Abstract
Background:
In X-ray imaging with fluoroscopy/angiography modalities, long exposure time may cause a high received dose by the physician due to the scattered photons from the patient and device. Using lead aprons significantly decreases the physician dose, but long-term disadvantages to health that are found with using this high-weight and toxic material make it interests to find alternatives. This study attempts to compare the radiation protection of different shields based on the effective physician organ doses to find the most effective radioprotection materials for each body site.
Materials and Methods:
Investigations on the protective efficiency of the aprons with different material compositions were performed using MCNPX Monte Carlo code to simulate the models as close as possible to a real imaging room and anthropomorphic phantoms.
Results:
According to the results, tungsten and its multilayer composites containing gadolinium and bismuth demonstrated the highest level of protection for all physician organs across the primary beam energy range of 80–120 kVp. Among them, the greatest reductions of radiation transmission were observed for Gd-W and Gd-W-Bi multilayers, respectively. These both were also the most effective shields for 70 kVp in lower organs but not more than Sb-W and Sn-W bilayers for upper and middle organs.
Conclusion:
A selection based on the used energy can be there between these four compositions due to their higher protection produced by aprons with lower thickness and lower final weight, but the same efficiency as lead garments.
Keywords: Interventional radiology, lead-free apron, occupational exposure, radiation protection, simulation
INTRODUCTION
Increasing the distance, reducing the time and using the shields are three important strategies in general external radiation protection. Imaging procedures including some special radiology modalities such as fluoroscopy due to the long time required for many frames and catheterization in angiography cause increased received dose of the patients and the radiologists (or cardiologists). Therefore, using suitable shields like aprons, Lead glass, thyroid shields, etc., by persons in the imaging room can help to reduce their received doses.[1,2,3,4,5] In 2000, the International Commission on Radiological Protection (ICRP) warned about the possible high-level doses received by patients and radiologists in using these imaging techniques that may exceed the dose limits.[2,3] The primary X-ray radiation field is directed toward the patient and the scattered radiations from the patient’s body or the equipment in the room provide the majority of the radiations received by the radiologist. The scattering angle of the photons depends on the photon energy. On the other hand, the higher probability of scattering with a larger angle related to the incident photon direction occurs for lower photon energies. By increasing the distance of the radiologist from the patient’s table, its received radiation decreases but in interventional radiology procedures, increasing the distance is limited because the radiologist must be present near the patient’s table for long time during the imaging caused receiving a lot of radiation.[1,2,3,6] In 1991, Boone et al. compared different fluoroscopic imaging conditions. Their study demonstrated that received dose to the physician′s upper waist area was higher in the anterior-posterior (AP) geometry than posterior-anterior (PA) geometry. In the AP geometry, the detector is placed under the table and closed to it that yields a sharper image of posterior structures. Consequently, the gantry exposes the patient from above, leading to considerable radiation exposure to the physician if the AP configuration is selected for the image quality purposes. The study also reported that using a larger field of view (FOV) produces more scattered radiation to the physician. However, small FOVs are often preferred for areas that require high resolution evaluations. The greater magnification leads increasing the received dose to achieve an acceptable signal-to-noise ratio. Therefore, for the large areas like abdomen with appropriate contrast using extended FOVs properly results patient dose reduction.[7,8]
Using radiation absorbing shields is an important method to reduce dose to radiation workers. In energy range of diagnostic X-rays (60–120 kVp with average energies of 35–60 keV), photoelectric absorption is the most important effect causing attenuation of the photons.[9] Accordingly, the lead with atomic number 82 has been the first choice as the main material for making aprons for radiation attenuation. Many regulatory agencies have recommended 0.5 mm lead for making aprons.[1,6,9,10] However, lead shields are toxic and also have a high weight associated with the risk of chronic injuries and back pain. Therefore, efforts are being made to make lighter shields that can create an equal or greater attenuation per unit of mass than the lead.[10,11,12] Nonlead heavy metals, lead and lead-free metal alloys, and polymer matrix loaded with heavy metal powders, because of their attenuations, are among the materials evaluated by researchers. Nonlead elements with k absorption edge energies can provide a higher attenuation peak even than the lead at low energies. There are several studies that have completely confirm this theory by simulations and measurements. For example, in 2012, McCaffrey et al.[1] used Monte Carlo simulations to evaluate the attenuated spectra and calculation of the k absorption edge energies for lead, tungsten, barium, gadolinium and some other elements. Therefore, depending on the kVp and the mean energy of the spectrum, more photoelectric absorption than the lead can be produced.[1,9,10,11,13,14] This property is specified in designing the multilayer shields. Using the bilayer shields improves attenuation because the absorption of radiation with lower energy occurs by a lighter metal that has a lesser k-edge.[1]
With using aprons, thyroid shields and lead glasses, a suitable dose reduction for the radiologist/cardiologist can be provided but using a lighter shield with greater or similar attenuation efficiency in long-term exposures looks at the other aspects of people health protection in working situations. Different shields have been proposed and evaluated for their protective efficiencies. Using dosimetry measurement is a time-consuming method to investigate the attenuation performance for the radiologist/cardiologist shields because the received dose rate is low and recording the measurable, meaningful and comparable values by dosimeters requires long times. Additionally, using required anthropomorphic phantoms and tissue equivalent dosimeter such as thermoluminescent dosimeters need sufficient time for reliable effective organ dose measurements. However, simulations can be useful for this purpose. Several previous studies are performed based on the relative dosimetry parameters such as the ratios of the effective doses and personal dose equivalents in mathematical anthropomorphic phantoms to the dose-area product (DAP) or kerma-area product (KAP).[4,15,16,17] The current study comprehensively evaluates the efficiency of the several proposed shields including the multilayer and alloy compounds to reduce the occupational dose in interventional radiology. Evaluations are performed for sufficient number of beam qualities introducing diagnostic X-ray energy range. This study investigates the angular dependence of scattered photons and the precise definition of the energy spectra for those received by the physician organs in different body sites. Therefore, radiation protections for different shields are investigated based on the comparison of the effective organ doses for site to site of the body to find the most effective radioprotection material for each body site. Additionally, probabilities for the multipiece aprons are considered.
MATERIALS AND METHODS
Material setting
In this study, simulations were conducted using MCNPX Visual Editor software version X_22s to perform dosimetry calculations under realistic imaging conditions. According to this purpose, this study models the Platinum DRF imaging system manufactured by Apelem-DMS installed in Abuzar teaching hospital of Jundishapur University of Medical Sciences, Ahvaz. This system is capable of performing several diagnostic radiology techniques, including fluoroscopic interventional radiology and peripheral angiography. The imaging room and system are shown in Figure 1.
Figure 1.
The simulated imaging room and its simulation: (a) the imaging room; (b) simulation in MCNPX Visual editor
The main part of the scattered radiation received by the physician comes from the patient’s body. Additionally, the devices and the components of the system and environment can cause radiation scattering. It was tried to simulate the real room with the exact composition and geometry of the system in the outer body shell (including standing column, electronic cabinet, and gantry), X-ray tube, table (including 43 × 43 cm2 flat panel of cesium iodide detectors under the carbon fiber panel, etc.) and collimation system in addition to the objects near the table in the imaging room.
The physician and the patient were modeled by an MIRD-type human phantom. The patient’s phantom is simplified in the composition and geometry of the organs. It only includes soft tissue, lung, and bone skeleton. However, the phantom used as the physician model is introduced with the organs of a 30-year-old adult, including the vital organs. It can be used to simulate male/female radiation workers. Figure 2 shows the ORNL phantom used, obtained from the MCNPX Visual editor software version X_22s. The patient is on the table, and the physician covered by the radiation-protecting shields is standing beside the table at least 14.8 cm distance.
Figure 2.
ORNL phantom used for MCNPX simulation of the physician: (a) coronal view; (b) sagittal view
The investigated shields, including the apron, glass, and thyroid shield, are defined as shown in Figure 3. These shields are simulated with different compositions containing elements listed in Table 1.
Figure 3.
Defined shield models to cover the neck, thorax, abdomen, pelvic, and upper portion of the femurs: (a) axial view; (b) sagittal view
Table 1.
Physical properties of the used elements in the simulation
| Material | Atomic number | Density (g/cm3) | K absorption edge (keV) | kg/m2 (0.5 mm thickness) | ||||
|---|---|---|---|---|---|---|---|---|
| Lead (Pb) | 82 | 11.36 | 88.0 | 5.68 | ||||
| Barium (Ba) | 56 | 3.5 | 37.4 | 1.75 | ||||
| Bismuth (Bi) | 83 | 9.75 | 90.5 | 4.875 | ||||
| Gadolinium (Gd) | 64 | 7.90 | 50.4 | 3.95 | ||||
| Tin (Sn) | 50 | 7.30 | 29.2 | 3.65 | ||||
| Tungsten (W) | 74 | 19.3 | 69.5 | 9.65 | ||||
| Antimony (Sb) | 51 | 6.69 | 30.5 | 3.345 | ||||
| Cadmium (Cd) | 48 | 8.35 | 26.7 | 4.17 |
The dose received by the physician’s organs is calculated for each presented shield, and the results are evaluated for their radiation protection capabilities in different areas of the body. Table 2 lists the alloys and multipure layer compounds with lead and nonlead-based compositions that are investigated in this study. Finally, the received organ dose using each shield is compared to the lead one.
Table 2.
Density and elemental composition of the evaluated shields
| Shield name | Material | Density (g/cm3) | kg/m2 (0.5 mm thickness) | Ref. | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Single-layer (0.5 mm thickness) | Shield-1 | Pb (67%)-Si (33%) | 4.98 | 2.49 | [11] | |||||
| Shield-2 | Pb (87%)-EPVC (13%) | 4.745 | 2.3725 | [11] | ||||||
| Shield-3 | W (67%)-Si (33%) | 5.70 | 2.85 | [11] | ||||||
| Shield-4 | W (52.2%)- Sn (30.45%)- Ba (4.35%)-EPVC (13%) | 4.650 | 2.325 | [11] | ||||||
| Shield-5 | W (36.54%)-Sn (46.11%)-Cd (4.35%)-EPVC (13%) | 4.517 | 2.2585 | [11] | ||||||
| Shield-6 | W (34.8%)-Sn (43.5%)-Cd (8.7%)-EPVC (13%) | 4.506 | 2.253 | [11] | ||||||
| Shield-7 | Sb (0.2 mm)-W (0.3 mm) | 14.256 | 7.128 | [13] | ||||||
| Shield-8 | Sb (0.2 mm)-Bi (0.3 mm) | 8.526 | 4.263 | [13] | ||||||
| Bilayer (pure layers, each one 0.25 mm thickness) | Shield-9 | Sn-Gd | 7.6 | 3.8 | [10] | |||||
| Shield-10 | Gd-Sn | 7.6 | 3.8 | [10] | ||||||
| Shield-11 | Gd-W | 13.6 | 6.8 | [10] | ||||||
| Shield-12 | W-Gd | 13.6 | 6.8 | [10] | ||||||
| Shield-13 | Sn-W | 13.3 | 6.65 | [10] | ||||||
| Shield-14 | W-Sn | 13.3 | 6.65 | [10] | ||||||
| Shield-15 | Bi-Sn | 8.525 | 4.2625 | [10] | ||||||
| Shield-16 | Sb-W | 12.995 | 6.4975 | [13] | ||||||
| Shield-17 | Sb-Bi | 8.22 | 4.11 | [13] | ||||||
| Shield-18 | Ba-Bi | 6.625 | 3.3125 | [13] | ||||||
| Shield-19 | Ba-W | 11.4 | 5.7 | [13] | ||||||
| Three-layers (pure layers each one 0.167 mm thickness) | Shield-20 | W-Bi-Gd | 12.317 | 6.1585 | [10] | |||||
| Shield-21 | Gd-W-Bi | 12.317 | 6.1585 | [10] |
Radiation setting and estimations
The X-ray source is defined as a 1 × 2 mm focal spot. Simulations are performed for the X-rays energy spectrum of 70, 80, 90, 100, 110, and 120 kVp. In order to investigate the maximum amount of possible radiation scattering, the largest field size of 43 × 43 cm is introduced to expose the abdominal-pelvic area of the patient body in all simulations. The Spektr 3.0 software is used to generate the required energy spectrum of X-ray primary beam for simulation purposes. In several studies by Poludniowski et al.,[18,19,20] Spektr models are validated in agreement with measured outputs. In this project, due to the nature of computerized simulation in order to increase the calculation accuracy and to reduce the errors, 2e8 particle histories were followed for F6 tally output in each organ. F6 tallies calculate the absorbed energy per mass (MeV/gr) of each organ per particle. In this study, relative comparison for each organ is performed in the same setting (source and exposure rate). Therefore, due to the relative nature of the evaluations, there is no need to use any correction factor for estimations.
A PTW dosimeter model of a NOMEX multimeter was utilized to validate estimations. According to the used measurement setup, a dosimeter with 115 × 50 × 9 mm3 dimensions was simulated on the table. MCNPX Monte Carlo F6 tally ratio of NOMEX multimeter and measured dose by DAP meter mounted on the gantry head of the system were used to estimate the multimeter dose. DAP value measured by the Platinum DRF system. Calculated and measured dose in a multimeter for a single pulse of 3.8-second exposure with 80 kVp X-ray were 140.74µGy and 111.4µGy, respectively. Actually, an accuracy of ±1.5% is reported for dose measurement with the NOMEX multimeter. Therefore, about MCNPX calculations with 2.99% accuracy based on the NOMEX measurement agreed with the estimations in this study. Additionally, the results show an agreed X-ray energy spectrum generated by Spektr software. NOMEX multimeter and its radiograph are shown in Figure 4.
Figure 4.
(a) NOMEX multimeter and (b) its radiograph
Dosimetry analysis
The percentage relative absorbed dose for physician’s organ with lead apron related to without it in graphs was employed, which shows the radioprotection effect of the lead apron. Graphs show the percentage relative organ doses calculated as follows:
Additionally, to demonstrate the attenuation efficiency for the investigated shields, the relative dose difference (RDD) parameter is defined for different organs of the physician’s body. As shown in Equation 2, RDD is the related organ dose difference for each shield to the lead one. Thus, RDD is equal to zero for the lead apron, and the compositions with the negative values have a better protection function related to the lead. Therefore, shields with positive RDD values are not preferred because of lower efficiency than lead. For each shield, the mean relative dose difference (MRDD) is the average of the RDDs in all the upper, middle, or lower organs (MRDDupper, MRDDmiddle, and MRDDlower, respectively).
Since simulation parameters are held constant, the shields with the highest dose reduction are reported.
RESULTS
Distribution of the scattered photons incident on the physician
The physician is beside the couch and receives dose in each exposure pulse of the fluoroscopy/angiography imaging. As mentioned in the previous sections, this dose is caused by radiation scattered from the patient’s body and the environment. The angular distribution of scattered photons depends on the particle energies. Figure 5 shows the mean energy of the scattered radiations that are received by different heights of the physician’s body caused from six different primary beam energies in addition to their required angle for such scattering.
Figure 5.
The mean energy of the scattered photons received by the physician’s body
Lead radioprotection efficiency
Figures 6–8 show the ratio of the received organ dose in using a lead apron compared to without it. As it can be seen in the graphs. In a 70 kVp primary beam, all the organ doses except for testes and male genitalia are reduced to less than one percent when a lead apron is used. Testes and male genitalia, because of the higher mean energy of the scattered photon that they receive, show a little more percentage relative dose than lead up to about 2%. At higher energies, radiation protection is decreased, but strongly effective organ dose reduction is still seen. For example, kidneys only receive 0.87% of absorbed dose if a lead apron is used (70 kVp primary beam), which shows nearly complete protection, but for a higher energy of 120 kVp, with using a lead apron, kidneys still receive 7.7% absorbed dose of kidneys of an uncovered physician. In current simulations, because of the phantom neck position, about 3 mm from the upper surface of the thyroid is not covered by the shield. Therefore, even in 70 kVp energy, the thyroid has received higher relative absorbed dose values than the other organs close to it. It is strongly recommended to pay attention to full coverage of the neck when using the thyroid shield. This is also seen for the upper part of the leg bone, which shows the need to use an apron with a long enough length to provide better coverage of this area, and the necessity of using an apron with a final weight as low as possible.
Figure 6.
The percentage relative organ doses received in the upper region of the physician’s body in using lead apron to without it
Figure 7.
The percentage relative organ doses received in the middle region of the physician’s body in using lead apron to without it
Figure 8.
The percentage relative organ doses received in the lower region of the physician’s body in using lead apron to without it
Radiation attenuation comparison of the pure layer of elements
In Table 3, the results of the MRDD calculation for using the pure single layers are reported for each investigated element in this study.
Table 3.
Mean relative dose difference (MRDD) for the considered elements in different primary beam energies
| Primary Beam Energy (kVp) | Region of the Physician body | MRDD for elemental aprons |
||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ba | Bi | Gd | Sn | W | Sb | Cd | ||||||||||
| 70 | Upper | 38.277 | 0.505 | 15.963 | 2.147 | −0.551 | 3.633 | 0.645 | ||||||||
| Middle | 20.687 | 0.492 | 11.225 | 0.989 | −0.607 | 1.702 | 0.267 | |||||||||
| Lower | 13.780 | 0.343 | 6.397 | 0.849 | −0.416 | 1.373 | 0.267 | |||||||||
| 80 | Upper | 12.888 | 0.338 | 5.181 | 0.944 | −0.425 | 1.476 | 0.339 | ||||||||
| Middle | 9.194 | 0.394 | 4.310 | 0.634 | −0.528 | 0.995 | 0.205 | |||||||||
| Lower | 7.062 | 0.294 | 2.708 | 0.603 | −0.423 | 0.914 | 0.231 | |||||||||
| 90 | Upper | 7.426 | 0.287 | 2.591 | 0.664 | −0.429 | 0.993 | 0.261 | ||||||||
| Middle | 5.551 | 0.330 | 2.018 | 0.489 | −0.557 | 0.726 | 0.180 | |||||||||
| Lower | 4.651 | 0.258 | 1.391 | 0.488 | −0.512 | 0.704 | 0.207 | |||||||||
| 100 | Upper | 5.030 | 0.250 | 1.449 | 0.533 | −0.489 | 0.775 | 0.222 | ||||||||
| Middle | 3.842 | 0.281 | 1.002 | 0.403 | −0.641 | 0.581 | 0.160 | |||||||||
| Lower | 3.457 | 0.231 | 0.758 | 0.423 | −0.604 | 0.539 | 0.194 | |||||||||
| 110 | Upper | 3.799 | 0.225 | 0.872 | 0.462 | −0.553 | 0.651 | 0.210 | ||||||||
| Middle | 2.992 | 0.255 | 0.535 | 0.372 | −0.709 | 0.516 | 0.163 | |||||||||
| Lower | 2.897 | 0.237 | 0.479 | 0.431 | −0.658 | 0.579 | 0.226 | |||||||||
| 120 | Upper | 3.113 | 0.212 | 0.562 | 0.433 | −0.601 | 0.597 | 0.212 | ||||||||
| Middle | 2.580 | 0.255 | 0.314 | 0.397 | −0.749 | 0.525 | 0.210 | |||||||||
| Lower | 2.662 | 0.241 | 0.373 | 0.501 | −0.686 | 0.636 | 0.308 | |||||||||
The greatest amount of the transmitted radiation through the elemental shields that cause the highest absorption dose of the organs was seen for barium, antimony, and tin, respectively. These three elements have a lower density and atomic number compared to the other investigated elements. Barium has a higher atomic number than tin and antimony, but a lower density than half of the others. Almost the greatest differences in the lead apron radiation reduction were observed for the neck and thoracic areas (upper region). Among these elements, bismuth and cadmium show the closest received organ dose to lead. The best attenuation was observed for tungsten with a decreased radiation transmission compared to lead for all the investigated energies in all the organs, but as Table 1, using a high kg/cm2 of tungsten only layer instead of lead does not have a preferred efficiency.
Radiation attenuation comparison of the considered shields
According to the results of the calculations for the studied nonlead shields that are shown in Figures 9–11, the best protective performance in upper organs in 70 kVp energy were seen for the tungsten and shields 7, 13, and 16 compositions, respectively. MRDDupper for them was in the range of −0.424 to −0.136. RDD for these four shields had negative values in all the upper organs. Another negative MRDDupper of −0.054 was estimated for shield 14; however, it was not for all upper organs, it just shows that, although shield 14 (W-Sn) was often good attenuator, this behavior was not seen for all the organs that demonstrates lower protection efficiency than the other mentioned shields. The best MRDDmiddle values in abdominal and lumbar organs were calculated for tungsten and shields 7, 13, 14, 16, and 21 in the range of −0.607 to −0.022. With these shields, RDD for all organs in this area was negative and very close to MRDDmiddle (with a standard deviation of 0.02 to 0.05). Additionally, for shields 11 and 21, while MRDDmiddle had a negative value, the RDDs were calculated with 0.133 and 0.089 in stomach, 0.118 and 0.072 in liver and the values less than 0.06 for the pancreas, spleen and gall bladder. Generally, in upper and middle organs, shield 7 [Sb (0.2 mm)-W (0.3 mm)], which has the same materials but different thicknesses with shield 16 [Sb (0.25 mm)-W (0.25 mm)] with higher density and weight provided about twice RDDs (respectively, about −0.2 to −0.3 vs −0.1 to −0.2).
Figure 9.
RDD values for shields 1–21 in the upper physician organs
Figure 10.
RDD values for shields 1–21 in the middle physician organs
Figure 11.
RDD values for shields 1–21 in the lower physician organs
In the lower organs, tungsten and 7, 13, 11, 16, and 21 shields, respectively, showed MRDDlower in the range of −0.416 to −0.097. Additionally, for the shield 14, RDD showed values greater than zero (0.116 and 0.148, respectively) for testes and male genitalia, but not for the other organs and MRDDlower (equal to −0.06). However, shield 12 with MRDDlower equal to 0.013 and standard deviation of 0.062 was not very differed from lead.
In 80 kVp energy, tungsten and shields 11, 21, 7, 12, 13, 16, 20, and 14 with MRDDtotal from −0.346 to −0.084 showed better attenuation efficiency than lead. In the upper organs, RDD values greater than zero were not found for any organs in using tungsten and 11, 7, 21, 13, and 16 shields. MRDDupper was calculated with −0.425 to −0.117 values for them. MRDDupper with values of −0.105, −0.066, and −0.057 were calculated for shields 12, 14, and 20, respectively. However, the values less than 0.1 for the breast and ribs and less than 0.01 for thyroid were also seen in this area with using the mentioned shields. In the middle organs, MRDDmiddle was calculated with values from −0.528 to −0.03 for tungsten and shields 11, 21, 12, 7, 13, 14, 20, and 16, respectively. RDD of all organs in this area was less than zero. In the lower organs, MRDDlower values were obtained from −0.423 to −0.132 for using tungsten and shields 11, 21, 12, 7, 13, 20, and 16. MRDDlower for shield 14 was also calculated as −0.095, but in the male genitalia and testes, RDDs were 0.097 and 0.051, respectively.
In 90 kVp energy, better radiation protections than lead were reported for tungsten and shields 11, 21, 12, 7, 20, 13, 16, and 14, with MRDDtotal in the range of −0.375 to −0.146. MRDDupper in the upper organs for these shields were seen about −0.429 to −0.145, and only for shield 14 with MRDDupper equal to −0.111, a RDD greater than zero was observed with a value of 0.06 in the Breast organ. In the middle organs, tungsten and shields 11, 12, 21, 20, 7, 13, 14, and 16, respectively, showed MRDDmiddle from −0.557 to −0.218. The standard deviation of the RDDs in this area were also lower than the upper area and were calculated with values ranging from 0.008 for tungsten to 0.057 for shield 12. In the lower region, MRDDlower was obtained with values of −0.523 to −0.236 for shields 11, tungsten, 21, 12, 7, 20, 13, 16, and 14.
In 100 kVp energy radiations, MRDDtotal was calculated with values from − 0.446 to − 0.038 for shields 11, tungsten, 12, 21, 20, 7, 13, 14, 16, and 19, respectively. In the upper region, the best results were obtained for shields 11, tungsten, 21, 12, 7, 20, 13, 16, and 14 with MRDDupper about −0.493 to −0.227 which were found with standard deviations of 0.11 to 0.21. In the middle area, MRDDmiddle was calculated with values of −0.667 to −0.374 for shields 11, tungsten, 12, 21, 20, 7, 14, 13, and 16 and a value of 0.066 for shield 19. In addition, MRDDmiddle for shield 10 was −0.111, but there were also RDDs greater than zero for stomach and liver (0.079 and 0.018, respectively). In the lower area, MRDDlower was obtained for shields 11, tungsten, 21, 12, 7, 20, 13, 16, and 14 with values of −0.604 to −0.382 and for shield 19 with a value of −0.150. MRDDlower was calculated as −0.034 for shield 10, but for the organs of the bladder, testis, and male genitalia, radiation attenuation was not better than lead (RDDs of 0.01, 0.175, and 0.214, respectively).
In 110 kVp primary beam energy, MRDDtotal for shields 11, tungsten, 12, 21, 20, 7, 13, 14, 16, 19, and 10 were obtained with values from −0.491 to −0.045. In the upper region, MRDDupper ranging from −0.553 to −0.116 for tungsten and shields 11, 12, 21, 20, 13, 14, and 19 showed more radiation reduction than lead. Although, shield 16 caused a relatively high RDD for cervical vertebrae (3.83), but it was not same as the other upper organs and MRDDupper without that was equal to −0.341. In the organs of the middle region, MRDDmiddle with values of −0.726 to −0.166 were obtained for shields 11, tungsten, 12, 21, 20, 7, 14, 13, 16, 19, and 10. The standard deviations from 0.01 for tungsten to 0.07 for shield 10 showed low differences between RDDs related to the mean values. Additionally, MRDDupper for shield 9 were calculated as − 0.039, the positive RDD values observed for colon, gallbladder, liver and stomach were also very closed to zero (from 0.006 to 0.092) and. MRDDlower about −0.659 to −0.057 were calculated for shields 11, tungsten, 12, 21, 7, 20, 13, 14, 16, 19, and 10.
MRDDtotal in 120 kVp energy were obtained from − 0.495 to −0.026 for tungsten and shields, 11, 12, 21, 7, 20, 13, 14, 16, 19, and 10. In all organs of the upper region, RDDs for shields 11, tungsten, 12, 21, 7, 20, 13, 16, 14, and 19 had negative values ranging from −0.606 to −0.223. In shield 10, despite of the positive RDDs for thymus, thyroid, ribs and breast, MRDDupper showed a value of −0.028. In the middle organs, MRDDmiddle for shields 11, tungsten, 12, 21, 20, 7, 14, 13, 16, 19, and 10 were calculated with values of −0.753 to −0.153. shield 10, having RDD values from 0.008 to 0.07 for gallbladder, SI wall, colon, liver, and stomach, showed MRDDmiddle equal to −0.034. In the lower region, tungsten and shields 11, 12, 21, 7, 20, 13, 14, 16, and 19 with MRDDlower from −0.686 to −0.230 caused better radioprotective efficiency than lead shields for all the organs in this area. MRDDlower was calculated as −0.018 for shield 10, but for testes and male genitalia, RDDs were calculated as 0.165 and 0.195, respectively. Additionally, in energies higher than 100 kVp, Ba-W shield is also seen among the more effective shields than lead for about all organs.
DISCUSSION
According to the results of the study, in the upper and middle physician organs, only bilayer shields including tungsten and a layer of antimony or tin have shown better protection than lead in 70 kVp primary beam energy. Although higher radiation protection of these shields can also be seen in lower organs, tungsten with layers of gadolinium and bismuth had also demonstrated more protection than lead. The best attenuations of tin and antimony in upper organs may be due to the lower mean energy of the received scattered photons. It can be obviously related to the greater attenuation that occurs in slightly more than the k-edge absorption energies and follows by a descending exponential attenuation in higher energies. K-edge absorption energies of tin and antimony are 29.2 and 30.5 keV, respectively, and the received photons in the upper region from 70 kVp primary beam have the closest mean energies among the all considered kVps and physician body levels. However, there is high probability of photoelectric collision in shields including gadolinium (with 50.4 keV k-edge absorption) for almost the all organs in 80–100 kVp. Generally, by increasing the primary beam energy, more decreased transmission of the scattered radiation was resulted when two/three-layer shields including tungsten with gadolinium, bismuth, and then antimony and tin lighter metals were used.
In 80 kVp, Gd-W, W-Gd, and Gd-W-Bi shield have the best performance after tungsten. However, tungsten bilayers containing antimony and tin were also effective. This behavior was seen for 90 kVp in the upper and middle areas but also Gd-W showed slightly better protections than tungsten in lower organs. Gd-W efficiency in 100–120 kVp energies was similar or better than tungsten. The other shields including tungsten and layers of gadolinium, bismuth, antimony, and tin have also been observed with slightly lesser attenuation but closed to Gd-W and tungsten radiation protection in these energies. All the results are in good agreement with previous study[10] that was performed in 80 kVp and 120 kVp. They were reported Gd-W and Gd-W-Bi as the best attenuators and finally Gd-W-Bi were proposed by them as the optimal selection for aprons because of lower mass versus the other one. In spite of our study, their results were shown a little lowered protection efficiency of the Gd included shields in 120 kVp against 80 kVp energies but it is required to mention that their investigations were performed for shields against the X-ray primary beam that has a little higher mean energy related to the scatter radiations. The mean energies of 41.3 and 56.3 keV for 80 and 120 kVp primary X-ray beam spectra and lesser values in scattered radiations that were calculated in our investigation show the expected behavior based on the attenuation curve closed to k-edge energy.
As in a previous study by Mccaffrey et al.,[13] it was shown that low-Z upstream with high Z downstream bilayer composed of pure metals produces more radiation protection; in the current study, bilayers of Gd-W and Sn-W were clearly better attenuators against the reverse configurations (W-Gd and W-Sn) for all the organs. The RDD ratios of two configurations were varied by a factor of about 2 in 70 kVp to about 1 in 120 kVp. Current study also considered bilayers with greater thickness of the high-Z material such as Sb (0.2 mm)-W (0.3 mm) compared to Sb (0.25 mm)-W (0.25 mm) that have shown better attenuation, but it is not significantly optimized due to their higher weight so the same thickness bilayers can be optimum selections.
Barium is another element with a suitable k-edge absorption (37.5 keV) for attenuation in higher radiologic radiations (more than 100 kVp) but very low density has lowered its efficiency. As mentioned in the results, in energies higher than 100 kVp, Ba-W is also seen among the more effective shields than lead for about all the organs. Additionally, in an investigation by Kazempour et al., which several materials were considered for their attenuation properties (shields 1–6 of the current study), the attenuation efficiency for one material containing Barium in 120 kVp was the best but not in the lower energies (40, 60 and 90 kVp) (9). According to the results of the current study, this material has shown the best protection between six proposed materials by Kazempour et al., but related to lead was not significantly efficient. However, their low densities probably allow using some bigger thicknesses. Future studies should determine the optimal thickness-to-weight ratio through experimental validation.
Therefore, due to the more effective protection, the mentioned compositions can be used to produce aprons with lower thickness and lower final weight but equal efficiency compared to lead. Investigation on the sufficient thickness can be the perform in further studies.
CONCLUSION
According to the results, aprons containing tungsten has the best radiation protection. The greatest attenuations in higher diagnostic energies are found for a layer of tungsten with layers of gadolinium, bismuth, or both of them (Gd-W and Gd-W-Bi, respectively). In lower energies, using bilayers of tin or antimony with tungsten can be effective. Optimal thickness of the layers should be considered. Additionally, investigations show that there are no significantly difference for received radiation in different part of the physician body and one-piece apron that is constructed of the same material for all the body is an optimal selection to protect against the diagnostic X-ray.
Ethics approval and consent to participate
This research was approved by the ethics committee of Ahvaz Jundishapur University of Medical Sciences (Approval Number: IR.AJUMS.REC.1400.035).
Consent for publication
Not applicable.
Author’s contributions
M. Papie: Methodology, data analysis, interpretation, and writing the original draft.
L. Mansi: Conceptualization, methodology, and investigation.
S. Kitson: Conceptualization, methodology, and investigation.
M. Cheki: Conceptualization, supervision, and reviewing.
All authors read and approved the final manuscript.
Availability of data and materials
The data and supportive information are available within the article.
Conflict of interest
The authors declare no conflict of interest, financial or otherwise.
Acknowledgements
Declared none.
Funding Statement
This research was supported by grants (U-00027) from the vice chancellor of research at Ahvaz Jundishapur University of Medical Sciences (Iran).
REFERENCES
- 1.McCaffrey JP, Tessier F, Shen H. Radiation shielding materials and radiation scatter effects for interventional radiology (IR) physicians. Med Phys. 2012;39:4537–46. doi: 10.1118/1.4730504. [DOI] [PubMed] [Google Scholar]
- 2.Eder H, Seidenbusch MC, Treitl M, Gilligan P. A new design of a lead-acrylic shield for staff dose reduction in radial and femoral access coronary catheterization. Rofo. 2015;187:915–23. doi: 10.1055/s-0034-1399688. [DOI] [PubMed] [Google Scholar]
- 3.Vano E, Sanchez RM, Fernandez JM, Bartal G, Canevaro L, Lykawka R, et al. A set of patient and staff dose data for validation of Monte Carlo calculations in interventional cardiology. Radiat Prot Dosimetry. 2015;165:235–9. doi: 10.1093/rpd/ncv032. [DOI] [PubMed] [Google Scholar]
- 4.Siiskonen T, Tapiovaara M, Kosunen A, Lehtinen M, Vartiainen E. Monte Carlo simulations of occupational radiation doses in interventional radiology. Br J Radiol. 2007;80:460–8. doi: 10.1259/bjr/26692771. [DOI] [PubMed] [Google Scholar]
- 5.Siiskonen T, Tapiovaara M, Kosunen A, Lehtinen M, Vartiainen E. Occupational radiation doses in interventional radiology: Simulations. Radiat Prot Dosimetry. 2008;129:36–8. doi: 10.1093/rpd/ncn017. [DOI] [PubMed] [Google Scholar]
- 6.Monzen H, Tamura M, Shimomura K, Onishi Y, Nakayama S, Fujimoto T, et al. A novel radiation protection device based on tungsten functional paper for application in interventional radiology. J Appl Clin Med Phys. 2017;18:215–20. doi: 10.1002/acm2.12083. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7.Boone JM, Levin DC. Radiation exposure to angiographers under different fluoroscopic imaging conditions. Radiology. 1991;180:861–5. doi: 10.1148/radiology.180.3.1871307. [DOI] [PubMed] [Google Scholar]
- 8.Kobayashi T, Hirshfeld Jr-JW. Radiation exposure in cardiac catheterization: Operator behavior matters. Circ Cardiovasc Interv. 2017;10:e005689. doi: 10.1161/CIRCINTERVENTIONS.117.005689. [DOI] [PubMed] [Google Scholar]
- 9.McCaffrey JP, Shen H, Downton B, Mainegra-Hing E. Radiation attenuation by lead and nonlead materials used in radiation shielding garments. Med Phys. 2007;34:530–7. doi: 10.1118/1.2426404. [DOI] [PubMed] [Google Scholar]
- 10.Zehtabian M, Piruzan E, Molaiemanesh Z, Sina S. Design of light multi-layered shields for use in diagnostic radiology and nuclear medicine via MCNP5 Monte Carlo code. Iran J Med Phys. 2015;1:12. 223-8. [Google Scholar]
- 11.Kazempour M, Saeedimoghadam M, Shooli FS, Shokrpour N. Assessment of the radiation attenuation properties of several lead free composites by Monte Carlo simulation. J Biomed Phys Eng. 2015;5:67. [PMC free article] [PubMed] [Google Scholar]
- 12.Moore B, VanSonnenberg E, Casola G, Novelline RA. The relationship between back pain and lead apron use in radiologists. AJR. AJR Am J Roentgenol. 1992;158:191–3. doi: 10.2214/ajr.158.1.1530763. [DOI] [PubMed] [Google Scholar]
- 13.McCaffrey JP, Mainegra-Hing E, Shen H. Optimizing non-Pb radiation shielding materials using bilayers. Med Phys. 2009;36:5586–94. doi: 10.1118/1.3260839. [DOI] [PubMed] [Google Scholar]
- 14.Scuderi GJ, Brusovanik GV, Campbell DR, Henry RP, Kwon B, Vaccaro AR. Evaluation of non–lead-based protective radiological material in spinal surgery. Spine J. 2006;6:577–82. doi: 10.1016/j.spinee.2005.09.010. [DOI] [PubMed] [Google Scholar]
- 15.Bozkurt A, Bor D. Simultaneous determination of equivalent dose to organs and tissues of the patient and of the physician in interventional radiology using the Monte Carlo method. Phys Med Biol. 2006;52:317. doi: 10.1088/0031-9155/52/2/001. [DOI] [PubMed] [Google Scholar]
- 16.Carinou E, Ferrari P, Koukorava C, Krim S, Struelens L. Monte Carlo calculations on extremity and eye lens dosimetry for medical staff at interventional radiology procedures. Radiat Prot Dosimetry. 2011;144:492–6. doi: 10.1093/rpd/ncq573. [DOI] [PubMed] [Google Scholar]
- 17.Compagnone G, Giampalma E, Domenichelli S, Renzulli M, Golfieri R. Calculation of conversion factors for effective dose for various interventional radiology procedures. Med Phys. 2012;39:2491–8. doi: 10.1118/1.3702457. [DOI] [PubMed] [Google Scholar]
- 18.Poludniowski GG, Evans PM. Calculation of X-ray spectra emerging from an X-ray tube. Part I. Electron penetration characteristics in X-ray targets. Med Phys. 2007;34:2164–74. doi: 10.1118/1.2734725. [DOI] [PubMed] [Google Scholar]
- 19.Poludniowski GG. Calculation of X-ray spectra emerging from an X-ray tube. Part II. X-ray production and filtration in X-ray targets. Med Phys. 2007;34:2175–86. doi: 10.1118/1.2734726. [DOI] [PubMed] [Google Scholar]
- 20.Poludniowski G, Landry G, Deblois F, Evans PM, Verhaegen F. SpekCalc: A program to calculate photon spectra from tungsten anode X-ray tubes. Phys Med Biol. 2009;54:N433. doi: 10.1088/0031-9155/54/19/N01. [DOI] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data and supportive information are available within the article.