磁振造影技備應用於新型含氧NIPAM凝膠劑量計之特性探討

Analysis of tbe Dosimetric Characteristics in Novel Normoxie NlPAM Gel by Magnetic Resonance Imaging

李博元(Po-Yuan Lee) ； 謝栢滄(Bor-Tsung Hsieh) ； 李覃(Tain Lee) ； 楊石崇(Shih-Chung Yang) ； 陳子勇(Tzu-Yung Chen) ； 謝玲玲(Ling-Ling Hsieh)

《中華放射線技術學雜誌》 36卷3期 (2012/09) Pp. 157-164

https://doi.org/10.30045/CJRT.201209.0007

摘要

聚合物凝膠劑量計主要是依靠輻射作用使水分子分解產生自由基，單體分子和自由基不斷結合形成的高分子鏈狀化合物與明膠基質共構成三維網狀結構。在形成的高分子化合物中，質子遲豫特性的改變程度與其吸收的輻射劑量關係密切，從而使輻射劑量訊息被保存。本研究以磁振造影儀（MR1）為凝膠劑量計讀出工具，並以低毒性NIPAM（N-isopropylacrylamide）單體所製成的凝膠劑量計為研究對象，探討MRI掃描參數與NIPAM凝膠劑量計之關係，包括凝膠的遲豫率R（下標 2）（=1/T2）與輻射劑量關係、劑量解析度（DAP）、劑量準確度、再現性及3D劑量準確度評估等。研究結果顯示0-15Gy輻射劑量照射下，R（下標 2）與輻射劑量線性關係可達0.9966回音間隔（Echo spacing）50ms時，靈敏度最大值為0.1434S^(-1) Gy^(-l)。NIPAM凝膠劑量計在95%信賴區間，其劑量解析度可達0.018 Gy。另外，輻射照射後置放約2個月，線性度及靈敏度變化不大，證明NTPAM凝膠劑量計具有高度穩定性。臨床放射治療驗證結果顯示，NIPAM凝膠劑量計中心照射區劑量分佈量測值與模擬治療計劃系統（TPS）差異度僅小於3%以內，可見得NIPAM凝膠劑量計具有好的3D劑量分佈並適合做為臨床劑量驗證工具。

關鍵字

磁振造影技術 ； 含氧聚合物凝膠劑量計 ； NIPAM

並列摘要

Polymer gel dosimeters according to radiation induced a number of free radicals from water hydrolysis to initiate a polymerization reaction of the monomers, which is directly related to the absorbed dose. The process results in the change of the chemical and physical properties of the irradiated gel such as MR relaxation rates. In this work, a new normoxic polymer gel based on a less toxic monomer, N-isopropyl acrylamide (NIPAM) was study with MRl readout method. The characteristics of NIPAM gel (i.e., relaxivity rate R (subscript 2) (=I/T2) of MRI, sensitivity, linearity, dose resolution (DAP), temporal stability and dose characteristics of therapeutic radiation) were evaluated. The results showed that R(subscript 2) and the degree of polymerization were proportional to the absorbed dose in the range of 0~15Gy, and its sensitivity was found to be 0.1434s^(-1) Gy^(-1) (r^(2)=O.9966) with echo spacing of 50ms. This new polymer gel results in dose resolution (DA^(95%)) ~0.018 Gy. In addition, the results showed that this polymer gel dosimeters response remains stable for up to two months after irradiation. NIPAM gel dosimeter was applied to an IMRT, the doses measured in the 100% dose variance of the therapeutic plan low than 3% for the axial planes. Therefore, NIPAM gel dosimeter is expected to be an effective tool for 3-dimensional QA suitable for therapeutic systems.

並列關鍵字

MRI ； Normoxic polymer gel ； NlPAM