超小型塑膠閃爍光纖偵檢器之研製－小照野放射治療上的應用

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研究生：	廖信發 Liao Hsin-fa
論文名稱：	超小型塑膠閃爍光纖偵檢器之研製－小照野放射治療上的應用 The study of the miniature plastic scintillating fiber detector — A dosimeter for small field radiotherapy application
指導教授：	袁立基 Yuan Liq-Ji
口試委員:
學位類別：	碩士 Master
系所名稱：	原子科學院 - 生醫工程與環境科學系 Department of Biomedical Engineering and Environmental Sciences
論文出版年：	2002
畢業學年度：	90
語文別：	中文
論文頁數：	83
中文關鍵詞：	閃爍、光纖、劑量率、半影區
外文關鍵詞：	scintillation, optic fiber, dose rate, penumbra
相關次數：	點閱：2 下載：0
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本研究的目的旨在研製一超小型塑膠閃爍光纖的輻射量測系統，利用閃爍光纖受輻射照射後釋出螢光，度量其發光強度用以對輻
射進行劑量率的評估。

工作的主要內容包括(1)開發一高阻抗高放大倍率之放大器，將光電轉換後之微弱訊號放大成可計讀之電壓輸出。(2)研製輻射偵測及光電轉換組件，此組件係採用Bicron公司BCF-20型綠色塑膠閃爍光纖1 mm × 5 mm L，耦合於10 m長之一般塑膠光纖上，分別構成輻射偵測之探針及光訊號之傳導，光電轉換則分別以光電倍增管或

光二極體為之。

實驗共以兩組分別進行，第一組係以光電倍增管為光電轉換之偵測組件，第二組則以光二極體為光電轉換之偵測組件。每組又分為偵測探針包以純金及未包金者各一。實驗結果顯示包純金者與未包金者在偵測靈敏度上並未發現有顯著的差異。各組可測量劑量率的範圍分別(1)採用光電倍增管者為350 cGy/min以內，(2)採用光二極體者為5 Gy/min以上。

在小照野射束水假體內進行測試發現，此開發之系統較游離腔在半影區不論於空間解析度上及劑量梯度上均有更加的辨識能力。

The purpose of this study is trying to develop a miniature plastic scintillation fiber detecting system used for radiation measurement. The fluorescence light released promptly from the scintillator under the ionizing radiation exposed, therefore, the dose rate can be evaluated by its
intensity of the light emitted.

The work of the developed detecting system consists mainly (1) to develop a high impendence of high amplification current amplifier, which could convert the very low current signal into readable voltage output, and (2) to construct the detector of opto-electric device, which the Bicron type BCF-20 plastic scintillating fiber of 1 mm × 5 mm L was used as the detection probe to integrate with a 10 m long plastic optic fiber as the light transmission medium, and the opto-electric converting device was

either by a photomultiplier tube or a photodiode.

The experiments divided into two groups. One has photomultiplier-coupled of optic fiber system and the other has photodiode-coupled one. Of the group content two different type probe, one was clad with thin sheet of pure gold and the other was bared. The results show the detection sensitivity were no significantly difference between the gold clad and bared one. The photomultiplier-coupled device is suitable to determine the dose rate below 350 cGy/min, and the photodiode-coupled one is suitable only for the dose rate above 5 Gy/min.

In small field cone beam experiments, which carried out of the dose profile measurements of different depth in water phantom. Our developed system shows much better performance than the conventional ion chamber, especially in the region of penumbra not only has excellent

spatial resolution but also has accurate of dose gradient.

摘  要  ………………………………………………………………Ⅰ
Abstract  ……………………………………………………………Ⅱ

誌  謝  ………………………………………………………………Ⅲ

目  錄  ………………………………………………………………Ⅳ

圖  目  錄  …………………………………………………………Ⅶ

表  目  錄  ………………………………………………………ⅩⅠ

附  錄  目  錄  …………………………………………………ⅩⅡ

第一章   緒論  ………………………………………………………1

1-1   閃爍光纖的發展與回顧  …………………………………1

1-2   目前光纖於輻射量測上的應用  …………………………4

1-3   研究的動機、目的及實驗系統概述  ………………………5

第二章   原理  ………………………………………………………8

2-1   光子與物質作用及能量的吸收  …………………………8

2-1-1  光電效應（Photoelectric Effect）  ……………9

2-1-2  康普吞效應（Compton Effect）  …………………10

2-1-3  成對產生（Pair Production）  ……………………11

2-1-4  能量在物質內的吸收  ……………………………12

2-2   有機螢光材料閃爍發光原理  ……………………………16

2-3   閃爍光在光纖內的傳輸  …………………………………17

2-3-1  光纖構造與光傳輸原理  …………………………18

2-3-2  閃爍光纖的組成與構造  …………………………20

2-3-3  閃爍光的收集與傳輸  ……………………………21

2-4   光訊號的轉換  ……………………………………………23

2-4-1  光電倍增管—光電轉換  …………………………23

2-4-2  PIN光二極體—光電轉換  ………………………24

第三章   實驗裝備的研製  …………………………………………27

3-1   高阻抗放大器的研製  ……………………………………27

3-1-1  放大器原理  ………………………………………27

3-1-2  放大器電路設計  …………………………………29

3-2   塑膠光纖與閃爍光纖的耦合  ……………………………30

3-3   塑膠光纖與光電倍增管或PIN光二極體間的耦合  ……31

第四章   實驗設置與測試  …………………………………………32

4-1   實驗系統之設置  …………………………………………32

4-1-1  光纖與照射源  ……………………………………32

    4-1-2  訊號擷取  …………………………………………33

4-2  基本測試  …………………………………………………34

4-2-1  高阻抗放大器之線性放大測試  …………………34

4-2-2  小型閃爍光纖偵檢器對鋂-241射源的回應  ……35

4-2-3  鈷-60射源測量  …………………………………35

4-3  假體內劑量分佈測試  ……………………………………36

4-3-1  醫用加速器假體內劑量分佈測試  ………………36

4-3-2  近接治療銥-192射源的測量  ……………………37

第五章   結果與討論  ………………………………………………38

5-1  高阻抗放大器之線性放大測試結果與討論  ……………38

    5-2  小型閃爍光纖偵檢器對鋂-241射源的回應  ……………41

    5-3  鈷-60射源測量  …………………………………………42

5-3-1  輸出端為光電倍增管時  …………………………42

5-3-2  輸出端為PIN光二極體時  ………………………45

    5-4  假體內劑量分佈量測與比較  ……………………………48

5-4-1  組織假體比值的測量  ……………………………48

5-4-2  10 × 10照野百分比深度劑量量測比較  ………50

5-4-3  圓柱型小照野百分比深度劑量量測比較  ………52

5-4-4  剖面劑量分佈的測量  ……………………………55

    5-5  近接治療銥-192射源的測量  ……………………………67

第六章   結論  ………………………………………………………69

6-1 系統比較  …………………………………………………69

6-1-1 光電倍增管為光電轉換系統  ……………………69

6-1-2 光二極體為光電轉換系統  ………………………69

6-2 謝倫可夫輻射相關之討論  ………………………………70

6-3 未來展望  …………………………………………………71

參考文獻  ……………………………………………………………72

附錄  ……………………………………………………………75

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