Radiometric surveys in radiotherapy bunkers have been carried out in Brazil for many years, both by the same radiotherapy facility for verification of shielding as by the regulatory agency for licensing and control purposes. In recent years, the Intensity Modulated Radiation Therapy (IMRT) technique has been gradually incorporated into many facilities. Therefore, it has been necessary to consider the increased leakage component that has an important impact on the secondary walls. For that, a radiometric survey method has been used that considers an increased ‘time of beam—on’ for the secondary walls. In this work we discuss two methods of doing this: the first considers that this ‘time of beam—on’ affects the sum of the two components, leakage and scattered. In another method it is considered that only the leakage component is affected by this extended ‘time of beam—on’. We compare the methods and show that for secondary walls with U = 1 the first method overestimates dose rates by important percentages and for secondary walls with U < 1 it can both overestimate or underestimate the dose rates, depending on the parameters of the project. An optimized procedure is proposed, according to the use factor (U) of the secondary wall to be measured.

中文翻译：

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放射治疗掩体辐射测量方法探讨

巴西已对放射治疗掩体进行辐射测量多年，既由同一放射治疗设施进行屏蔽验证，也由监管机构进行许可和控制目的。近年来，调强放射治疗（IMRT）技术已逐渐融入许多设施中。因此，有必要考虑对次墙有重要影响的增加的渗漏分量。为此，采用了辐射测量方法，考虑增加次墙的“光束开启时间”。在这项工作中，我们讨论了两种实现此目的的方法：第一种方法认为“光束开启时间”会影响泄漏和散射这两个分量的总和。在另一种方法中，认为只有泄漏分量受到这种延长的“波束开启时间”的影响。我们比较了这些方法并表明对于次生墙来说U= 1 第一种方法高估了重要百分比的剂量率，并且对于具有U< 1 它可能会高估或低估剂量率，具体取决于项目的参数。根据使用系数（U）要测量的次生壁。