型號FWT-70-40(M)劑量計應用於BNCT輻射場的加馬劑量度量

Application of FWT-70-40(M) Dosimeter for Gamma Dose Measurement in BNCT Facility

許彬杰(Pin-Chieh Hsu) ； 劉鴻鳴(Hong-Ming Liu) ； 黎雪萍(Hsueh-Ping Lee) ； 劉朝錦(Chao-Chin Liu) ； 蔡文旗(Wen-Chyi Tsai) ； 江祥輝(Shiang-Huei Jiang)

《放射治療與腫瘤學》 15卷4期 (2008/12) Pp. 311-322

https://doi.org/10.6316/TRO/200815(4)311

摘要

目的：本文係控討型號FWT-70-40(M)劑量計，應用於中子、加馬(n、Y)混合輻射場中加馬劑量度量的可行性及其影響因素，以提供作為硼中子捕獲治療(BNCT)癌症的另一劑量度量劑量計的可行性。
材料與方法：本研究所探討劑量計為FWT-70系列的型號FWT-70-40(M)劑量計；中子、加馬混合輻射場為清華大學原子科學技術發展中心額定功率2MW水池式核子反應器(THOR)的BNCT照射治療室所提供，加馬劑量敏度校正輻射場則為清華大學原子科學技術發展中心活度1.08 E 15Bq（2.919萬居里）高劑量（率）鈷60加馬照射實驗室。，實驗過程係利用0.69立方公分游離腔標定鈷60加馬照射場各照射點的劑量率，將型號FWT-70-40(M)劑量計，分別置於各照射點照射不同的劑量，以獲得其對加馬的輻射敏度與劑量線性反應範圍；另將其置於THOR爐心接受高熱中子通量照射，以觀察其對中子通量（劑量）照射的耐受度。
結果：實驗結果顯示型號FWT-70-40(M)劑量計(1)對平均能量1.25MeV加馬的最低劑量限值為2Gy：最高劑量限值為7k Gy。(2)被中子活化的產物為鈉24(24Na)，此鈉24活化產物在相對於總熱中子通量3.6E12 nth/平方公分的中子通量照射下，於平均壽命時間產生的累積自激劑量僅1.12±0.12mGy。
結論：型號FWT-70-4O(M）劑量計於BNCT高中子通量（率）與劑量（率）的中子、加馬混合輻射場所產生的自激劑量，對加馬劑量度量干擾可忽略，且對加馬的最低劑量限值為2Gy，因此除可應用於鈷60加馬高劑量（率）輻射場與放射治療用高能量、高劑量（率）電子射束的劑量度量外，亦可應用於BNCT照射治療用高能量、高劑量（率）的中子、加馬混合輻射場的加馬劑量度量。

關鍵字

輻射色染劑量計 ； 綜性劑量反應低限值 ； 硼中子捕獲治療 ； 中子加馬混合輻射場

並列摘要

Purpose: The feasibility of FWT-70-40(M) dosimeter was studied for gamma dose measurement in a neutron and gamma mixed field. Furthermore, it was adopted as another dosimeter to determine the gamma dose in an epithermal neutron beam for Boron Neutron Capture Therapy (BNCT).
Material and Methods: The dosimeter used in this article was FWT-70 series of type FWT-70-40 (M). Using the Co-60 source of 29190 curies, which located in the Nuclear Science and Technology Development Center of National Tsing Hua University, performed calibration of the gamma dose sensitivity. The radiation sensitivity and the range of the linear response were obtained by irradiating the dosimeter with various dose rates and different total dose. Besides, this dosimeter was also irradiated with high neutron flux in the reactor core of the Tsing Hua Open pool Reactor (THOR) to investigate the neutron influence and activation. And then it was adopted as another dosimeter to measure the gamma dose in the BNCT facility at THOR.
Results: Experimental data show that: (1) the threshold of linear response is 2 Gy, while the up limitation is 7 kGy for average gamma energy of 1.25 MeV; (2) the major product of the neutron activation is Na-24. The accumulated self-exciting dose for Na-24 is only 1.12 mGy during its average life-time for irradiation of total thermal neutron fluence of 3.6E12 nth/cm^2.
Conclusions: Because of the self-exciting dose reduced from neutron activation can be neglected for gamma dose measurement in neutron and gamma mixed field, and the threshold of linear response is 2 Gy, the FWT-70-40 (M) dosimeter not only can be used for high dose rate Co-60 irradiation field and the high energy electron beam for medical purpose, but also can be used for gamma dose measurement in an epithermal neutron beam for boron neutron capture therapy.

並列關鍵字

Radia-Chromic dye dosimeter RDD ； Threshold of linear response ； Boron Neutron Capture Therapy BNCT ； Neutron and gamma mixed field