Room: ePoster Forums
Purpose: To illustrate the importance of medical physics personnel vetting their test equipment prior to actual use, a case study is presented pertaining to CT pencil ion chambers. A testing procedure was later developed by our organization to mitigate the issues experienced in this example.
Methods: CT pencil chambers from two different vendors (Vendor A & Vendor B) were initially tested with both a CT and radiographic x-ray system using various technique factors. The displayed measurements were then compared. By utilizing annual physics evaluation data from the preceding 12 months, system displayed CTDI_vol values were compared to those calculated by chamber measurements. Final testing, following Vendor A re-calibration, was performed using a portable x-ray system.
Results: Measurements indicated a difference of approximately 10% between Vendor A and Vendor Bâ€™s CT pencil chambers. Vendor A performed additional testing off-site. Calibration reports from Vendor A indicated deviations from reference values between -6.1% and -11.9% for all chambers tested. The average difference between CTDI_vol values calculated from Vendor Aâ€™s chamber measurements and those displayed by CT acquisition workstations differed by was -7.3%, where Vendor B only differed by 1.6%. Following re-calibration, average measurements from Vendor A chambers differed by -0.1 to +3.9% from a reference chamber manufactured by Vendor B that had previously been evaluated for accuracy.
Conclusion: In this case, all of Vendor Aâ€™s CT pencil ion chambers deviated by more than the manufacturerâ€™s tolerance limit of 5%. It is important that physicists working in a clinical environment perform test equipment evaluations to reduce the potential for erroneous readings. Our institution later established a policy and QC procedure for new, repaired, or re-calibrated test equipment. It was validated using the re-calibrated CT pencil chambers from Vendor A.