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J Korean Soc Ther Radiol > Volume 9(2); 1991 > Article
Journal of the Korean Society for Therapeutic Radiology 1991;9(2): 333-336.
The Physical Penumbra of the 6MV X-ray
Moon June Cho, Wee Saing Kang
1Department of Radiology, College of Medicine and Cancer Research Institute, Chungnam National University, Taejon, Korea.
2Department of Therapeutic Radiology, College of Medicine, Seoul National University, Seoul, Korea.
High energy photon beam margin due to a less side scatter and the other things. But there still remains a penumbra where the dose changes rapidly in the region near the edge of a radiation beam, although it is short in width. It is suggested that the width of the penumbra depends on the source size, distance from source to diaphragm, source to skin distance, and depth in tissue. However, it is also supposed that the other factors influence the penumbra width. In this paper, we investigate changes of the physical penumbra widths according to various field sizes and depths, by using the three dimensional dosimetry system. As a result, we found that as field size and depth increase, the physical penumbra width also increases.
Key Words: Physical penumbra, 6MV X-ray, Field size, Depth
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