Zwicker R D, Wu A, Curran B H, Sternick E S
Med Phys. 1984 Jul-Aug;11(4):534-8. doi: 10.1118/1.595523.
The presence of the Lucite blocking tray in a 45-MV betatron beam leads to a considerable loss in the skin-sparing properties of this unit. Measurements conducted with a parallel-plate chamber show that the surface dose is approximately doubled (up to 58% of the maximum absorbed dose) and the depth of maximum dose is reduced by as much as 1.5 cm by the Lucite. These results suggest that separate dosimetry data should be kept for blocked and unblocked fields. The penetration of the electron contamination to the open field depth of maximum dose can lead to erroneous results if attenuation measurements are made at that depth. Studies of the effect of the lead sheet and leaded acrylic on the surface dose showed that under normal circumstances the presence of high-Z materials increases the surface dose, hence these materials cannot in general be used as electron filters on very high energy x-ray units. A Luciteless blocking tray with universal triangular corner blocks has been designed for use in special cases requiring a reduced surface dose.
在45兆伏电子感应加速器射束中使用有机玻璃挡块托盘会导致该装置的皮肤保护特性出现相当大的损失。用平行板电离室进行的测量表明，表面剂量大约增加了一倍（高达最大吸收剂量的58%），并且有机玻璃使最大剂量深度减少了多达1.5厘米。这些结果表明，对于有挡块和无挡块的射野，应保留单独的剂量测定数据。如果在最大剂量的开放射野深度处进行衰减测量，电子污染对该深度的穿透可能会导致错误结果。对铅板和含铅丙烯酸对表面剂量影响的研究表明，在正常情况下，高原子序数材料的存在会增加表面剂量，因此，这些材料通常不能用作超高能X射线装置的电子滤过器。一种带有通用三角形角块的无有机玻璃挡块托盘已被设计用于特殊情况下，以降低表面剂量。
