Instituto de Radioproteção e Dosimetria.
J Appl Clin Med Phys. 2014 Nov 8;15(6):5035. doi: 10.1120/jacmp.v15i6.5035.
The necessity to build or adapt radiotherapy rooms in reduced areas leads to the search for unconventional solutions for shielding projects. In most cases, adding metals to the primary barriers is the best alternative to shield rooms properly. However, when photons with energies equal or higher than 10 MV interact with high atomic number nuclei, neutrons are ejected and may result in a radioprotec- tion problem for both outside and inside the room. Currently, the most widely used mathematical model to estimate the neutron dose equivalents, beyond the barriers composed by concrete and metal, is applicable only in very specific conditions. Moreover, a validation work of this model had not yet been performed. In this work, the Monte Carlo code MCNPX was used to check the validity of the aforementioned mathematical model for cases of primary barriers containing steel or lead sheets, considering the existence of linear accelerators of 15 or 18 MV. The results of the study showed that over 80% of the values obtained by computational simulations revealed deviations above a factor of 2, when compared to the analytical formula. This led to the conclusion that the McGinley method cannot be considered an adequate mathematical model to describe the mentioned physical phenomenon.
在较小的区域内建造或改造放射治疗室的必要性促使人们寻求非常规的屏蔽方案。在大多数情况下，向初级屏蔽添加金属是对屏蔽室进行适当屏蔽的最佳选择。然而，当能量等于或高于 10MV 的光子与高原子序数的原子核相互作用时，会逐出中子，这可能会导致房间内外的辐射防护问题。目前，最广泛用于估算混凝土和金属构成的屏蔽体之外的中子剂量当量的数学模型，仅适用于非常特定的条件。此外，尚未对该模型进行验证工作。在这项工作中，使用蒙特卡罗代码 MCNPX 检查了包含钢或铅板的初级屏蔽的情况下，上述数学模型的有效性，同时考虑了 15 或 18MV 的线性加速器的存在。研究结果表明，与分析公式相比，计算模拟得出的超过 80%的值存在 2 倍以上的偏差。这得出的结论是，McGinley 方法不能被视为描述所述物理现象的合适数学模型。
