Analysis of patient exposure dose for mammography. Estimation of average glandular dose in 1998 questionnaire

Recently, patient exposure dose for mammography are varied because of a great demand for mammography, which non-palpable lesion can be detected, diffusion of special X-ray equipment, progress of CR and enlightenment or study on mammography in Japanese society of radiological technology. Therefore, the newest patient exposure dose obtained from '98 questionnaire carried out to the whole country in Japan was investigated. Furthermore, the average glandular dose based on '98 was compared with that of '93. The average glandular dose can be calculated from the product of the breast entrance skin exposure and DgN (the average glandular dose per unit entrance skin exposure). The breast entrance skin dose was estimated from the dose of 782 institutions in '98, which was calculated from data measured at 51 institutions in Tokai and Hokuriku area. DgN was used published table of 50% adipose-50% glandular breast composition and 4.2 cm breast thickness corresponding to measured half-value layer (HVL) on each tube voltages. Then, patient exposure dose for mammography was estimated from exposure condition (tube voltage, mAs value) obtained '98 questionnaire. The dose in '98 estimated 1.422 mGy was reduced that compared with in '93 estimated 1.610 mGy. The dose of '98 without grid was reduced about 30% of '93. The dose of 98 with grid was not any reduced than the dose of '93. However, the number of institution of '98 with grid was about 2.8 times than '93. The patient exposure dose for mammography was reduced approximately 10% during 5 years. There are probability that mammography with grid for guidance level will be 1.5 mGy. (author)