A Survey on mean glandular dose in mammography examination and the factors affecting it in Shahid Sadoughi hospital, Yazd, Iran

Introduction and objective : Breast cancer (BC) has become one of the public health challenges with an increasing trend. In Iran, BC ranks first among women's cancers and the fifth cause of death (۱,۲). Mammography, with its ability to detect masses early, has become the gold standard in diagnosing this malignancy. Mammography is an imaging method based on ionizing radiation. Despite using low-energy X-rays, some studies have reported the effect of mammography on the induction of secondary cancer in patients undergoing mammography (۳,۴). Since breast mammary glands are most sensitive to ionizing radiation, the mean glandular dose (MGD) is the most suitable parameter to evaluate the absorbed dose in patients undergoing mammography and the risk caused by this imaging. The standard dose limit for MGD is recommended by International Commission on Radiological Protection (ICRP) to be less than ۳ mGy (۵,۶).Methods: In this study, was conducted on women aged ۳۰-۷۰ referring to the mammography unit of Shahid Sadoughi Hospital in Yazd city from May to August ۲۰۲۲. Since the direct calculation of MGD is not possible, the most common method to estimate the MGD of patients undergoing mammography examination is the measurement of the entrance surface dose (ESD). To this end, by placing the TLD-GR ۲۰۰ on the breast of the patients before the compression of the breast tissue for both Craniocaudal (CC) and Mediolateral oblique (MLO) projections, the surface entrance dose was obtained (formula ۱). Then, ESD was multiplied by the normalized glandular dose (DgN) extrapolated from the study by WU et al. (۷), and finally, the MGD was obtained (formula ۲) (۸).ECCi = TLD/TLDi (۱)MGD = ESD * DgN (۲)Results: In the present study ESD and MGD of all mammograms were ۷.۷۵ and ۱.۳۰ mGy, respectively. The mean value of MGD per woman was ۱.۳۱ mGy. MGD in CC projections was ۰.۹۷ mGy and ۱.۶۳ mGy for MLO projection. To observe the relationship between MGD and CBT, age, BMI and exposure parameters (kVp, mAs), data analysis of ۲۵۶ mammograms was performed using the linear regression method. The highest correlation was obtained between MGD and CBT, as well as between MGD and age with the correlation coefficient R = ۰.۶۲ , R= -۰.۵۷. This means that the MGD increased with increasing CBT (direct relationship) and decreased with increasing age (inverse relationship). The relationship between irradiation parameters and MGD, as well as MGD and BMI with the same correlation coefficient R = ۰.۳, was a direct and positive relationship.Conclusion: In this study, the mean±SD MGD per woman was ۱.۳۱ ± ۰.۳۱ mGy, which was less than the amount recommended by ICRP (۳ mGy) (۶). It indicates the correct operation of the mammography machine of Shahid Sadoughi Hospital in Yazd. Based on the reported correlation coefficients between dose and parameters, it can be stated the importance of performing compression in mammography examinations to reduce breast thickness during mammography to avoid increasing the dose of patients. On the other hand, the results of the present study can justify the reason for not performing mammography examinations on women under ۴۰ years old.

کلیدواژه ها:

Breast cancer ، Mammography ، Cranio Caudal Projection ، Mediolateral Oblique Projection ، Mean Glandular Dose ، Entrance Surface Dose ، Thermoluminescence Dosimeter