利用NIPAM凝膠劑應用於磁振造影立體劑量評估之研究

Evaluation of Magnetic Resonance Imaging Scanning for 3-Dimentional NIPAM gel dosimetry

陳奕壇(Mac Yi-Tan Chen)

指導教授 ： 謝玲鈴 ； 江志明

中臺科技大學/健康科學院/放射科學研究所/碩士(2010年)

摘要

聚合凝膠(polymer gel)劑量計具有高輻射靈敏度，因其單元體經由輻射照射會產生聚合和交聯反應，可藉此特性應用於臨床輻射照射劑量驗證之工具。然而大多數凝膠單元體具有毒性及氧氣影響靈敏度高，造成在臨床應用上受限制，近年來研究開發低毒性的單元體為聚合物凝膠劑之主要研究方向，以低毒性的N-isopropylacrylamide (NIPAM)單元體製成的凝膠劑量計並利用三維劑量分布圖可以在臨床腫瘤科進行大體積之三維模擬應用於放射治療之立體定位手術(SRS)、近接治療(Brachytherapy)及全身治療(TBI)劑量評估之依據。
NIPAM凝膠劑以光學電腦斷層掃描儀(OCT)測量在0Gy~5Gy劑量範圍，具有良好劑量關係曲線且無能量依存性現象，但卻很少相關研究探討利用核磁造影(MRI)技術進行凝膠劑量劑量量測及如何改善磁場不均問題所造成影像不佳效果。
本研究主要利用田口實驗設計方法探討MRI 影像最佳條件並利用最佳化條件進行凝膠劑量劑研究。透過新研發的磁振造影專用釓愛玉固定假體 (Capsule phantom)可以同時量測1~17個NIPAM凝膠樣本，經由影像分析取R2值獲得照射凝膠之線性度關係圖。田口實驗設計法找出最佳磁振造影掃描參數為TR=3200ms、TE=28, 224ms、Gph=128ms及切面=3mm，以此參數量測NIPAM劑量計可大幅度提升了線性度為0.9984，並配合量測假體修改為固定的釓愛玉假體更可進一步解決位移和不穩的問題及提高線性度，探討NIPAM凝膠劑之穩定度研究。

關鍵字

NIPAM凝膠劑 ； 聚合凝膠 ； 釓愛玉 ； 單元體 ； 磁振造影 ； 田口實驗設計方法 ； 三維劑量分布

並列摘要

Polymer gel dosimeters have high radiation sensitivity. The monomer component exposed to radiation, radiation induced polymerization and cross-linking reactions. As the result of this polymerization, the gel can be used as a dosimetric verification tool in clinics. But the performance of current polymer gel dosimeters were limited by the high toxicity and oxygen inhibition of the polymerization processes. The new less toxic monomer N-isopropyl acrylamide (NIPAM) was evaluated for use in new dosimeters and used as a dosimeter to obtain 3-D dose distribution. For future using in large volume radiotherapy like stereotactic surgery(SRS), brachytherapy(HDR), and total body irradiation(TBI), as an potential dosimeter. NIPAM gel dosimeter have been studied using Optical Computer Tomography (OCT) and have good linearity for the dose response from 0Gy to 5Gy. The polymer gel also revealed the characteristic of non-energy dependence, but very few studies on magnetic resonance imaging (MRI), through the field inhomogeneity problem effects the image.
In this study, we used the Taguchi method for optimizing MRI parameter of the gel dosimeter. Through the new evaluated Gd jelly phantom for MRI imaging, we could solve the field inhomogeneity, and measured samples could be maximized to 1~17 tubes of NIPAM gel in the new phantom. Analyzing the images could obtain the relaxation rate(R2) for each exposed NIPAM gel, then finding the relation on the linearity of the gel. Through Taguchi method, we have indicated that the optimum combination of levels of the factors providing NIPAM gel with MRI were ：repetition time(TR), 3200ms; echo time(TE), 28 and 224 ms; phase encoding (Gph),128; and slice thickness, 3mm. The result shows a great increase in the linearity of 0.9984. By using the stabilized Gd jelly phantom, we could greatly solve the motion and instability problem, to find better linearity; we could then prove the higher stability of NIPAM gel.
NIPAM gel is able to achieve high linearity with MRI by using the optimized parameters. With the Gd jelly is also able to solve the field inhomogeneity of the high Tesla MRI machines.

並列關鍵字

Gd jelly ； 3D dose profiler ； Polymer gel ； Taguchi method ； NIPAM dosimeter ； Magnetic Resonance imaging ； monomer

參考文獻

Po-Hsiu Lee(李博修), The study of polymer gel dosimeter:the optimal composition of n-NIPAM gel, Central Taiwan University of Science and Technology Master Thesis, National Digital Libraryof Thesis and Dissertations in TAIWAN(NDLTD),(2007),095CTC05605009.

Avanish Kumar Dubey and Vinod Yadava, Multi-objective optimization of Nd: YAG laser cutting of nickel-based superalloy sheet using orthogonal array with principle component analysis, Optic and Lasers in Engineering (2008), 46, 124-132.

Bankamp A. , Schad L.R., Comparison of TSE, TGSE, and CPMG measurement techniques for MR polymer gel dosimetry,Magnetic Resonance Imaging (2003), 21, 929–939.

Baustert I. C., Oldham M., Smith T. A. D., Hayes C., Webb S. and M. O. Leach, Optimized MR imaging for polyacrylamide gel dosimetry, Phys. Med. Biol. (2000),45, 847-858.

Bjorn H. Knutsen, Arne Skretting, Taran P. Hellebust, Dag R. Olsen, Determination of 3D dose distribution from intercavitary brachytherapy of cervical cancer by MRI of irradiated ferrous sulphate gel, Radiotherapy and Oncology (1997), 43, 219-227.