螺旋断层加速器自屏蔽结构对机房屏蔽防护厚度的影响

Impact of tomotherapy beam block on the room shielding thickness

目的探讨新型放射治疗设备螺旋断层加速器机房的屏蔽计算方法以及该型加速器自屏蔽结构对机房屏蔽防护厚度的影响，为螺旋断层加速器机房的屏蔽防护设计提供依据。方法根据国家相关标准要求，结合机房几何结构，分别计算无自屏蔽存在情况下屏蔽主射线、散射线和漏射线所需的屏蔽厚度；根据螺旋断层加速器自屏蔽特点以及其辐射场特性，计算自屏蔽存在情况下机房辐射防护屏蔽厚度。结果有自屏蔽结构的螺旋断层加速器机房防护屏蔽体的厚度与没有自屏蔽结构相比，其计算结果差异有统计学意义（t=3．576，P〈0．05）；主射束区包括南墙、北墙、顶棚和地板，自屏蔽结构可以分别减少约95．59％、63．63％、80．73％和51．30％的屏蔽厚度。结论螺旋断层加速器自屏蔽结构可显著减少其机房主射束区所需的辐射防护屏蔽厚度。对有自屏蔽结构的加速器机房的屏蔽厚度，应该根据其辐射场数据进行计算，也可将无自屏蔽情况下主射束区的计算结果减去自屏蔽等效屏蔽材料厚度来估算。

Objective To study the calculation of the room shielding thickness of tomotherapy accelerator, a new type of radiotherapy facility, especially the impact of the beam block on the shielding design. Methods According to the relevant standards, combined with the room geometry, the shielding thickness was calculated without the presence of the beam block, considering the primary beam, the scattered beam and leakage. Meanwhile, the shielding thickness was also calculated as comparison with the presence of the beam block, based on the characteristics of tomotherapy facility and its radiation field. Results There was statistical difference between the shielding thicknesses calculated with the presence of the beam block and those without the beam block, to the primary beam direction including the south wall, north wall, the roof and the floor, the shielding thickness were decreased by 95.59% , 63.63% , 80.73% and 51.30% , respectively. Conclusions For the tomotherapy accelerator, the beam block could be of great help to minify the shielding thickness of the room. The radiation field of the tomotherapy facility could be used for the calculation to improve accuracy, and the shielding thickness can also be estimated by subtracting the initial shielding thickness without beam block of the beam block equivalent thickness in the primary beam direction alternatively.