The precision and accuracy of dose measurement by Fricke MRI gel dosimeter

• Main Authors: Jyh-Der Leu, 呂志得
• Other Authors: Woei-Chyn Chu
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/22454740159974841007

碩士 === 國立陽明大學 === 醫學工程研究所 === 96 === Purpose: Recent advances in radiation treatment technologies, such as intensity modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT), had provided more delicate and accurate treatment protocol, therefore how to verify the 3-dimensional dose becomes a significant issue. Gel dosimetry is one of the most promising tools to fill the 3D verification void in modern radiation therapy practice. This research is to define the precision and accuracy of dose measurement in Fricke MRI gel dosimeter and evaluate the diffusion of ferrous ion that affects the precision and accuracy of gel dosimeter by gamma evaluation. Methods & materials:The Fricke-Gel was manufactured and introduced into the phantom. Then the phantom was irradiated with different protocol, planned by radiotherapeutic planning system, and those protocols composed of different dosage. The MRI imaging data of phantom were got before and after irradiation and were related to radiation dose by image-intensity method. In the mean time the dose of irradiation was detected by film-based dosimetry and ionization chamber. These data were investigated and compared for the presicion and accuracy of gel and the effect of dose gradient on diffusion. For diffusion study the images over different time after irradiation were compared by gamma evaluation. Results: The precision of Fricke gel, film-based dosimeter and ion-chamber is 3.12% ,1.23 % and 0.62% .and the accuracy of Fricke gel is 8 %. As comparison to the data detected from the three methods by Bland-Altman plot there were significant difference under the does of 3Gy . The series images after irradiation were compared by gamma evaluation and the time after irradiation , that gamma value is more than one, with the dose gradient under 0.5 Gy/mm, between 0.5 &1 Gy/mm, and over 2.79Gy/mm is 120minutes, 90minutes, and 45minutes respectively. Discussion: As the precision of accuracy is much low than ionization chamber, we can use the Fricke-MRI-gel for qualitive evaluation of radiotherapeutic plan. While the dose distribution of radiotherapeutic plan was investigated by Fricke-MRI-gel, the gel should be irradiated with morethan 5 Gy and san by MRI less than 45 minutes after irradiation.