Thyroid doses and risk to paediatric patients undergoing neck CT examinations

To estimate thyroid doses and cancer risk for paediatric patients undergoing neck computed tomography (CT).

We used average CTDI(vol) (mGy) values from 75 paediatric neck CT examinations to estimate thyroid dose in a mathematical anthropomorphic phantom (ImPACT Patient CT Dosimetry Calculator). Patient dose was estimated by modelling the neck as mass equivalent water cylinder. A patient size correction factor was obtained using published relative dose data as a function of water cylinder size. Additional correction factors included scan length and radiation intensity variation secondary to tube-current modulation.

The mean water cylinder diameter that modelled the neck was 14 ± 3.5 cm. The mathematical anthropomorphic phantom has a 16.5-cm neck, and for a constant CT exposure, would have thyroid doses that are 13-17% lower than the average paediatric patient. CTDI(vol) was independent of age and sex. The average thyroid doses were 31 ± 18 mGy (males) and 34 ± 15 mGy (females). Thyroid cancer incidence risk was highest for infant females (0.2%), lowest for teenage males (0.01%).

Estimated absorbed thyroid doses in paediatric neck CT did not significantly vary with age and gender. However, the corresponding thyroid cancer risk is determined by gender and age.

• Thyroid doses can be estimated from the CTDI(vol) in paediatric neck CT . • Scan length, neck size, and radiation intensity variation should be accounted for. • Estimated absorbed thyroid doses did not significantly vary with age and gender. • Thyroid cancer incidence risk is primarily determined by gender and age.