Doses metrics and patient age in CT

Area of Science:

• Medical Physics
• Radiology
• Radiation Dosimetry

Background:

• Computed tomography (CT) radiation doses require age- and size-specific adjustments for accurate risk assessment.
• Current dose metrics like CTDIvol may not fully reflect patient radiation exposure across different age groups.

Purpose of the Study:

• To investigate the age- and size-dependency of effective dose and size-specific dose estimate (SSDE) in pediatric and adult CT examinations.
• To compare the trends of SSDE and effective dose with patient age for head and abdominal/pelvic CT scans.

Main Methods:

• Patient CT data (head and abdomen/pelvis) were modeled using water-equivalent cylinders based on effective diameter.
• Doses were assessed using CTDIvol, AAPM TG 204 conversion factors for SSDE, and age/sex-specific E/DLP factors based on ICRP 103.
• Age-specific scan lengths were incorporated to calculate dose-length product and effective dose.

Main Results:

• For head CT, SSDE increased by 31% and effective dose by 270% from adults to newborns.
• For abdominal CT, SSDE increased by 68% and effective dose by 140% from adults to newborns.
• Effective dose showed a substantially greater increase with decreasing patient size than SSDE.

Conclusions:

• Size- and age-specific effective dose provides a more comprehensive quantification of patient radiation exposure in CT.
• Effective dose calculations that account for scan length and organ sensitivity are crucial for pediatric radiation safety.
• SSDE alone underestimates the age-related increase in radiation risk due to its exclusion of scan length and scattered radiation effects.