Purpose: To evaluate the potential effectiveness of adaptive collima-tion in reducing computed tomographic (CT) radiation dose owing to z-overscanning by using dose measurements and Monte Carlo (MC) dose simulations.
Materials and Methods: Institutional review board approval was not necessary.Dose profiles were measured with thermoluminescent dosimeters in CT dose index phantoms and in an Alderson-Rando phantom without and with adaptive section collima-tion for spiral cardiac and chest CT protocols and were compared with the MC simulated dose profiles. Additional dose measurements were performed with an ionization chamber for scan ranges of 5-50 cm and pitch factors of 0.5-1.5.
Results: The measured and simulated dose profiles agreed to within 3%. By using adaptive section collimation, a substantial dose reduction of up to 10% was achieved for cardiac and chest CT when measurements were performed free in air and of 7% on average when measurements were performed in phantoms. For scan ranges smaller than 12 cm, ionization chamber measurements and simulations indicated a dose reduction of up to 38%.
Conclusion: Adaptive section collimation allows substantial reduction of unnecessary exposure owing to z-overscanning in spiral CT. It can be combined in synergy with other means of dose reduction, such as spectral optimization and automatic exposure control.