電腦斷層加權劑量指引之度量與應用
陳拓榮1，李超群2，鍾國晃2
1慈濟技術學院放射技術系，
2慈濟醫學中心影像醫學部
摘 要
本文介紹與導入電腦斷層加權劑量指引(computed tomography dose index, CTDI)、CTDI100、CTDIw、劑量長度積(dose length product, DLP)等電腦斷層劑量表示單位之含義與測量。並以筆型游離腔(pencil-type ion chamber)配合PMMA頭部與身體假體，度量評估相關劑量。當採用X光掃描條件為：120 kVp，厚度5毫米，軸向(Axial)方式掃描時，空氣中的CTDI100、頭部的CTDIw、身體的CTDIw分別是36.4 mGy、23.8 mGy和10.9 mGy。頭部的CTDIw為CTDI100的65 %；身體的CTDIw為CTDI100的30 %。換算成每單位mAs所造成的CTDI，空氣中的CTDI100、頭部和身體的CTDIw分別是0.13 mGy/mAs、0.085 mGy/mAs和0.039 mGy/mAs。DLP可合理地描述電腦斷層掃描面積的總劑量，由本實驗掃描50毫米為例，頭部DLP為118.8 mGy cm；而身體DLP為54.5 mGy cm。
關鍵字：電腦斷層、電腦斷層加權劑量指引、劑量長度積、游離腔
----------------------------------------------------------------------------------
Measurement of weighted computed tomography dose index and its application
Tou-Rong Chen1, Chau-Chin Lee 2, Kao-Hwu Chung2
1 Department of Radiological Technology, Tzu Chi College of Technology, Hualien
2 Department of Medical Imaging, Buddhist Tzu Chi General Hospital, Hualien
Abstract
The study introduces the computed tomography dose index (CTDI), CTDI100, CTDIw, and dose-length product (DLP) that recommended to be adopted in the dose description of computed tomography. A pencil-type ion chamber inserts in a head PMMA phantom or a body PMMA phantom to measure and assess the dose of computed tomography. The measurement was performed in the condition of 120 kVp of tube voltage, 5 mm thickness per slice, and axial rotation scan. The CTDI in free air, the CTDIw of head, and the CTDIw of body are 36.4 mGy, 23.8 mGy, and 10.9 mGy, respectively. The head’s and body’s CTDIw is 65% and 30% of CTDI100. To translate the dose unit to CTDI per mAs, the CTDI in free air, the CTDIw of head, and the CTDIw of body are 0.13 mGy/mAs, 0.085 mGy/mAs, and 0.039 mGy/mAs, respectively. DLP can reasonably describe the total dose that deposit in the exposure range. The head’s and body’s DLP are 118.8 mGy cm and 54.5 mGy cm in our measurement.
Keywords：computed tomography, CTDI, DLP, ion chamber