Grant W H, Cundiff J H, Gagnon W F, Hanson W F, Shalek R J
Med Phys. 1977 Jan-Feb;4(1):68-9. doi: 10.1118/1.594294.
In the United States it is common practice to calibrate Cobalt-60 teletherapy machines "in air," despite recommendations by the International Commission on Radiation Units and Measurements (ICRU) and other organizations that calibration be accomplished by measurement at 5-cm depth in a water phantom. A comparison has been made between the results of ionization measurements in air at 80.5-cm distance from the source and in water at 80-cm source-skin distance (SSD) for the determination of absorbed dose at three depth (5, 10, and 15 cm) for each of three fields sizes (6 X 6, 10 X 10, and 20 X 20 cm2), for a total of 42 Cobalt-60 machines. The mean of the ratio, absorbed dose from in-water measurements to absorbed dose at the same depth calculated from in-air measurements, ranged frt 5-cm depth for a 20 X 20-cm2 field size. Reasons for the differences are offered, and compliance with ICRU recommendations is suggested.
在美国，校准钴 - 60远距离治疗机“在空气中”进行是常见做法，尽管国际辐射单位与测量委员会（ICRU）和其他组织建议应在水模体中5厘米深度处进行测量来完成校准。已对42台钴 - 60机器进行了比较，比较了在距源80.5厘米处空气中的电离测量结果与源皮距（SSD）为80厘米时水中的电离测量结果，以确定三种射野尺寸（6×6、10×10和20×20平方厘米）中每个射野在三个深度（5、10和15厘米）处的吸收剂量。水中测量的吸收剂量与根据空气中测量结果计算出的相同深度处吸收剂量之比的平均值，对于20×20平方厘米的射野尺寸，在5厘米深度处范围为……给出了差异的原因，并建议遵守ICRU的建议。 （原文“ranged frt 5-cm depth for a 20 X 20-cm2 field size”这里“frt”有误，推测可能是“from”，按此理解翻译）
