XY strip 探測器均勻度校準

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姓名

陳攻善(Cong-Thien Tran) 查詢紙本館藏

畢業系所

物理學系

論文名稱

XY strip 探測器均勻度校準
(Uniformity calibration for XY strip PPIC)

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摘要(中)

最近質子治療利用先進筆形束掃描 (PBS)非均勻束的特性，掃描大面積輻射場並完成高緊緻性治療。其質子束輪廓具有高劑量梯度是其特徵之一。為確保質子束傳輸系統的可靠性，每日進行每日品質保證（daily QA）工作是有其必要性。據有大面積、高空間分辨率和大動態範圍的二維 IC 陣列或 XY 條平行板電離室 (PPIC) 均為用於此類目的的潛在候選方案。與二維 IC 陣列相比，PPIC 使用較少的讀出通道並呈現更好的空間分辨率 [1]。為了將來自 PPIC 的信號轉換為輻射劑量，均勻性校準和標準源校準是必不可缺。本研究將校準 345.44 × 345.44 mm2 大面積的 PPIC 的均勻性。利用一個點狀微型 X 射線源提供穩定且小的局部輻射，在PPIC 的整個表面掃描 16x16 = 256 個 X 射線點。迷你 X 射線的穩定性和小體積使得操作變得簡單。PPIC 的 2D 增益圖可由 X 射線掃描重建。此時 PPIC 整體增益分佈的相對標準偏差為 3.5%，這對於質子治療中的劑量測量是不可接受的。從 PPIC 的 2D 增益圖中確定了增益因子的兩種變化。變異的第一個原因來自大面積PCB板的變形。變化的第二個原因被認為源於電極和讀出板之間的連接線的長度差異。論文中引入校準算法以提升 PPIC 的均勻性，並將增益相對標準偏差顯著降低至 0.6%。同時均勻性校準算法與探測器及輻射源的操作選項並無關聯。此項改進使 PPIC 能夠用於質子治療劑量測量，充分發揮 PPIC 的功能，可顯著減少日常 QA 的時間要求。

摘要(英)

Recent advanced pencil beam scan (PBS) in proton therapy deploys non-uniform beam which scans across a large radiation field and complete high conformity treatment. High dose gradient in beam profile is one of its characters. To ensure the reliability of the beam delivery system, daily quality assurance (daily QA) is required. 2D array of ICs or XY strip Parallel Plate Ionization Chamber (PPIC) occupying large area, high spatial resolution and large dynamical range, are potential candidates for such purpose. PPIC uses less readout channel and renders better spatial resolution in comparison to 2D array of ICs [1]. In order to convert signal from PPIC into radiation dosage, uniformity calibrations and standard source calibrations are essential. In this study, uniformity of large area PPIC, characterized by a large area of 345.44 × 345.44 mm2, will be calibrated. A point-like mini X-ray source is used to provide a stable and small localized radiation. The total surface of the PPIC was scanned by 16x16 = 256 spots of X-rays. The stability and compact size of the mini X-ray renders an operational simplicity. 2D gain maps of PPIC are reconstructed from the X-ray scan. Fractional standard deviation of gain distribution over the total area of PPIC is found to be 3.5% which is not acceptable for dose measurement in proton therapy. Two variations in gain factor are identified from 2D gain maps of PPIC. The first cause of variation is from the deformation of the large area PCB boards. The second cause of variation is suggested to originate from the differences in length of the connection lines between electrodes and the readout board. Calibration algorithms are introduced to improve uniformity of PPIC and they have significantly reduced gain fractional standard deviation to 0.6%. The uniformity calibration algorithms are indicated to be independent from the operation options of the detector and external radiation source. Such improvement enables the use of PPIC in proton therapy dose measurement. Time requirement of daily QA can be significantly reduced as functions of PPIC will be fully exploited.

關鍵字(中)

★ 質子治療利
★ 每日進行每日品質保證
★ 先進筆形束
★ 高空間分辨率和大動態範圍的二維 IC
★ 均勻性校準

關鍵字(英)

★ proton therapy
★ pencil beam scan
★ daily quality assurance
★ large area IC
★ uniformity calibration

論文目次

Abstract i
Abstract 摘要 ii
Acknowledgements iii
Table of Contents iv
List of Abbreviations vi
List of Tables vii
List of Figures viii
Chapter I Introduction 1
1.1. Proton therapy 1
1.2. Daily quality assurance in proton therapy 3
1.3. Role of ion chamber 4
1.4. Objective and aims 5
1.5. Thesis structure 6
Chapter II Theory 7
2.1. Proton interactions with mater 7
2.2. Proton Bragg peak 12
2.3. Photon interaction with mater 14
2.4. Radiation dose 16
2.5. Ionization chamber 18
Chapter III Instruments and Method 22
3.1. Large area XY strip Parallel Plate Ion Chamber (PPIC) 22
3.2. Selections of operation conditions 24
3.3. Signal processing 27
3.4. Stability of X-ray source 31
3.5. Uniformity experimental setup 33
3.6. Workflow 34
3.7. Analysis method 35
3.7.1 Reconstruction for 2D intensity map and normalization 35
3.7.2 First calibration algorithm 37
3.7.3 Second calibration algorithm 38
3.7.4 Uniformity validation 38
Chapter IV Result and Discussion 40
4.1. Variation of 2D gain maps 40
4.2. First calibration approach 46
4.3. Second calibration approach 51
Chapter V Conclusion 61
Bibliography 62
Appendix 64

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指導教授

陳鎰鋒(Chen, Ei-Fong)

審核日期

2021-7-6

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