SU-E-I-39: Intensive Monitoring of System Performance and Protocols on CT Systems

The regulatory response to the recent CT overdoses is still in the process of being implemented. The more action taken before the regulations take effect reduces the exposure of the institution to medical and legal problems. Therefore, eighteen months ago we implemented an intensive QC program to ensure CT safety. The first component was to monitor the dose and SNR produced by a single CT examination weekly to identify changes. The second was to monitor changes in the protocols.

We measured the CTDI and SNR for the routine head examination. We developed a script to identify and log changes in any of the 234 protocols.

Surprisingly, there were many changes to the protocols: on one unit 388 protocols were changed on 26 dates over the 18 month period. The reasons included: protocol optimization, scanner service, software reloads, mistakes, mistakenly loading the protocols from another section's scanner. The standard deviation of the CTDI was 2% to 3%. The dominant source of variation was probably positioning. The standard deviation of the SNR was 4% to 9%. The entire procedure requires 30min to 50min to test five CT scanners each week.

The standard deviations of the CTDI values and of the SNR values are sufficiently small to allow anomalies to be identified using these relatively simple methods. Frequent protocol checking is an important component to any QC program.