| Summary: | 碩士 === 元培科學技術學院 === 影像醫學研究所 === 96 === Abstract
Gafchromic EBT film is the new generation high-sensitive Radiochromic film, and has been used to measure the dose of IMRT. The purpose of this study is to investigate the characteristics of Gafchromic EBT film scanning with different light sources, and the verification and measuring dose distributions of IMRT.
The film was placed in solid water phantom, and radiated with 6 MV photon beam ranged from 50 cGy to 800 cGy. After radiation, the film was scanned with platform color scanner, and the scanned image was separated into red, green, and blue images. The characteristics of film of were analyzed. To investigate the doses in field abutment region of head and neck IMRT, a Gafchromic EBT film was placed on the surface of RANDO phantom, and radiated with an IMRT plan. The measurements were repeated 10 times with different pieces of Gafchromic EBT film. A dose analyzer tool, DoseLab 4.00 was used to further analysis of dose distribution of irradiated films.
The results showed that the sequence of sensitivity of the Gafchromic EBT film was red≧green>blue when scanned with different light sources. The response of Gafchromic EBT film tended to saturate with an irradiated dose over 400 cGy when scanned with red light channel. However, it tended to saturate in higher dose level when scanned with blue light channel. It was indicated that Gafchromic EBT film with blue-light-scan is suitable for high dose measurement compared with red-light-scan. For leakage dose measurement of leaf-junction, a significant dose was observed in the leaf-end when MLC was applied to spinal-cord-blocking. However, the leakage dose of leaf-junction was not observed in the IMRT plan. For the junction dose evaluations in head and neck region, the dose variations were minimized after 10 measurements. The surface dose of head region (irradiated with intensity modulate fields) is higher than that of neck region (irradiated with single filed).
The dosimetric system of Gafchromic EBT film with DoseLab 4.00 dose analyzer tool is easy to handle and provides a two-dimensional dose map with good spatial resolution, making it is suitable to measure the dose distributions in radiotherapy.
Keywords: Gafchromic EBT film, IMRT, multileaf collimator
dose verification, surface dose
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