Radiation doses received by patients during dental x-ray examinations were measured in 95 patients referred to the X-ray Department of the Teaching Dental Hospital, University of Nairobi. The mean skin dose for single periapical films was 5.96 milligray (596 millirads) with the bitewing view recording a mean dose of 5.57 milligray (mGy). During a 14-film full-mouth periapical survey, mean doses ranged from 10.3-16.2 mGy for the upper jaw and 10.1-13.5 mGy for the lower jaw, respectively, depending on the region of dentition. In these full-mouth examinations, the distribution of skin dose over different parts of the dentition showed a characteristic pattern which may be explained by the overlap of radiation fields in the aggregated series of exposure. Orthopantomography recorded lower mean skin doses of 3.26 mGy in the molar region and 2.67 mGy at the posterior midline at the level of the 2nd cervical vertebra. The relative merits of intra-oral radiography versus orthopantomography are discussed, with radiation dosage as one of the factors to be considered. Some observations are made on measures to reduce patient dose

The development of radiation protection guidelines as contained in the 'Ten Day Rule' are reviewed. Facts for and against the rule and the changing altitudes in radiation protection leading to the 'death' of the 'Ten Day Rule' (I) are discussed. The current recommendation by the International Commission on Radiation Protection (ICRP) and the adaptation of the recommendation by the National Radiation Protection Board (NRPB) UK, and the Royal College of Radiologists (RCR) UK, are given. Some policy statements by the American College of Radiology (ACR) are also discussed. A few recommendations are put forward for the professional bodies and teaching institutions, in order to make them aware of the new radiation protection measures.

Radiation doses received by patients during chest X-ray examinations have been measured at six X-ray centres in Kenya. Absorbed doses from full-size radiography were found to be within acceptable limits at mean values of 29 millirad (0.29 milligray) per exposure for the postero-anterior view in adults and 20 millirad (0.20 milligray) for the antero-posterior view in children. The lateral view in full- ize examinations in children delivered a mean dose of 36 millirad (0.36 mGy). Photofluorography without image intensification delivered much higher doses, amounting to skin-entry doses of several hundred mrad per exposure, and showing large inter-hospital dose variations. Some observations are made on dose reduction measures.

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.

Cavity ionization methods have been employed to show that the amOUI1l of X-radiation produced by a newly installed x-ray tube was grossly reduced. Qualitative information based on the techniques of radiological photography suggests that there was no fault with the kilovoltage generator and that the tube was therefore the source of the anomaly. Observations of tube current avalanche and sparking at high potentials provide further clue as to the nature of the fault. A discussion of the possible causes of the anomaly is presented. This study demonstrates that, when specialised equipment for detecting the origin of some faults in x-ray machines is not available, radiation dosimetry and sensitometry can provide a most useful alternative.