Hugo de las Heras PhD, MSc, Abstract Co-Author: Research Consultant, QUART GmbH

Ulrich Heil DIPLENG, Abstract Co-Author: Nothing to Disclose

Ricardo de las Weigel MA, Presenter: Officer, QUART GmbH

Oliver Weinheimer, Abstract Co-Author: Nothing to Disclose

Felix Schofer PhD, Abstract Co-Author: Officer, QUART GmbH

Quality control for mammography and tomosynthesis systems requires accurate measurements of dose, especially since these devices are or may be used for screening. Current dosemeters are mostly dependent on the incidence angle, the photon energy, backscatter and environmental conditions (pressure, temperature, etc). The purpose of this work was to evaluate the dependence of a new-generation, solid-state detector on these factors and test it for the practice of quality control.

The dosemeter is shielded on the back to avoid backscatter measurements and it is not dependent on environmental conditions, which is usual for solid-state detectors. To calibrate its dependence on x-ray beam incidence angle and energy, the dosemeter was sent to the national primary standard dosimetry laboratory. After calibration, the dosemeter was placed on a 46 mm-thick phantom to measure entrance surface air kerma from a digital breast tomosynthesis system (31 kVp and W/Al) at different levels of the tube current-time product.

The dosemeter showed an angular dependence below 1 % for angles between 0 and 30 degrees (0.2, 0.1, 0.7 and 0.1 % for 8, 20, 26 and 30 degrees respectively), which contain the ones currently used in breast tomosynthesis examinations. Energy dependence was between 0.2 and 0.5 % for photon energies between 26 and 36 keV. During the measurements with the DBT system, the dose values displayed by the console and the dosemeter measurements showed no significant difference, which means that the dosimetry within the x-ray system was correct. An additional field comparison with measurements from an ionisation chamber is planned to be presented at the meeting.

The calibration measurements showed that the dependence on the angular beam incidence and the x-ray energy was below 1 %. The device can thus be used for the praxis of quality control in mammography and tomosynthesis. For this system, using the AEC settings, the dose from one mammography projection was similar to the dose received by one tomosynthesis scan.

http://abstract.rsna.org/uploads/2014/14017368/14017368_cusy.jpg

de las Heras, H, Heil, U, Weigel, R, Weinheimer, O, Schofer, F, Entrance Dose Measurements for Mammography and Tomosynthesis with Angular and Energy Dependence Below 1%.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14017368.html