Evaluation of the shielding efficiency and space dose of the tungsten shielding system

Transcription

1 Volume 118 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu Evaluation of the shielding efficiency and space dose of the tungsten shielding system Chang-Gyu Kim 1 1 Department of Radiological Science, Gimcheon University, Gimcheon City, Gyung- buk, South Korea, radkcg@hanmail.net January 27, 2018 Abstract Background/Objectives: The purpose of this paper is to demonstrate the shielding effectiveness of tungsten shield through using tungsten shielding and glass dosimeter in medical X-ray examination to evaluate the usefulness of shielding and by understanding the absorption dose and spatial dose distribution of each body part by measuring and analyzing space dose. Methods/Statistical analysis: For the experimental method, by producing a tungsten shield, using a dose meter and a glass dosimeter that measure the absorbed dose according to the angle and distance in the medical radiation energy field, the space dose was measured according to the angle before and after the shielding, and the absorbed dose according to the thickness of the tungsten shielding sheet was measured. Findings: In case of the shielding performance using shielding, for 0.1mm it was 69.01%, for 0.2mm it was 84.77%, for 0.3mm it was 91.00%, for 0.4mm it was 94.20%, for 0.5mm it was 95.99%, and for 0.6mm it was 97.33%. In case

2 of using 0.1mm tungsten shield at 75kVp 320mA 40mAS energy condition, shielding efficiency was shown to be 44.35% in lens area, 62.50% in breast area and 47.50% in genital gland area. In case of using 0.1mm tungsten shield at 85kV 320mA 100mAs energy condition, shielding efficiency was shown to be 42.73% in the lens area, 54.30% in the breast area and 45.80% in the genital gland area. Improvements/Applications: Based on the results, it is expected that tungsten shields will be widely used as an eco-friendly shields that can replace lead. Key Words : space dose, shield, lead, eco-friendly shields, tungsten 1 Introduction Radiation has been discovered by Rntgen in 1895 and more than 100 years later, radiation has been used not only in the medical field but also in various fields 1,2. The fields that utilize radiation include nuclear power plants, breeding of plants, diagnosis and treatment of diseases, fire alarms, resource investigation and analysis, materials processing, and airport retrieval systems 3. According to the 2008 report by UNSCEAR, the United Nations Scientific Committee on the Effects of Atomic Radiation (UN- SCEAR), which studies human exposure dose in various different countries, next to natural radiation, medical radiation is considered to be the cause of most exposure, and there has been a report that the medical radiation exposure figure by country varies according to the level of living and income level of each country. This is due to the increasing interest in health screening, which is a result of a much larger number of screenings in countries with high income levels 4 6. The medical exposures can be classified into the exposures due to health examinations, the exposures due to diagnostic radiography, the exposures due to radiotherapy, and the exposures due to interventional radiotherapy. Due to the increased interest in health, health screenings of many people will be done more often. Therefore, exposure to medical radiation is expected to continue to rise. Radiation shielding materials have been developed to prevent radiation exposure. Lead, tungsten, and bismuth are used as shielding

3 materials. In the past, shields using lead were mostly used, but lead shields are relatively heavy compared to other shields, and they are classified as heavy metals, raising the issue of environmental pollution and have a fatal disadvantage of lead poisoning. Accordingly, the International Atomic Energy Agency (IAEA) and OECD countries recommend the use of eco-friendly radiation shields without lead when warning of the risks to radiation exposure Recently, bismuth and tungsten shields have been known as ecofriendly radiation shields. The use of a bismuth shield is known to have good shielding efficiency in radiological examinations including CT and has been verified through a number of studies Tungsten shields have not been studied comprehensively as radiation shields. Tungsten is the element with the highest atomic number among the elements known to have a biological role, and is harmless in everyday life. It is also hard and has a very high density, which is excellent in X-ray shielding efficiency and as it can be used as heavy metal alloy, it is used in various fields. Tungsten can be made in the form of a thin sheet, and it is known to be the lightest in weight when made into a shield Therefore, this study was carried out to provide basic data for the utilization of tungsten shield by analyzing the spatial dose distribution and absorbed dose by self-fabricating a tungsten shield which is known to be an environmentally friendly shielding with high radiation shielding efficiency. 2 Materials and Methods 2.1 Tungsten shielding sheet production In the examination using medical radiation, tungsten which does not contain lead and which is harmless to the human body and can be lightened was made into nano powder, to manufacture a shielding sheet is by mixing silicone polymer and tourmaline which are excellent in mixing property. The tungsten shield sheet was produced 0.1 mm thick and was made to be used up to 0.6 mm thick[figure 1]

4 [Figure 1]Tungsten Shielding Sheet 2.2 Materials and equipment FPD (Flat Panel Detector) was used for the radiation generator, and JW medical CXD-R185 System was used for the system. To measure the dose of the subject, a human body phantom (Model PBU-31, Kyoto Kangaku, Japan) composed of a human equivalent material, and glass dosimeter Dose Ace (Model GD-352M and FGD-1000, Asahi Techno Glass Cooperation, Shizuoka, Japan) was used [Figure 2]. The measurement of the spatial dose distribution was performed by using a calibrated Ionization Chamber (Model 20x5 1,800cc, Monrovia, California USA) and Electrometer (Radiation Monitor Controller Model 2026)

5 [Figure 2] Radiation generator and phantom 2.3 Spatial scattering dose and absorbed dose measurement In the measurement of the spatial dose distribution, the distance between the X-ray tube and the detector was fixed at 100 cm, and the irradiating dosimeter was irradiated with 75 kvp 320 ma 32 ma as the angle was changed at a distance of 30 cm and 100 cm. The absorbed dose was changed from 0.1 mm to 0.6 mm under the conditions of 75 kvp 320 ma 32 mas and the absorbed dose change according to the thickness was measured [Figure 3]. [Figure 3] Measurement of space-specific dose distribution

6 2.4 Glass dosimeter dose measurement Glass dosimeter Dose Ace (Model GD-352M and FGD-1000, Asahi Techno Glass Cooperation, Shizuoka, Japan) was used[figure 4, 5]. Calibration of the glass dosimeter was performed using a glass element irradiated with 6 mgy using a CS-137 standard source at the Japan Radiation Standards Agency. In consideration of the characteristics of the element, the annealing process was conducted through heating at 400 C for 1 hour before irradiation, and µgy was measured by measuring the background value after cooling, and after a panoramic scan, pre-heating was performed at 70 C for 1 hour, and after cooling, the radiation dose was calculated for dose accumulated value through the reader 10 times repeatedly, and the mean value and standard deviation were calculated. The background value was subtracted from the calculated value to derive the dose value 22,23. The absorption dose distribution by site of the tungsten shield was measured by placing a glass dose element on the lens of the eye, genital glands, and both breasts. In order to reduce the measurement error, the average value was calculated by irradiating 10 times 22. [Figure 4] The Photoluminescence Dosimetry Glass elements

7 [Figure 5] The Photoluminescence Dosimetry Reader 3 Results and Discussion 3.1 Results of measurement of space dose distribution of tungsten shielding To determine the characteristics of tungsten, an environment-friendly shield, dose was measured at each angle, at distances of 30 cm and 100 cm without using tungsten. The measured dose was 28.1mR at a distance of 30cm from 60 and 38mR at 120, showing a higher spatial dose distribution than other locations. The measured dose was 5.9mR at a distance of 100cm from 60 and 8.1mR at 120 position, showing a higher spatial dose distribution than other positions. The dose measured at 100 cm distance was 86% less than the dose measured at 30 cm distance. As the distance from the source increased, the spatial dose decreased, which was consistent with the study by Kim 17 [Table 1].. Table 1. Space dose for angles and distances (No Shielding) To determine the difference in the distribution of space dose when the tungsten shield was used and when it was not used, measurements were made at 0, 30, and 60 at a distance of 30 cm

8 away using a 0.1 mm tungsten shield. When the tungsten shield was not used, the highest space dose was measured at 28 mr at 60 and the lowest space dose was measured at 19 mr at 0. When the shield was used, the maximum space dose was measured at 11.5 mr at 60 and the lowest space dose was measured at 7.1 mr at0. The distribution of space dose by position was similar according to the use of shielding. It was confirmed that 60% 70% was reduced from 28.1mR to 11.5mR after use of shielding at 60 that showed the highest space dose [Table 2]. Table 2. Before and after shielding, Space dose differences according to the angle 3.2 Evaluation of space dose shielding performance according to thickness of tungsten shielding sheet In the medical radiation field, the study of lightweight and harmless tungsten shields is very inadequate and is at an early stage. Although there is a theoretical study on the shielding effect of tungsten 13, no actual clinical studies have been conducted. For this, in this paper, the space dose shielding efficiency was measured by fabricating a tungsten shield from 0.1mm to 0.6mm thick. In case of the shielding performance, for 0.1mm it was 69.01%, for 0.2mm it was 84.77%, for 0.3mm it was 91.00%, for 0.4mm it was 94.20%, for 0.5mm it was 95.99%, and for 0.6mm it was 97.33%. These results show that the tungsten shield can be applied as a sufficient shield in the medical radiation energy field [Table 3]

9 Table 3. Variation of absorbed dose for tungsten shield thickness 3.3 Results of shielding performance evaluation of tungsten sheet using glass dosimeter Recently, the glass dosimeter is a widely used dosimeter for studying radiation exposure doses because it has repeatable measurement and readability, wide measuring range, low fading effects and excellent direction and energy dependence. In this study, the dose reduction effect of lens, thyroid, and breast was measured by using tungsten shield and glass dosimeter. Shielding performance was measured and evaluated with tungsten sheet 0.1 mm under conditions of 75 kvp 320 ma 40 maas, 85 kv 320 ma 100 maas, which are frequently used energy sources for medical radiation. In case of using 0.1mm tungsten shield at 75kVp 320mA 40mAS energy condition, shielding efficiency was shown to be 44.35% in lens area, 62.50% in breast area and 47.50% in genital gland area [Table 4]. Table 4. Measurement of the shielding efficiency of the tungsten sheet using glass dosimeter in75kvp 320mA 40mAs

10 In case of using 0.1mm tungsten shield at 85kV 320mA 100mAs energy condition, shielding efficiency was shown to be 42.73% in the lens area, 54.30% in the breast area and 45.80% in the genital gland area[table 5]. Table5. Measurement of the shielding efficiency of the tungsten sheet using glass dosimeter in 85kVp 320mA 100mAs. These results are expected to be useful reference materials for the development and application of environmentally friendly and lightweight tungsten radiation shields to obtain optimal medical images and to reduce the radiation dose for medical radiation. In order to minimize the radiation exposure dose of human beings, in related organizations that utilize the radiation, the radiation workers should be aware of the concept of the dose and obtain the optimal medical image by minimizing the dose to ensure the legitimacy and to achieve the optimization of the radiation defense of the patient. 4 Conclusion In this study, the space dose distribution and the shielding efficiency were measured and evaluated through using shielding materials using a tungsten shielding material which is not harmful to the human body that can be made into lightweight shielding material. When the tungsten shield was not used, the highest space dose was measured at 28.1mR at 60 and the lowest space dose was measured at 19.3mR at 0. When the shield was used, the maximum space dose was measured at 11.5 mr at 60 and the lowest space dose

11 was measured at 7.1 mr at 0. The distribution of space dose by position was similar according to the use of shielding materials. In case of the shielding performance using shielding, for 0.1mm it was 69.01%, for 0.2mm it was 84.77%, for 0.3mm it was 91.00%, for 0.4mm it was 94.20%, for 0.5mm it was 95.99%, and for 0.6mm it was 97.33%. In case of using 0.1mm tungsten shield at 75kVp 320mA 40mAS energy condition, shielding efficiency was shown to be 44.35% in lens area, 62.50% in breast area and 47.50% in genital gland area. In case of using 0.1mm tungsten shield at 85kV 320mA 100mAs energy condition, shielding efficiency was shown to be 42.73% in the lens area, 54.30% in the breast area and 45.80% in the genital gland area. Based on the results, it is expected that tungsten shields will be widely used as an eco-friendly shields that can replace lead. 5 Acknowledgment This research was supported by a Gimcheon University research grants in References [1] Chang-Gyu Kim, Exposure dose reduction during lateral spine test with water filter, Technology and Health Care, 2016, Vol. 24, pp [2] Chang-Gyu Kim, The Development of Bismuth Shielding to Protect the Thyroid Gland in Radiations Environment, Indian Journal of Science and Technology, 2016, Vol. 9(25), pp.1-6. [3] Chang-Gyu Kim, Sun-Youl Seo, A Study on Reducing Exposure Dose of Radiographer Assistants during CT Scan of Injury Patients without Spontaneous Breath, Jour of Adv. Research in Dynamical & Control Systems, 2017, S(10), pp.1-6. [4] S. S. Kang, C. S. Kim, J. H. Kim, Radiation Exposure Evaluation of Visual Organs using Bismuth Shielding Material on

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14 [22] Chang-Gyu Kim, The Effect of Reducing Exposure Dose in Neurocranium Angiography CT Scan based on 3D Computer Image Processing, Jour of Adv Research in Dynamical & Control Systems, 2017, S(10), pp.1-6. [23] Jeong-Eun Rah, Ju-Young Hong, Gwe-Ya Kim, Yon-Lae Kim, Dong-Oh Shin, Tae-Suk Suh, A comparison of the dosimetric characteristics of a glass rod dosimeter and a themoluminescent dosimeter for mailed dosimeter, Radiation Measurements, 2009, Vol. 44, pp

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