[논문]몬테카를로 모의 모사를 이용한 의료용 사이클로트론의 Targetry 방사화 및 피폭선량 분석

장동근; 김동현

doi:10.7742/jksr.2018.12.5.565

몬테카를로 모의 모사를 이용한 의료용 사이클로트론의 Targetry 방사화 및 피폭선량 분석
A Study of Targetry Activation and Dose Analysis of PET Cyclotron Using Monte Carlo Simulation 원문보기

한국방사선학회 논문지 = Journal of the Korean Society of Radiology, v.12 no.5, 2018년, pp.565 - 573

장동근 (동남권 원자력의학원 핵의학과) , 김동현 (부산가톨릭대학교 보건과학대학 방사선학과)

초록
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의료용 사이크로트론은 방사성의약품을 생산하기 위해 양성자를 고속으로 가속시켜 핵반응을 일으키게 되며, 핵반응을 통해 불필요한 중성자가 발생하게 된다. 중성자는 사이클로트론의 부품에 방사화를 일으키는 원인으로 종사자들의 피폭의 원인이 된다. 이에 본 연구에서는 핵반응이 일어나는 Targetry 부품들인 Aluminum body, Silver body, Havar foil의 방사화 정도를 분석하여 피폭선량을 알아보고자 하였다. 실험결과 Aluminum body와 Silver body는 방사화된 핵종들의 에너지가 작고, 반감기가 짧아 종사들에게 미치는 선량이 미미하였으며, 재사용하는데 문제가 없었다. 하지만 Havar foil의 경우 방사화된 핵종들의 에너지가 높고 반감기가 길어 종사자들에게 미치는 영향이 매우 높았으며, 방사성폐기물로써 특별한 관리가 필용한 것으로 나타났다.

Abstract ▼ AI-Helper

Cyclotron for medical purposes generates nuclear reaction by accelerating protons in high speed, in order to produce radiopharmaceuticals, and unnecessary neutrons are generated through such nuclear reaction. Neutrons cause activation in the parts of cyclotron which then cause exposure to radiation for people working in the field. This study, in that regard, aims to analyze exposure level by finding out the degree of activation of aluminum body, silver body, and havar foil which are the parts of Targetry where the nuclear reaction takes place. The results of the experiment showed that aluminum body and silver body had no problems re-using them as the energy and half-life of activated nuclides were small and short, making the affect on the people working in the field extremely low. However for havar foil, its activated nuclides had a high level of energy which resulted in high level of affect to the people working in the field. The activation factors of the cyclotron were analyzed, and the results showed that the Havar foil was activated the most among the targetry parts, and greatly exposed workers due to regular replacement, and needed special management as radioactive waste.

주제어

표/그림 (17)

그림 Fig. 1. Geometry using Monte Carlo Simulation.
그림 Fig. 2. Elements and their weight percents in Targetry.
그림 Fig. 3. ORNL MIRD Phantom.
표 Table 1. Manufacturer's ¹⁸F-FDG production volume
그림 Fig. 4. Radioactivated nuclides generated in the target.
그림 Fig. 5. ²⁴Na that was generated by activation in the aluminum body.
그림 Fig. 6. ^110mAg that generated by activation in the silver body.
표 Table 2. Self-Disposal tolerance level for each radioactive nuclide
표 Table 3. ²⁶Al that was generated by activation unit : Bq
표 Table 4. Radiation exposure level per organ that will be received from aluminum body
표 Table 5. Radiation exposure level per organ that will be received from Silver body
표 Table 6. Nuclides generated by acyivation in havar foil
표 Table 7. Radiation exposure level per organ that will be received from havar foil (25 μm) Unit : μSv/hr
표 Table 8. Radiation exposure level per organ that will be received from havar foil (50 μm) Unit : μSv/hr
표 Table 9. Percentage of dose per nuclide
표 Table 10. Havar's shielding dose according to the width of lead unit : μSv/hr
표 Table 11. Comparison research on radioactive Havar foil

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제안 방법

Based on the data provided in the manufacturer's manual as shown in Table 1[18], protons of 16.5 MeV, 60 μA were studied for two hours in order to find out reproducibility of the targetry manufactured in this experiment.
In this study, due to the neutrons generated when a cyclotron for medical purposes is operated, the experiment was conducted after analyzing the radiation of the Targetry parts. Firstly, when the production level of ¹⁸F was compared by studying the protons of 16.
3 shows the MIRD Phantom. The dose conversion factor (ICRP 74) of the de/df card installed in MCNPX was used to measure the equivalent dose, and the measured equivalent dose was comparatively analyzed after converting to valid dose using the organizational weight ratio of ICRP 103.
The experiment was conducted by setting cyclotron's operating time at four hours a day, five days a week in weekly basis.
Therefore, in this study, Monte Carlo simulation was used to accurately evaluate the activation of the components of the targetry.

대상 데이터

Radioactivated nuclide's radiation level was measured by FLUKA's RESNUCLEi, and aluminum body, silver body, and havar foil were set as measuring areas.

이론/모형

In this experiment, two types of Monte Carlo simulation codes FLUKA code^[15] and MCNPX code^[16] were used. Fig.

성능/효과

Ag was generated. As a result of measuring on a weekly basis, it was confirmed that activation attains equilibrium at 1.21E+8 Bq after about 1500 weeks (30 years), and as a result of testing radiation exposure level through radiation level at the state of equilibrium, it showed about 2.01E-1 mSv/hr. Fig.
As a result, Aluminum body's 24Na attained equilibrium at more than 5 weeks, and the result of measuring valid dose using the equilibrium radiation value showed about 2.79E-02 mSv/hr.
For havar foil, it was confirmed that there were a total of 14 types of radioactivated nuclides. The effect on human body was shown to be about 4.13 mSv/hr, and 3 nuclides of ⁵²Mn, ⁵⁸Co, and ⁵⁶Co consisted more than 97% of the dose. Havar foil is replaced periodically, and it has been known that the time to replace is six minutes (five minutes for replacement and one minute for moving to the storage 20).
Such neutrons become the main cause of exposure to radiation by the people working in the field as they activate surrounding substances. With regards to that, as a result of testing the degree of activation in the parts of Targetry in this study, it was revealed that the main cause of radiation exposure received when replacing the parts was due to havar foil, and the aluminum body and the silver body were less than 5% of the total dose. Additionally, it was confirmed that the replaced havar foil needs to be replaced as it has a high dose of radiation, and the aluminum body and the silver body have low dose of radiation which can be re-used without replacing them as they have short half-lifes.

참고문헌 (21)

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저자의 다른 논문 :

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