利用128電腦斷層掃描於假體頭部進行三種不同檢查偵測的有效劑量

利用國際公認的擬人侖道假體對於三種執行不同掃描範圍及相異的參數執行頭部電腦斷層來探討三者之間所吸收的有效劑量以及各組織器官等價劑量的差異。 TLD熱發光劑量計分布於擬人侖道假體於個組織及器官，經由三組不同的掃描範圍及參數，執行頭部電腦斷層檢查。這三組不同參數及範圍掃描執行於飛利浦128切CT。掃描後的TLD劑量計由Harshaw 3500計讀儀算出。各組織器官的等價劑量及全身有效劑量由國際輻射防護委員會ICRP 60號及103號報告計算得知。 有效劑量由方法A為軸切面掃描為1.49±0.21 mSv 和2.44±0.37 mSv；方法B為螺旋式掃描為2.26±0.19和2.83±0.22 mSv；方法C為軸切面掃描為2.41±0.06和3.38±0.06 mSv分別由ICRP 60號及103號報告計算。此實驗更發現執行頭部電腦斷層掃描時，性腺器官幾乎為背景輻射，同理可證，遠離性腺以下的器官幾乎沒有接受到劑量。此外，由工作站的螢幕上所顯示之電腦斷層劑量指標(Computer Tomography Dose Index, CTDIvol)，經由美國醫學物理協會(American Association of Physicists in Medicine ) 96號報告所提供之公式計算出全身有效劑量。三種掃描DLP值的差異，經由AAPM 96報告，算得方法A、B、C三種有效劑量分別為2.04、2.91及3.05 mSv。 全身有效劑量對於方法B螺旋式掃描明顯大於方法A軸切面掃描，因為方法B螺旋式掃描範圍，包含頸椎及其他紅骨髓器官。方法B螺旋式掃描所吸收的全身有效劑量為方法A的1.51和1.16倍，由ICRP 60號及103號報告計算。除此之外，對於方法B和C而言，相同掃描範圍但不同的CTDIvol將產生不同的結果。經由ICRP 103號報告之危險度評估，經由一次頭部電腦斷層的掃描，在三種參數之全身危險度約為0.29 %～0.33 %，處於安全範圍內。由此實驗可知，身為一位專業人員，應該在執行電腦斷層檢查時，選擇適當的參數及掃描範圍，以減少病患所吸收的劑量及降低所造成的輻射傷害。

Effective dose (E) and organ or tissue dose (DT) of Rando phantom undergoing three kinds of protocol from brain CT examinations were evaluated using thermoluminescent dosimeters (TLD-100H) approach. TLDs were inserted into organ or tissue from Rando phantom using three kinds of protocol that have different scan areas and parameter Examinations were conducted by Philips computer tomography (Brilliance CT) at Lukang Christian Hospital. TLDs were measured by using Harshaw 3500 TLD reader. E and DT were calculated by ICRP 60、103 and AAPM 96. E was (A) 1.49±0.21 and 2.44±0.37 mSv using axial scan, (B) 2.26±0.19 and 2.83±0.22 mSv using helical scan, (C) 2.41±0.06 and 3.38±0.06 mSv using axial scan, respectively. Gonads equivalent, Dgonads , is nearly background dose due to far away from scan area. Moreover,due to different scan length from three kinds of protocol, the result of E was (A) 2.04 mSv, (B) 2.91 mSv and (C) 3.05 mSv calculated by AAPM 96. E from Protocol (A) and (B) is obviously different because helical scan had longer scan range than axial scan. Helical method included c-spine and other bone marrow organ. In addition, E from Protocol (B) is larger 1.51 and 1.16 times than Protocol (A) calculated by ICRP 60 and 103. In addition, due to the same scan region and different CTDIvol from Protocol (B) and (C), E results in distinct consequence. The risk evaluated by ICRP 103 was estimated 0.29 %～0.33 % during one CT scan for these protocols and found the extra risk was negligible. Radiologists should adjust and choose suitable protocol to prevent unnecessary radiation to patient and achieve ALARA principle.