BODY SIZE-SPECIFIC EFFECTIVE DOSE CONVERSION COEFFICIENTS FOR CT SCANS.

Area of Science:

• Medical Physics
• Radiological Science
• Radiation Dosimetry

Background:

• Effective dose in computed tomography (CT) is typically estimated using scanner-provided dose-length product and age-specific k-factors.
• These conventional k-factors are based on standard body sizes and may not accurately reflect individual patient anatomy.
• Patient body sizes often deviate from the standard, leading to potential inaccuracies in effective dose estimation.

Purpose of the Study:

• To develop and validate a method for deriving body size-specific k-factors for CT examinations.
• To compare effective dose estimations using conventional age-specific k-factors versus the new body size-specific k-factors.
• To improve the precision and individualization of radiation dose assessment in CT.

Main Methods:

• Developed a regression-based model for k-factors using patient diameter and Monte Carlo simulations with ICRP reference phantoms.
• Modeled k-factors for various CT scan regions including head-neck, head, neck, chest, abdomen, pelvis, abdomen-pelvis (AP), and chest-abdomen-pelvis (CAP).
• Applied the derived regression functions to 105 paediatric and 279 adult CT scans.

Main Results:

• Age-specific k-factors led to significant underestimates of effective dose in paediatric patients (up to 3-fold).
• Underweight adults showed underestimates (up to 2.6-fold), while overweight adults had overestimates (up to 4.6-fold) using age-specific factors.
• Body size-specific k-factors provide a more precise and individualized effective dose assessment.

Conclusions:

• Body size-specific k-factors offer a more accurate alternative to conventional age-specific factors for CT effective dose estimation.
• This approach enhances awareness of true radiation exposure on an individual patient level.
• Improved dose assessment is crucial for the clinical community to better understand patient radiation exposure.