1975, British Journal of Radiology, 48,\\S2

Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents) THE EDITOR—SIR, CONGENITAL DIAPHRAGMATIC HERNIA AND 13 PAIRS OF RIBS

In view of the recently described association of congenital oesophageal atresia and 13 pairs of ribs (W. BondTaylor, F. Starer and J. D. Atwell, 1973; C. J. Hodson and D. G. Shaw, 1973) we wish to draw attention to the association of an extra pair of ribs with congenital diaphragmatic herniae. Review of the last 13 cases of congenital diaphragmatic herniae admitted to Westminster Children's Hospital revealed the presence of 13 pairs of ribs in three cases. There is thus a higly increased incidence of this skeletal anomaly in both these congenital disorders, the incidence of an extra pair of ribs in the general population being of the order of 0-5 per cent (W. Bond-Taylor etal.,1973). Yours, etc., F. M. KELVIN. F. STARER,

Westminster Children's Hospital, London, S.W.I. REFERENCES BOND-TAYLOR, W., STARER, F., and ATWELL, J. D., 1973.

Vertebral anomalies associated with oesophageal atresia and tracheo-oesophageal fistula with reference to the initial operative mortality. Journal of Paediatric Surgery, 5,9-13. HODSON, C. J., and SHAW, D. G., 1973. Congenital atresia

of the oesophagus and thirteen pairs of ribs. Paediatric Radiology, 1, 248-249.

both of these ratios are low due to some experimental error! 3. Three different dose-options were used on six pigs available for measurement of fields 12 months after 30 fraction treatment. For this group of animals, Table II shows that the ratio of length of treated field to length of untreated field is greater for the areas given "tolerance dose plus 15 per cent" than for those given the predicted tolerance dose. Table II also reports that a single dose of 2,380 rads ("tolerance + 30 per cent") caused less growth impairment than the single 1,800 rad exposure. Almost half of the data from these parts of the experiment imply that increasing the dose 15-30 per cent reduces delayed skin damage. In view of these strange results, we should not only consider data from the small 6f ./18d. group statistically invalid; we should also ask why only these two animals exhibited skin damage more severe than predicted. 4. The authors compare a slope of 0-46 of their so-called isoeffect curve with the number obtained from combined fractionation and time factors of 0-33 in the NSD formula. The number 0 33 is a slope obtained from an isoeffectcurve where dose against number of days is plotted and not dose against number of fractions as the authors have done. Needless to say, such comparison is non-scientific. 5. The authors do not describe or illustrate the arrangement of 4 fields on each flank. We are not actually told if the fields on the opposite flank are identical controls for each of the fields irradiated. This is quite important because normal skin growth patterns are variable, from one area to another and skin response to radiation may be related to thickness. The spacing of fields and combinations of fractionation pose difficult dosimetry problems. Did half of the pigs die of visceral radiation damage? SUMMARY

THE EDITOR—SIR, EXCESS LATE SUBCUTANEOUS FIBROSIS

We would like to comment on the paper entitled "Excess late subcutaneous fibrosis after irradiation of pig skin, consequent upon the application of the NSD formula" (Berry et al., 1974). Comparative measurement of fieldlength growth rates seems to be a promising method of studying a combination of delayed radiation effects (not just fibrosis); but from the results of this experiment one should not draw any conclusions one way or the other concerning the NSD formula or its clinical applications. 1. Quoting the authors' "The NSD formula was never intended to apply to irradiation with single doses (Ellis, 1971)", we believe it improper to use results of single-dose irradiation in criticism of the NSD equation. Although single-fraction "tolerance" should have been disregarded, Table II shows three different dose-options for the single fraction treatment on eight animals reported at 12 months. Why, then, only one dose-option (6x632 rads) for the very small number of pigs treated with six fractions in 18 days? The most important point of the discussion is statistically the least significant! 2. Careful study of Fig. 1 and both tables indicates that the critical conclusion is based almost exclusively on measurements of two fields on two pigs that survived 12 months (6f./18d.), one of them apparently a "runt". The authors fail to mention how many pigs were used in the experiment, but from Tables I and 11 one gathers that least 18 survived the first three months, of which only nine are accounted for at the end of the experiment. The fate of the other nine could have some bearing on the results in the small group given 6f./18d., the only data suggesting radiation effects more severe than predicted by the NSD formula. We think

The results of this experiment allow no valid conclusions regarding the NSD formula. The technique described would appear to provide one quantitative test of the NSD formula if two changes could be made: firstly, interaction of adjacent fields and other artifacts must be eliminated, possibly by using more animals, widely separating fields and using fewer fields per animal; secondly, a new experiment should provide adequate data and measure effects of three dose-options at two levels of "unconventional" fractionation such as 6f./18d. and 12f./26d. in addition to the conventional 3Of./39d. Admitting some bias, we suggest that clinical evaluations be not dismissed too lightly. Our experience with three times weekly fractionation dates back to the 1950's, including all anatomical regions. We are in the process of analysing for publication five years follow-up data of 400 breast cancer patients and 130 prostate cancer patients. Delayed radiation effects fit the NSD formula very well, and excessive late fibrosis does not occur if one avoids the mistake of treating opposed or converging fields alternately. Yours, etc., W. L. DEGINDER, V. D. MISTRY.

Capital Area Radiation and Research Center, 2600 East 19th Street, Austin, Texas 78702. REFERENCE BERRY, R. J., WIERNIK, G., PATTERSON, T. J. S.,

152

and

HOPEWELL, J. W., 1974. Excess late fibrosis after irradiation of pig-skin consequent upon application of the NSD formula. British Journal of Radiology, 47, 277-281.

Letter: Excess late subcutaneous fibrosis.

1975, British Journal of Radiology, 48,\\S2 Correspondence (The Editors do not hold themselves responsible for opinions expressed by correspondents)...
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