中文摘要
醫用直線加速器可產生各種不同能量之光子及電子束，而光子與電子束可能會與靶、準直儀、整平濾片及空氣等材料發生(γ,n)、(γ,2n)、(γ,pn)等光核反應進而造成光子-中子混合輻射場。本論文之目的即在於以微劑量學的觀點來度量不同能量光子與電子束所造成此一混合輻射場其線能分布，其中，微劑量學係研究組織中以微觀的角度來決定高直線能量轉移輻射之能量沉積事件，藉由微劑量學能譜分布來定量混合輻射場中任何單一事件其線能與比能之分布函數與機率密度。本論文使用組織等效比例計數器(tissue equivalent proportional counter)來度量微劑量學參數，並充填以丙烷為主之組織等效氣體，來模擬評估2 µm微觀組織能量沉積。度量之前，以鋂-241阿伐射源置於組織等效腔壁作能量校正，計算出校正射源之能峰分布與其所對應頻道位置之相對關係。本研究獲得之微劑量學能譜，可觀察到光子與光中子之線能分布，藉以評估頻率平均線能、劑量平均線能與相對生物效應等參數，這些參數亦可提供臨床放射治療做為重要之參考。

Abstract
Medical linear accelerators generate two radiation beams including photon and electron beams. These beams could interact with target, collimators, flattening filter, air and even patient body. Several types of photonuclear reactions such as (γ,n)、(γ,2n)、(γ,pn) occurs to make the photon-neutron mixed fields. The purpose of this research is to measure the distributions of the lineal energy in these mixed fields which induced by different energies of photon and electron beams. Microdosimetry distinguishes the energy deposition events of high linear energy transfer radiations in microdosimetric view, and defines the probability function and probability density of lineal energy and specific energy in single event. A tissue equivalent proportional counter (TEPC) was chosen to measure the parameters of microdosimetry in this work. TEPC was filled with the propane based tissue equivalent gas to simulate a 2 µm size cell or tissue and the energy imparted irradiated with different energy of photons and electrons were measured. Am-241 calibrated source was placed on the wall surface of the TEPC to perform the energy calibration before the clinical measurement trial, therefore, relationship between imparted energy and channel of the spectra can be calculated. Microdosimetric spectra estimated from this work could estimate the frequency mean lineal energy, the dose mean lineal energy and relative biological effectiveness (RBE), these parameters are also the important references indexes for clinical radiotherapy.

目 錄
頁 次
誌謝............................................................................................................................................................I
中文摘要................................................................................................................................................II
英文摘要..............................................................................................................................................III
目錄........................................................................................................................................................IV
圖目錄....................................................................................................................................................V
表目錄...............................................................................................................................................VIII
第一章 序論........................................................................................................................................1
1.1 前言............................................................................................................................................1
1.2 研究動機..................................................................................................................................3
第二章 微劑量學基本原理.........................................................................................................5
2.1 微劑量學的量與單位........................................................................................................5
2.2 微小體積的模擬..................................................................................................................6
2.3 帶電粒子平衡與腔壁效應.............................................................................................9
第三章 材料與方法......................................................................................................................14
3.1 實驗設計...............................................................................................................................14
3.2 組織等效比例計數器.....................................................................................................18
3.3 氣體放大作用.....................................................................................................................21
3.4 能量校正...............................................................................................................................23
第四章 結果與討論......................................................................................................................28
4.1 校正能譜分析.....................................................................................................................28
4.2 光子微劑量學能譜..........................................................................................................32
4.3 電子微劑量學能譜..........................................................................................................45
4.4 頻率平均線能與劑量平均線能................................................................................48
4.5 生物加權函數與相對生物效應................................................................................50
第五章 結論.....................................................................................................................................54
參考文獻.............................................................................................................................................56

參考文獻
1. 許芳裕，「硼中子捕獲治療的微劑量學應用與治療計畫驗證之研究」，國立清華大學原子科學系博士論文，民國九十二年。
2. Goodhead, D.T. An assessment of the role of microdosimetry in radiobiology. Radiat. Res. 91(1982) 45.
3. Bradley, P.D. The development of a novel silicon microdosimeter for high LET radiation therapy. Thesis, Department of Engenieering Physics, University of Wollongong, (2000).
4. Mao, X., Kase, K.R., Liu, J.C., Nelson, W.R., Kleck, J.H. and Johnsen, S. Neutron sources in the Varian Clinac 2100C/2300C medical accelerator calculated by the EGS4 code. Health Phys. 72 (1997) 523.
5. Kase, K.R., Mao, X., Nelson, W.R., Liu, J.C., Kleck, J.H. and Elsalim, M. Neutron fluence and energy spectra around the Varian Clinac 2100C/2300C medical accelerator. Health Phys. 74 (1998) 38.
6. Swanson, W.P. Calculation of neutron yields released by electrons incident on selected materials. Health. Phys. 35 (1978) 353.
7. Swanson, W.P. Improved calculation of photoneutron yields released by incident electrons. Health. Phys. 37 (1979) 347.
8. Amols, H.I. and Zellmer, D.L. Microdosimetry of 10-15 MeV bremmsstrahlung x rays. Med. Phys. 11 (1983) 247.
9. Schuhmacher, H. and Krauss, O. Area monitoring of photons and neutrons from medical electron accelerators using tissue-equivalent proportional counters. Radiat. Prot. Dosim. 14 (1985) 325.
10. Amols, H.I. and Kliauga, P. Microdosimetry of 10-18 MeV electrons and photons using walled and wall-less detectors. Radiat. Prot. Dosim. 13 (1985) 365.
11. Kliauga, P. and Amols, H.I. Photoneutrons from high energy medical linear accelerators: measurement of the spectrum and dose using a miniature proportional counter. Radiat. Onc. Biol. Phys. 31 (1995) 629.
12. International Commission on Radiation Units and Measurements, Microdosimetry. (ICRU report; 36), Bethesda, Maryland, (1983).
13. Fano, U. Note on the Bragg-Gray cavity principle for measuring energy dissipation. Radiat. Res. 1 (1954) 237.
14. Waker, A.J. Principal of Experimental Microdosimetry. Radiat. Prot. Dosim. 61(4) (1995) 297.
15. Rossi, H.H. and Zaider, M. Microdosimetry and its applications. Springer 1996.
16. Braby, L.A., Johnson, G.W. and Barthe, J. Practical consideration in the design and construction of tissue-equivalent proportional counter. Radiat. Prot. Dosim. 61 (1995) 351.
17. Kliauga, P., Waker, A.J. and Barthe, J. Design of Tissue-Equivalent Proportional Counters. Radiat. Prot. Dosim. 6 (1995) 309.
18. Ségur, P., Olko, P. and Colautti, P. Numerical modelling of tissue-equivalent proportional counters. Radiat. Prot. Dosim. 6 (1995) 323.
19. Srdoc, D. Experimental technique of measurement of microscopic energy distribution in irradiated matter using Rossi Counters. Radiat. Res. 43 (1970) 302.
20. Dietze, G., Menzel, H.G. and Bühler, G. Calibration of tissue-equivalent proportional counters used as radiation protection dosemeters. Radiat. Prot. Dosim. 9 (1984) 245.
21. Gerdung, S., Pihet, P., Grindborg, J.E., Roos, H., Schrewe, U.J. and Schuhmacher H. Operation and application of tissue equivalent proportional counters. Radiat. Prot. Dosim. 61 (1995) 381.
22. International Commission on Radiation Units and Measurements, Stopping Power and Ranges for Protons and Alpha Particles. (ICRU report; 49), Bethesda, Maryland, (1993).
23. Schrewe, U.J., Brede, H.J., Pihet, P. and Menzel, H.G. Improvement on the calibration of TEPCs with built-in α particle sources. Radiat. Prot. Dosim. 23 (1988) 249.
24. Pihet, P., Menzel, H.G., Schmidt, R., Beauduin, M. and Wambersie, A. Biological weighting function for RBE specification of neutron therapy beams. Intercomparison of 9 European centres. Radiat. Prot. Dosim. 31 (1990) 437.