DOSIMETRY IN CONVENTIONAL AND SPIRAL CT I N 8 SPIRAL-CT SCANNERS OF THE LATEST GENERATION

Purpose: Measurement of scanner-dependent differences in PCTDI for con ventional and spiral CT and evaluation of PCTDI/100 mAs in eight spira l CT scanners of the latest generation. Methods: Central PCTDI was eva luated in a PMMA phantom for different scan lengths of conventional an d spiral CT in four scanners. Central and peripheral PCTDI/100 mAs, av erage dose and the quotient between peripheral and central PCTDI/100 m As were measured with a dedicated 10 cm ionisation chamber positioned within a PMMA phantom using the parameters of a standardised liver pro tocol and a high-resolution inner ear protocol for eight spiral CT sca nners. Results: Depending on scanner type and scan length PCTDI for th e spiral mode is in a range between 11.3% higher and 4.3% lower than t hat for the conventional mode. PCTDI/100 mAs varies considerably betwe en different CT scanners. For the standardised liver protocol PCTDI/10 0 mAs varies up to a factor of 2, for the inner ear protocol up to a f actor of 4. Conclusion: Even in comparable modern CT scanners there ar e considerable protocol and scanner-dependent differences in PCTDI/100 mAs. The values for his own scanner should be known to each CT user s o that he can develop a dose-optimised, patient and problem-orientated examination strategy.