Measurement of outdoor terrestrial gamma radiation in the Sultanate of Oman.

The terrestrial gamma radiation level was determined throughout the Sultanate of Oman over a 3-y period. The dose rate at 1 m above the ground was measured at 512 locations using a compensated Geiger-Miller detector. The activity concentration of soil/rock samples, collected from 112 locations, was determined by gamma spectrometry. Dose rates calculated from the activity concentrations compared well with the measured values corrected for the cosmic ray contribution. Some of the highest terrestrial dose rates, up to 110 nGy h(-1), were measured in shales (Wadi Bani Awf, Saih Hatat, and the Huqf) and exposed basement granites (Jebal Jalan and the Mirbat peninsula). Two small hot spots were found where the maximum dose rate was 1,024 nGy h(-1). The average dose rate in the main population area of the Batinah is 38.5 nGy h(-1) (0.29 mSv y(-1)) and Muscat 44.9 nGy h(-1) (0.34 mSv y(-1)). The mean population weighted dose rate is 39.8 nGy h(-1) (0.30 mSv y(-1)). Most of Oman's surface rock is limestone, which is low in concentrations of radionuclides from the uranium and thorium series. Hence, the average dose rate is well below the world average of 0.45 mSv y(-1).

Radiation doses from CT in the Sultanate of Oman.

The computed tomography dose index (CTDI), dose-length product (DLP) and the effective dose were determined for a range of CT examinations in the Sultanate of Oman. There was a wide variation in CTDI. This shows that there is a variation in both scanner design and the exposure settings used by hospitals. There was also a wide variation in DLP and effective dose, suggesting that in some cases too many slices are taken. Therefore, standard protocols should be designed and adhered to in order that radiation doses may be reduced in the future.

Routine receiver operating characteristic analysis in mammography as a measure of radiologists' performance.

A system for calculating receiver operating characteristic (ROC) curves from routine audit data is described. Both diagnostic opinion and pathology outcome data from the symptomatic mammography department were recorded in an audit database, from which ROC curves were calculated. A comparison of overall radiologists' performance was made and the appropriate performance indices discussed. Similar data were collected from the breast screening centre where the same radiologists read mammograms. The radiologists' performance in the symptomatic department was compared with that in the breast screening centre and was found to be better in the screening centre. The difference could not be wholly attributed to the different age distribution of women and highlighted the different nature of the diagnostic task and the differing sampled populations. ROC curves were drawn for different clinical signs to determine any particular area of difficulty the radiologist may experience. ROC analysis as part of routine audit can be used for maintaining and improving the quality of an individual's performance, and targeting learning on areas of particular weakness.