Radiation exposure to patients during radiological examinations of the gastro-intestinal tract: intrahospital dose variations
Tole, N M
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Skin and gonad doses have been measured in 144 adult patients undergoing barium meal and barium enema examina-tions at a University Teaching Hospital. Intrahospital variations are discussed and their implications for national dose surveys considered, It is suggested that, due to differences in leakage and scattered radiation levels, overcouch tube machines may deliver higher doses to organs outside the useful beam than undercouch units, The study also points towards increased film consumption in GIT studies, National surveys of radiation doses to patients in diagnostic radiology are restricted to selected institutions over short periods of time. Consequently, although the dose data from such exercises may provide a broad picture of a national situation, detailed studies of intrahospital and interhospital variations for anyone type of examination are made difficult by the small numbers of examinations carried out at anyone institution during national surveys. Detailed surveys of doses received in selected examinations at single institutions, or within limited regions, enable better analysis of such variations to be made. Matthews and Miller (1969) have reported the results of a regional survey in Great Britain. A large hospital with staff of varying levels of skill provides a suitable environment for studying within-hospital dose variations. When a particular type of examination is performed by several radiologists in rotation, the "personal factor" in dose variation tends to be evened out in the mean values obtained. Furthermore, the use of uniform film¬processing conditions removes another of the , traditional causes of variations. The present survey was undertaken at the University Hospital of South Manchester in Great Britain. Studies of the radiation exposure to patients in diagnostic examinations of the gastro-intestinal tract (GIT) are important because this group of investigations gives large doses to the active bone marrow as well as the gonads of the irradiated individuals. Following a sharp decline in the frequency of mass miniature chest radiography, GIT studies now probably make the largest contribution to the annual ner canut mean bone marrow dose in Great Britain. despit~ their low frequency compared to othe; diagnostic examinations. The relatively low con¬tribution of GIT studies to the genetically-significant dose (Wall et ai, 1980) is due to a combination of their low frequency and the age distribution of the patients examined (Kendall et ai, 1980). It may be possible that the somatic stochastic risks associated with this group of examinations are more important than the genetic risks. However, the computation of mean bone marrow doses, which requires a model combining data on the distribution of active bone marrow in different segments of the body with estimated radiation doses to the bone marrow in those segments, is beyond the objectives of this paper. In the present work, gonad doses in male patients, and abdominal skin doses in female patients, have been measured for larger numbers of patients than are normally achieved at individual institutions during national surveys. In female patients, ovary doses have been calculated from the skin doses. In the case of barium enema examinations the skin doses may be found useful in estimating mean bone marrow doses.