電腦斷層攝影應用於n-NIPAM凝膠劑量計特性之檢測

Investigation of the characteristics of an n-NIPAM gel dosimeter with computed tomography

史天宇(Tain-yu Shih)

指導教授 ： 吳杰

中臺科技大學/健康科學院/放射科學研究所/碩士(2011年)

摘要

目前的放射治療已朝向複雜的三度空間治療計畫發展，凝膠劑量計可量測三維劑量分佈以確保授與劑量的正確性，然而一般廣泛使用的丙烯醯胺 ( acrylamide ) 單體具有神經毒性，不易於臨床的推廣與應用。本研究以異丙基丙烯醯胺 ( N-isopropyl-acrylamide ) 為單體，製作改良型NIPAM凝膠劑量計(n-NIPAM)，並利用電腦斷層掃描儀評估此劑量計之特性。n-NIPAM採用凝膠 ( 6% )、單體 ( 5% ) 及交聯劑 ( 2.5% )，並加入5 mM THPC 以排除氧氣，我們利用直線加速器給予2 Gy 至15 Gy 的吸收劑量進行研究。在時間穩定性、能量依存性、劑量率依存性、和空間解析度均有良好的結果，聚合反應過程中不會受到溫度的影響。n-NIPAM的平均敏感度為0.552 HU/Gy、線性度與傳統NIPAM相當 ( R2=0.998 ) 。時間穩定度n-NIPAM於照射後48小時可達穩定狀態，不同能量的劑量反應敏感度並無顯著的差異，在劑量率方面，敏感度差異最大可達33%，表示其具有輕微的劑量率依存性。我們認為n-NIPAM具有高的線性度與敏感度，因可廣泛的應用於臨床，以提升放射治療劑量驗證的準確性。

關鍵字

NIPAM ； 電腦斷層掃描儀 ； 單體

並列摘要

Nowadays, radiotherapy is aiming at giving complex 3-D dose distribution. Gel dosimeter can measure the 3-D dose output and can be applicable in clinical usage. In this study, we developed an n-NIPAM gel dosimeter based on N-isopropylacrylamide monomer and used computed tomography to evaluate the characteristics of n-NIPAM gels. The n-NIPAM was composed of 6% gelatin, 5% monomer, and 2.5% cross-linker and inserted with 5 mM THPC for deoxygenation. The dose responses of 2 to 15 Gy delivered by a linear accelerator were examined. The temporal stability, energy dependency, dose rate dependency, and spatial resolution were evaluated as well. Polymerization process is not affected by temperature. The average sensitivity of n-NIPAM was 0.552 HU/Gy. The linearity ( R2= 0.998 ) was comparable to the conventional NIPAM gel. The temporal instability appeared before 48 hrs post-irradiation. For the dose rate response, the maximum difference of the sensitivity can be up to 33% in the range of clinical practices. We conclude that the n-NIPAM has high linearity and high sensitivity. Although the energy dependency is minor, the dose rate dependency slightly exists. It could be used in clinical radiotherapy to increase the correctness of dose delivery.

並列關鍵字

monomer ； computed tomography ； NIPAM

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