptoms rather than death. A survey of consultant radiotherapists and of radiotherapy centres was therefore carried out and replies have been received from about three-quarters (157 consultants out of 210 and 45 centres out of 60). These radiotherapists indicated that over the last three years they had treated about 340 patients with ankylosing spondylitis, though a considerable number of them thought that additional patients would be referred in the event of a trial being set up. However, at least one large centre which treated 60 patients is doubtful as to whether it would contribute to a trial, another treating 40 patients has decided not to take part, two regional centres are unwilling to contribute patients to a proposed trial and at least one major London teaching hospital feels that such a trial would not be justified. I presented these figures to a recent meeting of the Medical Committee of the Institute with my own personal feeling that there is not enough support or potential support from radiotherapists to warrant an approach to rheumatologists and orthopaedic surgeons to enlist their support for a trial. I think it unlikely that a sufficiently large number of patients would be recruited and I further think that, as there would be at best relatively few patients from each of a large number of centres, there would be problems in collecting information and ensuring that the protocol was exactly observed. The Medical Committee agreed with this assessment, but there would of course be no objection to any other Body looking into the matter further. Yours, etc., W. M. Ross. Radiotherapy Department, Royal Victoria Infirmary, Queen Victoria Road, Newcastle upon Tyne NE1 4LP. {Received November, 1978)

The effective atomic number of mix D T H E EDITOR—SIR,

It is well known that mix D, which was introduced by Jones and Raine (1949), has been widely used as a phantom material for photons and electrons in radiotherapy. By adding fillers of magnesium oxide and tianium dioxide to wax, they made an improvement for mix D compared with wax alone in terms of mechanical properties and the attenuation characteristics of photons. In their paper, they reported that "We, therefore, calculated a modified prescription to adjust the value to 7.42" and "Dr. Spiers found an experimental Z-value of 7.47 for mix D". Recently, we calculated a value of the effective atomic number (Z) for mix D by using the following formula. ( r 2 9 4 i / 2 9 4 ( ) where at is the fractional electron content of element Zu We have found a Z-value of 6.971 and an electron density of 3.401 x10 2 3 electrons per gram for mix D, of which the elemental composition was taken from the table of HPA (1977). Jayachandran (1971) reported calculated values of 7.46 and 3.395 X1023. Yours, etc., T. HlRAOKA, K. KAWASHIMA.

National Institute of Radiological Sciences, Anagawa, Chiba, 280, Japan. {Received October, 1978) REFERENCES JONES, D. E. A., and RAINE, H. C. (1949). Correspondence,

British Journal of Radiology, 22, 549-550. HPA 1977. Phantom materials for photons and electrons. Scientific Report Series-20. JAYACHANDRAN, C. A., 1971. Calculated effective atomic number and kerma values for tissue-equivalent and dosimetry materials. Physics in Medicine and Biology, 16, 617-623.

The calculation of effective atomic number, Z. T H E EDITOR—SIR,

Your correspondents (Hiroaka and Kawashima, 1979) are, I find, correct in stating that 6.97 is the value of Z for mix D (Jones and Raine, 1949) as calculated from the formula of Mayneord (1937), i.e., Z 2 9 4 = 2;aiZi2-94, where ai is the electron contribution of the element i and Zi is its atomic number. Unfortunately, the work sheets for this 30year-old investigation are no longer available, so that the source of the regrettable error, responsible for the then published value, 7.42, can no longer be traced. I can only surmise that, having arrived at an effective atomic number in exact agreement with that similarly calculated for water, we were too ready to accept it without further check. Moreover, Spiers's experimentally determined value for mix D (Spiers, 1946), 7.46, was in satisfactory accord with it. The

330

Treatment of ankylosing spondylitis.

1979, British Journal of Radiology, 52, 330 Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents)...
155KB Sizes 0 Downloads 0 Views