Williamson J F, Khan F M, Sharma S C, Fullerton G D
Radiology. 1982 Feb;142(2):511-5. doi: 10.1148/radiology.142.2.7054845.
Two types of routine geometry calibrators, the nuclear medicine dose calibrator and a Lucite jig holding a 30-ml external beam ion chamber with the source in a rigid geometry, were compared with open-air measurements for 137Cs, 192Ir, and 226Ra brachytherapy sources. The proximity of scattering surfaces in the second apparatus resulted in significant distortion of the buildup effect and deviation from the inverse square law (5% to 15%). For the dose calibrator, the response/Roentgen was found to be dependent not only on source energy, but on source capsule thickness as well. Approximately one half of the observed variation (27%) in calibration factors was accounted for by differences in filtration among sources. A mathematical logarithm that corrects for these geometric and filtration effects is presented. In addition, the activity assay procedure provided by the manufacturer of the dose calibrator is shown to be unsuitable for brachytherapy sources. Steps to overcome these problems are discussed.
将两种常规几何校准器，即核医学剂量校准器和一个装有30毫升外照射离子室的有机玻璃夹具（源处于刚性几何结构中），与针对137Cs、192Ir和226Ra近距离治疗源的露天测量结果进行了比较。第二种仪器中散射面的接近导致积累效应出现显著畸变，并偏离平方反比定律（5%至15%）。对于剂量校准器，发现响应/伦琴不仅取决于源能量，还取决于源胶囊厚度。在校准因子中观察到的约一半变化（27%）可由源之间过滤差异来解释。提出了一个校正这些几何和过滤效应的数学对数。此外，剂量校准器制造商提供的活度测定程序被证明不适用于近距离治疗源。讨论了克服这些问题的步骤。
