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Estimation of organ absorbed dose in pediatric chest X-ray examination: A phantom study
Radiation Physics and Chemistry 166 (2020) 108472
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Estimation of organ absorbed dose in pediatric chest X-ray examination: A phantom study
T
Nurul H.M. Jamala, Inayatullah S. Sayeda,∗, Waliullah S. Syedb a
Department of Diagnostic Imaging and Radiotherapy, Kulliyyah of Allied Health Sciences, International Islamic University Malaysia, Jalan Sultan Ahmad Shah, Bander Indera Mahkota, 25200, Kuantan, Pahang, Malaysia b School of Health Sciences, Universiti Sains Malaysia, Health Campus, 16150 Kuban Kerian, Kota Bharu, Kelantan, Malaysia
A R T I C LE I N FO
A B S T R A C T
Keywords: Absorbed dose Chest X-ray Pediatrics Phantom OSLD
Children have a greater risk of developing lifetime cancer and other biological effects from ionizing radiation exposure than adults. The aim of this study was to measure the absorbed dose received by lungs and heart in pediatric chest X-ray examination using nanoDot optically stimulated luminescent dosimeter (OSLD). The X-ray system, Siemens Multix Top was used. A pediatric phantom developed by using beeswax and polyurethane foam was exposed at 50 kVp, 52 kVp, 55 kVp, 57 kVp and 60 kVp, with fixed tube current-exposure time (3 mAs), which is normally used in pediatric clinical chest X-ray examinations. The nanoDot OSLDs were placed in different parts in the thorax of the phantom according to the position of organs in the chest area, which are lungs and heart. For lungs, absorbed dose measurement nanoDot OSLDs were placed in the apex and base at three different depths. The phantom was exposed three times for each kVp value, and the absorbed doses were measured in mGy. The findings show that the measured absorbed dose to the heart increased with the increase in kVp. Overall, a 22% increase in absorbed dose to heart and a 29% increase in lungs with the increase in kVp was recorded. In addition, absorbed dose to the base of left and right lungs was recorded higher up to 9% as compared to the apex of lungs. In conclusion, the absorbed dosage increases with exposure, while the absorbed dose decreases with depth. It is necessary for the radiographer to select an appropriate exposure setting based on the physical characteristics of the pediatric patient.
1. Introduction Diagnostic imaging modalities are the most preferred procedure for diagnosing the pathological condition in both the adults and children. Chest radiography is the frequently used imaging procedure in adults and children. A great concern arises in the medical imaging, especially in pediatrics as majority of the modalities use ionizing radiation. The Xrays or ionizing radiation provide diagnostic information and assessment of pathology. However, there are some risks associated, and its consequences towards the human body cell (Emadeldin and Abukonna, 2016). Studies have shown that the children and neonate are more sensitive to the ionizing radiation as compared to the adults (Khong et al., 2013; Ladia et al., 2016; Tahiry et al., 2017). According to the International Atomic Energy Agency (IAEA, 2013), the risk of biological effects and the lifetime cancer risk from radiation exposure to children is higher because the radiation sensitivity during the child's development stage is higher and the children have a longer life expectancy. The probability of the development of leukaemia naturally in children with
∗
age between 0 and 10 years is higher than older children and adults (Chukwuemeka et al., 2013). Absorbed dose is the amount of energy deposited by radiation in a human tissue. It can cause the biological effects damaging the DNA in human cells. The biological effects are divided into stochastic effects and deterministic effects. The stochastic effects are the long-term effects of radiation. There is no threshold for the stochastic effect to occur and the probability of occurrence increases with the radiation dose. Other than the effective dose, organ absorbed dose can help in determining the risk of radiation to a patient. The Society for Paediatric Radiology initiated the Image Gently campaign in 2008. The aim of this campaign was to increase the awareness of radiation dose in pediatrics through proper education. Food and Drug Administration (FDA) has adopted principles in the radiation protection: justification for each procedure and optimization in the use of radiation dose for each examination. The concept of optimization implies increase the benefits to patient's health, and decreasing the risk of biological effects (Ladia et al., 2016; Yakoumakis et al., 2003). The important part of the optimization
Corresponding author. E-mail address: [email protected] (I.S. Sayed).
https://doi.org/10.1016/j.radphyschem.2019.108472 Received 29 July 2019; Received in revised form 25 August 2019; Accepted 29 August 2019 Available online 31 August 2019 0969-806X/ © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
2.4. Absorbed dose measurement
is to determine radiation dose to the patients. Hence, radiographer should have an understanding and knowledge of the clinical examination including practice the principle of justification, optimization, dose limitation and technique in handling pediatric patient. This can be achieved by applying the concept of ALARA (as low as reasonably achievable). It will help to make necessary measurement for pediatric dose determination and reduce the risk of biological effect. Phantoms are utilized to estimate radiation dose delivered to patients and evaluate the quality of imaging systems. To simulate radiation transport processes in human body, phantoms have been developed using a variety of tissue mimicking materials (Watanabe and Constantinou, 2006). Beeswax is a mixture of hydrocarbons, free fatty acids, esters of fatty acids and fatty alcohol, diesters and exogenous substances (Tulloch, 1970, 1971; 1980). The composition of the beeswax is variable and depends on their families, breeds, genetics and diet (Buchwald et al., 2006). Beeswax use, economy and trade date from very early age and is very well documented. Children receive higher radiation dose than adults since they tend to move during the examination, this situation forces radiographer for repeat examination. However, to avoid repetition of examination, radiographers do not apply proper exposure setting and collimation by not considering the physical characteristics of pediatric patients accordingly. Thus, the purpose of this study was to estimate the organ absorbed dose received by lungs and heart in pediatric chest X-ray examination using nanoDot optically stimulated luminescent dosimeter (OSLD).
The nanoDot OSLDs were placed at different parts in the thorax of the phantom according to the position of organs in the chest area, which are lungs and heart (Fig. 1). The nanoDot OSLDs were placed at the apex and base of the lungs at three different depths (Fig. 1). A layer of beewax as a skin was placed over the phantom to cover the organs of interest for absorbed dose measurement as shown in Fig. 2. The pediatric phantom was collimated in four border sides. The collimation used was fixed for all exposures. The Source to Image Distance (SID) used was 100 cm. Since the moving grid was not applied, measuring tape was used to measure the SID. Five different exposures were selected in this study which are; 50 kVp, 52 kVp, 55 kVp, 57 kVp and 60 kVp with a 3 mAs constant tube current-exposure time. The pediatric phantom was exposed three times for each kVp value. The reading of the nanoDots OSLDs was recorded and the mean reading value for each exposure was obtained. 3. Results 3.1. Estimated absorbed dose to heart The measured value in the heart was 0.474 mGy at 50 kVp, and 0.603 mGy at the highest kVp, 60 kVp. The measured value of organ absorbed dose increased with the increase of exposure. The measured value was found to drop slightly at 57 kVp, as there is no solid reason for the drop in absorbed dose. Overall, the measured value of absorbed dose showed increasing trend as depicted in Fig. 3.
2. Materials and method
3.2. Estimated absorbed dose to lungs
2.1. X-ray system
The nanoDot OSLDs were placed at left and right apex and base of the lungs at three different depths; top (1st level), middle (2nd level) and bottom (3rd level). The measured absorbed dose is shown in Figs. 4–7. The nanoDot OSLDs reading (Fig. 4) is higher at the first level as compared to the second and third levels. At the 50 kVp, the values of absorbed dose at the first, second and third levels are 0.3995 mGy, 0.3563 mGy and 0.3378 mGy, respectively. Similar trend can be seen for the other exposures. The measured value of organ absorbed dose (Fig. 5) in first level slightly dropped at 52 kVp, from 0.533 mGy to 0.515 mGy. At 55 kVp, the measured value of absorbed dose increased for all exposures and then, the trend changed at 57 kVp. The measured value of absorbed dose decreased at 60 kVp at second and third level. Fig. 6 shows the results of nanoDot OSLDs reading in the apex of left lung at three different depths. The measured value of absorbed dose in this group shows a significant increase as the exposure increased at all levels. It can be observed (Fig. 7) that the nanoDot OSLDs readings at the first level, for all exposures are higher than in the second and third level. The value of the absorbed dose in the base of left lung showed similar increasing trend for all different depths. The results also show the measured absorbed dose increase as the exposure increased.
The general X-ray system Siemens Multix Top consists of X-ray tube OPTITOP 150/40/80, and POLYDOROS IT 80 with high-frequency generator. The large focal spot was used, and the tube voltage ranged 50 kVp – 60 kVp with mAs fixed at 3.0 mAs tube current-exposure time. These exposure parameters are commonly practiced in different hospitals in Malaysia for pediatric chest X-ray examinations. Furthermore, the reason behind using a large focal spot is due to the short exposure time required in all chest X-ray examinations.
2.1. Optically stimulated luminescence dosimeter (OSLD) To measure the absorbed dose, the nanoDot OSLDs and microStar reader Landauer Inc., were used. The density of the dosimeter is 1.03 g/ cm3 and it contains 5.0 mm diameter disc of aluminum oxide with carbon. A calibrated microStar reader system was used to read the nanoDot OSLDs. After the exposure, the nanoDot OSLD was scanned and inserted into the microStar reader. MicroStar 4.3 software was used to display the reading. The sensitivity of the microStar system is 0.70. The SI unit used is in mGy. In addition, prior to exposing nanoDot OSLDs to X-rays, bleaching test was conducted on all nanoDOT OSLDs to ensure the absence of remaining radiation dose from earlier studies.
2.3. Pediatric phantom
3.3. Comparison of absorbed dose to apex and base of left and right lung
The thorax phantom of pediatric was developed to simulate the body size of children and the organ position. The average chest size of children with age 2 years was taken from the kindergartens for the development of the thorax phantom. Dimensions of the thorax of 1–2 years old children, pediatric phantom (thorax) and lungs are shown in Table 1. Table 2 shows the density of the organs and the tissue substitute materials (Akhlaghi et al., 2015; Amin et al., 2018; Jones et al., 2003; Vidal and Souza, 2012). Beeswax and polyurethane foam were used to design the phantom as it is easily available and affordable.
The measured value of absorbed dose for three different depths was calculated together. These values were used to compare the absorbed dose to both lungs as depicted in Table 3. Table 3 show the measured value of absorbed dose in the apex of the lungs is lower than in the base of the lungs. At 50 kVp, the values of absorbed dose in apex of both left and right lungs are 0.365 mGy and 0.381 mGy, respectively. In contrast, at the same exposure, the values of absorbed dose are 0.471 mGy and 0.509 mGy in base of left and right lungs respectively. For all parts in the lungs, there is steadily increase in 2
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
Table 1 Dimensions of the thorax of 1–2 years old children, pediatric phantom (thorax) and lungs.
Size Circumference of the chest Thickness of the body Depth of lungs
Size of 1–2 years old children (average)
Pediatric phantom (thorax)
Lungs
18 × 22 cm 56 cm 7.5 cm
18 × 20 cm 50 cm 7 cm 5 cm
Width of apex of both lungs Width of base of both lungs Length of lungs Depth of lungs
12 cm 16 cm 13 cm 5 cm
Table 2 Density of human tissues and proposed tissue substitute materials. Organs
Density of the organs (g/m³)
Proposed tissue substitute materials
Density of the materials (g/m³)
Soft tissue and heart
1.04
Lungs (ICRU 44)
0.26
PMMA Water Beewax Paraffin wax Polyurethane foam Cork
1.17 1.00 0.96 0.94 0.30 0.2–0.4
absorbed dose as the exposure increased. Table 3 show the highest percentage differences for apex and base of the lungs is at 52 kVp. For the apex of the lung at 52 kVp, the percentage difference is 5.88% while the base of the lung recorded 8.99%. At 55 kVp, the apex of the lung recorded the lowest percentage difference, which is 0.24%. The lowest percentage difference in the base of the lung is 1.48%, at 57 kVp. In overall, all the percentage difference between left and right lungs is below 10%.
Fig. 2. Show the thorax of pediatric phantom covered with a layer of beewax as a skin.
applied to MCNP 3.1 code. Ladia et al., 2015, calculated the organ dose in pediatric chest X-ray examination using Monte Carlo based software PCXMC 2.0 version. According to their findings, in chest radiography lungs received highest dose. In addition, Nahangi and Chaparian, 2015, used real patient data including entrance skin exposure (ESE) values and incorporated into the PCXMC code for organ dose measurement. In our study, heart and lungs absorbed doses are higher as compared to the above-mentioned studies except the lungs dose, estimated by Kiljunen et al. (2009). For comparison with other studies, heart and lungs absorbed doses are shown in Table 4. Furthermore, findings of this study show that the measured absorbed dose at the higher depth is less as compared to the shallow depths. The reason is the attenuation of X-ray photons within the phantom. As the X-ray photon penetrates to the phantom, the photons are attenuated by the tissues it passes through. The intensity of the Xray photons is decreased. In addition, the X-ray photons are either absorbed in the phantom or scattered. As the intensity of X-ray photon decreases, the radiation dose absorbed into the nanoDot OSLDs at higher depth is reduced. Tube voltage is the variable in this study with a fixed tube currentexposure time (mAs). Different exposures were used to measure the absorbed dose. The findings of this study indicate that the measured absorbed dose increased with the increase in the tube voltage (kVp).
4. Discussion Chest X-ray examination in pediatric was chosen because it is a common examination in pediatric population. There are issues in chest X-ray examination in pediatric as many pediatric patients receive high dose during the examination. First, the radiographers do not apply proper collimation (Alatts and Abukhiar, 2013). The reason is, to avoid repetition of examination as children tend to move during the examination. The unnecessary wide collimation will increase radiation dose in children. Second, the children are more radiosensitive as compared to the adults. This is because the cells are in the developing stage. The results of the organ absorbed dose were analyzed in the area of interest, heart and lungs (at different depths). Measurements of absorbed dose to different organs in pediatric chest X-ray examination have been conducted by a small group of researchers. Kiljunen et al. (2009), collected the data relating to the pediatric patients’ organ dose in Finnish hospitals. Entrance surface dose (ESD) and dose-area product (DAP) were obtained, these values were incorporated into a Monte Carlo based PCXMC code. For lungs, highest dose 166 mGy was reported. In 2011, Kumaresan et al. performed the pediatric organ dose study, ESD was estimated using the TLD and it was
Fig. 1. Images A and B, show the nanoDot OSLDs placed at apex and base of the lungs at different depths. Image C shows nanoDot OSLDs placed at surface of apex and base of lungs and the location of heart. 3
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
Fig. 3. Measured absorbed dose to the heart.
Fig. 4. Absorbed dose to apex of right lung at three different depths.
Fig. 5. Absorbed dose to base of right lung at three different depths.
indicate the difference with respect to the positioning of the phantom. The phantom was positioned as; the apex of the lungs towards the anode side and the base of the lung to the cathode side. The intensity of the X-ray beam is higher at cathode area compared to anode. This eventually increases the absorbed dose to the base of the lung. Therefore, this suggests that head of child be positioned towards the
The increase in kVp causes the increase in potential difference between cathode and anode. This results in an increase in the mean energy of the X-ray photon. This causes the increase in beam penetration and as a result, the measured value of the absorbed dose increases. The organ absorbed dose in the base of left and right lungs was higher compared to the apex of the lungs. The absorbed dose results
4
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
Fig. 6. Absorbed dose to apex of left lung at three different depths.
Fig. 7. Absorbed dose to base of left lung at three different depths. Table 3 Absorbed dose and percentage differences in left and right lung. kVp
Apex of Right Lung (mGy)
Apex of Left Lung (mGy)
Percentage difference (%)
Base of Right Lung (mGy)
Base of Left Lung (mGy)
Percentage difference (%)
50 52 55 57 60
0.364 0.424 0.480 0.506 0.597
0.380 0.450 0.481 0.520 0.566
4.37 5.88 0.23 2.75 5.29
0.470 0.482 0.544 0.596 0.623
0.509 0.527 0.577 0.605 0.640
7.87 8.98 5.96 1.48 2.67
( ± 0.087) ( ± 0.019) ( ± 0.014) ( ± 0.008) ( ± 0.017)
( ± 0.013) ( ± 0.013) ( ± 0.011) ( ± 0.016) ( ± 0.008)
Heart Lungs
Absorbed Dose (mGy)
0.549 0.516
This Study
Ladia et al. (2015)
Nahangi and Chaparian (2015)
Kumaresan et al. (2011)
1 to 2y
1y
5y
1y
5y
1y
– 0.047
– 0.046
0.009 –
0.015 –
– –
0.109 0.078
( ± 0.008) ( ± 0.012) ( ± 0.014) ( ± 0.015) ( ± 0.012)
anode side, to reduce the absorbed dose to the thyroid, as it is a sensitive organ. The factors that might have compromised the accuracy of organ dose measurements are; the difference between the density of beewax and human tissue as well as the styrofoam that mimicked the body of a child and lungs, respectively. Therefore, attenuation of x-ray photons would be different while travelling towards nanoDot OSLDs through the media as compared to real tissues/organs. Thus, this condition leads to the uncertainty in the organ dose measurement. Another source of error in the organ dose values could be the thorax bones (sternum and ribs) which shield the heart and lungs, in our study, the phantom used was without thorax bones. Thus, the probability of reaching more x-ray photons to nanoDot OSLD is higher; hence, more dose deposition into the nanoDot OSLD. Our study shows higher absorbed dose received by
Table 4 Comparison of organ absorbed dose values (heart and lungs) in pediatric chest X-ray examination with other studies. Organ
( ± 0.079) ( ± 0.012) ( ± 0.015) ( ± 0.017) ( ± 0.093)
5y
5
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
heart and lungs as compared to the findings of other studies presented in Table 4, possibly due to the different type of dosimeters and the Monte Carlo code used for the measurement of organ absorbed dose. Additionally, another reason for the higher dose of heart could be due to the inaccurate placing of nanoDOT OSLD since our phantom does not include the design of a heart.
R. (Ed.), 3rd International Conference on Radiation Safety & Security in Healthcare Services. Lecture Notes in Bioengineering. Springer, Singapore. https://doi.org/10. 1007/978-981-10-7859-0. Buchwald, R., Breed, M.D., Greenberg, A.R., Otis, G., 2006. Interspecific variation in beeswax as a biological construction material. J. Exp. Biol. 209 (20), 3984–3989. https://doi.org/10.1242/jeb.02472. Chukwuemeka, P., Gregory, O., Harcourt, P., Harcourt, P., State, R., 2013. Optimisation of absorbed dose in chest x-rays of paediatric patients at braithwaite memorial specialist hospital , Port Harcourt. Am. J. Sci. Ind. Res. 4 (4), 349–358. Emadeldin, B., Abukonna, A., 2016. Estimation of radiation dose in neotatal intensive care uint (NICU). J. Med. Phys. Appl. Sci. 1 (2), 3–5. IAEA, 2013. Human health series 24: dosimetry in daignostic radiology for paediatric patients. Hum. Health Ser. 24, 176. Retrieved from. http://www-pub.iaea.org/ MTCD/publications/PDF/Pub1609_web.pdf%5Cnhttp://www.vomfi.univ.kiev.ua/ assets/files/IAEA/Pub1462_web.pdf. Jones, A.K., Hintenlang, D.E., Bolch, W.E., 2003. Tissue-equivalent materials for construction of tomographic dosimetry phantoms in pediatric radiology. Med. Phys. 30 (8), 2072–2081. https://doi.org/10.1118/1.1592641. Khong, P., et al., 2013. ICRP publication 121: radiological protection in paediatric diagnostic and interventional radiology. Ann. ICRP 42 (2), 1–63. Kiljunen, T., Tietäväinen, A., Parviainen, T., Viitala, A., Kortesniemi, M., 2009. Organ doses and effective doses in pediatric radiography: patient-dose survey in Finland. Acta Radiol. 50 (1), 114–124. Kumaresan, M., Kumar, R., Biju, K., Choubey, A., Kantharia, S., 2011. Measurement of entrance skin dose and estimation of organ dose during pediatric chest radiography. Health Phys. 100 (6), 654–657. https://doi.org/10.1097/HP.0b013e3182092963. JUN 2011. Ladia, A., Messaris, G., Delis, H., Panayiotakis, G., 2015. Organ dose and risk assessment in paediatric radiography using the PCXMC 2.0. J. Phys. Conf. Ser. 637 (2015), 012014. https://doi.org/10.1088/1742-6596/637/1/012014. Ladia, A.P., Skiadopoulos, S.G., Kalogeropoulou, C.P., Zampakis, P.E., Dimitriou, G.G., Panayiotakis, G.S., 2016. Radiation dose and image quality evaluation in paediatric radiography. Int. J. New Technol. Res. (IJNTR) 2 (3), 9–14. Nahangi, H., Chaparian, A., 2015. Assessment of radiation risk to pediatric patients undergoing conventional X-ray examinations. Radioprotection 50 (1), 19–25. Tahiry, R., Anjarasoa Luc, R.M., Harimalala, R.T., Andriambololona, R., Solofonirina, R.D., Randriantsizafy, R.D., 2017. Doses evaluation of some body organs of pediatric patients undergoing chest X-ray examination using thermoluminescent dosimeter. Radiat. Sci. Technol. 3 (3), 24–28. https://doi.org/10.11648/j.rst.20170303.12. Tulloch, A.P., 1970. The composition of beeswax and other waxes secreted by insects. Lipids 5 (2), 247–258. https://doi.org/10.1007/BF02532476. Tulloch, A.P., 1971. Beeswax - structure of esters and their important hydroxy acids and diols. Chem. Phys. Lipids 6, 235–238. Tulloch, A.P., 1980. Beeswax-composition and analysis. Bee World 61 (2), 47–62. https:// doi.org/10.1080/0005772X.1980.11097776. Vidal, R.M., Souza, N., 2012. A model for the characterization and selection of beeswaxes for use as base substitute tissue in photon teletherapy. Mater. Sci. Appl. 3, 218–223. Watanabe, Y., Constantinou, C., 2006. Phantom materials in radiology. In: Encyclopedia of Medical Devices and Instrumentation. John Wiley & Sons, Inc. doi.org/10.1002/ 0471732877.emd201. Yakoumakis, E.N., Gogos, K.A., Tsalafoutas, I.A., 2003. Radiation dose considerations in common paediatric X-ray examinations. Pediatr. Radiol. 33, 236–240. https://doi. org/10.1007/s00247-002-0861-x.
5. Conclusion In conclusion, with the use of phantom the organ absorbed dose in the pediatric population of the age of two years old was successfully estimated. Since no previous studies have been done, the findings of this study can be used as a baseline/guideline for future studies. There are many factors that contribute to the absorbed dose. Based on this study, the different exposure factors used produced different absorbed dose values. The increase in tube voltage (kVp) increased the absorbed dose. Thus, it is necessary for radiographers to select the suitable exposure during the examination. The absorbed dose reduced with the increase in depth. The position of the anode and cathode plays a role in the absorbed dose. The body part at the cathode side receives a higher radiation dose as the attenuation of X-ray photon at the cathode side is higher compared to anode side. It is suggested, to position the head of the child to the anode side, to reduce the radiation dose to the thyroid. Acknowledgments Authors greatly acknowledge International Islamic University Malaysia (IIUM), Malaysia for financial support through Research Initiative Grant Scheme, RIGS #16-302-0466. The Department of Diagnostic Imaging and Radiotherapy of IIUM is also acknowledged for providing the facilities and equipment to carry out the study. References Akhlaghi, P., Miri Hakimabad, H., Rafat Motavalli, L., 2015. Determination of tissue equivalent materials of a physical 8-year-old phantom for use in computed tomography. Radiat. Phys. Chem. 112, 169–176. https://doi.org/10.1016/j.radphyschem. 2015.03.030. Alatts, N.O., Abukhiar, A., 2013. Radiation doses from chest X-ray examinations for pediatrics in some hospitals of Khartoum State. Sudan Med. Monit. 8 (4), 186–188. https://doi.org/10.4103/1858-5000.133018. Amin, N.A.B., Kabir, N.A., Zainon, R., 2018. Determination of mass attenuation coefficient of paraffin wax and sodium chloride as tissue equivalent materials. In: Zainon,
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Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Estimation of organ absorbed dose in pediatric chest X-ray examination: A phantom study
T
Nurul H.M. Jamala, Inayatullah S. Sayeda,∗, Waliullah S. Syedb a
Department of Diagnostic Imaging and Radiotherapy, Kulliyyah of Allied Health Sciences, International Islamic University Malaysia, Jalan Sultan Ahmad Shah, Bander Indera Mahkota, 25200, Kuantan, Pahang, Malaysia b School of Health Sciences, Universiti Sains Malaysia, Health Campus, 16150 Kuban Kerian, Kota Bharu, Kelantan, Malaysia
A R T I C LE I N FO
A B S T R A C T
Keywords: Absorbed dose Chest X-ray Pediatrics Phantom OSLD
Children have a greater risk of developing lifetime cancer and other biological effects from ionizing radiation exposure than adults. The aim of this study was to measure the absorbed dose received by lungs and heart in pediatric chest X-ray examination using nanoDot optically stimulated luminescent dosimeter (OSLD). The X-ray system, Siemens Multix Top was used. A pediatric phantom developed by using beeswax and polyurethane foam was exposed at 50 kVp, 52 kVp, 55 kVp, 57 kVp and 60 kVp, with fixed tube current-exposure time (3 mAs), which is normally used in pediatric clinical chest X-ray examinations. The nanoDot OSLDs were placed in different parts in the thorax of the phantom according to the position of organs in the chest area, which are lungs and heart. For lungs, absorbed dose measurement nanoDot OSLDs were placed in the apex and base at three different depths. The phantom was exposed three times for each kVp value, and the absorbed doses were measured in mGy. The findings show that the measured absorbed dose to the heart increased with the increase in kVp. Overall, a 22% increase in absorbed dose to heart and a 29% increase in lungs with the increase in kVp was recorded. In addition, absorbed dose to the base of left and right lungs was recorded higher up to 9% as compared to the apex of lungs. In conclusion, the absorbed dosage increases with exposure, while the absorbed dose decreases with depth. It is necessary for the radiographer to select an appropriate exposure setting based on the physical characteristics of the pediatric patient.
1. Introduction Diagnostic imaging modalities are the most preferred procedure for diagnosing the pathological condition in both the adults and children. Chest radiography is the frequently used imaging procedure in adults and children. A great concern arises in the medical imaging, especially in pediatrics as majority of the modalities use ionizing radiation. The Xrays or ionizing radiation provide diagnostic information and assessment of pathology. However, there are some risks associated, and its consequences towards the human body cell (Emadeldin and Abukonna, 2016). Studies have shown that the children and neonate are more sensitive to the ionizing radiation as compared to the adults (Khong et al., 2013; Ladia et al., 2016; Tahiry et al., 2017). According to the International Atomic Energy Agency (IAEA, 2013), the risk of biological effects and the lifetime cancer risk from radiation exposure to children is higher because the radiation sensitivity during the child's development stage is higher and the children have a longer life expectancy. The probability of the development of leukaemia naturally in children with
∗
age between 0 and 10 years is higher than older children and adults (Chukwuemeka et al., 2013). Absorbed dose is the amount of energy deposited by radiation in a human tissue. It can cause the biological effects damaging the DNA in human cells. The biological effects are divided into stochastic effects and deterministic effects. The stochastic effects are the long-term effects of radiation. There is no threshold for the stochastic effect to occur and the probability of occurrence increases with the radiation dose. Other than the effective dose, organ absorbed dose can help in determining the risk of radiation to a patient. The Society for Paediatric Radiology initiated the Image Gently campaign in 2008. The aim of this campaign was to increase the awareness of radiation dose in pediatrics through proper education. Food and Drug Administration (FDA) has adopted principles in the radiation protection: justification for each procedure and optimization in the use of radiation dose for each examination. The concept of optimization implies increase the benefits to patient's health, and decreasing the risk of biological effects (Ladia et al., 2016; Yakoumakis et al., 2003). The important part of the optimization
Corresponding author. E-mail address: [email protected] (I.S. Sayed).
https://doi.org/10.1016/j.radphyschem.2019.108472 Received 29 July 2019; Received in revised form 25 August 2019; Accepted 29 August 2019 Available online 31 August 2019 0969-806X/ © 2019 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Radiation Physics and Chemistry 166 (2020) 108472
N.H.M. Jamal, et al.
2.4. Absorbed dose measurement
is to determine radiation dose to the patients. Hence, radiographer should have an understanding and knowledge of the clinical examination including practice the principle of justification, optimization, dose limitation and technique in handling pediatric patient. This can be achieved by applying the concept of ALARA (as low as reasonably achievable). It will help to make necessary measurement for pediatric dose determination and reduce the risk of biological effect. Phantoms are utilized to estimate radiation dose delivered to patients and evaluate the quality of imaging systems. To simulate radiation transport processes in human body, phantoms have been developed using a variety of tissue mimicking materials (Watanabe and Constantinou, 2006). Beeswax is a mixture of hydrocarbons, free fatty acids, esters of fatty acids and fatty alcohol, diesters and exogenous substances (Tulloch, 1970, 1971; 1980). The composition of the beeswax is variable and depends on their families, breeds, genetics and diet (Buchwald et al., 2006). Beeswax use, economy and trade date from very early age and is very well documented. Children receive higher radiation dose than adults since they tend to move during the examination, this situation forces radiographer for repeat examination. However, to avoid repetition of examination, radiographers do not apply proper exposure setting and collimation by not considering the physical characteristics of pediatric patients accordingly. Thus, the purpose of this study was to estimate the organ absorbed dose received by lungs and heart in pediatric chest X-ray examination using nanoDot optically stimulated luminescent dosimeter (OSLD).
The nanoDot OSLDs were placed at different parts in the thorax of the phantom according to the position of organs in the chest area, which are lungs and heart (Fig. 1). The nanoDot OSLDs were placed at the apex and base of the lungs at three different depths (Fig. 1). A layer of beewax as a skin was placed over the phantom to cover the organs of interest for absorbed dose measurement as shown in Fig. 2. The pediatric phantom was collimated in four border sides. The collimation used was fixed for all exposures. The Source to Image Distance (SID) used was 100 cm. Since the moving grid was not applied, measuring tape was used to measure the SID. Five different exposures were selected in this study which are; 50 kVp, 52 kVp, 55 kVp, 57 kVp and 60 kVp with a 3 mAs constant tube current-exposure time. The pediatric phantom was exposed three times for each kVp value. The reading of the nanoDots OSLDs was recorded and the mean reading value for each exposure was obtained. 3. Results 3.1. Estimated absorbed dose to heart The measured value in the heart was 0.474 mGy at 50 kVp, and 0.603 mGy at the highest kVp, 60 kVp. The measured value of organ absorbed dose increased with the increase of exposure. The measured value was found to drop slightly at 57 kVp, as there is no solid reason for the drop in absorbed dose. Overall, the measured value of absorbed dose showed increasing trend as depicted in Fig. 3.
2. Materials and method
3.2. Estimated absorbed dose to lungs
2.1. X-ray system
The nanoDot OSLDs were placed at left and right apex and base of the lungs at three different depths; top (1st level), middle (2nd level) and bottom (3rd level). The measured absorbed dose is shown in Figs. 4–7. The nanoDot OSLDs reading (Fig. 4) is higher at the first level as compared to the second and third levels. At the 50 kVp, the values of absorbed dose at the first, second and third levels are 0.3995 mGy, 0.3563 mGy and 0.3378 mGy, respectively. Similar trend can be seen for the other exposures. The measured value of organ absorbed dose (Fig. 5) in first level slightly dropped at 52 kVp, from 0.533 mGy to 0.515 mGy. At 55 kVp, the measured value of absorbed dose increased for all exposures and then, the trend changed at 57 kVp. The measured value of absorbed dose decreased at 60 kVp at second and third level. Fig. 6 shows the results of nanoDot OSLDs reading in the apex of left lung at three different depths. The measured value of absorbed dose in this group shows a significant increase as the exposure increased at all levels. It can be observed (Fig. 7) that the nanoDot OSLDs readings at the first level, for all exposures are higher than in the second and third level. The value of the absorbed dose in the base of left lung showed similar increasing trend for all different depths. The results also show the measured absorbed dose increase as the exposure increased.
The general X-ray system Siemens Multix Top consists of X-ray tube OPTITOP 150/40/80, and POLYDOROS IT 80 with high-frequency generator. The large focal spot was used, and the tube voltage ranged 50 kVp – 60 kVp with mAs fixed at 3.0 mAs tube current-exposure time. These exposure parameters are commonly practiced in different hospitals in Malaysia for pediatric chest X-ray examinations. Furthermore, the reason behind using a large focal spot is due to the short exposure time required in all chest X-ray examinations.
2.1. Optically stimulated luminescence dosimeter (OSLD) To measure the absorbed dose, the nanoDot OSLDs and microStar reader Landauer Inc., were used. The density of the dosimeter is 1.03 g/ cm3 and it contains 5.0 mm diameter disc of aluminum oxide with carbon. A calibrated microStar reader system was used to read the nanoDot OSLDs. After the exposure, the nanoDot OSLD was scanned and inserted into the microStar reader. MicroStar 4.3 software was used to display the reading. The sensitivity of the microStar system is 0.70. The SI unit used is in mGy. In addition, prior to exposing nanoDot OSLDs to X-rays, bleaching test was conducted on all nanoDOT OSLDs to ensure the absence of remaining radiation dose from earlier studies.
2.3. Pediatric phantom
3.3. Comparison of absorbed dose to apex and base of left and right lung
The thorax phantom of pediatric was developed to simulate the body size of children and the organ position. The average chest size of children with age 2 years was taken from the kindergartens for the development of the thorax phantom. Dimensions of the thorax of 1–2 years old children, pediatric phantom (thorax) and lungs are shown in Table 1. Table 2 shows the density of the organs and the tissue substitute materials (Akhlaghi et al., 2015; Amin et al., 2018; Jones et al., 2003; Vidal and Souza, 2012). Beeswax and polyurethane foam were used to design the phantom as it is easily available and affordable.
The measured value of absorbed dose for three different depths was calculated together. These values were used to compare the absorbed dose to both lungs as depicted in Table 3. Table 3 show the measured value of absorbed dose in the apex of the lungs is lower than in the base of the lungs. At 50 kVp, the values of absorbed dose in apex of both left and right lungs are 0.365 mGy and 0.381 mGy, respectively. In contrast, at the same exposure, the values of absorbed dose are 0.471 mGy and 0.509 mGy in base of left and right lungs respectively. For all parts in the lungs, there is steadily increase in 2
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Table 1 Dimensions of the thorax of 1–2 years old children, pediatric phantom (thorax) and lungs.
Size Circumference of the chest Thickness of the body Depth of lungs
Size of 1–2 years old children (average)
Pediatric phantom (thorax)
Lungs
18 × 22 cm 56 cm 7.5 cm
18 × 20 cm 50 cm 7 cm 5 cm
Width of apex of both lungs Width of base of both lungs Length of lungs Depth of lungs
12 cm 16 cm 13 cm 5 cm
Table 2 Density of human tissues and proposed tissue substitute materials. Organs
Density of the organs (g/m³)
Proposed tissue substitute materials
Density of the materials (g/m³)
Soft tissue and heart
1.04
Lungs (ICRU 44)
0.26
PMMA Water Beewax Paraffin wax Polyurethane foam Cork
1.17 1.00 0.96 0.94 0.30 0.2–0.4
absorbed dose as the exposure increased. Table 3 show the highest percentage differences for apex and base of the lungs is at 52 kVp. For the apex of the lung at 52 kVp, the percentage difference is 5.88% while the base of the lung recorded 8.99%. At 55 kVp, the apex of the lung recorded the lowest percentage difference, which is 0.24%. The lowest percentage difference in the base of the lung is 1.48%, at 57 kVp. In overall, all the percentage difference between left and right lungs is below 10%.
Fig. 2. Show the thorax of pediatric phantom covered with a layer of beewax as a skin.
applied to MCNP 3.1 code. Ladia et al., 2015, calculated the organ dose in pediatric chest X-ray examination using Monte Carlo based software PCXMC 2.0 version. According to their findings, in chest radiography lungs received highest dose. In addition, Nahangi and Chaparian, 2015, used real patient data including entrance skin exposure (ESE) values and incorporated into the PCXMC code for organ dose measurement. In our study, heart and lungs absorbed doses are higher as compared to the above-mentioned studies except the lungs dose, estimated by Kiljunen et al. (2009). For comparison with other studies, heart and lungs absorbed doses are shown in Table 4. Furthermore, findings of this study show that the measured absorbed dose at the higher depth is less as compared to the shallow depths. The reason is the attenuation of X-ray photons within the phantom. As the X-ray photon penetrates to the phantom, the photons are attenuated by the tissues it passes through. The intensity of the Xray photons is decreased. In addition, the X-ray photons are either absorbed in the phantom or scattered. As the intensity of X-ray photon decreases, the radiation dose absorbed into the nanoDot OSLDs at higher depth is reduced. Tube voltage is the variable in this study with a fixed tube currentexposure time (mAs). Different exposures were used to measure the absorbed dose. The findings of this study indicate that the measured absorbed dose increased with the increase in the tube voltage (kVp).
4. Discussion Chest X-ray examination in pediatric was chosen because it is a common examination in pediatric population. There are issues in chest X-ray examination in pediatric as many pediatric patients receive high dose during the examination. First, the radiographers do not apply proper collimation (Alatts and Abukhiar, 2013). The reason is, to avoid repetition of examination as children tend to move during the examination. The unnecessary wide collimation will increase radiation dose in children. Second, the children are more radiosensitive as compared to the adults. This is because the cells are in the developing stage. The results of the organ absorbed dose were analyzed in the area of interest, heart and lungs (at different depths). Measurements of absorbed dose to different organs in pediatric chest X-ray examination have been conducted by a small group of researchers. Kiljunen et al. (2009), collected the data relating to the pediatric patients’ organ dose in Finnish hospitals. Entrance surface dose (ESD) and dose-area product (DAP) were obtained, these values were incorporated into a Monte Carlo based PCXMC code. For lungs, highest dose 166 mGy was reported. In 2011, Kumaresan et al. performed the pediatric organ dose study, ESD was estimated using the TLD and it was
Fig. 1. Images A and B, show the nanoDot OSLDs placed at apex and base of the lungs at different depths. Image C shows nanoDot OSLDs placed at surface of apex and base of lungs and the location of heart. 3
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Fig. 3. Measured absorbed dose to the heart.
Fig. 4. Absorbed dose to apex of right lung at three different depths.
Fig. 5. Absorbed dose to base of right lung at three different depths.
indicate the difference with respect to the positioning of the phantom. The phantom was positioned as; the apex of the lungs towards the anode side and the base of the lung to the cathode side. The intensity of the X-ray beam is higher at cathode area compared to anode. This eventually increases the absorbed dose to the base of the lung. Therefore, this suggests that head of child be positioned towards the
The increase in kVp causes the increase in potential difference between cathode and anode. This results in an increase in the mean energy of the X-ray photon. This causes the increase in beam penetration and as a result, the measured value of the absorbed dose increases. The organ absorbed dose in the base of left and right lungs was higher compared to the apex of the lungs. The absorbed dose results
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Fig. 6. Absorbed dose to apex of left lung at three different depths.
Fig. 7. Absorbed dose to base of left lung at three different depths. Table 3 Absorbed dose and percentage differences in left and right lung. kVp
Apex of Right Lung (mGy)
Apex of Left Lung (mGy)
Percentage difference (%)
Base of Right Lung (mGy)
Base of Left Lung (mGy)
Percentage difference (%)
50 52 55 57 60
0.364 0.424 0.480 0.506 0.597
0.380 0.450 0.481 0.520 0.566
4.37 5.88 0.23 2.75 5.29
0.470 0.482 0.544 0.596 0.623
0.509 0.527 0.577 0.605 0.640
7.87 8.98 5.96 1.48 2.67
( ± 0.087) ( ± 0.019) ( ± 0.014) ( ± 0.008) ( ± 0.017)
( ± 0.013) ( ± 0.013) ( ± 0.011) ( ± 0.016) ( ± 0.008)
Heart Lungs
Absorbed Dose (mGy)
0.549 0.516
This Study
Ladia et al. (2015)
Nahangi and Chaparian (2015)
Kumaresan et al. (2011)
1 to 2y
1y
5y
1y
5y
1y
– 0.047
– 0.046
0.009 –
0.015 –
– –
0.109 0.078
( ± 0.008) ( ± 0.012) ( ± 0.014) ( ± 0.015) ( ± 0.012)
anode side, to reduce the absorbed dose to the thyroid, as it is a sensitive organ. The factors that might have compromised the accuracy of organ dose measurements are; the difference between the density of beewax and human tissue as well as the styrofoam that mimicked the body of a child and lungs, respectively. Therefore, attenuation of x-ray photons would be different while travelling towards nanoDot OSLDs through the media as compared to real tissues/organs. Thus, this condition leads to the uncertainty in the organ dose measurement. Another source of error in the organ dose values could be the thorax bones (sternum and ribs) which shield the heart and lungs, in our study, the phantom used was without thorax bones. Thus, the probability of reaching more x-ray photons to nanoDot OSLD is higher; hence, more dose deposition into the nanoDot OSLD. Our study shows higher absorbed dose received by
Table 4 Comparison of organ absorbed dose values (heart and lungs) in pediatric chest X-ray examination with other studies. Organ
( ± 0.079) ( ± 0.012) ( ± 0.015) ( ± 0.017) ( ± 0.093)
5y
5
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heart and lungs as compared to the findings of other studies presented in Table 4, possibly due to the different type of dosimeters and the Monte Carlo code used for the measurement of organ absorbed dose. Additionally, another reason for the higher dose of heart could be due to the inaccurate placing of nanoDOT OSLD since our phantom does not include the design of a heart.
R. (Ed.), 3rd International Conference on Radiation Safety & Security in Healthcare Services. Lecture Notes in Bioengineering. Springer, Singapore. https://doi.org/10. 1007/978-981-10-7859-0. Buchwald, R., Breed, M.D., Greenberg, A.R., Otis, G., 2006. Interspecific variation in beeswax as a biological construction material. J. Exp. Biol. 209 (20), 3984–3989. https://doi.org/10.1242/jeb.02472. Chukwuemeka, P., Gregory, O., Harcourt, P., Harcourt, P., State, R., 2013. Optimisation of absorbed dose in chest x-rays of paediatric patients at braithwaite memorial specialist hospital , Port Harcourt. Am. J. Sci. Ind. Res. 4 (4), 349–358. Emadeldin, B., Abukonna, A., 2016. Estimation of radiation dose in neotatal intensive care uint (NICU). J. Med. Phys. Appl. Sci. 1 (2), 3–5. IAEA, 2013. Human health series 24: dosimetry in daignostic radiology for paediatric patients. Hum. Health Ser. 24, 176. Retrieved from. http://www-pub.iaea.org/ MTCD/publications/PDF/Pub1609_web.pdf%5Cnhttp://www.vomfi.univ.kiev.ua/ assets/files/IAEA/Pub1462_web.pdf. Jones, A.K., Hintenlang, D.E., Bolch, W.E., 2003. Tissue-equivalent materials for construction of tomographic dosimetry phantoms in pediatric radiology. Med. Phys. 30 (8), 2072–2081. https://doi.org/10.1118/1.1592641. Khong, P., et al., 2013. ICRP publication 121: radiological protection in paediatric diagnostic and interventional radiology. Ann. ICRP 42 (2), 1–63. Kiljunen, T., Tietäväinen, A., Parviainen, T., Viitala, A., Kortesniemi, M., 2009. Organ doses and effective doses in pediatric radiography: patient-dose survey in Finland. Acta Radiol. 50 (1), 114–124. Kumaresan, M., Kumar, R., Biju, K., Choubey, A., Kantharia, S., 2011. Measurement of entrance skin dose and estimation of organ dose during pediatric chest radiography. Health Phys. 100 (6), 654–657. https://doi.org/10.1097/HP.0b013e3182092963. JUN 2011. Ladia, A., Messaris, G., Delis, H., Panayiotakis, G., 2015. Organ dose and risk assessment in paediatric radiography using the PCXMC 2.0. J. Phys. Conf. Ser. 637 (2015), 012014. https://doi.org/10.1088/1742-6596/637/1/012014. Ladia, A.P., Skiadopoulos, S.G., Kalogeropoulou, C.P., Zampakis, P.E., Dimitriou, G.G., Panayiotakis, G.S., 2016. Radiation dose and image quality evaluation in paediatric radiography. Int. J. New Technol. Res. (IJNTR) 2 (3), 9–14. Nahangi, H., Chaparian, A., 2015. Assessment of radiation risk to pediatric patients undergoing conventional X-ray examinations. Radioprotection 50 (1), 19–25. Tahiry, R., Anjarasoa Luc, R.M., Harimalala, R.T., Andriambololona, R., Solofonirina, R.D., Randriantsizafy, R.D., 2017. Doses evaluation of some body organs of pediatric patients undergoing chest X-ray examination using thermoluminescent dosimeter. Radiat. Sci. Technol. 3 (3), 24–28. https://doi.org/10.11648/j.rst.20170303.12. Tulloch, A.P., 1970. The composition of beeswax and other waxes secreted by insects. Lipids 5 (2), 247–258. https://doi.org/10.1007/BF02532476. Tulloch, A.P., 1971. Beeswax - structure of esters and their important hydroxy acids and diols. Chem. Phys. Lipids 6, 235–238. Tulloch, A.P., 1980. Beeswax-composition and analysis. Bee World 61 (2), 47–62. https:// doi.org/10.1080/0005772X.1980.11097776. Vidal, R.M., Souza, N., 2012. A model for the characterization and selection of beeswaxes for use as base substitute tissue in photon teletherapy. Mater. Sci. Appl. 3, 218–223. Watanabe, Y., Constantinou, C., 2006. Phantom materials in radiology. In: Encyclopedia of Medical Devices and Instrumentation. John Wiley & Sons, Inc. doi.org/10.1002/ 0471732877.emd201. Yakoumakis, E.N., Gogos, K.A., Tsalafoutas, I.A., 2003. Radiation dose considerations in common paediatric X-ray examinations. Pediatr. Radiol. 33, 236–240. https://doi. org/10.1007/s00247-002-0861-x.
5. Conclusion In conclusion, with the use of phantom the organ absorbed dose in the pediatric population of the age of two years old was successfully estimated. Since no previous studies have been done, the findings of this study can be used as a baseline/guideline for future studies. There are many factors that contribute to the absorbed dose. Based on this study, the different exposure factors used produced different absorbed dose values. The increase in tube voltage (kVp) increased the absorbed dose. Thus, it is necessary for radiographers to select the suitable exposure during the examination. The absorbed dose reduced with the increase in depth. The position of the anode and cathode plays a role in the absorbed dose. The body part at the cathode side receives a higher radiation dose as the attenuation of X-ray photon at the cathode side is higher compared to anode side. It is suggested, to position the head of the child to the anode side, to reduce the radiation dose to the thyroid. Acknowledgments Authors greatly acknowledge International Islamic University Malaysia (IIUM), Malaysia for financial support through Research Initiative Grant Scheme, RIGS #16-302-0466. The Department of Diagnostic Imaging and Radiotherapy of IIUM is also acknowledged for providing the facilities and equipment to carry out the study. References Akhlaghi, P., Miri Hakimabad, H., Rafat Motavalli, L., 2015. Determination of tissue equivalent materials of a physical 8-year-old phantom for use in computed tomography. Radiat. Phys. Chem. 112, 169–176. https://doi.org/10.1016/j.radphyschem. 2015.03.030. Alatts, N.O., Abukhiar, A., 2013. Radiation doses from chest X-ray examinations for pediatrics in some hospitals of Khartoum State. Sudan Med. Monit. 8 (4), 186–188. https://doi.org/10.4103/1858-5000.133018. Amin, N.A.B., Kabir, N.A., Zainon, R., 2018. Determination of mass attenuation coefficient of paraffin wax and sodium chloride as tissue equivalent materials. In: Zainon,
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