光刺激發光劑量計之能量依存性修正方法研究

Modification method of the energy dependence of optically stimulated luminescent dosimeter

陳姿妙(Chen, Tzu Miao)

指導教授 ： 許靖涵 ； 許芳裕

國立清華大學/原子科學院/生醫工程與環境科學系/碩士(2014年)

摘要

光刺激發光劑量計(OSLD)因高靈敏度、可重複計讀等優點，近些年已普遍被使用在研究或臨床上的劑量量測，但有著能量依存性的缺點，對低能量之光子有較高劑量響應而造成劑量高估。本研究使用OSLD與熱發光劑量計(TLD)以100 kV、120 kV、6 MV三種光子能量，分別量測探討在不同深度下，照野內與照野外之劑量響應並計算無濾片及有濾片之OSLD劑量響應比值(ROSLD1/ROSLD2)，再搭配蒙地卡羅方法模擬不同能量下的比值結果，推得有效能量與相關之修正因子後進行修正，以減少劑量誤差。結果顯示，在高能量6 MV光子照射下，OSLD能量依存性較小，修正後OSLD與TLD之誤差約為-20.26 %~27.46 %，低能量100 kV、120 kV光子照射下，OSLD能量依存性明顯，經修正後與TLD之誤差約為-15.58 %~25.47 %，本研究所建立之修正方法能適度降低能量依存性所造成OSLD的劑量誤差。

關鍵字

光刺激發光劑量計 ； 熱發光劑量計 ； 能量依存性

並列摘要

Optically simulated luminescent dosimeters (OSLDs) have been commonly used in research or clinical dose measurements due to their high sensitivity and can be read out multiple times. However, they have energy dependence, and they exhibit an over-response to low energy photons to misestimate the dose.
This study used OSLDs and thermoluminescent dosimeters (TLDs) irradiating with three photon energy (100 kV, 120 kV,6 MV) to measure the doses at in-field and out-of-field locations in different depth. Moreover, we calculated the dose response ratio (ROSLD1/ROSLD2) from measurement and used Monte Carlo methods to simulate the ratio of with and without filters in different energies. Effective energy and the correction factor would be decided to reduce the error.
The results show that OSLD have less energy dependence in the 6 MV high-energy photon irradiation. The dose errors after the verification compared to TLD are ranged from -20.26 %~27.46 %. In the low-energy photon irradiation (100 kV and 120 kV), OSLD showed energy dependence seriously and the dose errors compared to TLD are range from 66.67 % to 175 % before modification and 15.58 % to 25.47 % after modification. In this study we established a method to reduce the dose errors of OSLD caused by the energy dependence, by means of the modification, errors due to energy dependence can be reduced effectively.

並列關鍵字

OSLD ； TLD ； Energy dependence

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