硼中子補獲治療超熱中子束之中子特性研究

Neutronic Characterization of an Epithermal Neutron Beam in Boron Neutron Capture Therapy

劉淵豪(Yuan-Hao Liu)

指導教授 ： 江祥輝

國立清華大學/原子科學院/工程與系統科學系/博士(2009年)

摘要

本論文總結了清華水池式反應器(THOR)超熱中子束於投入硼中子捕獲治療(BNCT)臨床前，過往多年中子束特性測定的發展與結果。本論文的撰寫與完成乃是得助於多年來數人的協力與投入。他們的貢獻使今天清華超熱中子束擁有世界最好的特性測量研究。
為精確提供硼中子捕獲劑量，本論文建立了一套全面性的系統方法，用以測定、調整BNCT超熱中子束之中子特性。此系統方法含括了中子束強度於數個物理範疇上的特徵：涵蓋時間、能量、空間、及角度四個象限，為一獨步全球的突破發展。
第一章提供了BNCT的基本概念及本論文之研究目的，並介紹了筆者從事論文研究的二處BNCT設施：台灣清華水池式反應器及歐盟聯合研究中心所屬之高通率反應器(HFR)。第二章中，筆者將介紹清華自行建立之即時中子束監測系統；此系統係用以觀測中子束於時間象限中的變化。第三章，則將講述超熱中子束通率測量中常用的活化偵檢器，以及雙箔片法；第四章則為第三章之實踐與THOR超熱中子束通率的測定結果。此前部分均為2006前所進行之研究。
自2006年夏天起，筆者開始發展中子間接造影技術(INR)於超熱中子束測量上的應用，使我們得以觀測中子束在空間象限中的分佈。第五章講述了INR所應用之影像板，文中將介紹其基本原理與對活化偵檢器之響應特性。第六章則是利用INR測定超熱中子束之空氣中通率分佈，及講論所測影像與中子源檔中之角度分佈描述的關係；第七章則是應用INR測定假體中熱中子通率的空間分佈。
第八章，則是利用多重活化偵檢器與中子能譜反解術，進行超熱中子束之能譜研究，並利用一自行發展之反解技術求得相當精細(六百四十群)之THOR與HFR中子能譜。第九章中，筆者利用蒙地卡羅方法求取了一系列之「自我屏蔽群化截面」，利用此一技術可以相當精確地解決多重活化偵器的缺點：嚴重的自屏蔽效應。第十章則是集合了第六、八、九章的技術，加上創新的觀點，求出超熱中子束其中子源檔之空間與角度分佈；利用第六章建立之技術，我們測得了不同位置的中子通率切面資料，同時採用第九章的技巧計算各對應位置之偵檢器對中子源的群化響應函數，如此一來，即可以透過適當的方法，利用第八章的反解技術求得空間與角度分佈。
至此，超熱中子束之各項參數均為可決。

關鍵字

硼中子補獲治療 ； 超熱中子束 ； 能譜反解術 ； 間接中子造影

並列摘要

This dissertation summarizes the neutronic characterization work performed in the epithermal neutron beam at Tsing Hua Open-pool Reactor (THOR) in the past years, before entering the clinical trial of Boron Neutron Capture Therapy (BNCT). Part of this study was also performed at the High Flux Reactor (HFR) in Petten, The Netherlands. The completion of this dissertation owes to many conscientious people and their hard work.
In order to provide a reliable estimation of boron dose in tumor and in normal tissue, a well-characterized epithermal neutron beam is demanded for BNCT. In this dissertation, we have established a new systematic methodology to characterize the neutron beam in time, energy, spatial, and angular domains. This is a breakthrough for BNCT dosimetry based on many other previous studies and efforts; this is the first time we are able to determine all these parameters of interest, especially the spatial and angular distributions.
Chapter 1 introduces the basic concept of BNCT, the THOR and HFR facilities, and the aims of this dissertation. Chapter 2 presents the on-line neutron monitoring system installed at THOR, which is applied to monitor the beam variation in the time domain. In Chapter 3, it introduces the idea of the activation detector and the two-foil method, which are generally used for determining the absolute neutron fluence rates. Following Chapter 3, Chapter 4 is the implementation of the two-foil method in the THOR beam.
The application of Indirect Neutron Radiography (INR) is one of the main features of this dissertation. The INR can map the neutron flux distribution in space. In Chapter 5, the key component of INR, the imaging plate (or imagine plate) is presented and its responses to activation detectors is discussed. The neutron flux mappings free-in-air and in-phantom are shown in Chapters 6 and 7.
Chapter 8 presents the spectra adjustment of the epithermal neutron beam of the THOR and HFR. It utilizes a creative algorithm named “coarse-scaling adjustment” to provide smooth fine-group energy spectra (640 groups) based on multiple activation detectors and unfolding techniques. The common self-shielding problem is discussed in Chapter 9, in which the idea of Monte Carlo determined self-shielded cross-sections is brought in. The most interesting part, Chapter 10 shows you an integrated methodology to determine the spatial and angular distribution of the THOR epithermal neutron beam, which utilizes the INR from Chapter 7, the unfolding techniques from Chapter 8, and the Monte Carlo determined groupwise detector responses from Chapter 9.
All the parameters of an epithermal neutron beam can now be determined.

並列關鍵字

boron neutron capture therapy ； epithermal neutron beam ； spectrum unfolding ； indirect neutron radiography

參考文獻

[1]Current Status of Neutron Capture Therapy, IAEA, Vienna, 2001.

[2]W.O. Voorbraak, Recommendations for the Dosimetry of Boron Neutron Capture Therapy (BNCT), NRG, Petten, 2003.

[3]I. Auterinen, T. Seren, K. Anttila, A. Kosunen, S. Savolainen, "Measurement of free beam neutron spectra at eight BNCT facilities worldwide", Applied Radiation and Isotopes 61 (2004) 1021.

[4]Y.D. Harker, R.A. Anderl, G.K. Becker, L.G. Miller, "Spectral Characterization of the Epithermal Neutron Beam at the Brookhaven Medical-Research Reactor", Nuclear Science and Engineering 110 (1992) 355.

[5]Y. Sakurai, T. Kobayashi, "Spectrum evaluation at the filter-modified neutron irradiation field for neutron capture therapy in Kyoto University Research Reactor", Nuclear Instruments & Methods in Physics Research Section A-Accelerators Spectrometers Detectors and Associated Equipment 531 (2004) 585.