Butson Martin J, Yu Peter K N, Cheung Tsang
Department of Physics and Materials Science, City University of Hong Kong, Kowloon Tong, Hong Kong, People's Republic of China.
Phys Med Biol. 2003 Sep 7;48(17):N247-52. doi: 10.1088/0031-9155/48/17/402.
Multi-leaf penumbral doses have been investigated for 6 MV x-rays and a Varian millennium multi-leaf collimator (MLC) using Gafchromic MD-55-2, radiochromic film and X-omat V radiographic film. An advantage of Gafchromic film for multi-leaf penumbral dose measurement is the relatively low energy dependence of the film. A comparison of penumbral dose measurements has also ascertained the effects of energy response on radiographic film in this region. Similar 80%/20% penumbral doses have been measured with both types of films. Thus there is a relatively low energy effect on penumbral dose measurements in film dosimetry. The 80%/20% dose penumbral distances for rounded leaf end multi-leafs for a 10 cm x 10 cm field at Dmax were found to be 4.6 mm and 4.3 mm for radiochromic and radiographic film respectively. This is compared to 2.6 mm and 2.6 mm for the leaf edge penumbra. Radiochromic film also measured leaf end/interleaf leakage doses in the penumbral region, which was shown to produce approximately 4% of maximum dose wave across the penumbral region with maximum doses delivered at the MLC leaf interfaces.
已使用Gafchromic MD - 55 - 2型放射变色胶片、X - omat V射线胶片，针对6兆伏X射线和瓦里安千年多叶准直器（MLC）研究了多叶半影剂量。Gafchromic胶片用于多叶半影剂量测量的一个优点是胶片的能量依赖性相对较低。半影剂量测量的比较也确定了该区域射线胶片上能量响应的影响。两种类型的胶片都测量到了相似的80%/20%半影剂量。因此，在胶片剂量测定中，半影剂量测量的能量效应相对较低。对于10厘米×10厘米射野在最大剂量深度（Dmax）处，圆形叶端多叶准直器的80%/20%剂量半影距离，放射变色胶片和射线胶片分别为4.6毫米和4.3毫米。相比之下，叶边缘半影为2.6毫米和2.6毫米。放射变色胶片还测量了半影区域中叶端/叶间泄漏剂量，结果显示在半影区域产生的剂量约为最大剂量的4%，最大剂量出现在MLC叶界面处。
