Radiation Protection Dosimetry Advance Access published online on April 21, 2008
Radiation Protection Dosimetry, doi:10.1093/rpd/ncn139
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AN ESTIMATE OF THE INFLUENCE OF THE MEASUREMENT PROCEDURE ON PATIENT AND PHANTOM DOSES IN BREAST IMAGING
Department of Radiation Protection at Medical Exposure, National Centre of Radiobiology and Radiation Protection, 132 Kliment Ohridsky blv., Sofia 1756, Bulgaria
* Corresponding author: j.vassileva{at}ncrrp.org
This work is aimed to study the variability of dosimetry results owing to various measurement methodologies for breast dosimetry. This is performed in the frame of the development of a national protocol for breast dosimetry. Doses for standard phantom and group of patients were calculated for two mammography systems from the tube output measured with a calibrated ionisation chamber. The backscatter from the phantom under the chamber contributes to an increase in dosimeter readings of 
0.8–1.5%, whereas the proximity of the compression plate to the chamber causes increase in the measured air kerma value by 6.5–7%. High value layer (HVL) measured with solid-state detector without corrections for energy dependence was 17% higher than the one measured with ionisation chamber, which causes corresponding overestimation of average glandular dose (AGD). The use of conversion factors based on typical but not measured HVL values leads to 3.5–5.6% overestimation of AGD. Although the sources of uncertainty were taken into account, the difference between the phantom and patient doses was 24%. Some practical recommendations to be included in the national dosimetry protocol are summarised.