Radiation exposure of the Yazd population from medical conventional X-ray examinations

The effective dose is a dosimetry parameter which takes into account the dose received by all irradiated radiosensitive organs, and may be taken as a measure of the stochastic risk (1). This dose descriptor is being increasingly used to quantify the amount of radiation received by patient undergoing diagnostic Xray examinations (2-4). Medical exposures are not distributed uniformly around the population, so the annual per caput dose provides a better indication of overall trends in individual dose, as radiology practice changes, than the annual collective dose (2). According to the National Radiation Protection Bored (NRPB) report, contribution from patients undergoing X-ray examinations are nearly 90% of the total per caput effective dose from all artificial sources in the UK, with diagnostic nuclear medicine procedures contributing a further than 8% (excluding radiotherapy) (5). All occupational and public exposures arising from medical and other uses of ionizing radiation amount to less than 3% of the total (5). Although a vital feature of medical exposure is the direct benefit they provide to the healthcare of the exposed individual, medical exposures should be justified on an individual basis by offsetting the very small radiation risks for patients. A large per caput dose will be justified if all the individual medical exposures are justified (and optimized) (5). The patient dose is highly dependent on the medical diagnostic X-ray procedures, so the population dose and dose distribution may be altered by the development of medical diagnostic X-ray techniques. Therefore the per caput dose result of medical X-ray Background: Radiation dose knowledge through Xray examinations and their distribution in Iran provides useful guidance on patient dose reduction. The results of the entrance skin dose (ESDs) of five common radiographies in all radiology centers in Yazd province were reported in our previous study (2003). In the present study we have evaluated the collective effective dose of conventional X-ray examinations, as well as the annual per caput of Yazd population. Materials and Methods: The annual frequencies of 18 different types of conventional radiology examinations during April 2005 to March 2006 were recorded from all 35 radiology centers in Yazd province. The exposure conditions consisted of kVp, mAs, and Focus surface distance (FSD) of the examinations for the mode of exposure in each X-ray unit. 620 ESD were measured by diode dosimeter in 35 hospitals and clinics. The real exposure kVp for each radiology unit was measured by a Molt-O-Meter. The conversion coefficient (effective dose ESD ratio) for each radiology examination was determined by using SR262 tables. Finally, the patients' effective dose was calculated by multiplying the conversion factor to the ESD. Results: The patients' annual collective effective dose due to the conventional radiology examinations was 31.159 man-Sv (0.03 mSv per inhabitant). The frequency of examinations was 311813 i.e. 0.36 examinations per head of the population for one year. Conclusion: According to our findings, the effective per caput dose seems to be optimally relative to HCL-II countries, which may be due to low mean effective dose that could obscure high examination frequency. The number of radiology conventional examinations and frequency of radiologist per1000 population of Yazd was more and lower than HCL-II countries respectively. Thus the justification of radiography requests in this province must be revised. Iran. J. Radiat. Res., 2007; 4 (4): 195-200