Reducing absorbed dose to eye lenses in head CT examinations: the effect of bismuth shielding

Abstract

The eye lens is considered to be among the most radiosensitive human tissues. Brain CT scans may unnecessarily expose it to radiation even if the area of clinical interest is far from the eyes. The aim of this study is to implement a bismuth eye lens shielding system for Head-CT acquisitions in these cases. The study is focused on the assessment of the dosimetric characteristics of the shielding system as well as on its effect on image quality. The shielding system was tested in two set-ups which differ for distance ("contact" and "4 cm" Set up respectively). Scans were performed on a CTDI phantom and an anthropomorphic phantom. A reference set up without shielding system was acquired to establish a baseline. Image quality was assessed by signal (not HU converted), noise and contrast-to-noise ratio (CNR) evaluation. The overall dose reduction was evaluated by measuring the CTDIvol while the eye lens dose reduction was assessed by placing thermoluminescent dosimeters (TLDs) on an anthropomorphic phantom. The image quality analysis exhibits the presence of an artefact that mildly increases the CT number up to 3 cm below the shielding system. Below the artefact, the difference of the Signal and the CNR are negligible between the three different set-ups. Regarding the CTDI, the analysis demonstrates a decrease by almost 12 % (in the "contact" set-up) and 9 % (in the "4 cm" set-up). TLD measurements exhibit an eye lens dose reduction by 28.5 ± 5 and 21.1 ± 5 % respectively at the "contact" and the "4 cm" distance. No relevant artefact was found and image quality was not affected by the shielding system. Significant dose reductions were measured. These features make the shielding set-up useful for clinical implementation in both studied positions.

Prevalence of Protective Shielding Utilization for Radiation Dose Reduction in Adult Patients Undergoing Body Scanning Using Computed Tomography

“…Another recent study investigating the effects of bismuth for eye shielding during brain CT scans demonstrated a 21% to 29% dose reduction to the lens of the eye, with no negative effect on CT image quality. 7 Identically, Hopper and colleagues reported radiation dosage reduction of up to 50% when bismuth-coated latex shielding of the eye is used during cranial CT. 30 A similar study concerning breast and thyroid shielding during chest CT scans recorded a 30% and 50% dose reduction, respectively. 31 Other studies have similarly corroborated significant dose reduction due to shielding techniques.…”

“…32 Some studies have indicated an increase in image noise in the area directly underlying the protective shield 31,33,34 ; in contrast, other studies indicate no significant effect on diagnostic image quality. 7,8,35 Radiation shields can be placed either over the area being studied and thus in the path of the radiation beam (i.e., ''in-plane'' shielding), or placed over areas outside of the …”

“…[5][6][7][8] Within the past decade, several studies have shown the effectiveness of shielding in decreasing radiation dose exposure to the thyroid, [9][10][11][12] breasts, 11,13 eyes, 7,9,10,14 and testes. Accordingly, our objective was to evaluate the prevalence of protective shield utilization in adult patients undergoing routine abdominopelvic, chest, or head CT scans in a randomly selected group of U.S. hospitals.…”

Corneal Dose Reduction Using a Bismuth-Coated Latex Shield over the Eyes During Brain SPECT/CT

“…The radiation dose was reduced by about 60% at the top of the CT dose index phantom at each tube current. For comparison, Ciarmatori et al (16) reported that B-shielding can reduce the entrance surface dose by 21%-29% during head CT examinations and Wang et al (17) reported that a B-shield and tube current modulation reduced the radiation dose to the eye lens by 26.4%. Our results are essentially consistent with these previous findings, but the dose reduction was significantly greater during CT imaging in the present study.…”

Avaliação de doses em órgãos em procedimentos de tomografia computadorizada utilizando dosímetros TL e OSL

“…This study is relevant because the rat radiation cataract model is similar to the human lens opacification. Recently, the investigation conducted by Ciarmatori (2016), for instance, aimed to assess the effect of a bismuth shielding system applied to this organ and its effect on image quality, since a head CT scan can expose it to an unnecessary radiation, even when the region of interest is far from the eyes. This study was performed by stablishing a reference set up without shielding and dose reduction was assessed by placing TLD on the eye lenses of an anthropomorphic phantom.…”