About

Radiological protection requires precise estimation of patient exposure during Computed Tomography (CT) procedures. The metric typically reported by scanners, Dose Length Product (DLP), reflects the total energy output but does not directly account for biological sensitivity. To assess stochastic risks, such as radiation-induced carcinogenesis, medical physicists convert DLP into Effective Dose (E), measured in millisieverts (mSv).

This conversion relies on specific coefficients, known as k-factors, derived from Monte Carlo simulations of human phantoms (AAPM Report 96, EC 16262). Tissue radiosensitivity varies significantly across anatomical regions; for instance, the pelvis contains highly sensitive reproductive organs and red bone marrow, requiring a different conversion factor than the head. Furthermore, pediatric patients possess higher radiosensitivity and smaller geometries, necessitating age-dependent coefficients. This tool applies these variables to provide a biologically relevant dose estimate and compares it to natural background radiation for context.

Formulas

The calculation of Effective Dose utilizes the linear relationship between the total energy absorbed and tissue weighting factors:

E = DLP × k

Where:

E is the Effective Dose in mSv.
DLP is the Dose Length Product in mGy⋅cm.
k is the region and age-specific conversion coefficient mSv/(mGy⋅cm).

Background Radiation Equivalence is calculated assuming a global average annual background dose:

T_bg = E2.4 years

Reference Data

Body Region	Age Group	k-factor (mSv ⋅ mGy^-1 ⋅ cm^-1)
Head	Adult	0.0021
Head	1 year	0.0067
Neck	Adult	0.0059
Chest	Adult	0.0140
Abdomen	Adult	0.0150
Pelvis	Adult	0.0150
Chest	5 year	0.0260
Legs / Peripheral	Adult	0.0004

Frequently Asked Questions

Pediatric patients have smaller body diameters, meaning less attenuation of the X-ray beam before it reaches internal organs, resulting in a higher absorbed dose per unit of output. Additionally, developing tissues in children are inherently more radiosensitive than mature adult tissues.

There is no strict threshold for "safe" radiation, as the model used (Linear No-Threshold) assumes risk increases linearly with dose. However, standard medical diagnostic procedures typically range from 0.01 mSv (limb X-ray) to 20 mSv (complex CT/PET). For context, radiation workers are often limited to 20 mSv per year.

Yes. If a patient undergoes a multiphase exam (e.g., non-contrast, arterial, and venous phases of the liver), the total DLP is the sum of the DLP from each sequence. This total should be used to calculate the cumulative effective dose for the entire procedure.

This method provides a population-based estimate, typically within 15% to 20% accuracy for standard physiques. It is not patient-specific dosimetry, which would require analyzing the individual's exact body mass index (BMI) and organ geometry.