Computed tomography of the head: An experimental study to investigate the effectiveness of lead shielding during three scanning protocols

Abstract 

Purpose

The purpose of this experimental study, carried out in 2002, was to investigate the effectiveness of lead shielding during three scanning protocols for Computed Tomography (CT) head examinations.

During CT, the thyroid is irradiated via scattered radiation outside the primary beam. Scientists have proved a definite link between thyroid cancer and radiation but have struggled to quantify the risks from low doses such as those in medical exposures. Children are known to be at higher risks from the effects of radiation than adults.

Method

An anthropomorphic phantom was used to simulate the patient. Shielding in the form of a standard lead thyroid shield was used due to the nature of the rotating X-ray beam involved with CT. Thermoluminescent detector chips were used to measure the approximate dose to the thyroid with and without the application of the shield.

Results

The effectiveness of shielding varied with scanning technique, as did the thyroid dose due to scattered radiation. The lead shield significantly reduced the dose to the thyroid by 46–58% at the surface of the thyroid and by 37–44% within the thyroid tissue at 1cm depth.

Conclusion

In light of the increasing number of CT scanners, and the fact that head scans account for 50% of all CT examinations and 25% of the collective dose from CT to the UK population, it is important that all methods of dose reduction are considered. The use of shielding is a simple yet effective method of dose optimisation that has not been extensively investigated.

Keywords: Dose, Reduction, Thyroid, CT, Lead shielding