Radiation Dose of the Eye Lens in Ct Examinations of the Brain in Clinical Practice—the Effect of Radiographer Training to Optimise Gantry Tilt and Scan Length

Abstract

Lenses are always exposed to radiation in brain computed tomography (CT) scans. However, the lens dose can be reduced by excluding lens from scanning area by optimising gantry tilt and scan length. The object of this study is to retrospectively analyse if the optimisation by gantry tilt and scan length have been adequate in the CT scan of the brain, and to prospectively analyse the effect of radiographer training to the quality of the CT examinations. This study was conducted in two parts. In all, 329 brain CTs performed in the Tampere University Hospital from 2017 to 2019 were revised retrospectively. The prospective part included 51 brain CT studies conducted in October 2021. Dose to the eye of the lens was modelled using CT-Expo using zero-degree beam angle and scan lengths to expose the lens either to the primary or scattered radiation. Non-zero gantry tilt had been used in a large proportion of the CT examinations in the retrospective setting, 84.8%. However, the lenses were successfully excluded from the scan area in only 1.8% of the examinations. In the prospective part, the gantry tilt was used in 98% of the studies and the proportion of successful examinations rose from 1.8 to 11.8%. The lens dose decreased significantly when the eyes were excluded from the imaging area. The modelled lens dose in the large retrospective part was 25.9 mGy (17.8–49.2 mGy) when the eyes were included and 1.5 mGy (0.4–1.9 mGy) when the eyes were excluded. The lens dose was similar in the small prospective part. Despite the gantry tilt is widely used, unnecessary lens irradiation occurs extensively because of suboptimal gantry tilt and scan length. The training of radiographers reduces the radiation exposure to the lens by more optimal gantry tilt and scan length.

Decreasing Lens Irradiation on Brain Imaging: A Multi-CT Scanner Quality Improvement Project

“…To our information, there are only two other articles that were recently published in 2023 that suggest that lens exclusion can help with reducing lens irradiation and cataracts formation [7,13]. Our article differs from these articles by incorporating one scanner with a gantry tilt and one without, enabling us to see the difference between the scanners.…”

“…The gantry tilt has demonstrated its effectiveness in significantly diminishing the radiation dose delivered to the lens, as evidenced by Tarkiainen et al's findings. Successful exclusion of lens was increased to 11.8% from 1.8% when the gantry tilt was used in 98% of the cases [13].…”

“…Lens dose reduction varies from 9% to 30% in the literature [14][15][16]. In a comprehensive retrospective analysis, the estimated lens dose was recorded at 25.9 mGy (with a range of 17.8-49.2 mGy) when the eyes were included within the scan field, in contrast to a substantially lower dose of 1.5 mGy (with a range of 0.4-1.9 mGy) when the eyes were deliberately excluded through the use of a gantry tilt [13]. Although Poon et al [6] reported that a gantry tilt is the most effective way to reduce lens dose in CT scans, the chin-tuck position can be used in machines lacking the ability of a gantry tilt with significant numbers of lenses excluded as evidenced by our study.…”

The Dose Optimization and Evaluation of Image Quality in the Adult Brain Protocols of Multi-Slice Computed Tomography: A Phantom Study

“…Computed tomography (CT) is a diagnostic imaging modality that uses high radiation doses to create images and may expose the patient to radiation risk [12,13]. CT scans of the head expose sensitive tissue, especially the lenses of the eyes, which can be damaged and develop cataracts if the radiation dose exceeds a certain level [13][14][15][16][17].…”

“…Many parameters affect the patient's radiation exposure, such as kVp, mA, mAs, pitch, scan range, slice thickness, and the reconstruction algorithm. Acquisition parameters also affect image quality and the performance of images for diagnosis [15,[19][20][21][22].…”