- 學位論文
小兒頭部電腦斷層掃瞄之劑量評估
Dose Assessment of Pediatric Head Computed Tomography
摘要
世界衛生組織之調查顯示，自1993年以來，病人接受電腦斷層掃描檢查之數量大約每年10%的成長，然而，2004年至2006年間之電腦斷層掃描檢查中，亦有10%是兒童病患；在本研究中，將針對兒童頭部電腦斷層掃描檢查時所接受之劑量進行探討，亦將探討兒童於接受頭部電腦斷層掃描過程中敏感器官如:眼睛之水晶體、甲狀腺等所接受之輻射劑量。利用10歲之兒童擬人假體並使用篩選過後的熱發光劑量計來量測兒童於接受頭部電腦斷層掃描時接受的輻射劑量，藉由實驗之設計，將鉍屏蔽與敏感器官眼睛及甲狀腺部分間隔分別為0、2、4 公分，進一步分析此間隔之設計對劑量減少與影像品質是否有所助益；實驗過程分別依頭部電腦斷層不同的操作模式(Helical模式與Axial模式)下進行實驗。在結果方面，在Helical模式，眼睛部分未使用屏蔽的吸收劑量達到103.23±8.01 mGy，使用鉍屏蔽時則下降到66.10±7.90 mGy，劑量下降的幅度達35.97% ；在Axial模式下，眼睛部分未使用屏蔽的吸收劑量達到92.31±11.90 mGy，使用鉍屏蔽時則下降到64.20±8.76 mGy，劑量下降的幅度達30.45%，本研究中使用鉍屏蔽置放於眼睛及甲狀腺部分，預期可減少此敏感器官所接受之輻射劑量。我們發現在Helical模式下鉍屏蔽與眼睛部分間隔4公分時，劑量下降的幅度最為明顯，另外在Axial 模式下鉍屏蔽與眼睛部分間隔為2 cm或4 cm時，劑量也有明顯下降的趨勢。
並列摘要
Since 1993, the number of CT examination has been dramatically increasing by approximately 10% per year. According to World Health Organization examine, from 2004 to 2006, approximately 10% of the procedures were in children. In this study use two different CT scanner with helical and axial scan mode, the radiation dose to organs such as eye lens and thyroid were measured during the procedures. For each scan, three TLDs were initially placed next to each other over the center of the eye and thyroid without shielding. The eye and thyroid were covered with a randomized thickness of bismuth shielding and three TLDs were placed over the center of both eyes and thyroid on top of the material, the eye and thyroid were rescanned on the ATOM Dosimetry Phantom. For helical mode, the eye effective dose was 103.23±8.01 mGy and 66.10±7.90 mGy, with and without bismuth shielding respectively, the dose reduction has been 35.97% . For axial mode, the eye effective dose was 92.31±11.90 mGy and 64.20±8.76 mGy, with and without bismuth shielding respectively, the dose reduction has been 30.45% . According to the result, we found that the dose at 4cm between the bismuth shielding and measured organs is the most significantly decreased for the helical mode of both CT scanner. For the axial mode of both CT scanner, the doses at 2 and 4 cm are the most significant decreased.