Meetings » 2nd CTUG Meeting » Stability of CT numbers over a long period of time

Stability of CT numbers over a long period of time

Jonathan Eatough

Addenbrookes Hospital


The IPEM and the European Study Group (ESG) give quite different quality criteria for stability of CT numbers over time. In East Anglia measurements have been made on a dozen scanners at approximately six monthly intervals using a phantom with a range of inserts. Measurements have been carried out over a period of up to 12 years using the same phantom. The results confirm the theoretical prediction that it is not appropriate to set a single criterion for stability across the full range of CT numbers. With modern equipment the CT number should remain within +/- 5 Hounsfield units or +/- 5% of the baseline value whichever is the greater. Meeting these criteria will assist in demonstrating that image quality is being maintained and will also ensure acceptable precision for radiotherapy treatment planning.

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