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KMID : 1143620160200010032
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Korean Journal of Nuclear Medicine Technology
2016 Volume.20 No. 1 p.32 ~ p.36
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Consideration on Shielding Effect Based on Apron Wearing During Low-dose I-131 Administration
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Kim Il-Su
Kim Ho-Sin
Ryu Hyeong-Gi
Kang Yeong-Jik
Park Su-Young
Kim Seung-Chan
Lee Gui-Won
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Abstract
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Purpose : In nuclear medicine examination, 131I is widely used in nuclear medicine examination such as diagnosis, treatment, and others of thyroid cancer and other diseases. 131I conducts examination and treatment through emission of ? ray and ß-ray. Since 131I (364 keV) contains more energy compared to 99mTc (140 keV) although it displays high integrated rate and enables quick discharge through kidney, the objective of this study lies in comparing the difference in exposure dose of 131I before and after wearing apron when handling 131I with focus on 3 elements of external exposure protection that are distance, time, and shield in order to reduce the exposure to technicians in comparison with 99mTc during the handling and administration process. When wearing apron (in general, Pb 0.5 mm), 99mTc presents shield of over 90% but shielding effect of 131I is relatively low as it is of high energy and there may be even more exposure due to influence of scattered ray (secondary) and bremsstrahlung in case of high dose. However, there is no special report or guideline for low dose (74 M㏃) high energy thus quantitative analysis on exposure dose of technicians will be conducted based on apron wearing during the handling of 131I.
Materials and Methods : With patients who visited Department of Nuclear Medicine of our hospital for low dose 131I administration for thyroid cancer and diagnosis for 7 months from Jun 2014 to Dec 2014 as its subject, total 6 pieces of TLD was attached to interior and exterior of apron placed on thyroid, chest, and testicle from preparation to administration. Then, radiation exposure dose from 131I examination to administration was measured. Total procedure time was set as within 5 min per person including 3 min of explanation, 1 min of distribution, and 1 min of administration. In regards to TLD location selection, chest at which exposure dose is generally measured and thyroid and testicle with high sensitivity were selected. For preparation, 74 MBq of 131I shall be distributed with the use of 2 ㎖ syringe and then it shall be distributed after making it into dose of 2 ㎖ though dilution with normal saline. When distributing 131I and administering it to the patient, 100 ㎖ of water shall be put into a cup, distributed 131I shall be diluted, and then oral administration to patients shall be conducted with the distance of 1m from the patient. The process of withdrawing 2㎖ syringe and cup used for oral administration was conducted while wearing apron and TLD. Apron and TLD were stored at storage room without influence of radiation exposure and the exposure dose was measured with request to Seoul Radiology Services.
Results : With the result of monthly accumulated exposure dose of TLD worn inside and outside of apron placed on thyroid, chest, and testicle during low dose 131I examination during the research period divided by number of people, statistics processing was conducted with Wilcoxon Signed Rank Test using SPSS Version. 12.0K. As a result, it was revealed that there was no significant difference since all of thyroid (p = 0.345), chest (p = 0.686), and testicle (p = 0.715) were presented to be p > 0.05. Also, when converting the change in total exposure dose during research period into percentage, it was revealed to be -23.5%, -8.3%, and 19.0% for thyroid, chest, and testicle respectively.
Conclusion : As a result of conducting Wilcoxon Signed Rank Test, it was revealed that there is no statistically significant difference (p > 0.05). Also, in case of calculating shielding rate with accumulate exposure dose during 7 months, it was revealed that there is irregular change in exposure dose for inside and outside of apron. Although the degree of change seems to be high when it is expressed in percentage, it cannot be considered a big change since the unit of accumulated exposure dose is in decimal points. Therefore, regardless of wearing apron during high energy low dose 131I administration, placing certain distance and terminating the administration as soon as possible would be of great assistance in reducing the exposure dose. Although this study restricted 131I administration time to be within 5 min per person and distance for oral administration to be 1m, there was a shortcoming to acquire accurate result as there was insufficient number of N for statistics and it could be processed only through non-parametric method. Also, exposure dose per person during lose dose 131I administration was measured with accumulated exposure dose using TLD rather than through direct-reading exposure dose thus more accurate result could be acquired when measurement is conducted using electronic dosimeter and pocket dosimeter.
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KEYWORD
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131 I, TLD, Apron, Wilcoxon Signed Rank Test
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