ABSTRACT
A wide variety of existing combinations of target and filter materials (target/filter combinations) are used in mammography equipment. The patient dose depends on the X-ray quality that is derived from the target/filter combination, and a calibration of the dosimeter that is used in the measurement that corresponds to the specific target/filter combination is necessary. However, dosimeters in mammography are generally calibrated with reference to the X-ray quality of Mo/Mo or W/Al combinations, and it is unclear whether or not the X-ray quality that is derived from other target/filter combinations will affect the calibration coefficients. In this paper, the calibration coefficients of different dosimeters were evaluated for target/filter combinations. For an ionization chamber-type dosimeter, good energy dependence was found and the effect of the target/filter combination was small. However, for a semiconductor dosimeter, a large energy dependence was found, and different calibration coefficients that depended on the target/filter combination used were required.
Subject(s)
Mammography/instrumentation , Radiometry/instrumentation , Calibration/standards , Equipment Design , Female , Humans , Mammography/standards , Mammography/statistics & numerical data , Radiation Dosage , Radiometry/standards , Radiometry/statistics & numerical data , Semiconductors , X-RaysABSTRACT
In order to produce a cheap and stable X-ray generator system for calibration of dosimeters used in mammographic field, a dummy source of mammographic X-ray was developed using a tungsten (W) target X-ray tube and a molybdenum (Mo) filter. The photon fluence spectra of mammographic equipment were calculated using Birch's formula and aluminum (Al) attenuation curves were derived. The Al attenuation curves of X-rays from W target with Mo filter of various thicknesses were similarly obtained. Comparing the similarities of attenuation curves, the best fit Mo filter thickness was chosen. Consequently, a 0.04 mm thick Mo plus a 4 mm thick poly-methylmethacrylate filter were chosen to be added to W target industrial X-ray tube. The similarity of Al attenuation curves were verified by ionization chamber measurements.
