小兒電腦斷層之個別病人劑量評估:回溯性分析84位小兒病人

電腦斷層(CT)之技術發展，使其成為診斷利器；然而，受檢者接受CT 檢查的頻次逐年增加，造成群體劑量攀升的議題需審慎面對，其中小兒族群對輻射相較成人更加敏感，因此其接受CT檢查造成之劑量與輻射風險更加值得關注，國際上亦紛紛成立相關組織關注小兒接受游離輻射檢查並提出建議掃描參數。為了評估電腦斷層劑量，現有的評估方式分為實際量測與模擬計算，其中模擬計算常使用數學假體或是代表平均體型的分齡參考人體素假體，但是這些並不能確切描述個別病人的劑量分布。因此亟需建立一套針對個別病人具有專一性的器官劑量與有效劑量評估系統，對於個別病人劑量監控或紀錄都是非常有意義的。再者，國際間對於個別病人之體型與劑量關係之研究日漸熱絡，顯示劑量與單獨個體之資訊具有相當密切的關係。因此從輻射防護與掃描條件優化的角度來看，實際探討臨床作業中體型因子與劑量的相互關係就顯得相當重要。本研究回溯分析臨床小兒受檢者的胸部CT影像，量化影像品質及體型，並使用不同方法計算每位病人之有效劑量與特定體型下之劑量評估(size-specific dose estimation，SSDE)，並由病人體型分佈製作卵圓形假體與進行假體實驗。另外本研究借助BEAMnrc蒙地卡羅程式，建立一台電腦斷層掃描儀模型，對此模型的劑量特性進行驗證，確認了臨床應用的可行性。同時使用臨床病人的電腦斷層影像建製成數位化體素假體輸入模擬系統，並進行圓柱形假體之電腦斷層劑量指標CTDI及多次掃描平均劑量MSAD的量測與模擬，找出合適的絕對劑量轉換因子，進而計算出個別病人的器官劑量與有效劑量。本研究找出合適的體型指標供臨床應用，並分析目前臨床使用的掃描條件，由假體實驗結果提出可改善之參數，同時建立個別病人劑量評估系統，以作為往後劑量監控(dose monitor)的紀錄或依據，本研究成果對於學術研究或實際發展應用，都是極具價值的。

關鍵字

小兒電腦斷層；器官劑量；個別病人

並列摘要

The technological development of Computed tomography (CT) makes it a powerful diagnostic tool, with the increasing utilization of CT, the rising population dose needs to be carefully considered. The stochastic effect of children caused by CT examinations worth more concern due to the pediatric population are more sensitive to radiation than adults, a lot of international organizations have been established to care about the children undergoing CT examination and recommendate scan parameters to achive ALARA (as low as reasonably achiveable) pricinple. There are two methods to estimate CT dose, one is physical measurement, the other is simulation, the latter commonly used mathematical phantoms or age-based voxel phantoms, both represent the general size of human anatomy, they have no ability to accurately depict the dose distribution of individual patient, therefore it is urgent and meaningful to establish a patient-specific dose evaluation system. Besides, more and more studies showed the individual body size has significance impact on dose distribution, it is important to investigate the relationship between body size and dose clinically from the perspective of optimization and radiation protection. This study retrospectively analyzed clinical pediatric chest CT images, quantified the image quality and body size, calculated the size-specific dose estimation (SSDE) and effective dose for each patient by various methods. To obtained patient-specific dose, we used BEAMnrc Monte Carlo system to establish a CT sanner model, validated the dose characteristics to match clinical application. On the other hand, we conducted the simulation and measurement of CTDI (computed tomography dose index) and MSAD (multi-slice average dose) of cylindrical PMMA phamtom to decide the absolute dose conversion factor. Finally the CT images of each patient were used to create voxel phantom, then individual organ doses and effective dose can be calculated. This study identified the appropriate body size index for clinical applications, and analyzed the function of current protocol, we provide the improved scan parameters by the result of phantom study. This study also established individual patient dose assessment system that can be served as dose tracking or dose monitoring; this study is highly valuable both for the academic research or practical applications.

並列關鍵字

Pediatric CT ； Organ dose ； Patient specific

參考文獻

(25) 江謝鎮至,董傳中,蔡惠予, "使用蒙地卡羅方法評估多切面電腦斷層掃描劑量:假體研究," 2007

(29) 吳書瑋,董傳中et al. "組織不均質及多葉式準直儀所造成能譜改變對蒙地卡羅方法模擬強度調控放射治療計畫的影響," 2007

(1) NCRP, Report No.160 - Ionizing Radiation Exposure of the Population of the United States, 2009

(2) FDA Public Health Notification: Reducing Radiation Risk from Computed Tomography for Pediatric and Small Adult Patients.2001

(4) International Electrotechnical Commission, International Standard 60601-2-44,

國際替代計量

小兒電腦斷層之個別病人劑量評估:回溯性分析84位小兒病人

全文下載

主題瀏覽