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研究生:徐儒琳
研究生(外文):Hsu, Ju-Lin
論文名稱:乳房攝影的劑量校正
論文名稱(外文):Dose Calibration in Mammography
指導教授:陳為立
指導教授(外文):Chen, Wei-Li
學位類別:碩士
校院名稱:國立陽明大學
系所名稱:放射醫學科學研究所
學門:醫藥衛生學門
學類:醫學技術及檢驗學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:中文
中文關鍵詞:乳房攝影X射線校正系統平板型游離腔劑量轉換因子
外文關鍵詞:mammographic calibration systemflat cavity ion chamberdose conversion factor
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本研究主要目的在於建立乳房攝影能量範圍的低能量射質,根據NIST(National Institute of Standards and Technology) 設定規範,使用陽極靶為鉬靶的X光機,在操作電壓23kV、25kV、28kV、30kV、35kV之下,配合不同厚度附加鉬濾片,建立半值層由0.282 mm Al至0.389 mm Al的射質,並且測量不同射質下的能譜、計算有效能量。在此鉬靶系統下,以RC-6M(sn:9110)平板型游離腔為標準,建立乳房攝影能量範圍內的劑量校正系統,提供國內校正需求。
國際間各國家實驗室互相比對低能量X射線校正系統時,多採用設於法國的國際度量衡局(BIPM: Bureau International des Poids et Mesures)制訂的規範,其陽極靶為鎢靶。本研究比較在NIST及BIPM兩種不同低能量X光劑量校正系統的差異,除了量測半值層、能譜以外,還在兩種系統下校正同一支平板型游離腔,結果發現校正因子之間有6.2%的差異。
本研究的第三部分,使用蒙地卡羅法搭配鉬靶系統下量測的能譜,試算平均乳腺劑量轉換因子。由於入射X光的設定、游離腔的設定不同,照野大小設定不一定相同,所以結果與文獻上有一定程度的差距,程式方面還有改善的空間。
The aim of this study is to establish low energy beam qualities in mammographic energy ranges. According to specifications set by NIST(National Institute of Standard and Technology), five beam qualities were established by using an X-ray machine with Molybdenum anode and Molybdenum filters of different thicknesses under operation voltages of 23 kV, 25 kV, 28 kV, 30 kV, and 35 kV. The half value layers of the five beam qualities are 0.282 mm Al, 0.302 mm Al, 0.342 mm Al, 0.358mm Al, and 0.389 mm Al. We measured the spectrums and calculated effective energies for the five beam qualities. We established this dose calibration system of Molybdenum anode and used the RC-6M flat cavity ion chamber as the standard because it can meet calibration needs in our nation.
Internationally, many laboratories followed BIPM’s standard to set low energy calibration systems for comparisons. The BIPM system adopts tungsten as their anode material. We compared these two systems of different anodes. Besides measuring half value layers and spectrums, we calibrated the same flat cavity ion chamber under both systems. The results showed that the difference of the calibration factors between the two systems is about 6.2 %.
The third part of this study was to calculate mean glandular dose conversion factors by Monte Carlo simulations with spectrums data. The simulated conversion factors were a little different from that developed by Dance. It might be because of the difference of shapes of entrance x ray, flat cavity ion chambers, and radiation fields. For our program design, it still has room for further improvement.
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