An evaluation of in-plane shields during thoracic CT

Organ-based tube current modulation versus spectral shaping via tin prefiltration: What does bismuth breast shielding add in low-dose lung CT?

PURPOSE

Since organ-based tube current modulation (OBTCM) and tin prefiltration are limited on their own in lowering the dose of lung CT examinations, this experimental study was designed to investigate whether combinations with anterior patient shielding can increase the dose reduction potential.

MATERIAL AND METHODS

Three pairs of scan protocols without/with breast shield (P1/P2: standard 120kVp, P3/P4: OBTCM at 100 kVp, P5/P6: Sn 100 kVp) were employed for radiation exposure and image quality comparisons on an anthropomorphic Alderson-Rando phantom. Equivalent doses were measured in eleven sites via thermoluminescent dosimetry and the effective dose was obtained by summation of the weighted organ doses. Dose-weighted contrast-to-noise ratios (CNRD) were calculated and four radiologists independently assessed the quality of images generated with each protocol.

RESULTS

While no significant difference was determined between standard and OBTCM protocols regardless of breast shield (p ≥ 0.068), equivalent doses with spectral shaping were substantially lower (p ≤ 0.003). The highest effective dose was ascertained for standard scans (P1/P2: 7.3/6.8 mSv) with a dose reduction of 8.0 % via breast shielding. The use of a bismuth shield was more beneficial in OBTCM (P3/P4: 6.6/5.3 mSv) and spectral shaping (P5/P6: 0.7/0.6 mSv), reducing the effective dose by 19.8 % and 13.9 %, respectively. Subjective assessment favoured standard protocol P1 over tin prefiltration low-dose scans (p ≤ 0.032), however, no scan protocol entailed diagnostically insufficient image quality.

CONCLUSIONS

Whereas breast shielding is particularly beneficial in combination with OBTCM, spectral shaping via tin prefiltration facilitates the most pronounced dose reduction in lung CT imaging with acceptable image quality.

Breast Shielding Combined With an Optimized Computed Tomography Pulmonary Angiography Pregnancy Protocol: A Special Use-Case for Shielding?

OBJECTIVES

To determine the impact of breast shields on breast dose and image quality when combined with a low-dose computed tomography pulmonary angiography (CTPA) protocol for pregnancy.

METHODS

A low-dose CTPA protocol, with and without breast shields, was evaluated by anthropomorphic phantom and 20 prospectively recruited pregnant participants from January to October 2019. Thermoluminescent dosimeters measured surface and absorbed breast dose in the phantom and surface breast dose in participants. The Monte-Carlo method estimated the absorbed breast dose in participants. Image quality was assessed quantitatively by regions of interest analysis and subjectively by the Likert scale. Doses and image quality for CTPA alone were compared with CTPA with breast shields.

RESULTS

Mean surface and absorbed breast dose for CTPA alone were 1.3±0.4 and 2.8±1.5 mGy in participants, and 1.5±0.7 and 1.6±0.6 mGy in the phantom. Shielding reduced surface breast dose to 0.5±0.3 and 0.7±0.2 mGy in the phantom (66%) and study participants (48%), respectively. Absorbed breast dose reduced to 0.9±0.5 mGy (46%) in the phantom.Noise increased with breast shields at lower kV settings (80 to 100 kV) in the phantom; however, in study participants there was no significant difference between shield and no-shield groups for main pulmonary artery noise (no-shield: 34±9.8, shield: 36.3±7.2, P =0.56), SNR (no-shield: 11.2±3.7, shield: 10.8±2.6, P =0.74) or contrast-to-noise ratio (no-shield: 10.0±3.3, shield: 9.3±2.4, P =0.6). Median subjective image quality scores were comparable (no-shield: 4.0, interquartile range: 3.5 to 4.4, shield: 4.3, interquartile range: 4.0 to 4.5).

CONCLUSION

Combining low-dose CTPA with breast shields confers additional breast-dose savings without impacting image quality and yields breast doses approaching those of low-dose scintigraphy, suggesting breast shields play a role in protocol optimization for select groups.

Use of bismuth shield for protection of superficial radiosensitive organs in patients undergoing computed tomography: a literature review and meta-analysis

The study aimed to assess the effect of bismuth (Bi) shielding on dose reduction and image quality in computed tomography (CT) through a literature review. A search was conducted in the following databases: Web of Science, PubMed, Google Scholar, and Scopus. Studies that reported estimated dose reduction with bismuth shielding during imaging of the eye, thyroid, and breast were included, and a meta-regression analysis was used to examine the influence of the CT scanner type on the dose reduction. The studies included a total of 237 patients and 34 pediatric and adult anthropomorphic phantoms for whom the radiation dose was reported. Bismuth shielding was recommended in 88.89% of the studies based on the maintenance of appropriate image quality under shielding. Noise associated with Bi shielding was 7.5%, 263%, and 23.5% for the eye, thyroid, and breast, respectively. The fixed-effects pooled estimate of dose reduction was 34% (95% CI: 13-55; p < 0.001) for the eye, 37% (95% CI 14-61; p < 0.001) for the thyroid, and 36% (95% CI 36-55; p < 0.001) for the breast. The image quality, usage of foams, CT scanner type, beam energies, and backscatter radiation were important factors that directly affected the efficacy of Bi shielding to reduce the radiation dose at the superficial radiosensitive organs.

Application of Different methods for Reducing Radiation Dose to Breast during MDCT

The increased use of computed tomography (CT) and its high radiation dose have led to great concerns about its potential for radiation induced cancer risks. Breast is a radiosensitive tissue based on tissue weighting factors assigned by the International Commission on Radiological Protection (ICRP). Moreover, the dose is maximal on the surface of the patient. Therefore, strategies should be taken to reduce radiation dose to the breast. The aim of this review is to introduce methods used for reducing radiation dose to breast in thoracic CT and review related performed studies. The literature indicates that bismuth shielding increases image noise and CT numbers as well as introducing streak artifacts. Tube current modulation (TCM) technique and iterative reconstruction algorithms can provide some levels of dose reduction to radiosensitive organs and superior image quality without the disadvantages of bismuth shielding. However, they are not available on all CT scanners, especially in low-income countries. Such centers may have to continue using bismuth shields to reduce the dose until these superior techniques become available at lower costs in all CT scanners. Furthermore, design and manufacture of new shields with the lower impact on image quality are desirable.

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

PURPOSE

Ionizing radiation is implicated in nearly 2% of malignancies in the United States; radiation shields prevent unnecessary radiation exposure during medical imaging. Contemporary radiation shield utilization for adult patients in the United States is poorly defined. Therefore, we evaluated the prevalence of protective shielding utilization in adult patients undergoing CT scans in United States' hospitals.

MATERIALS AND METHODS

An online survey was sent to established radiology departments randomly selected from the 2015 American Hospital Association Guide. Radiology departments conducting adult CT imaging were eligible; among 370 eligible departments, 215 departments accepted the study participation request. Questions focused on shielding practices during CT imaging of the eyes, thyroid, breasts, and gonads. Prevalence data were stratified per hospital location, size, and type. Main outcomes included overall protective shielding utilization, respondents' belief and knowledge regarding radiation safety, and organ-specific shielding prevalence.

RESULTS

Sixty-seven of 215 (31%) hospitals completed the survey; 66 (99%) reported familiarity with the ALARA (as low as reasonably achievable) principle and 56 (84%) affirmed their belief that shielding is beneficial. Only 60% of hospitals employed shielding during CT imaging; among these institutions, shielding varied based on CT study: abdominopelvic CT (13, 33%), head CT (33, 83%), or chest CT (30, 75%).

CONCLUSIONS

Among surveyed hospitals, 40% do not utilize CT shielding despite the majority acknowledging the ALARA principle and agreeing that shielding is a beneficial practice. Failure to address the low prevalence of protective shielding may lead to poor community health due to increased risk of radiation-related cancers.

[Practical radiation protection of the patient in radiological diagnostics]

BACKGROUND

The use of radiation protection equipment can reduce the radiation exposure of patients.

OBJECTIVES

The aim was to show which patient shields should be used for the different types of examination.

METHODS

The results of multiple studies were compiled and analyzed and recommendations made for the use of patient shields. The absolute dose values and the protective effect were considered.

RESULTS

Radiological protection should be used in many investigations; particularly in the case of CT investigations, a reasonable dose reduction potential exists due to the higher radiation dose.

CONCLUSIONS

Based on these recommendations, workflow changes in some types of investigation are expected due to the use of additional patient shields.

An evaluation of organ dose modulation on a GE optima CT660-computed tomography scanner

Organ Dose Modulation or ODM (GE Healthcare, Milwaukee, WI) was evaluated to characterize changes in CTDIvol, image noise, effective dose, and organ dose saving to patients. Three separate investigations were completed: a tube current modulation phantom was scanned with and without ODM, a CTDIvol phantom was scanned with ODM, and Monte Carlo simulations were performed. ODM was found to reduce the CTDIvol by approximately 20% whilst increasing the noise by approximately 14%. This was reflected in the dose distribution, where the anterior peripheral dose was reduced by approximately 40% whilst the identical posterior dose remained largely unaffected. Enabling ODM for the entire scan would reduce the effective dose by approximately 24%; however, this saving reduces to 5% if the images are matched for CTDIvol. These savings mostly originated from reductions in dose to the stomach, breasts, colon, bladder, and liver. ODM has the effect of a global reduction in CTDIvol with an associated increase in image noise. The benefit of ODM was found to be reduced when the dose‐saving contribution from the reduced CTDIvol was removed. Given that there is a higher contribution to effective dose throughout the body from the anterior projections, consideration should be given to applying ODM throughout.

PACS number(s): 87.10.Rt, 87.53.Bn, 87.57.C‐, 87.57.Q‐

A Monte Carlo study on quantifying the amount of dose reduction by shielding the superficial organs of an Iranian 11-year-old boy

A method for minimizing organ dose during computed tomography examinations is the use of shielding to protect superficial organs. There are some scientific reports that usage of shielding technique reduces the surface dose to patients with no appreciable loss in diagnostic quality. Therefore, in this Monte Carlo study based on the phantom of a 11-year-old Iranian boy, the effect of using an optimized shield on dose reduction to body organs was quantified. Based on the impact of shield on image quality, lead shields with thicknesses of 0.2 and 0.4 mm were considered for organs exposed directly and indirectly in the scan range, respectively. The results showed that there is 50%–62% reduction in amounts of dose for organs located fully or partly in the scan range at different tube voltages and modeling the true location of all organs in human anatomy, especially the ones located at the border of the scan, range affects the results up to 49%.

Characterization of a lead breast shielding for dose reduction in computed tomography

Objective

Several studies have been published regarding the use of bismuth shielding to protect the breast in computed tomography (CT) scans and, up to the writing of this article, only one publication about barium shielding was found. The present study was aimed at characterizing, for the first time, a lead breast shielding.

Materials and Methods

The percentage dose reduction and the influence of the shielding on quantitative imaging parameters were evaluated. Dose measurements were made on a CT equipment with the aid of specific phantoms and radiation detectors. A processing software assisted in the qualitative analysis evaluating variations in average CT number and noise on images.

Results

The authors observed a reduction in entrance dose by 30% and in CTDI_vol by 17%. In all measurements, in agreement with studies in the literature, the utilization of cotton fiber as spacer object reduced significantly the presence of artifacts on the images. All the measurements demonstrated increase in the average CT number and noise on the images with the presence of the shielding.

Conclusion

As expected, the data observed with the use of lead shielding were of the same order as those found in the literature about bismuth shielding.

Lens dose in routine head CT: comparison of different optimization methods with anthropomorphic phantoms

OBJECTIVE

The purpose of this study was to study different optimization methods for reducing eye lens dose in head CT.

MATERIALS AND METHODS

Two anthropomorphic phantoms were scanned with a routine head CT protocol for evaluation of the brain that included bismuth shielding, gantry tilting, organ-based tube current modulation, or combinations of these techniques. Highsensitivity metal oxide semiconductor field effect transistor dosimeters were used to measure local equivalent doses in the head region. The relative changes in image noise and contrast were determined by ROI analysis.

RESULTS

The mean absorbed lens doses varied from 4.9 to 19.7 mGy and from 10.8 to 16.9 mGy in the two phantoms. The most efficient method for reducing lens dose was gantry tilting, which left the lenses outside the primary radiation beam, resulting in an approximately 75% decrease in lens dose. Image noise decreased, especially in the anterior part of the brain. The use of organ-based tube current modulation resulted in an approximately 30% decrease in lens dose. However, image noise increased as much as 30% in the posterior and central parts of the brain. With bismuth shields, it was possible to reduce lens dose as much as 25%.

CONCLUSION

Our results indicate that gantry tilt, when possible, is an effective method for reducing exposure of the eye lenses in CT of the brain without compromising image quality. Measurements in two different phantoms showed how patient geometry affects the optimization. When lenses can only partially be cropped outside the primary beam, organ-based tube current modulation or bismuth shields can be useful in lens dose reduction.

Effects of shielding the radiosensitive superficial organs of ORNL pediatric phantoms on dose reduction in computed tomography

In computed tomography (CT), some superficial organs which have increased sensitivity to radiation, receive doses that are significant enough to be matter of concern. Therefore, in this study, the effects of using shields on the amount of dose reduction and image quality was investigated for pediatric imaging. Absorbed doses of breasts, eyes, thyroid and testes of a series of pediatric phantoms without and with different thickness of bismuth and lead were calculated by Monte Carlo simulation. Appropriate thicknesses of shields were chosen based on their weights, X-ray spectrum, and the amount of dose reduction. In addition, the effect of lead shield on image quality of a simple phantom was assessed quantitatively using region of interest (ROI) measurements. Considering the maximum reduction in absorbed doses and X-ray spectrum, using a lead shield with a maximum thickness of 0.4 mm would be appropriate for testes and thyroid and two other organs (which are exposed directly) should be protected with thinner shields. Moreover, the image quality assessment showed that lead was associated with significant increases in both noise and CT attenuation values, especially in the anterior of the phantom. Overall, the results suggested that shielding is a useful optimization tool in CT.