Mammographic practice and dosimetry in Britain

Abstract

A survey of mammographic techniques and dosimetry in 61 NHS centres in Britain has been completed. Physical parameters measured at each centre included tube output, half-value thickness, peak kilovoltage, surface dose and percentage depth dose. Ionisation and thermoluminescence dosimetry were employed and image quality was assessed subjectively using a test phantom. Absorbed doses are given at the plane surface of an average-sized, 5 cm thick homogenous breast composed of 50% fat and 50% water. The doses fall naturally into the four combinations of molybdenum (Mo) and tungsten (W) targets and film (F) and xerox (X) receptors. The Mo/X group produced the best images of the phantom but also the highest mean dose of 3.26 cGy (rad) for a cranio-caudad (c-c) view and its use does not seem justified for asymptomatic screening. The Mo/Lo-Dose or MIN-R film combination gave a mean dose of 0.95 cGy(rad) for a c-c view whereas the W/X group gave 0.89 cGy(rad) and superior image quality. The W/F group gave the poorest image quality and its continued use for mammography is questionable.