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dc.contributorChien-Chung Jengen_US
dc.contributor.authorYuan-Chun Laien_US
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dc.description.abstract執行腦部立體定位放射治療手術(Stereotatic Radiotherapy, SRT)的治療裝置有Linac Cone-based、Linac FFF-VMAT及Tomotherapy等技術,而輻射劑量輸出的準確性將影響這些裝置對腫瘤的治療成果,本研究第一部份將評估Linac Cone-based、 Linac FFF-VMAT及Tomotherapy三種不同裝置,執行腦部SRT時,其輻射劑量給予之差異,並透過臨床測量驗證其輸出輻射劑量之準確性。 放射治療使用小照野時,其射束經過組織與空腔交界面,會因為電子不平衡(electronic disequilibrium)的效應,而造成治療計劃系統錯估交界面劑量。本研究第二部分以輻射劑量計搭配自製頭型假體,針對鼻咽癌患者,評估旋繞疊加演算法於IMRT、VMAT及Tomotherapy三種治療技術,其鼻咽組織與空腔交界面處,劑量給予之準確度。 研究結果顯示對於不同大小及腦幹距離之腫瘤,Linac Cone-based可得到最佳之順形度及最大之劑量梯度,Linac FFF-VMAT對於大直徑腫瘤的劑量梯度比Tomotherapy好,而Tomotherapy對於小直徑腫瘤的劑量梯度比Linac FFF-VMAT好,當腫瘤需規畫高劑量梯度時,甚至當腫瘤略微不規則時,建議選擇Linac Cone-based進行SRT治療。當使用Linac FFF-VMAT進行SRT時,MLC位置的微小偏差仍會對高劑量梯度區域產生明顯之誤差而影響量測之加馬通過率,必須嚴格要求MLC位置之準確性。 當面積為2 × 2cm^2之光子小照野射束經過鼻咽空腔組織時,EBT3、GR-200F和TLD-100近端界面測量的平均劑量與計算值之間的差異分別為-1.2%,-3.5%和0.8% 。遠端界面測得的平均劑量與計算值之間的差異分別為-15.8%,-16.4%和-4.9%,EBT3量測之BUR^-1為0.58。當使用IMRT、VMAT及Tomotherapy技術於交界面的量測結果皆無顯著劑量不足之情形,GR-200F分別於IMRT及Tomotherapy量到-4.2%及-4.3%之劑量最大差異。當使用旋繞疊加演算法時,由於電子不平衡的影響,小照野射束將導致在鼻咽空氣與組織界面處的劑量高估。 然而,臨床使用多角度照射可以減少由於小照野電子不平衡效應引起的劑量誤差之影響,其影響與總處方劑量相比可忽略不計。zh_TW
dc.description.abstractThe modalities for performing stereotactic radiotherapy (SRT) on the brain include the cone-based linear accelerator (linac), the flattening filter-free (FFF) volumetric modulated arc therapy (VMAT) linac, and tomotherapy. In the first part of this study, the cone-based linac, FFF-VMAT linac, and tomotherapy modalities were evaluated by measuring the differences in doses delivered during brain SRT and experimentally assessing the accuracy of the output radiation doses through clinical measurements. When using small field sizes in radiotherapy, the electronic disequilibrium effect as the beam passes through an air-tissue cavity will lead to inaccurate estimations of interface doses in treatment planning systems (TPS). In the second part of this study combined the use of radiation dosimeteric measurements and a custom-made anthropomorphic phantom in order to evaluate the accuracy of therapeutic dose calculations at the nasopharyngeal air-tissue interface, using convolution/superposition algorithms for intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and tomotherapy, for the treatment of patients with nasopharyngeal carcinoma. The results of this study show that the cone-based linac had the best conformity and steepest dose gradient for tumors of different sizes and distances from the brainstem. The FFF-VMAT linac had a better gradient than tomotherapy for a large tumor diameter. Tomotherapy had better gradient than the FFF-VMAT linac for smaller-diameter tumors. SRT should be performed using the cone-based linac on tumors that require treatment plans with a steep dose gradient, even as the tumor is slightly irregular. Slight deviation in the position of the MLC significantly affected the results of gamma analysis. The accuracy of the MLC position must be strictly confirmed. When measured the single field 2 × 2 cm^2, the differences between the average dose measured at the proximal interface for EBT3, GR-200F, and TLD-100 and the calculation values were -1.2%, -3.5%, and 0.8%, respectively. The differences between the average dose measured at the distal interface and the calculation values were -15.8%, -16.4%, and -4.9%, respectively. The BUR^-1 measured using EBT3 was 0.58. When using the clinical techniques, the measurement results at the interface for all three techniques did not imply under dose. The dose differences measured using GR-200F for IMRT and tomotherapy were -4.2% and -4.3%, respectively. Small field beam will lead to dose overestimation at the nasopharyngeal air-tissue interface due to electronic disequilibrium when using convolution/superposition algorithms. However, utilizing of multi-angle irradiation clinically can reduce the impact of dose errors due to the small-field electronic disequilibrium effect, and may be negligible when compared to the total prescribed dose.en_US
dc.description.tableofcontents致謝 i 摘要 ii Abstract iv 目次 vi 圖目次 ix 表目次 xii 第一章 緒論 1 1.1 前言 1 1.2 研究目的 2 第二章 立體定位放射治療劑量比較 3 2.1 前言 3 2.1.1 直線加速器 4 2.1.2 斷層式螺旋治療儀 10 2.2 文獻回顧 11 2.3 實驗材料與方法 12 2.3.1 假體設計 12 2.3.2 治療計劃 13 2.3.3 劑量品質分析指標 15 2.3.4 加馬分析指標 16 2.3.5 熱發光劑量計 17 2.3.6 Gafchromic EBT3自顯影底片 19 2.3.7 劑量量測 22 2.4 實驗結果與討論 22 2.4.1 射束資料收集 22 2.4.2 劑量品質分析 26 2.4.3 劑量量測結果 29 2.5 結論 35 第三章 旋繞疊加演算法之空腔劑量準確度評估 37 3.1 前言 37 3.1.1 劑量學基礎 38 3.1.2 帶電粒子平衡 39 3.1.3 旋繞疊加劑量計算演算法 40 3.2 文獻回顧 46 3.3 實驗材料與方法 47 3.3.1 假體設計 47 3.3.2 治療計劃 47 3.3.3 劑量量測 48 3.4 實驗結果與討論 50 3.4.1 治療計劃結果 50 3.4.2 劑量計之劑量測量 50 3.5 結論 62 第四章 未來展望 64 4.1 立體定位放射治療 64 4.2 空腔劑量準確度評估 65 第五章 參考文獻 67zh_TW
dc.subjectstereotactic radiotherapyen_US
dc.subjectdose gradienten_US
dc.subjectconvolution/ superposition algorithmsen_US
dc.subjectelectronic disequilibriumen_US
dc.titlePhysical characteristics of small field Photon beam: comparison of dose characteristics for stereotactic radiotherapy and evaluation of accuracy for cavity dose of convolution/superposition algorithmen_US
dc.typethesis and dissertationen_US
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