Relationships between physical dose quantities and patient dose in CT.

Area of Science:

• Medical Physics
• Radiology
• Radiation Dosimetry

Background:

• Patient dose in CT scans is typically quantified by organ dose and effective dose, crucial for assessing stochastic risk.
• Direct measurement or calculation of these doses can be labor-intensive and time-consuming.
• Investigating simpler physical dose quantities for accurate dose estimation is essential for routine clinical practice.

Purpose of the Study:

• To evaluate the effectiveness of physical dose quantities in describing organ dose and effective dose in CT examinations.
• To compare dose free-in-air on the axis of rotation (Dair) and weighted computed tomography dose index (CTDIw) with organ doses.
• To assess the correlation between dose-length product (DLP) and effective dose.

Main Methods:

• Organ doses and effective doses were determined for various head, neck, and trunk CT examinations using conversion factors.
• Dose free-in-air on the axis of rotation (Dair) and CTDIw were compared to absorbed doses of organs fully within the scanned region.
• Dose-length product (DLP) was compared to the effective dose for different anatomical regions.

Main Results:

• The ratio of organ dose to CTDIw ranged from 0.87 to 1.79 mSv mGy⁻¹, with an average of 1.37 mSv mGy⁻¹.
• Dose-length product (DLP) demonstrated a statistically significant correlation with effective dose (p < 0.005).
• Average ratios of effective dose to DLP were 0.0028, 0.0062, and 0.0190 mSv (mGy cm)⁻¹ for head, neck, and trunk CT, respectively.

Conclusions:

• Weighted computed tomography dose index (CTDIw) can effectively estimate organ doses for CT examinations of the head, neck, and trunk.
• Dose-length product (DLP) serves as a reliable indicator for estimating effective dose in these CT examinations.
• These physical dose quantities provide a more efficient approach to dose assessment in clinical CT practice.