1975, British Journal of Radiology, 48, 773

SEPTEMBER 1975

Correspondence experience with the six-fraction schedule at other sites had indicated that tolerance would be reached with a maximum Your editorial "Must Radiologists do all the Reporting" dose of only, 3,600 R, i.e. 16-6 per cent lower. and Dr. Emrys-Roberts's letter express well both sides of In terms of survival and control of local disease the an important argument. Like you I have misgivings. The results of the two techniques were very similar. Likewise the problems of reponsibility for radiation protection, only a early and late radiation effects up to five years were similar decade and a half after the Adrian reports and a month and acceptable. The skin changes were assessed and scored or two after a critical report by the Consumers' Association at two weeks, six months, one year and five years after {Which? 1975), are particularly disturbing. treatment. The early skin changes were less severe in the Ideally, we should have more and better radiologists. six-fraction group. However, the changes were progressive, However, I think that Dr. Emrys-Roberts's comparison particularly in the six-fraction group, and by five years with pathologists is apt. Is it not time that radiologists were very similar in both the six-fraction and 12-fraction became prepared to delegate more work to radiographers? groups. The severity of apical pulmonary fibrosis was also As you know this has been tried in the United States, ap- classified and scored and found to be similar at six months parently with success (Rosenbaum et al., 1973; Thompson, and one year, but with a tendency to improve rather than 1974). According to these reports, pattern recognition and progress in both groups. It is thus apparent that the clinia number of procedures involving screening are well within cally determined iso-effect doses for six fractions using the reach of many radiographers. If this sounds patronising, cobalt teletherapy are some 15 per cent less than would be it is not intended to be. Radiologists' assistants exist in predicted by the NSD formula. Sweden. We might consider introducing Felson's Rad-Ad, The chest wall surrounding the mastectomy scar was the radiological administrator (Felson, Van Tuinen and irradiated with a direct field using 70 kVp X rays (9 mA, Kereiakes, 1970) to ease managerial burdens if these 1 -5 mm Al HVL) at 25 cm FSD. An incident dose, including prevent us from practising radiology. Within such a system a correction for the back-scatter factor, of 4,000 R was given in lies a clear chain of command (a seemingly reactionary 12 fractions over 28 days, while it was found that to produce remark which I use without apology) and a line of res- equivalent reactions in six fractions over 18 days required ponsibility which is not, in my view, possible if clinical 3,400 R, which is in fact some 5 per cent more than the assistants are introduced. 3,226 R incident dose predicted by using the NSD equation. I do not think that radiologists must do all the reporting We 60suggest that this apparent inconsistency with respect to the Co iso-effect doses is due to the invalidity of applying or, indeed, all the radiology, but I am not sure that these the NSD formula, which is said to be based on vasculoare jobs for general practitioners. connective tissue tolerance, to the incident dose from a Yours, etc., beam of this quality where the percentage depth dose was M. S. F. MCLACHLAN. only60 88 per cent at 0-5 cm (corresponding to the maximum Department of Radiodiagnosis, for Co) and 70 per cent at 1 -0 cm. The integral dose to the The General Infirmary, vasculoconnective tissues from the 70 kVp beam is obviously Leeds LSI 3EX. much lower than from telecobalt irradiation and a calculation of NSDs at 0-5 cm 60depth (taking f=0-93 and an RBE FELSON, B., VAN TUINEN, R., and KEREIAKES, J., 1970. The of 115 with respect to Co) gives 1,515 rets for the sixRadiology Administrator. Radiology, 97,191-194. fraction treatment and 1,437 rets for 12 fractions. The corROSENBAUM, H. D., SELKE, A. C , jun., BAKER, E. G., jun., responding 60Co "tolerance" NSDs were 1,636 rets HENDERSON, D. R., and KIERNAN, B., 1973. Progress of the training program in advanced radiologic technology and 1,961 rets respectively. We therefore suggest that the at the University of Kentucky Medical Center. Radiologic clinical tolerance of the 70 kVp X-ray treatments as used may be determined by the epithelium and not the connective Technology, 44, 325-330. tissues. If this is the case, it would not be surprising that the THOMPSON, T. T., 1974. The evaluation of physician's six-fraction schedule is so well tolerated as substantial assistants in radiology. Radiology, 111, 603—606. repopulation would occur between the larger, more widely WHICH? REPORT 1975. Public safety: Radiation. Which? spaced fractions. 100-103. The important conclusion however, is that the straightforward application of the NSD formula to a six-fraction THE EDITOR—SIR, technique using cobalt teletherapy would be well above DANGERS OF THE CLINICAL USE OF THE NSD FORMULA tolerance at most sites, with the implied risk of serious late FOR SMALL FRACTION NUMBERS effects. Twenty years of clinical experience of twice and thrice Yours, etc., weekly dose fractionation techniques and recent clinical THELMA D. BATES, research at St. Thomas' Hospital support the view held by Radiotherapy Department, the Oxford group that the NSD formula is unsuitable for St. Thomas' Hospital, London, S.E.I. use when planning a new treatment schedule in which the L. J. PETERS. number of dose fractions is reduced (Berry et al., 1974). Richard Dimbleby Research Laboratory, In a five-year prospective trial comparing post-operative St. Thomas' Hospital, London, S.E.I. radiotherapy delivered in six fractions over 18 days (twice weekly) versus 12 fractions over 28 days (thrice weekly) in REFERENCES 411 patients with breast carcinoma, observations were made BATES, Thelma D. A prospective clinical trial of postof the early and late radiation effects on a variety of normal operative radiotherapy delivered in 3 fractions per week tissues, namely the skin, subcutaneous tissues, lung, bone versus 2 fractions per week in breast carcinoma. Clinical and oesophagus (Bates, 1975). Radiology (in press). Dose levels thought to be biologically equivalent were BERRY, R. J., WIERNIK, G., PATTERSON, T. J. S., and HOPEselected on the basis of previous clinical experience. WELL, J. W., 1974. Excess late subcutaneous fibrosis The cervico-axillary and internal mammary nodes were after irradiation of pig skin, consequent upon the applicatreated with cobalt 60 teletherapy to maximum tissue doses* tion of the NSD formula. British Journal of Radiology, 47, of 5,350 R in 12 fractions or 3,600 R in six fractions. A dose 277-281. of 5,350 R in 12 fractions over6028 days corresponds to an NSD of 1,961 rets (taking f for Co = 0 96). To deliver the *The physical measurement is of exposure in rontgen units same NSD in six fractions over 18 days would require a and doses are expressed in this unit in clinical practice withmaximum tissue dose of 4,315 R whereas previous clinical out conversion. THE EDITOR—SIR, MUST RADIOLOGISTS DO ALL THE REPORTING

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Letter: Dangers of the clinical use of the NSD formula for small fraction numbers.

1975, British Journal of Radiology, 48, 773 SEPTEMBER 1975 Correspondence experience with the six-fraction schedule at other sites had indicated tha...
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