| Summary: | 碩士 === 中臺科技大學 === 醫學影像暨放射科學系暨研究所 === 105 === In this research, the measurement of small field absolute dose via Pin-Point ion chamber with different KQ to correct TG-51 protocol compared with clinical used ion chamber, Farmer and Semiflex ion chamber. We used PTW-31014 Pin-Point ion chamber and corrected TG-51 protocol published in Medical Physics at 2011 by P. Francescon to measure the absolute dose of 6 MV Elekta Synergy linear accelerator in 3x3 cm2 to 0.5x0.5 cm2 fields size as the standard dose in this research. We acquire the percentage error and small field dose conversion factor for PTW-30013 Farmer ion chamber, PTW-31010 Semiflex ion chamber of relative dose.
The percentage error of absolute dose measured via Farmer ion chamber for 0.5x0.5 cm2 is 82.08% and the SFDCF is 5.58, also for 3x3 cm2 the percentage error is 9.93% and the SFDCF is 1.11. The percentage error of the two fields size in Semiflex ion chamber are 39.26% and 0.24%, and the SFDCF are 1.65 and 1.00. The percentage error in Pin-Point ion chamber of relative dose are 9.43% and 0.01% and the SFDCF are 1.10 and 1.00. The fields size in the three ion chamber are bigger, the percentage error and SFDCF of measurement are smaller. The percentage error of measurement in Pin-Point ion chamber is the smallest of the three ion chamber, and Farmer is the largest. Among them, the SFDCF of Pin-point ion chamber and Semiflex ion chamber all are equal 1.00. We used the small fields size parameter from Monte Carlo method to calculate the absolute dose of small fields size in read clinical situation. The SFDCF obtain from different small fields size could be used to correct the error of absolute dose measured via these three ion chamber.
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