Saw C B, Pawlicki T, Korb L J, Wu A
Division of Radiation Oncology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown 26506.
Med Dosim. 1994 Summer;19(2):77-81. doi: 10.1016/0958-3947(94)90075-2.
The effects of extended source-to-surface distance (SSD) on the electron-beam depth dose curves were examined for five electron beam energies ranging from 6 MeV to 20 MeV. The depth dose curves were measured with the water phantom surface set at 100 cm, 110 cm, and 120 cm from the source. Except for the dose in the build-up region, negligible depth dose curve changes due to extended SSD were observed for electron energies less than or equal to 12 MeV. For electron beams greater than 12 MeV, the percent surface dose decreases and, additionally, the depth of maximum dose shifts deeper into the phantom as the SSD increases. Changes in the rapid falloff region of the depth dose curves were apparent only for the higher energy electron beams, in particular 20 MeV. Extended SSD has no observable effect on the tail portion of the depth dose curves. As such, the energies of the electron beams are not changed significantly by increasing the SSD.
研究了源皮距（SSD）延长对6兆电子伏至20兆电子伏范围内五种电子束能量的电子束深度剂量曲线的影响。深度剂量曲线是在水模体表面距离源100厘米、110厘米和120厘米处测量的。对于能量小于或等于12兆电子伏的电子，除了剂量建成区外，观察到由于SSD延长导致的深度剂量曲线变化可忽略不计。对于能量大于12兆电子伏的电子束，随着SSD增加，表面剂量百分比降低，此外，最大剂量深度向模体内更深位置移动。深度剂量曲线的快速下降区域的变化仅在较高能量的电子束（特别是20兆电子伏）中明显。SSD延长对深度剂量曲线的尾部没有可观察到的影响。因此，增加SSD不会显著改变电子束的能量。
