Three-dimensional dose verification for intensity-modulated radiation therapy in the multi-fields treatment planning system using optical computed tomography scans of NIPAM gel dosimeter

• Main Authors: Wan-Ting Hsu, 許琬婷
• Other Authors: 姚俊旭
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/sy35t3

碩士 === 中國醫藥大學 === 臨床醫學研究所碩士班 === 100 === The study assessed the dosimetric characteristics of the N-isopropylacrylamide (NIPAM) polymer gel dosimeter used in intensity-modulated radiation therapy (IMRT). Experiments on the intra-dosimeter consistency and reproducibility of NIPAM polymer gels were performed. The NIPAM polymer gel used in the study was composed of 5% gelatin, 5% NIPAM (97%, Sigma-Aldrich), 3% Bis (N,N''-methylene bisacrylamide), and 5 mM Tetrakis (hydroxymethyl) phosphonium chloride. A cylindrical NIPAM gel phantom measuring 10 cm (diameter) by 10 cm (height) by 3 mm (thickness) was irradiated using the four-field box and six-field box treatment plans with a field size of 3 cm?e3 cm. The gel phantom was irradiated with prescribed dose 10 Gy through IMRT (SIEMENS ONCOR Impression, 6MV, 250 cGy/min). A fast, optical computed tomography scanner(MGS OCTOPUSTM 10X optical CT scanner, wavelength 785 nm, 30 mW) was used to scan the gel phantoms. The results showed that the dose profiles were consistent at various depths and at various post-irradiation times. The deviation was less than 1.83% for post-irradiation time 24h, 48h, 72h and 96h. The isodose lines agreed quantitatively with the calculated TPS dose and the measured NIPAM polymer gel dose within the 30 to 90 percentage isodose lines. In addition, the quantitative evaluation was conducted using Gamma index between treatment plans and measured data from OCT. The Gamma pass rates were greater than 95% and 99% for four-field box and six-field box irradiation respectively, using 5% dose difference and 5 mm distance-to-agreement criteria. The results indicated that the NIPAM polymer gel dosimeter in conjunction with OCT was stable and reliable in dose verification. Therefore, the NIPAM polymer gel dosimeter indicated a potential dose verification tool for intensity-modulated radiation therapy. Keywords: Three-dimensional gel dosimetry, NIPAM polymer gel, Optical computed tomography, Intensity modulated radiation therapy, Gamma index.