Radiological hazards to patients / interim report of the Committee.

  • Great Britain. Committee on Radiological Hazards to Patients
Date:
1959
Catalogue details

Licence: Public Domain Mark

Credit: Radiological hazards to patients / interim report of the Committee. Source: Wellcome Collection.

    16/24 page 16
    Method 12. Observations were made by placing an ionisation chamber over the clothing: of the patient at the centre of the field. Since in most cases the chamber used was that provided for the general survey of gonad dose the size of the chamber was such that its mid-point was about 1 inch from the clothing. It is likely that the clothing. might be up to 4 inch from the skin. Thus the chamber was in fact closer to the tube than the skin and the recorded dose might therefore be greater than the actual skin dose. The factor of increase is unlikely to be in excess of that calculated from the inverse square law, i.e., of the order 10 per cent. Thus the figures quoted in this paper may be up to 10 per cent greater than the actual skin dose. Results 13. The results of the survey are given in Table II. A histogram for the observations. is given in Fig. 1, which shows a distribution of doses sufficiently uniform to justify the use of a simple arithmetic mean. The value of this mean dose is 0-63 r per examina- tion. Conclusion 14. For the purpose of estimating the somatic risk the best available figure for the skin dose is 0:63 roentgens delivered with radiation having an average quality of 72 kV. The range of skin dose is from 0:17 to 1-9 roentgens and the range of quality from 50 kV to 90 kV. C. Additional Observations made during the Survey 15. In addition to the measurements of the actual doses received by patients under- going mass X-ray investigations, we also made a number of observations on apparatus. or techniques which we consider should be reported to the Committee. These, however, were not made systematically; in the case of patients they were not numerous; and we do not attach any statistical significance to them. They are intended more as a guide in framing recommendations relating to procedure in Mass X-ray Units. Limitation of the X-ray beam 16. All the X-ray tubes were provided with pre-set lead diaphragms restricting the beam so that only the fluorescent screen in the camera unit was irradiated. In each case film was used to establish that the periphery of the beam did not exceed the area of the screen. Measurements made with a dosemeter showed that the intensity just within the beam was always more than two hundred times the intensity 2 inches outside the beam. Dose received by children 17. No provision was made on any of the apparatus for independently limiting the vertical dimension of the beam to less than the full height of the screen. The design of the camera unit was such that the patient’s chin must rest on the upper edge of the screen. With small adults and with children this necessarily resulted in the X-ray beam extending well below the lower edge of the lung field and in very young children as low as the head of the femur. A girl aged 10 radiographed on the 100 mm unit received an ovary dose of 0-28 mr despite the reduced exposure of 62 kV and 22 mAs. In this case the ovary was not in the direct beam but had it been so the phantom measurements suggest that the dose would have been increased by a factor of 20 times. Similar results were observed with boys of about the same age. Recommended improvements in apparatus 18. A reduction in the dosage currently received can be achieved by three simple measures :— (a) An adjustable protective shield should be attached to the apparatus sO that it can protect the individual’s abdomen from the direct beam, Le. provide a means of limiting the field size. :
    digitised image 1
    digitised image 2
    digitised image 3