正子電腦斷層掃描為準確率極高的檢查項目，廣泛應用於腫瘤病灶的定位及追蹤，並普遍用於健康檢查，其配合螺旋式之電腦斷層，並進行大範圍的全身性掃描，因此劑量及其危險度皆須詳細評估。
本論文使用熱發光劑量計、侖道假體、以及參考國際輻射單位與度量委員會48號報告和數學亞當假體所設計出的自製研發數學假體，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之biograph 16多切面電腦斷層進行掃描，找出不同體重之假體在進行PET/CT掃描下所得電腦斷層劑量之關係。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3 mm/slice。
全身有效劑量計算分為三大部分，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，經由美國醫學物理協會96號報告及204號報告所提供之公式計算出全身有效劑量。以及隨機取26名曾進行PET/CT受檢者之資訊，以AAPM 96及AAPM 204號報告分析。
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最多至3.5%，體重與劑量關係之方程式分別為mSv=7.14+8.9×10-2×kg及 mSv=6.63+9.9×10-2×kg；AAPM 96及 204報告提出之公式計算之有效劑量因轉換因子及k值的不同而造成其計算結果25%之差異。實際受檢者用AAPM 96及204所計算之有效劑量則分別在6.09至9.49和18.4至23.5 mSv的範圍中。
經由ICRP 60號報告之危險度評估，經由一次電腦斷層的掃描，10至90公斤假體之全身危險度約為0.037%至0.073%，在安全範圍內。假體體重與劑量相對應關係，所得到之方程式，未來可提供核子醫學科和放射科醫師、放射師臨床診斷之計量的評估參考。
PET/CT is a kind of high accuracy for functional image modality. It has been widely used in screening cancer for decades. Operation of the PET/CT scanner will be produce huge amount of x-ray scattered from the target, dose caused a significant increase.
To evaluate effective dose (E) of rando and self-developed mathematic phantom (SDM) 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 3 mm/slice, the same as patients, were carried out on the 16 slice of BioGraphy PET/CT at Lin Shin Hospital.
All scans wee 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. E was also discussed and compared with 26 volunteers selected in random undergoing PET/CT examinations and those of phantoms.
Calculated E based on ICRP 60 and 103 was different more than 3.5% among these SDM phantoms herein. The weight and dose relationship of equation are mSv=7.14+8.9×10-2×kg and mSv=6.63+9.9×10-2×kg, respectively. In addition, the conversion factor and k factor created 25% E difference between AAPM 96 and 204 between 10 and 30 kg phantoms. Volunteers’ E were ranging from 6.09 to 9.49 and 18.4 to 23.5 mSv by AAPM 96 and 204, respectively.
The risk evaluated by ICRP 60 was estimated 0.0037% to 0.073% during one CT scan for these phantoms and found the extra risk was negligible. 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.
