Dose Optimization for Computed Tomography Localizer Radiographs for Low-Dose Lung Computed Tomography Examinations

Area of Science:

• Medical Imaging
• Radiological Physics
• Radiation Dosimetry

Background:

• Computed tomography (CT) scans have achieved low radiation doses (0.1 mSv) for lung cancer screening and cardiac exams.
• CT localizer radiographs (LRs) may represent a significant portion of the total CT examination dose.
• Optimization techniques for CT scans necessitate evaluating LR dose contributions.

Purpose of the Study:

• To investigate the potential for reducing radiation dose from CT LRs.
• To adapt patient-specific acquisition parameters for LR dose reduction.
• To assess the impact of LR dose optimization on total CT examination dose.

Main Methods:

• Acquired lung LRs on conventional detector (CD) and integrated detector (ID) scanners using semianthropomorphic phantoms.
• Reduced tube voltage and current until LR image quality and automatic exposure control accuracy were compromised.
• Performed Monte Carlo calculations to determine organ and effective dose values for optimal settings.
• Evaluated dose efficiency by normalizing effective dose to CTDIvol across various tube voltages.

Main Results:

• Optimal LR settings were phantom size-dependent for the CD scanner.
• The ID scanner achieved uncompromised LR quality with the lowest settings (80 kV, 20 mA) for all phantoms.
• Optimal LR effective doses ranged from 6–53 μSv (CD) and 3–11 μSv (ID), depending on patient size and LR direction.
• Optimized settings on the ID scanner reduced LR dose from 53 μSv to 10 μSv for a normal patient (AP view).

Conclusions:

• LR dose can be a significant contributor to total effective dose in low-dose CT examinations.
• Substantial LR dose reduction is achievable through optimal settings.
• Adaptations must consider scanner characteristics, detector technology, and patient size for effective dose reduction.
• LR optimization offers significant dose reduction for low-dose CT exams like lung cancer screening and cardiac imaging.