Patient doses and projection angle in cone beam CT

Area of Science:

• Medical Physics
• Radiological Sciences
• Imaging Technology

Background:

• Cone beam CT (CBCT) is increasingly used in medical imaging.
• Understanding radiation dose is crucial for patient safety in CT examinations.
• The impact of x-ray tube projection angle on patient dose in CBCT requires detailed investigation.

Purpose of the Study:

• To evaluate the influence of x-ray tube projection angle on organ and effective doses in cone beam CT.
• To compare dose distributions between conventional gantry CT and C-arm CT systems.
• To assess the effect of varying x-ray tube voltage and filtration on patient dose.

Main Methods:

• Two CBCT systems (gantry CT and C-arm CT) with flat panel detectors were studied.
• PCXMC software was used to calculate organ and effective doses using a mathematical phantom.
• Dose calculations were performed at various projection angles (15-degree increments) and anatomical locations.
• The impact of different x-ray tube voltages (80-140 kV) and aluminum filtration (2.5-9.5 mm) was analyzed.

Main Results:

• Organ doses varied substantially with projection angle, being higher in anteroposterior and lower in lateral projections.
• Maximum to minimum organ dose ratios ranged from 2.2 (lungs) to 36 (stomach).
• Effective doses varied by factors of approximately 2.7 (chest) and 4.0 (abdomen/pelvis) with projection angle.
• Differences in source-to-isocenter distance between systems contributed to dose variations.

Conclusions:

• Significant variations in organ and effective doses occur with changes in x-ray tube projection angle during CBCT.
• X-ray tube current modulation presents a promising strategy for dose reduction in CBCT body imaging.
• Further research into optimized scanning protocols can enhance patient safety in CBCT procedures.