| Abstract: | 本論文使用熱發光劑量計(Thermoluminescent dosimeter, TLD)佈植於侖道假體(Rando phantom)，以及參考國際輻射單位與度量委員會48號報告(International Commission on Radiation Units and Measurements, ICRU-48)和數學亞當假體(Germany’s National Research Center for Environment and Health Institute for Radiation Protection Adam, GSF Adam)所設計出10、30、50、70和90公斤的自製研發數學假體(self-developed mathematic phantom, SDM)內，並利用林新醫院核子醫學科正子造影中心的西門子正子電腦斷層(Positron emission tomography Computed tomography, PET/CT)之biograph 16多切面電腦斷層進行掃描，其暴露條件與實際臨床上應用的條件相同，掃描條件設定為120 kV、Auto care dose 4D和5 mm/slice。而TLD佈點位置是依照每個器官的位置及大小，並參考Cheung等人及Kawaura等人之文獻[Cheung et al., 2007; Kawaura et al., 2006]及資深放射師審核後決定。
全身有效劑量計算分為二部分，第一，由每切片所代表器官之劑量，分別根據國際放射防護委員會(International Commission on Radiological Protection, ICRP)60號報告及103號報告進行加權平均，並依其報告制訂之等價劑量公式，計算出全身有效劑量。第二，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號報告及204號報告所提供之公式計算出全身有效劑量。器官吸收劑部份，進一步探討肝臟與皮膚劑量之計算，及其與體重大小之相關性。
本次實驗，10至90公斤假體用60號及103號報告計算結果相差由2.9%至6.5%；比較AAPM 96及 204報告提出之公式計算之有效劑量，10及30公斤自研假體在兩份報告中的計算結果相差37%，對於50至90公斤自研假體及侖道假體，AAPM 204較AAPM 96號報告高67%。肝臟劑量於權重後得到更精準之劑量為3.98±0.72至9.27±1.67 mSv，與TLD量測值具有一致性，皮膚劑量為2.46±0.31至6.56±0.79 mSv，與Tyan 等人之文獻中，以侖道假體及受檢者所測得之皮膚劑量範圍由1.1mSv到9.6mSv之劑量範圍相符合[Tyan et al., 2008]。
危險度部分，全身輻射危險度為0.018%至0.037%，對於ICRP 60報告中的全人口中致死癌病機率5.6%，是在安全範圍內，終身歸因危險度表示之所有癌症致癌率，腹部電腦斷層掃描下，接受輻射曝露產生的致癌率，最大值是10歲孩童為0.053%與Faletra 等人之CTCA(computed tomographic coronary angiography)及Smith等人文獻相較為低[Faletra et al., 2010; Smith et al., 2009]。
腹部電腦斷層掃描下，不同體重假體以CTDI與實際測量之劑量相對應關係，而得到一轉換方程式，未來可提供核子醫學科和放射科醫師、放射師臨床診斷之評估參考。
The effective dose (E) of rando and self-developed mathematic phantom (SDM), which was ranging from 10 to 90 kg derived from ICRU-48 therluminescence dosimeters (TLD-100H), was inserting into these phantoms undergoing PET/CT examinations. All scans, 120kV, auto care dose 4D and 5 mm/slice, the same as patients, were carried out on the 16 slice of BioGraphy PET/CT at Lin Shin Hospital. The locations of sensitive organs and tissues were determined by visually comparing sections to an atlas of cross-sectional anatomy published by Cheung and Kawaura.
All scans were performed by senior radiotherapist. E was calculated by (A) in the organs and tissues of interest using TLD and recommended by ICRP 60 and ICRP 103; (B) in DLP method, E was estimated according to CTDIvol that was recorded directly from the console display of PET/CT at the time of the scan and conversion coefficient (k) recommended by AAPM 96 and 204. Absorb dose of liver and skin was evaluated between the dose and phantom size.
Calculated E based on ICRP 60 and 103 was different from 2.9% to 6.5% among these SDM phantoms herein. In addition, 37% E differed
between AAPM 96 and 204 between 10 and 30 kg phantoms. E calculated by AAPM 204 was nearly higher 67% than that of AAPM 96. Use of each image J and TLD to measure out the dose of liver whereas the curves generated using the data obtained from the original dose are irregular across different body weights, the ones from weighting dose are similar and proportional by size. Absorb dose of skin was from 2.46mSv to 6.56 mSv and in good agreement with 1.1-9.6 mSv as published. The risk evaluated by ICRP 60 was estimated 0.0018% to 0.037% during one CT scan for these phantoms and found the extra risk was negligible. The maximum LAR was 0.053% in child by age 10. A simple equation of fit was derived to calculate of E for a patient of any weight that advisory, physician, radiotherapist, for diagnostic reference dose can be assessed. |
