Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran.
Jpn J Radiol. 2012 Feb;30(2):162-6. doi: 10.1007/s11604-011-0030-y. Epub 2011 Dec 17.
Different types of concretes are used for bunker construction for radiation therapy. As neutron production occurs in high-energy photon beams, the purpose of this study was to investigate the effect of different concretes on photoneutron doses at an isocenter and maze entrance door.
The 18-MV photon beam of a Varian 2100 C/D linear accelerator and a radiation therapy bunker were simulated using the MCNPX Monte Carlo code. Different commercially available concretes were used in photoneutron calculations for the simulated bunker.
Higher neutron doses of the water phantom were seen for barytes and galena concretes, while there was no significant (less than 1%) difference between the neutron dose of the phantom for all other concretes. Also, the neutron fluence at the inner and outer maze entrance varied up to 36% depending on the concretes' atomic compositions.
It can be concluded that application of high-density concretes in order to use limited space or for other purposes may cause higher neutron doses in the maze entrance door and consequently may impose stricter requirements for neutron shielding of maze entrance doors.
用于放射治疗的辐射防护室有不同类型的混凝土。由于在高能光子束中会产生中子，因此本研究的目的是研究不同类型的混凝土对等中心和迷宫入口处的光致中子剂量的影响。
使用 MCNPX 蒙特卡罗代码模拟瓦里安 2100 C/D 线性加速器的 18-MV 光子束和放射治疗防护室。在模拟的防护室中，对不同的市售混凝土进行了光致中子计算。
水模体的中子剂量对于重晶石和方铅矿混凝土更高，而对于所有其他混凝土，其模体的中子剂量没有明显差异（小于 1%）。此外，内迷宫和外迷宫入口处的中子通量取决于混凝土的原子组成，变化幅度高达 36%。
可以得出结论，为了利用有限的空间或出于其他目的而应用高密度混凝土可能会导致迷宫入口处的中子剂量更高，从而对迷宫入口处的中子屏蔽提出更严格的要求。
