Assessment of Absorbed Dose of PET (18F-FDG) Scanning Patients with MIRD and TLD Methods

利用MIRD與TLD方法評估氟－8-FDG正子斷層掃描病人之吸收劑量

張國平(Kwo-Ping Chang) ； 劉俊佑(Chun-Yu Liu) ； 林宥璇(Yu-Hsuan Lin) ； 張白容(Pai-Jung Chang) ； 李永康(Yung-Kang Lee) ； 邵佳和(Chia-Ho Shao)

《核子醫學雜誌》 20卷3期 (2007/09) Pp. 137-143

https://doi.org/10.6332/ANMS.2003.003

摘要

背景：輻射吸收劑量評估是診斷過程與比對之重要因子。利用PET/SPECT取得生物分佈資料很耗費時間，因此本研究除了針對氣－18-FDG使用MIRD方法評估劑量做爲標率，同時提出利用TLD評估器官體內劑量之修正方法。
方法：研究對象使用全身PET掃描並配帶l~2個TLD在選擇的器官，包括腦、甲狀腺、心臟、肺、肝、腎、脾以及膀胱。利用梯形法與衰減逼近及四個掃描時間點之數據求得置留時間，配合MIRD方法求得器官之劑量。量測到之TLD劑量求得經過修正後之器官劑量。
結果：氟－18-FDG在每個器官之置留時間與利用兩種方法求得之劑量均已求得。MIRD求得之劑量均大於TLD之劑量，腦與膀胱的劑量比值(MIRD/TLD)遠大於其它器官。
結論：病人的體態與病理狀況對利用TLD評估體內劑量影響很大。MIRD方法求得之劑量均大於TLD劑量主要是因爲TLD所量到的劑量已被介於TLD與器官之間之組織衰減。使用本研究得到之MIRD/TLD劑量比值，可方便的得到粗略的體內劑量評估。

關鍵字

氟－18-FDG ； 劑量 ； 置留時間 ； TLD ； MIRD

並列摘要

Background: Radiation dosimetry plays the crucial role for estimating the process of diagnosis as well as for the comparison of various diagnostic methods. PET/SPECT scanning is time-consuming if sufficient data are needed to derive the biodistribution. In this study, we propose using TLDs (thermoluminescent dosimeters) measurements to estimate the dosimetry of each interested organ for 18F-FDG administration. MIRD method used in this study will serve as a golden standard.
Methods: All studies were done with a whole-body PET Scanner (EXACT PET scanner HR(superscript +), Siemens). The source organs selected to scan are brain, thyroid, heart, lungs, liver, kidneys, spleen and bladder. Accumulated activities were estimated from the activity distribution of 4 time-points (including time zero) using the trapezoidal rule and physical decay fitting. One or two TLDs (CaSO4: Tm; Li2B4O: Cu) were attached to the surface of each of the eight sources organ. PET scanning with ROI selecting, MIRD method has been used to estimate dosimetry, simultaneously TLD dosimetry was measured and modified.
Results: Residence times of 18F-FDG for each organ of the subjects have been calculated. Dose estimated both from PET scanning with MIRD method as well as modified TLD measured dose were performed. Dose calculated by MIRD was always larger than that of TLD. The ratios (MIRD/TLD) for brain and bladder were significantly larger than those for other organs.
Conclusions: The anatomy and the pathological condition of a patient affected the dose assessment from TLD measurement. Dose calculated by MIRD was always larger than that of TLD, because the dose measured by TLD was attenuated by the tissues/organs which were between the real organ and TLD. Both MIRD and TLD methods can be used to assess the internal dosimetry of 18F-FDG. However, if we want to roughly derive the accumulated activity as well as the dose of each specified organ, TLDs method should be a more convenient approach if the MIRD/TLD ratios derived in this study are used.

並列關鍵字

18F-FDG ； dose ； residence time ； TLD ； MIRD