Leung P M, Sontag M R, Maharaj H, Chenery S
Med Phys. 1976 May-Jun;3(3):169-72. doi: 10.1118/1.594220.
The dose in the build-up region for four different Cobalt-60 therapy units was measured. It was found that, for large collimator openings and relatively short SSDs, a new dose peak occurs at a depth very much smaller than 0.5 cm. The dose at this peak is a function of collimator openings and SSDs and, in some extreme case, could be 15% or more higher than the dose at the conventional peak dose of 0.5 cm. The new dose peak is probably due to electrons produced in the source capsule and the part of the collimator close to the source; it can be almost eliminated by a filter placed just below the collimator.
测量了四个不同钴 - 60治疗单元在积累区域的剂量。结果发现，对于大准直器开口和相对较短的源皮距（SSD），在深度远小于0.5厘米处会出现一个新的剂量峰值。该峰值处的剂量是准直器开口和源皮距的函数，在某些极端情况下，可能比传统峰值剂量（0.5厘米处）高15%或更多。新的剂量峰值可能是由于源容器和靠近源的准直器部分产生的电子所致；通过在准直器下方放置一个滤过器，几乎可以消除该峰值。
