蒙地卡羅模擬法評估肝腫瘤患者之釔-90微球體放射栓塞治療的輻射劑量分布

Dosimetry of Y-90 selective internal radiotherapy in patients with hepatic tumor evaluated by Monte Carlo Simulation

李昕迪(Sin-Di Lee)

指導教授 ： 周銘鐘

共同指導教授 ： 林信宏(Hsin-Hon Lin)

高雄醫學大學/健康科學院/醫學影像暨放射科學系碩士在職專班/碩士(2019年)

摘要

背景與目的：90Y微球體放射栓塞治療(Selective internal radiotherapy with Yttrium-90 microsphere)是一種新興的肝腫瘤治療方式，它的療效除了來自動脈栓塞造成腫瘤缺血，亦包含90Y對腫瘤造成的放射線治療。現行推定90Y微球體放射栓塞的吸收劑量的方法皆假設肝腫瘤、正常肝組織以及肺部內的放射物質分布是均勻的，這會造成平均劑量足夠，但局部劑量可能會有不足的情況發生。本研究的主要目的為在GATE/GEANT4的框架下發展蒙地卡羅模擬，得到90Y微球體放射栓塞治療以體素為基礎的3D劑量分布。
材料與方法：本研究在影像成像方面，比較GATE模擬與實際在Siemens Symbia T SPECT所測量的99mTc與90Y點射源的空間解析度是否一致。在輻射劑量方面，利用90Y與1公升的水假體來模擬輻射劑量，並評估模擬與理論值之間的差異。最後以實際收集的21位肝腫瘤患者之影像資料為素材，模擬90Y微球體對組織造成的輻射劑量，並用下列三種劑量限制估算最大可注射活度 (maximal-injectable activity，MIA)：1. 現行分區模型平均劑量閾值 (PMmean模型)、2. 蒙地卡羅模擬平均劑量閾值 (MCmean模型)、3. 蒙地卡羅模擬劑量體積值方圖閾值 (MCDVH模型)。
結果：在影像成像方面，結果顯示模擬與實際的99mTc與90Y點射源的空間解析度具有一致性。在輻射劑量方面，結果發現所模擬的劑量與理論值相差約1.1%。在21位肝腫瘤患者的劑量估算方面，結果顯示整體趨勢PMmean 最保守，MCmean居中，MCDVH可容許最高的注射活度，僅一例例外。若不計唯一例外的案例，MCmean相較PMmean，MIA增加的幅度最少為2.86%，最多為7.69%。MCDVH相較PMmean，MIA增加的幅度最少為11.24%，最多為281.68%。PMmean與MCmean相關性極佳(ICC值為0.99，P值為<0.05)；PMmean與MCDVH相關性差(ICC值為0.30，P值為0.086)；PMmean與MCDVH相關性差(ICC值為0.33，P值為0.064)。
結論：本研究顯示GEANT4/GATE執行的蒙地卡羅模擬，應用於90Y微球體放射栓塞治療的輻射劑量評估是有相當的可行性。然而輻射劑量在90Y微球體放射栓塞治療應用於肝腫瘤治療的臨床意義，需要累積更多實證。

關鍵字

90Y微球體放射栓塞治療 ； 肝腫瘤 ； 蒙地卡羅模擬

並列摘要

Background and purpose: Selective internal radiotherapy with Yttrium-90 microsphere (90Y SIRT) is an emerging treatment for hepatic tumor. It can induce tumor necrosis not only by vascular occlusion related ischemia but also by the radiation of 90Y. Nowadays, the commonly used models to calculate the appropriate 90Y microsphere activity assume homogeneous activity distributions within organs at risk; however. it might lead to undertreatment in some regions of the tumor although the average radiation dose is enough. Therefore, the main purpose of the study is to develop a workflow for voxel-based radiation dose prediction of 90Y SIRT with Monte Carlo simulation by using GEANT4/GATE.
Materials and methods: First, we performed Monte Carlo simulation and experiments on a SPECT scanner for 99mTc and 90Y point sources to understand the agreement of spatial resolution between them. Second, we performed Monte Carlo to simulate the absorbed dose of 90Y within 1-liter water phantom and compared the results with theoretical value. Third, we performed Monte Carlo simulation on 21 enrolled patients with hepatic tumor, and established three methods to calculate the maximum-injectable activity (MIA): 1. conventional partition model with Dmean tolerance criteria (PMmean); 2. The model based on the dose distribution results from Monte Carlo simulation with Dmean tolerance (MCmean); and 3. the model based on the dose distribution results from Monte Carlo simulation with dose-volume histograms tolerance (MCDVH).
Results: In spatial resolution, the results showed good agreement of spatial resolution between simulation and experiments for both 99mTc and 90Y point sources. In radiation dose, the results demonstrated that the difference of radiation dose was about 1.1% between simulation and theorical value. For 20 of the 21 enrolled cases, the MIAs suggested by MCmean were greater than which by PMmean (about 2.86% to 7.69% increase), and the MIAs recommended by MCDVH were even higher than which by PMmean (about 11.24% to 281.68% increase). There was an excellent correlation between MIAs suggested by PMmean and MCmean (ICC value = 0.99, P <0.05); however, there were poor correlations between PMmean and MCDVH (ICC value = 0.30, P = 0.086) and between MCmean and MCDVH (ICC value = 0.33, P = 0.064).
Conclusion: We conclude that Monte Carlo simulation by using GEANT4/GATE is feasible in voxel-based radiation dose prediction for 90Y SIRT. However, it needs more evaluation of the clinical impact of radiation dosimetry on 90Y SIRT for hepatic tumor.

並列關鍵字

Selective internal radiotherapy with Yttrium-90 microsphere ； hepatic tumor ； Monte Carlo simulation

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