Research Focused on the Usefulness of the Bismuth Shield ...TLD-100H (HARSHAW Chemical Co., USA) is used and 2800M (VICTOREEN Co. USA) as a TLD reader to evaluate dose reduction in

Research Focused on the Usefulness ofthe Bismuth Shield by Changing theField of View for Dental CBCT

Taesung Kim1, Su Chul Han2,Cheong-Hwan Lim3, Hong-Ryang Jung4

and Beom-Hui Han5

2Division of radiation equipment,Korea institute of Radiological & medical sciences,

75 nowon-ro, Nowon-gu, Seoul 01812, Korea5Dept. of Radiological Science,

Seonam University,7-111, Pyeongchon-gil,Songak-myeon, Asan-si, Chungnam, 31556, Korea

January 27, 2018

Abstract

CBCT (Cone beam computed tomography) has been de-veloped and used widely as a new imaging technique. Theusefulness of Bismuth was evaluated for dose reduction inthe CBCT. TLD-100H (HARSHAW Chemical Co., USA) isused and 2800M (VICTOREEN Co. USA) as a TLD readerto evaluate dose reduction in the CBCT. A calibrated TLDdevice is attached to both eyes of the human phantom ac-cording to each test method with an adult male standard(80 kVp, 7 mA, 17 sec), and it is measured by placing thephantom on a test table of CBCT. In the CBCT, the sur-face dose is measured using TLD after changing the FOVfor each mode according to the presence or absence of theshield in the eye. We found that there is not much differencebetween the D-mode and the I-mode. In case of the left eye

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International Journal of Pure and Applied MathematicsVolume 118 No. 19 2018, 951-960ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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in the P-mode, the difference between the case with, andthe case without shielding with a Bismuth shield material,is reduced by 43.7% from 9.059 µ Gy to 3.965 µ Gy. Inthe case of the right eye, it is reduced by about 47.5% from10.213 µ Gy to 4.859 µ Gy. There are various test modesaccording to FOV size. When the CBCT includes a criticalorgan within the FOV size, it is feasible to reduce the doseusing Bismuth.

Key Words : CBCT (cone beam computed tomogra-phy), FOV (field of view), TLD, Dose reduction, Bismuth.

1 INTRODUCTION

THIS DOCUMENT is a Recently, CBCT (Cone beam computedtomography) has been developed and used widely as a new imagingtechnique. This technique uses the changes of acquisition informa-tion and its processing methods by using a new imaging techniquewhich is unlike the general radiography imaging devices which de-pend on the development of the computer (Kim et al 2008). Al-though CBCT causes high doses to the patient, proper manage-ment of this protocol has not been established due to a lack ofevidence. Therefore, the study of the usefulness of shielding ma-jor organs has been carried out using Bismuth shielding materialto minimize the diagnostic radiation exposure to the patient, in-cluding the justification of behavior and optimization of defenses(Lim et al 2011, Park et al 2014, Jung et al 2009). This studyaims to check the dose reduction rate achieved by using ShieldingMaterial (Bi), and to identify its effectiveness by measuring the ab-sorbed dose by each site according to the changes of the field ofview (FOV). The absorbed dose refers to the dose absorbed at ir-radiating, when Bismuth shielding material is attached using TLD(Thermoluminescence Dosimeter) on dental CBCT or irradiatingat opening state.

2 MATERIALS AND METHODS

A. Materials

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International Journal of Pure and Applied Mathematics Special Issue

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The human phantom in this experiment uses a male ART Phan-tom (Fluke Biomedical Co., USA) consisting of 10 sections of 2.5cm thickness with tissue distribution similar to the human body[Figure. 1. a]. In this study, TLD-100H (HARSHAW ChemicalCo., USA) is used as TLD chips and 2800M (VICTOREEN Co.USA) is used as a TLD reader [Figure. 1. b. c]. Attenurad CTShields (F & L Medical Products Co., USA) are used as a Shieldingmaterial and Cone Beam Computed Tomography (CBCT, Aiphard3030, Asahi, Japan) is used as a CBCT.

(a) (b)

(c)

Figure 1: Phantom and dosimetry system (a) head & neck phantom(b) TLD (c) reader system

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B. Methods

The RCF (Reader Calibration Factor) is determined by measur-ing the charge (nC) of each TLD device through the TLD Readerafter irradiating the TLD with the same dose of radiation to cali-brate the TLD to be used in this experiment. The dose is measuredusing a 5cc Ionization Chamber (Capintec, USA) and a Micro Am-meter (Capintec. MODEL 192. USA). The Element CorrectionCoefficient (ECC) of each device is measured and calibrated tomaintain the uniformity of each device throughout the entire ex-perimental process. To release the energy remaining in the TLDdevice before exposure to radiation, the irradiating of each test anddose is measured by annealing at 2400C for 10 minutes using anoven. In addition, it is preheated at 1350C for 10 seconds to re-move noise that might occur in the TLD after measuring the dose;this step is administered before measuring the charge value withthe TLD Reader. The surface dose is calculated using ”Eq. (1)”and ”Eq. (2)” to obtain the charge value with the TLD reader afterrepetitive irradiation for each test.

X(mR) = ECC×charge(nc)RCF

(1)

X: exposure dose in airRCF: reader calibration factorECC: element correction coefficient

Dtissue = X(cGy) × 0.876 × (µenρ

)tissue

(µenρ

)air(2)

Dtissue : Absorbed dose in tissue(cGy)X : Exposure dose in air(mR)(µenρ

)tissue : Mass absorption coefficient of tissue

(µenρ

)air : Mass absorption coefficient of air

A calibrated TLD device is attached to both eyes of the humanphantom according to each test method, with an adult male stan-dard (80 kVp, 7 mA, 17 sec) being examined in a hospital. It ismeasured by placing the phantom on a test table of CBCT. The firsttest is carried out by changing the FOV with D-mode (5.1cm5.1cm),I-mode (10.2cm10.2cm), and P-mode (15.4cm 15.4cm) according to

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each test mode in the open state without a shield, and the irradi-ation dose is measured [Figure. 2]. The next test is performed bychanging the FOV according to the test mode so that it correspondswith the first instance, by attaching the shield material to the eyeand measuring the surface dose value.

(a)

(b)

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(c)

Figure 2: Image of CBCT depending on FOV size (a) D-mode, (b)I-mode, (c) P-mode

3 RESULTS

In the CBCT test, the surface dose is measured using TLD afterchanging the FOV for each mode according to the presence or ab-sence of the shield in the eye. The study revealed that there is notmuch difference between the D-mode and the I-mode. In case ofthe left eye in the P-mode, the difference between the case with,and the case without shielding with a Bismuth shield material, isreduced by 43.7% from 9.059 µ Gy to 3.965 µ Gy. It is reducedby about 47.5% from 10.213 µ Gy to 4.859 µ Gy in the case of theright eye (Table I).

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Table I Comparison of usefulness of Bismuth Shielding material fordose reduction of Eye according to FOV Mode in CBCT Examina-tion.

4 DISCUSSION

Many studies have been conducted to reduce unnecessary doses ofpatient exposure to radiation in diagnostic radiology. For instance,Hopper et al 2001 confirmed a dose reduction effect of 50% in theeye using Bismuth shielding material in the computed tomography,and McLaughlin and Mooney 2004 investigated a dose reductioneffect of 18/56% in the eye / thyroid using using Bismuth shieldingmaterial in a CT scan. It takes a long time in general and Shorttet al 2007. confirmed a dose reduction effect of 48% in the thyroidusing a lead shielding material in the Neuro interventional proce-dures that had more radiation exposure. Han Su Chul Han andKwon Soon Chan8 confirmed a dose reduction effect of 20/64% inthe eye / thyroid using Bismuth shielding material.

In the CBCT test, the frequency of use of dental radiology re-cently has been increasing during dental radiography. On the otherhand, however, Tsiklakis et al 2005 confirmed the dose reductioneffect of 30% in the in Thyroid using lead shielding material. Prinset al 2011 also confirmed the dose reduction effect of 67% in the eye

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using lead-shielding material. As a result of a usefulness evaluationin this study based on the size of the FOV in the dental CBCT testin the eye using Bismuth shielding material, the difference betweenthe I-mode and the D-mode is not significant but it does confirmthat the dose reduction effect is about 45% in the P-mode (15.4 cm15.4 cm), which is the largest FOV. FOV size is small in comparisonwith the CT scan and interventional procedures, and the usefulnessof the shielding has not been verified without a direct shielding ina short dental test. Like Prins et al 2011, the dose reduction effectis confirmed in P-mode, which is directly shielded in this study. Inthe case of performing a dental CBCT test, therefore, it is desirableto reduce the dose by shielding through the shielding material if themain organs are included in the FOV. Like Prins et al 2011, thedose reduction effect is confirmed in the P-mode, which is directlyshielded in this study.

5 CONCLUSION

In the dental CBCT test, there are various test modes according toFOV size. The dependence FOV size was certified in our study. Inthe CBCT test, the larger the size of the FOV, the larger the dosereduction efficiency of Bismuth shielding material. In the largest Pmode, the dose reduction of about 45% was confirmed in the criticalorgans (Lt. eyes: 43.7%, Rt., eye: 47.5%). When the CBCT testincludes major organs (eye) within the FOV size, it is expectedthat a dose reduction effect can be expected through a shieldingmaterial such as Bismuth. To reduce dose of patient, should useoptimized field size or shielding material such as Bismuth.

References

[1] Han Su Chul and Kwon Soon, 2013. Radiation dose reductionto the critical organ with bismuth shielding during endovascularcoil embolisation for cerebral aneurysms, 156(3): 364371.

[2] Hopper, K. D., Neuman, J. D., King, S. H. and Kunselman,2001. Radioprotection to the eye during CT scanning. AJNRAm J Neuroradiol, 22(6):1194 1198.

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[3] Jung Mi-Young, Kweon Dae-Cheol, Kwon Soo-Il, 2009. Effec-tiveness of Bismuth Shield to Reduce Eye Lens Radiation DoseUsing the Photoluminescence Dosimetry in Computed Tomog-raphy Journal of radiological science and technology, 32 (3):307-312.

[4] Kim Sang Yeon, Han Jin-Woo, Park In-Woo, 2008. Compar-ison of cone beam CT and conventional CT in absorbed andeffective dose, Korean Journal of Oral and Maxillofacia Radi-ology,38(1): 7-15.

[5] Lim Cheonghwan, Kim Seungchul, Jung Hongryang et al,2011. The Study for Radio Protection According to a Possi-ble Danger of Exposure During dental X-ray Examination,TheKorea Society of Radiology, 5(5) : 237-244.

[6] McLaughlin, D. J. and Mooney, R. B, 2004. Dose reduction toradiosensitive tissues in CT: do commercially available shieldsmeet the users needs? Clinical Radiology,59(5): 446450.

[7] Park Hoon-Hee, Lee Juyoung, Kim Ji-Hyeon et al, 2014. Eval-uation of the Usefulness of Bismuth Shields in PET/CT Exam-ination, Journal of radiological science and technology, 37(1):49-56.

[8] Prins, R., Dauer, L. T., Colosi, D. C., Quinn, B., Kleiman,N., Bohle, G., Holohan, B., Al-Najjar, A., Fernandez, T.,Bonvento, M. et al., 2011. Signicant reduction in dental conebeam computed tomography (CBCT) eye dose through the useof leaded glasses. Oral Surg Oral Med Oral Pathol Oral RadiolEndod. 112(4): 502507

[9] Shortt, C. P., Fanning, N. F., Malone, L., Thornton, J., Bren-nan, P. and Lee, M. J., 2007. Thyroid dose during neuroin-terventional procedure: does lead shielding reduces the dose?Cardiovascular Interv. Radiol., 30(5): 922927.

[10] Tsiklakis, K., Donta, C., Gavala, S., Karayianni, K., Ka-menopoulou, V. and Hourdakis, C. J., 2005. Dose reductionin maxillofacial imaging using low dose cone beam CT. Eur JRadiol., 56(3), :413417.

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Documents

Research Focused on the Usefulness of the Bismuth Shield ...TLD-100H (HARSHAW Chemical Co., USA) is used and 2800M (VICTOREEN Co. USA) as a TLD reader to evaluate dose reduction in