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J Korean Soc Ther Radiol > Volume 7(2); 1989 > Article
Journal of the Korean Society for Therapeutic Radiology 1989;7(2): 293-298.
Study on the Reduction of Electron Contamination with A Cobalt-60 Gamma Ray
Tae Kyu Kim, Ha Chung Chun, Myung Za Lee
Department of Radiation Therapy, Hanyang University Hospital, Seoul, Korea.
ABSTRACT
Electron contamination due to the interaction between radiation beam and material was analyzed for the factors such as source-skin distance(SSD), field size, tray characteristics and position of filter, which can affect the surface dose in Cobalt teletherapy. Surface dose in open beam was more influenced by SSD with increasing field size. Relative surface charge(RSC) increased with the use of tray(solid, circular hole, slotted), compared with open beam, which is thought to be doe to increased electron contamination of the tray. To reduce the surface dose, 0.4mm thick Lipowitz metal filter was used. Compared with open beam, RSC decreased by 8.8%, 11.3%, 13.3%, 16.6%, 19.3% and 21.7% for the field size of 5x5, 10x10, 15x15, 20x20, 25x25 and 30x30 cm2, respectively. On the contrary, use of Lipowitz metal filter increased RSC at 60cm or less SSD. Suface dose was effectively reduced with Lpowitz metal filter placed right below solid tray in Cobalt teletherapy.
Key Words: Cobalt-60 gamma ray, Electron contamination, Relative surface charge
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