臺灣博碩士論文加值系統

高能直線加速器所產生之光子射束常被使用於放射治療中，由於高能
直線加速器所產生的光子經過靶、準直儀、整平濾片及空氣等材料時，會
由不同的光核反應( photonuclear reaction)如(γ,n)、(γ,2n)、(γ,pn)等反應而
產生中子。一般醫用之直線加速器能量範圍為6~18MV，其高能光子所造成
的中子污染劑量之影響乃臨床治療專業人員所關注的重要課題。本研究之
目的即在評估高能直線加速器在執行光子放射治療時，由光核反應產生之
熱中子劑量分佈，分別探討假體內之熱中子劑量分佈與治療室內的空間熱
中子劑量分佈，作為放射治療劑量評估之參考。
本研究採用TLD-600及TLD-700兩種熱發光劑量計做三維之空間佈
點，以獲取直線加速器進行一次光子放射治療時，高能光子之光核反應所
產生的熱中子劑量。假體中的熱中子劑量分佈乃利用置放於擬人假體
(Rando Phantom)中不同位置之TLD，在施行15MV之高能光子放射治療時，
度量評估各TLD所獲得之熱中子與光子通量，進而推算熱中子與光子劑量。
以直線加速器進行一次高能放射治療，光子輸出劑量為200MU時，治
療室內之空間熱中子劑量範圍為0.5~14μGy。而假體內之熱中子劑量分佈
方面，在照射條件gantry0°、238MU時，在Rando假體切片14至20中獲得之
熱中子平均劑量為118μGy，最大劑量為1187μGy，該點之熱中子劑量與靶
體積裡的最大光子劑量比例為0.069 %﹔照射條件分別gantry為0°、90°、
180°、270°，加速器輸出共給予244MU時，假體內獲得之熱中子平均劑量
為89μGy，最大劑量為603μGy，該點之熱中子劑量與靶體積裡的最大光
子劑量比例為0.035 %。
藉由熱發光劑量計對假體內之熱中子劑量分佈度量，可以評估病人每
次接受放射治療時，由光核反應所產生的熱中子，對病患造成之體內劑量。
而治療室內的空間熱中子劑量分佈可以瞭解在例行的放射治療中，治療室
內熱中子的劑量分佈。本研究結果可做為以直線加速器實行高能光子放射
治療時的熱中子劑量評估之參考，以使病患在接受放射治療時，獲得良好
的治療品質。

The photon beam produced by high energy linear accelerator used regularly in the radiotherapy. As the photon beam passes through tungsten target and flattening filter and other materials in the path, the photonuclear reactions might happen. Energy range of medical linear accelerator in clinical is from 6 to 18 MV. Effects of neutron contamination produced by high energy photons, therefore, become the high-light in photon therapy. The goal of this research is to estimate thermal neutron dose distribution in phantom and in room space as performing high energy photon therapy.
By the 3-plane placements of paired TLDs (TLD-600 and TLD-700) in the space of treatment room and the tool of extrapolation code, the special thermal neutron dose distributions of the treatment room when performed a single clinical irradiation were estimated. Phantom thermal neutron dose distributions were estimated by means of placing paired TLDs in the target and lung tissue in Rando phantom when delivering 15MV high energy photon radiotherapy. Thermal neutron dose can be figured out by the factor of flux-to-dose.
The range of the special thermal neutron dose distribution in the treatment room is 0.5~14μGy when executing high energy radiotherapy single time with linear accelerator output of 200 MU. The average and maximum thermal neutron doses in Rando phantom in the irradiated conditions of 0° gantry degree and 238MU are 118μGy and 1187μGy, the ratio of maximum thermal neutron dose to maximum photon dose in the target is 0.069 %. The average and maximum thermal neutron doses in Rando phantom in the irradiated conditions of 0°、90°、180°、270° gantry degree and total prescript output: 244MU are 89μGy and 603μGy, the ratio of maximum thermal neutron dose to maximum photon dose in the target is 0.035 %.
Paired TLD techniques were introduced in this research to estimate the dose distribution of thermal neutron and the dose ratio between thermal neutron and photon. Results of this research can be the reference in the clinical photon radiotherapy.

目錄
頁次
誌謝………………………………………………………………....I
中文摘要…………………………………………………………...II
英文摘要…………………………………………………………..IV
目錄………………………………………………………………..VI
表目錄……………………………………………………………VIII
圖目錄……………………………………………………………...IX
第一章緒論......................................................................................1
1.1 前言.....................................................................................1
1.2 文獻回顧.............................................................................2
1.3 研究目的.............................................................................2
1.4 實驗架構.............................................................................3
第二章原理......................................................................................1
2.1 中子來源.............................................................................1
2.2 中子分類.............................................................................1
2.3 中子作用機制.....................................................................1
2.3.1 彈性碰撞( n, n) ........................................................1
2.3.2 非彈性碰撞( n, n`γ) .................................................2
2.3.3 釋出質子( n, p) ........................................................2
2.3.4 釋出阿伐粒子( n, α) ................................................2
2.3.5 釋出加馬射線( n, γ) ................................................2
2.3.6 核分裂( n, f).............................................................2
2.4 中子劑量與度量原理.........................................................3
2.4.1 中子劑量..................................................................3
2.4.2 熱中子度量原理......................................................4
2.5 輻射加權因數.....................................................................5
第三章實驗儀器與設備..................................................................7
VI
3.1 直線加速器.........................................................................7
3.2 Rando 假體........................................................................10
3.3 熱發光劑量計...................................................................12
3.3.1 熱發光原理............................................................15
3.3.2 輝光曲線................................................................17
3.3.3 計讀儀器................................................................19
3.4 金箔...................................................................................20
3.4.1 金箔之活化原理....................................................20
3.4.2 金箔之活化分析....................................................21
3.5 HPGe 偵檢器....................................................................23
第四章步驟與方法........................................................................26
4.1 TLD回火............................................................................26
4.2 篩選...................................................................................27
4.3 劑量校正...........................................................................30
4.3.1 光子劑量響應校正................................................30
4.3.2 中子劑量響應校正................................................33
4.4 佈點與照射.......................................................................36
4.4.1 治療室內之熱中子分佈評估................................37
4.4.2 治療時Rando假體內之熱中子劑量評估.............39
4.5 TLD計讀............................................................................41
第五章結果與討論........................................................................42
5.1 治療室內之熱中子劑量分佈評估...................................44
5.2 假體內之熱中子劑量評估...............................................48
第六章結論....................................................................................56
參考文獻..........................................................................................58

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