| Summary: | 碩士 === 中臺科技大學 === 放射科學研究所 === 98 === 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.
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