隨著科技業的蓬勃發展，現今醫療儀器產業日新月異，放射遠隔治療透過快速且精確的電腦運算以及精密的儀器設備，可以將輻射劑量準確的投擲於病灶處並且有效的降低腫瘤周圍正常組織的輻射劑量，以達到保存正常組織之目的；然而在此不容差錯的情況下，導致了輻射劑量的驗證與安全問題變得更加繁瑣且關鍵；本論文主要目的為使用自製研發之輻射探測器(Pad detector)置於輻射源下進行量測，將量測所得之輻射游離計數，經由理論公式計算，轉換為輻射劑量單位；並且根據現有的劑量議定書之內容規範所提及會使游離腔讀出數值產生影響之項目進行校正。本研究中主要針對環境溫度壓力、再結合效應與空氣克馬校正項目進行校正；利用不同的實驗或者是透過Geant4程式模擬，得到不同的校正因子，將各個因素所導致游離訊號產生的差異進行校正；將此三種影響因子對於Pad detector之量測訊號進行修正後，比較Pad detector之量測計數與我國游離輻射標準實驗室所提供之量測數據，其相較後發現經過校正的Pad detector之量測數據與國家標準實驗室之量測結果差異<5%。並且透過持續追蹤Pad detector於同一Co60射源下的量測結果，除了可以觀察Co60射源自然衰減的情況之外，本研究同時利用衰減公式將每次實驗之量測結果回推至射源強度一致的情況下，比較每次實驗量測之差異<0.4%。

Modern external radiotherapy with photon beams takes advantage of computers, sophisticated algorithms and precise mechanics in order to let the damage close to the tumor while sparing normal tissue. Because of the accurate technique, it becomes more crucial for verification and safety issues. In this study we present the results of dosimetric evaluation of a two- dimensional Pad detector with the objective of its implementation for quality assurance in National Radiation Standard Laboratory (NRSL). The radiation dose conversion of the count reading on Pad detector is performed by means of formula and certain correction for the effect on reading of dosimeter according to the specification of the content of the dose protocols. To proceed with the correction, this research is mainly aimed at environmental temperature and pressure correction, recombination correction, and air Kerma calibration. Experiments and Geant4 simulation are designed to find recombination correction and air Kerma calibration, respectively to correct the difference in output readings between reference and user’s condition. The results show that this detector can be used for 2D dosimetry of beams. The difference of corrected statistic in this study is under 5% compared to the reference statistic provided by NRSL. Four measurements at different time of the same Co60 radiation source using the Pad detector are performed over a period of 43 days. The natural decay of Co60 source can be clearly observed from the measurements. After converting the readings of Pad detector to the same source strength by the decay formula of Co60, it is found that the difference among the four experimental measurements is < 0.4%.

目錄
摘要 I
Abstract II
誌謝 III
目錄 IV
圖目錄 VII
表目錄 IX
符號說明 X
第一章 緒論 1
1.1 前言 1
1.2 研究動機與目的 1
1.3 論文架構 2
第二章 輻射量測原理與規範 3
2.1 游離腔之簡介 3
2.1.1 游離腔的工作原理 3
2.1.2 游離腔(Ion chamber)的工作區域 5
2.2 輻射度量 6
2.2.1 輻射量的描述 6
2.2.2 能量轉移克馬(Kerma)與吸收劑量(Absorbed dose) 7
2.2.3 電子平衡 8
2.3 量測追溯體系 10
2.4 劑量議定書(Dosimetry protocols) 13
2.4.1 基於空氣克馬校正之劑量議定書 14
2.4.2 基於水吸收劑量校正之劑量議定書 16
2.5 游離腔影響量的校正 18
2.5.1 游離訊號之校正 18
2.5.2 環境之溫度、濕度、壓力校正 18
2.5.3 系統校正因子 19
2.5.3.1 電量計之校正 19
2.5.3.2 再結合校正因子 19
2.5.3.3 極性校正 23
2.5.3.4 射束強度校正 23
2.5.4 射質轉換因子與干擾因子 23
第三章 游離訊號擷取與劑量轉換 25
3.1 探測器設計 25
3.2 資料擷取系統(Data Acquisition System, DAQ) 27
3.2.1 轉阻放大器(Transimpedance Amplifier，TIA) 27
3.2.2 積分電路(integrator circuits) 28
3.3 探測器工作區域測定 29
3.4 增建區域量測 30
3.5 輸出訊號(ADC)之劑量換算 32
3.6 再結合校正因子(recombination correction) 34
3.7 電阻校正與溫度變化影響探討 35
第四章 探測器(Pad Detector)物理性質量測與射質轉換因子模擬 41
4.1 輻射場之量測 41
4.2 Pad Detector空氣克馬校正因子與射質轉換因子模擬 45
4.3 射束強度分佈(Beam profile)量測 51
第五章 結論與未來展望 56
5.1 結論 56
5.2 未來展望 56
參考文獻 58
附錄一 61
附錄二 64
附錄三 65
 

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