Dose Calibration in Mammography

• Main Authors: Hsu, Ju-Lin, 徐儒琳
• Other Authors: Chen, Wei-Li
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/58876397252369527199

碩士 === 國立陽明大學 === 放射醫學科學研究所 === 92 === The aim of this study is to establish low energy beam qualities in mammographic energy ranges. According to specifications set by NIST(National Institute of Standard and Technology), five beam qualities were established by using an X-ray machine with Molybdenum anode and Molybdenum filters of different thicknesses under operation voltages of 23 kV, 25 kV, 28 kV, 30 kV, and 35 kV. The half value layers of the five beam qualities are 0.282 mm Al, 0.302 mm Al, 0.342 mm Al, 0.358mm Al, and 0.389 mm Al. We measured the spectrums and calculated effective energies for the five beam qualities. We established this dose calibration system of Molybdenum anode and used the RC-6M flat cavity ion chamber as the standard because it can meet calibration needs in our nation. Internationally, many laboratories followed BIPM’s standard to set low energy calibration systems for comparisons. The BIPM system adopts tungsten as their anode material. We compared these two systems of different anodes. Besides measuring half value layers and spectrums, we calibrated the same flat cavity ion chamber under both systems. The results showed that the difference of the calibration factors between the two systems is about 6.2 %. The third part of this study was to calculate mean glandular dose conversion factors by Monte Carlo simulations with spectrums data. The simulated conversion factors were a little different from that developed by Dance. It might be because of the difference of shapes of entrance x ray, flat cavity ion chambers, and radiation fields. For our program design, it still has room for further improvement.