Establishment of Image Quality Baselines for Three Elekta Synergy MV EPIDs
J Donaghue*, S Gajdos, Akron General Medical Center, Akron, OHSU-E-P-6 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To determine the stability of MV image quality on an electronic portal imaging device (EPID), a commercially available QA phantom and software package was used to analyze parameters based on recommendations from AAPM TG-142. These parameters allowed for the institution to determine when EPID performance deteriorated and necessitated replacement.
Methods: An image quality phantom was used to perform QA on three EPIDs. Based on manufacturer recommendations, two consecutive exposures of the QA phantom were performed and the resulting images were transferred to the software system via DICOM Image. Data from the calendar year 2012 was used to establish average baseline for spatial resolution parameters (f30, f40, and f50), CNR, and noise.
Results: The average resolution measurements were found to be 0.6899 ±0.0127, 0.546 ±0.017, and 0.415 ±0.018 for f30, f40, and f50 respectively. The CNR and noise metrics were found to be 354.5 ±24.7 and 38.3 ±3.2 respectively . When one of the EPIDs failed, it was apparent in the noise and CNR measurements when data was further than 10 standard deviations from baseline. Calibration of inferior replacement EPIDs resulted in expected Noise and CNR measurements, but the process of eliminating the Noise on the EPIDs resulted in degraded image resolution data that was greater than 5 standard deviations from baseline.
Conclusion: Establishment of baseline data of image quality parameters is critical for assuring the device is operating correctly. EPID failure was easily determined because noise and CNR data points spiked out of the expected range. Also, there were established criteria in place for the replacement EPID to meet expected image quality standards.