1. Purpose N-isopropylacrylamide (NIPAM) polymer gel dosimeters were employed to verify the dose distribution of clinical intensity modulated radiation therapy (IMRT) treatment planning systems (TPS). Materials and Methods Gel preparation was primarily based on the formula proposed by Senden et al; and 5% NIPAM monomers, 5% gelatin, and 3% BIS were used. Finally, 5 mM of THPC was added to the solution to reduce oxygen content and enhance sensitivity and reproducibility. The gels were irradiated 0, 1, 2, 4, 5, 6, 8, and 10 Gy absorbed doses respectively by a Clinac iX linear accelerator using 6MV X-ray. After polymerization had completed, an X-ray computed tomography HiSpeed scanner was employed to extract the sliced images of the gel. In the present study, five irradiation field IMRT verification plans were created and the irradiation angles were 100°, 135°, 165°, 210°, and 250° respectively. To create these plans, we first extracted the complete treatment plans of brain tumor patients from the Eclipse TM treatment planning system. Cylindrical acrylic phantoms and MatriXX were then selected to simulate the patients. MATLAB was used to analyze the sliced images and the results of the gamma tests (γ-tests) were performed on the treatment plan and the NIPAM gel dosimeters. Results The results were then compared to those produced by the MatriXX. To verify the IMRT dose, γ-tests were performed according to the gamma criteria of 3% and 3 mm. Results indicated that the NIPAM gel achieved a 95.02% pass rate in the coronal section image and a 97.57% pass rate in the axial section image. The pass rate produced by MatriXX was 98.90%. Conclusion The study results confirmed the feasibility of using X-ray CT scanner to verify therapeutic radiation dose if imaging noise is minimized. Ｅ lectron density of computer tomography is used to calculate MU t and CT images are convenient to get from the radiation therapy department clinically. Therefore, using computer tomography as a reading tool of gel dosimeter is taken as the biggest advantage of convenience. Compared to the optical CT and MRI, the scanning time is shorter. Appling polymer gel dosimeters greatly promote convenience and feasibility on the verification of the dose distribution of the patients. Using NIPAM Gel to Verify the Dose Distributions in Intensity- Modulated Radiation Therapy Treatment Plans Hsi-Ya Chao 1,2, Yuk-Wah Tsang 2, Chih-Chia Chang 2, Bor-Tsung Hsieh 1 1 Department of Medical Imaging and Radiological Science, Central Taiwan University of Sciences and Technology, Taiwan (R.O.C.) 2 Department of Radiation Oncology, Ditmanson Medical Foundation Chia-Yi Christian Hospital, Taiwan (R.O.C.) Keywords: gel dosimeter ‧ HiSpeed computed tomography ‧ MatriXX, radiation sensitivity E-mail ： cych06261@gmail.com Figure2. TPS axial section image. The bottom left image is the irradiated-gel CT image without background. Bottom right image displays a gamma test (3%/3 mm) pass rate of 97.57%. The red zone in the bottom image suggests a γ value larger than 1 (failed). Unit = dose %, where 1 = 100% prescribed dose. Figure 3.Top left diagram presents the TPS image obtained using the IMRT software. Image in the top right is the MatriXX measurement diagram. The bottom image displays a pass rate of 98.9% in the high-dose regions of both images. The red zone in the bottom image suggests a γ value larger than 1 (failed). Unit: dose %, where 1 = 100% prescribed dose. Figure 3. Top left diagram presents the TPS image obtained using the IMRT software. Image in the top right is the MatriXX measurement diagram. The bottom image displays a pass rate of 98.9% in the high-dose regions of both images. The red zone in the bottom image suggests a γ value larger than 1 (failed). Unit: dose %, where 1 = 100% prescribed dose. Figure 1. NIPAM gel dosimeter DRCs; radiation sensitivity values was 1Gy 0.593±0.030 CTN/Gy R2=0.9989 for 1, 2, 4, 6, 8, and 10 Gy, respectively. Figure 1. NIPAM gel dosimeter DRCs; radiation sensitivity values was 1Gy 0.593±0.030 CTN/Gy R2=0.9989 for 1, 2, 4, 6, 8, and 10 Gy, respectively.