Issue
Radioprotection
Volume 57, Number 1, January-March 2022
Page(s) 41 - 48
DOI https://doi.org/10.1051/radiopro/2021031
Published online 10 November 2021

© SFRP, 2022

1 Introduction

With the enhancement of medical imaging facilities, exposure to the ionizing radiation from different modalities has been multiplied. Although the advantages of ionizing radiation in the diagnostic applications are well determined, evaluation of patient doses is not an easy undertaking. In this regard, the radiation risk to the patients has to be considered against its advantages. In other words, an arbitrary decreasing patient dose regardless of losing image quality is detrimental to the medical care provided to the patient (Kesari et al., 2018). Therefore, it is essential to balance the radiation induced risks and image quality. In this connection, medical physicists should become aware of the radiation dose received by the patients which plays an important role in inducing different radiation damages. For example, for the commonly performed orthopedic procedures such as intramedullary nailing of petrochanteric fractures, open reduction and internal fixation of malleolar fractures, the mean entrance skin dose rate is typically between 1 and 10 mGy/s while this dose rate for angiographic acquisition and projection radiographs ranges between 15 and 25 mGy/s and CT examinations can deliver 50 to 100 mGy/s dose rate (Kesari et al., 2018; Iversen and Vach, 2020). In CT examinations, superficial organs such as breasts might receive about 20 mGy (Saba and Keshtkar, 2019). Additionally, scattered radiations in different image modalities, especially in interventional radiology, though might deliver low dose to the patient, they increase the risk of the stochastic damages. These data have confirmed the importance of using different shielding techniques to reduce radiation risks to the patients (Kesari et al., 2018). To now, several shielding devices have been introduced to decrease unnecessary radiation to the patients while minimally affecting the image quality. These shields are generally classified into two main groups including in-plane and out-of-plane shields. In-plane shields typically used in CT examinations can protect superficial organs such as thyroid, eye, gonad, and breasts. However, out-of-plane shields such as lead shields are used in other diagnostic and interventional radiology modalities to protect patient organs located outside the imaging field (Blanc et al., 1995). The present paper aims at reviewing different shielding methods used for patients in medical imaging as well as investigating their merits and demerits.

2 Materials and methods

This paper was designed on the basis of the standards set out in PRISMA (Preferred Reporting Items for Systematic Reviews and Meta Analyses) checklist. The databases of PubMed (1985–2020), EMBASE (1985–2020), Scopus (1985–2020), Web of Sciences (1980–2020), and Google Scholar (1980–2020) were searched using a combination of the keywords based on the mesh heading of “shielding ionizing radiation”, “radiation safety”, “protective materials”, “shielding garments”, “lead aprons” in the title and abstracts. To perform a comprehensive search and to find relevant papers, manual search was conducted on the reference list of articles in particularly review papers. The search language was limited to English. The inclusion papers were those examining at least one of the mesh words techniques on human patients. The inclusion criteria were: the original papers, review papers, thesis and studies performed experimental procedures. The Exclusion Criteria comprised: (a) only abstracts, (b) studies with unrelated abstracts, (c) books, (d) letters, (e) conference documents, (f) case reports, (g) editorial, (h) pilot studies and (i) animal models. The items included were in-depth reviewed and listed in a grid comprising topics: authors, year of publication, target population, methods, results, and conclusions. The search results were summarized as a flowchart in Figure 1.

thumbnail Fig. 1

The study selection flowchart.

3 Different types of radiation shielding

Several techniques have been introduced to protect patients from unwanted ionizing radiation. These techniques are generally classified into two groups including in-plane and out-of-plane shielding.

3.1 In-plane shielding

In-plane shields have been typically used for patients during CT examinations. These shields can reduce received dose to the radiosensitive organs such as thyroid, breasts, gonads, and eyes (Saba and Keshtkar, 2019). Because of their superficial location, these organs are subjected to the considerable radiation dose. For example, a chest CT typically leads to delivering 0.02–0.035 Gy to the breast tissue which is more than 100–200 times the chest radiography dose (Tappouni and Mathers, 2012).

3.1.1 Bismuth shield

Hopper et al. originally introduced bismuth (Bi) coated onto latex shield to decrease the received dose of superficial organs of the patients during CT scan (Hopper et al., 1997). The Bi shield is directly located over the superficial organs, leading to the attenuation of radiation dose entering the patients. It was showed that using 1 thickness of Bi coated onto latex can diminish the X-ray dose to the breasts by relatively one half (Hopper, 2002). Similarly, two other studies demonstrated approximately 40–60% dose reduction for the breasts, thyroid, and eye organs as a result of using Bi-coated latex (Hopper et al., 1997, 2001). In this regard, Alonso et al. reported the radiation dose reduction of about 50% for the breasts following the use of Bi shield (Alonso et al., 2016). In addition, Wang et al. showed 37% breast dose reduction through using Bi shielding (Wang et al., 2011) while Fricke et al. found the breast dose reduction following the use of Bi shield on phantom to be 29% (Fricke et al., 2003). Although a Bi shield shows a great potential in decreasing radiation dose, several studies have reported its corrupting effects on image quality including increasing image noise, inducing streak artifacts, and changing the CT numbers (Wang et al., 2011; Einstein et al., 2012). In this regard, it was demonstrated that using Bi shield significantly elevates image noise affecting determination of the coronary artery location (Einstein et al., 2012). The second effect of using a Bi shield relates to the increase of CT number. It was revealed that using a Bi shield leads to the enhancement of the mean CT numbers in the chest areas by 12.4 HU (Lambert and Gould, 2016). Image artifact is the third effect of using Bi shielding. Wang et al. represented that Bi shielding causes streak and beam hardening artifacts in CT examinations (Wang et al., 2011). In this regard, the American Association of Physicists in Medicine (AAPM) has recently reported a recommendation against Bi shielding usage because of its negative effects on image quality (AAPM, 2017).

3.1.2 Saba shield

Saba shield is another in-plane shielding, introduced recently as an efficient alternative designed to resolve and fix the deficits and disadvantages of the Bi shields (Saba and Keshtkar, 2019). Saba shielding is made of two sublayers, wherein the first sublayer is made of high-pass radiation attenuation materials (Z = 21–30) and the second one is made of some other radiation attenuating materials, i.e., Bi or tungsten, which are different from the first sublayer.

Saba shield can decrease the entrance skin dose of the thyroid in neck CT and breast in thoracic CT examinations by about 50% during CT examination (Saba and Keshtkar, 2019; Saba et al., 2020). This shield with the thicknesses of 0.06 up to 0.12 mm Pb equivalent may be used in CT examinations and with the thicknesses of 0.02 up to 0.04 mm Pb may be used in radiography or angiography examinations (Saba and Keshtkar, 2019; Saba et al., 2020).

3.2 Out-of-plane shielding

The out-of-plane shields have been applied to protect patient organs located outside the radiation field against scattered radiations. This group indeed includes different lead shields placed on the gonad, thyroid, breasts, or eyes that are located outside the primary X-ray field. To meet ALARA regulatory guidelines for radiation protection, it is necessary to use at least 0.5 mm pure Pb against ionizing radiation (Saba and Keshtkar, 2019). The level of protection that should be provided by lead shields has been determined by majority of national standards, including European standards according to the IEC International Standard 61331-3:2014 (IEC, 2014; Lu et al., 2019).

All types of lead shields have been manufactured through covering lead sheets by nylon or polyester fabric (Ng et al., 1998). While lead shields and aprons have excellent protection features, they suffer from different disadvantages. For example, lead shields might develop cracks and holes because of their inflexibility leading radiation leakage (Saba and Keshtkar, 2019). The lead toxicity is another drawback of these shields. The intensive use of the lead-based materials into the industrial and medical fields causes the heavy release of lead into the environment which can induce severe health hazards (Christodoulou et al., 2003). Anyway, lead shields are still used as a first option for radiation protection though it is predicted that lead shields will be excluded and replaced with a lightweight lead-free sample in the future.

4 Efficiency and dose reduction of different shields

In-plane shields including conventional Bi and lead shields as well as Saba shield have been used in CT scan. The application of these shields in four important organs including breasts, gonad, thyroid, and eyes in CT examinations has been evaluated. We reviewed several publications about the amount of radiation attenuation and reported the data of the absorbed dose received from CT examinations in the mentioned organs without and with in-plane shields (Tab. 1). According to Table 1, using in-plane shields in CT scan can attenuate radiation more than 35% in all the organs. The highest radiation protection has been reported in breasts and gonad in which Bi and Saba shields can attenuate radiation by approximately 40–70%. Moreover, these shields can decrease the absorbed dose of thyroid by relatively 36–62%.

Table 2 presents the data related to using different out-of-plane shields on breasts, gonad, and thyroid as important radiosensitive organs obtained from various publications for radiography (chest, neck, thoracic, abdomen, and pelvis radiography procedures) (Blanc et al., 1995; Van der Stelt, 1996; Gori, 2000; Cohnen et al., 2002; Christodoulou et al., 2003; Souza et al., 2008; Chang et al., 2017; Livingstone et al., 2018), fluoroscopy (different procedures such as barium X-rays, arthrography, lumbar puncture, intravenous pyelogram, hysterosalpingogram, esophagram, and cystography) (Parry et al., 1999; Mahesh, 2001; Lederman et al., 2002; Crawley et al., 2004; IAEA, 2010; Heidbuchel et al., 2014; Wambani et al., 2014), and cardiac angiography (Neofotistou, 2001; Efstathopoulos et al., 2003; Morrish and Goldstone, 2008; Schauer and Linton, 2009; Miller et al., 2012; Kastrati et al., 2016; Nakamura et al., 2016; Karimi and Amoozgar, 2020). As reported in Table 2, using breast shields for patients can decrease the scattered dose received to the breasts more than 60% for angiography, fluoroscopy and radiography. Moreover, using these shields leads to the attenuation of scattered radiation to the thyroid and gonad by at least 55%, 50% and 52%, respectively in radiography, fluoroscopy, and angiography.

Table 1

The data of the effective dose received from CT examinations in the mentioned organs without and with in-plane shields.

Table 2

The data of the absorbed dose to the patients with and without protective shields in different imaging techniques.

5 Discussion

The most common in-plane shield used for patients is Bi shielding which can provide remarkable radiation protection for superficial organs such as the breasts, eye-lens, thyroid gland, and gonads (Hopper et al., 1997). However, Bi shields have some degrading effects on image quality such as increasing image noise, inducing streak artifacts, and changing the CT numbers (Hopper et al., 1997; Einstein et al., 2012). In this regard, Saba’s shield was introduced and used recently to attenuate low energy photons without considerable attenuation of high energy photons. The highest radiation protection was reported in breasts and gonad in which Bi and Saba shields can usually decrease the absorbed dose by 40–70%. These shields can decrease the received dose to the thyroid by relatively 30–60% (Tab. 1).

Table 3 summarizes some important recommendations for using in-plane shields which should be considered in different imaging modalities.

The AAPM has pointed out a number of significant disadvantages for using in-plane Bi shields during CT scan including: 1) Bi shielding may impinge on the detector forming part of the Automatic Exposure Control (AEC) mechanism. Should the patient contact shielding obscure the AEC in any way, the result may be significantly increased dose as compared with not using the patient shielding; 2) Bi shielding can lead to the degradation of the image quality and accuracy through inducing streak and beam hardening artifacts; 3) Patients contacting shielding may obscure anatomy of interest. This would necessitate repeating imaging which in turn leads to an increased radiation dose; 4) Bi shielding results in wasting radiation exposure (associated with the requirement in CT to collect projection data over at least 180°). The AAPM has recently recommended that breast and gonad shields should be discontinued as a routine option due to their little benefit compared with their potential to negatively affect the accuracy of the examination.

Addition to the patient shielding, the organ-based tube current modulation (OBTCM) method can cause organ dose reduction in CT examinations equal to Bi shields through decreasing the tube current from the reference scan current within a specific angular range over the anterior surface of the patient (Wang et al., 2011). X-CARE (Siemens HealthCare, Erlangen, Germany) (Siemens, 2014) is also an OBTCM method implemented by Siemens manufacturer. This method considerably increases the image noise in the posterior and central parts of the scanning area. More importantly, it elevates the radiation dose received to the posterior organs (Lambert and Gould, 2016). In this regard, Hoang et al. demonstrated that using OBTCM algorithm in thyroid CT examinations results in the dose enhancement to the upper lung and the spinal marrow by 29% and 15–20% respectively (Hoang et al., 2012). These demerits can challenge the applicability of OBTCM method confirmed in ICRP103 in CT examinations.

Organ Dose Modulation (ODM) (GE Healthcare, Milwaukee, WI) (Ge, 2011) is another method for protecting radiosensitive organs during CT examinations. Both X-CARE and ODM work on the same basis, but with two differences. First, X-CARE raises the tube current when it is in the posterior views while ODM does not. Furthermore, they set different angles for current modulation. For example, ODM applies a 180° arc for body scans and a 90° arc for head scan (Ge, 2013), while X-CARE utilizes a 120° arc exclusively (Hoang et al., 2012). ODM decreases the tube current in the anterior projections with negligible compensation in the posterior projections remarkably elevating the statistical noise. Wang et al. (2012) found that the received dose to the eye lens in the CT examination was 32.16 mGy; its dose reduced to 23.66 mGy using a Bi shielding and to 22.39 mGy using ODM algorithm (Wang et al., 2012). However, the accuracy and performance of ODM can be affected by the incorrect positioning of the patient (Wang et al., 2012). Another challenge in applying ODM is its inability for manual tube current scans of the head which restricts its performance for the eye lens applying fixed mA protocols. Moreover, with a low tube current, ODM algorithm could potentially induce photon starvation artifacts especially in the shoulder region or in patients with metal implants (Dixon et al., 2016).

The out-of-plane shields have been applied to protect patient organs outside the primary field of radiation. As illustrated in Table 2, using breast shields for patients can reduce scattered radiation received to the breasts, thyroid and gonad more than 40% for angiography, fluoroscopy and radiography. Though the results showed an appropriate dose reduction following the use of gonad shields in different imaging modalities, AAPM has recently reported that patient gonadal and fetal shielding during X-ray based diagnostic imaging should be discontinued as routine practice (AAPM, 2019). In fact, the amount of radiation dose required to negatively affect gonad activity is at least 100 times higher than the gonadal dose from a pelvis X-ray. Moreover, the major apprehension in relation to radiation exposure of the reproductive organs has been associated with the elevation of the risk of hereditary effects. Nevertheless, the 2007 Publication 103 of the International Commission on Radiological Protection (ICRP) pointed out that “no human studies report direct evidence of a radiation-associated excess of heritable disease” (AAPM, 2019). It was also demonstrated that the estimated dose of 0.1–1.2 Gy can reduce the number of spermatogonia and daughter cells, while irreversible damages usually happen at 4 Gy and a decrement in sperm count is evident at 4–6 Gy (Valentin, 2008; Kesari et al., 2018). Therefore, each planned reduction in gonadal radiation dose from shielding is negligible in comparison with the dose from radiation scattered within the patient’s body. Hence, using gonadal shields seems to do little or nothing to benefit the patient. Another guideline proposed by the American College of Obstetricians and Gynecologists (ACOG) stated that “the absorbed dose of the patients in radiography, CT scan, or nuclear medicine imaging modalities are always much lower than the exposure associated with fetal harm” (Jain, 2019). In this regard, National Council on Radiation Protection and Measurements (NCRP) Report 13 recommended that using gonadal shields in majority of situations cannot significantly decrease the risks from exposure and might provide unintended increased exposure and loss of diagnostic information (Stephens, 2021).

The data showed that using thyroid shield can remarkably reduce the absorbed dose. The American Thyroid Association (ATA) recommended that there is no need for thyroid shield in mammography due to the very low radiation dose and any risk to the thyroid is much lower than its benefit. However, according to the ATA recommendation, the thyroid shields should be used when possible to protect the patient thyroid in CT examinations and other diagnostic modalities (Hoogeveen et al., 2016). In this regard, the ATA confirmed the use of thyroid shield for dental X-rays as much as possible without affecting the quality of the image. Furthermore, the ATA agreed with the recommendations of the NCRP Report 145 and 177 Radiation Protection in Dentistry (NCRP, 2003).

Table 4 summarizes some important recommendations for using out-of-plane shields in different imaging modalities.

In case of applying out-of-plane shields, one consideration is that this protection cannot affect a large proportion of the scattered radiation, since majority of the scattered radiation is produced within the body (Iball and Brettle, 2011). Moreover, in comparison with in-plane shields, there is no image quality detriment, such as beam hardening and streak artifacts. In this regard, some factors should be considered for applying out-of-plane shields. First of all, the amount of scattered radiation is small vis-à-vis the primary radiation. The latter indicated that the scattered radiations are produced within the patient organs, and consequently adding surface shielding provides minimal profit. Additionally, using the shield might slip into the planned image volume and cause negative effects on the image or AEC performance. Therefore, the use of out-of-plane shielding, especially in CT, is not generally advised (Iversen and Vach, 2020).

For using patient shields in radiography, protection of organs located at least 5 cm from the primary beam seems to have a little effect on the radiation dose (Khong et al., 2013). According to the British Institute of Radiology (BIR) recommendation, if applying patient shields in radiography or fluoroscopy obscures an active AEC device, there would be a considerable risk to increase the radiation dose received to the patient (Khong et al., 2013). In this connection, using patient shielding needs some care to make sure that it does not interfere with the AEC setting. Should there be the risk of this encroaching, the patient shield is not advised. Moreover, good collimation (as close to the anatomy of interest as possible), especially in general radiography is of key importance to reducing the patient dose. It also reduces secondary radiation which can lead to improvements in image quality.

Table 3

Some recommendations about applying in-plane shields in CT examinations.

Table 4

Some recommendations about applying out-of-plane shields in different imaging modalities.

6 Conclusion

Though using in-plane shields such as Bi can effectively reduce patient dose, the AAPM has recently reported a recommendation against Bi shielding usage because of its negative effects on image quality. Saba shielding is a novel in-plane shielding method, introduced recently that protects radiosensitive organs as conventional Bi shielding without degrading image quality. It has also some superiority to tube current modulation methods since it is very cheap, available, user-friendly method and its use does not need special training. In the case of applying out-of-plan shields such as gonad or thyroid shields for patients, there is challenge and hence, the risk and benefit of their usage should be evaluated.

Conflicts of interest

The authors declare that they have no conflicts of interest in relation to this article.

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Cite this article as: Jalilifar M, Fatahi-Asl J, Saba V. 2022. Radiation protection to patients in radiology: A review study. Radioprotection 57(1): 41–48

All Tables

Table 1

The data of the effective dose received from CT examinations in the mentioned organs without and with in-plane shields.

Table 2

The data of the absorbed dose to the patients with and without protective shields in different imaging techniques.

Table 3

Some recommendations about applying in-plane shields in CT examinations.

Table 4

Some recommendations about applying out-of-plane shields in different imaging modalities.

All Figures

thumbnail Fig. 1

The study selection flowchart.

In the text

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