Radiation dose calculations for CT scans with tube current modulation using the approach to equilibrium function

Area of Science:

• Medical Physics
• Radiological Sciences
• Imaging Technology

Background:

• Previous methods calculated radiation dose for constant tube current CT scans.
• Tube current modulation (TCM) is widely used in clinical CT to optimize radiation dose.
• A need exists for accurate dose calculation methods that account for TCM.

Purpose of the Study:

• To adapt the equilibrium function approach for calculating radiation dose in CT scans with TCM.
• To validate the adapted method against experimental measurements and existing literature.

Main Methods:

• Dividing scans with variable tube current into subscan ranges with near-constant current.
• Applying a previously developed dose calculation algorithm to each subscan range.
• Efficiently computing longitudinal dose distribution for clinical TCM scans using a water-cylinder phantom.

Main Results:

• Dose calculations demonstrated agreement with published data for various tube current distributions.
• Measurements using an anthropomorphic phantom and optically stimulated luminescence dosimeters validated the method.
• Calculated doses for a water phantom simulating abdominal mass agreed with phantom measurements within 28.4%.

Conclusions:

• The adapted method effectively calculates CT dose, considering subject size, scan length, and TCM.
• Using a water-containing cylinder with equivalent mass to the subject simplifies clinical dose calculations.
• This approach offers potential for improved patient dose evaluation compared to CTDIvol, SSDE, or average-current methods.