X-ray multimeter performance under calibration laboratory conditions.

Background: Estimating dose delivered to patients for a typical mammographic or radiologic examination requires accurate knowledge of several beam quantities. X-ray multimeters (XMMs) are compact, solid-state semiconductor dosimeters that have become common for conventional QA measurements due to their ease of use.

Purpose: In this investigation, the performance of two XMMs in low-energy x-ray calibration beams was assessed, and the stability of the manufacturer's calibration over time was evaluated.

Methods: An RTI Piranha and Radcal Accu-Gold+ with AGMS-DM+ sensor were used to measure air-kerma rates and half-value layers of UW-MO and UW-M series calibration beams. Measurement results were compared to reference values collected with standard instruments. The same measurements were repeated every 3-5 months for 2.5 years to evaluate whether the XMMs' energy response changes over time.

Results: All air-kerma rate measurements and nearly all half-value layer measurements were within tolerance of the reference measurements. Both XMMs were satisfactorily stable over the course of the study, with all measured air-kerma rates within a 2% range relative to the reference for a specific beam. However, some drift in response was observed, particularly for the RTI Piranha.

Conclusions: Both XMMs met the performance standards provided by their respective manufacturers. An additional calibration would result in increased measurement accuracy for some beam series. One limitation of this study is that the detectors were not subject to more rigorous clinical conditions.