Traceability in Medical X-Ray Breast Imaging Dosimetry

In medical imaging for breast cancer screening and diagnosis using x-rays regular quality control measurements are crucial to achieve high diagnostic efficacy at an acceptable dose level for the patient. With the development of digital imaging detectors new imaging modalities such as 3D mammography (tomosynthesis) or contrast enhanced mammography are introduced. This results in a wide variation of radiation qualities used for breast imaging. Also, the tools used for quality control measurements are constantly being refined and optimized for their intended use. In contrast to ionization chambers, which represent the gold standard for quality control measurements, the handling of X-ray multimeters of the latest generation is easier and they allow the determination of various quantities at once. However, regular calibration for any instrument used for quality control measurements has to be performed to ensure that these devices are working properly. The conditions for calibration of instruments as well as performance limits are defined by international standards and reviewed in the international Code of Practice for Diagnostic Radiology Dosimetry. Despite developments, the calibration protocol has remained unchanged to date. As a consequence, they do not cover the spectrum of radiation qualities in use nor the variety of quantities provided by X-ray multimeters. Additionally, a measurement set up which complies with the current standards for calibration might result in an X-ray spectrum that differs from that of mammography x-ray systems. Ionization chambers are robust to slight changes in the spectrum but there is a lack of knowledge how this affects the response of X-ray multimeters. The corresponding international standards are currently under revision and the International Atomic Energy Agency assesses the need to update the Code of Practice. This research project targets the described challenges as follows: Firstly, a catalog of currently used radiation qualities for mammography and tomosynthesis will be established. Second, the performance of X-ray multimeters is determined and compared both when used in the calibration laboratory and when used with mammography and tomosynthesis systems from the most commonly used manufacturers. Third, the X-ray spectra of representative radiation qualities from the catalog established before will be determined and compared to nominally the same spectra in the calibration laboratory. The goal is to relate the characteristics of the spectra to the performance of the X-ray multimeters. With the newly gained knowledge, we formulate limits for the variation of the response and requirements for reference and field instruments for calibration of X-ray multimeters used for quality control of mammography and tomosynthesis X-ray systems. This could be a valuable input for future revisions of the international standards and Code of Practice in which the selected research institute is significantly involved.

In medical imaging for breast cancer screening and diagnosis using x-rays regular quality control measurements are crucial to achieve high diagnostic efficacy at an acceptable dose level for the patient. With the development of digital imaging detectors new imaging modalities such as 3D mammography (tomosynthesis) or contrast enhanced mammography are introduced. This results in a wide variation of radiation qualities used for breast imaging. Also, the tools used for quality control measurements are constantly being refined and optimized for their intended use. In contrast to ionization chambers, which represent the gold standard for quality control measurements, the handling of X-ray multimeters of the latest generation is easier and they allow the determination of various quantities at once. However, regular calibration for any instrument used for quality control measurements has to be performed to ensure that these devices are working properly. The conditions for calibration of instruments as well as performance limits are defined by international standards and reviewed in the international Code of Practice for Diagnostic Radiology Dosimetry. Despite developments, the calibration protocol has remained unchanged to date. As a consequence, they do not cover the spectrum of radiation qualities in use nor the variety of quantities provided by X-ray multimeters. Additionally, a measurement set up which complies with the current standards for calibration might result in an X-ray spectrum that differs from that of mammography X-ray systems. Ionization chambers are robust to slight changes in the spectrum but there is a lack of knowledge how this affects the response of X-ray multimeters. The corresponding international standards are currently under revision and the International Atomic Energy Agency assesses the need to update the Code of Practice. This research project targets the described challenges as follows: Firstly, a catalog of currently used radiation qualities for mammography and tomosynthesis will be established. Second, the performance of X-ray multimeters is determined and compared both when used in the calibration laboratory and when used with mammography and tomosynthesis systems from the most commonly used manufacturers. The goal is to correlate the performance of X-ray multimeters with the characteristics of the spectra that prevail under various measurement conditions in the calibration laboratory and on mammography and tomosynthesis systems. With the newly gained knowledge, we formulate limits for the variation of the response and requirements for reference and field instruments for calibration of X-ray multimeters used for quality control of mammography and tomosynthesis X-ray systems. Together with an updated catalog of the radiation qualities used, this could be a valuable contribution to future revisions of international standards and codes of conduct, in which the selected research institute is significantly involved.