Assessing the Long-Term Stability of Reference Dosimetry Systems In a Physics Consulting Intercomparison Network
Abstract
Purpose
To evaluate long-term calibration stability and measurement uncertainty in reference dosimetry systems through systematic intercomparison analysis, establishing evidence-based quality assurance recommendations for radiation oncology programs.
Methods
Comprehensive analysis of semiannual intercomparison reports (2002-2025) from the Northwest Medical Physics Center (NMPC) network encompassing reference-class Farmer ionization chambers, electrometers, HDR brachytherapy well chambers, barometers, and electronic thermometers across radiation oncology institutions. Measurements performed in NIST-traceable controlled environments with systematic comparison against reference standards.
Results
Reference dosimetry equipment demonstrated distinct performance hierarchies and temporal stability patterns. Ionization chamber calibration coefficients showed excellent long-term stability with systematic precision improvements observed across all device classes over the study period. Modern digital electrometers demonstrated superior stability compared to legacy analog systems, with measurable drift reduction documented. HDR well chambers maintained consistent calibration stability with no systematic drift patterns identified. Barometers and thermometers exhibited exceptional long-term stability over two decades. The intercomparison program successfully identified equipment failures including chambers with bent central electrodes and electrometers requiring recalibration, demonstrating the value of independent verification for detecting damaged or degraded dosimetry equipment.
Conclusion
Well-maintained reference dosimetry systems achieve high precision over extended periods when supported by rigorous quality assurance programs. Empirical evidence supports biennial external intercomparison frequency with annual verification for optimal calibration traceability. Transition to modern digital electrometers yields measurable stability improvements over analog systems. The intercomparison approach provides critical independent verification capable of detecting equipment failures such as mechanical damage to ionization chambers that may otherwise go undetected in routine institutional quality assurance. Results validate the robustness of systematic intercomparison programs and demonstrate value of regional quality assurance networks for maintaining long-term measurement standards compliance in radiation oncology.