TS32-Room Shielding for High Energy Linac, Neutron, IMRT Considerations

Raymond K. Wu, PhD

OhioHealth Hospitals

3535 Olentangy River Road,

Columbus, OH 43214

The method used in radiotherapy facility shielding calculations had been well documented in the NCRP Report #49.  However, since its publication almost 30 years ago, the design dose limits commonly adopted became lower by a factor of 10 to 40, and the photon energies of many accelerators have increased to well above 10 MV.  The radiotherapy treatment techniques also have become more sophisticated.  In some nations, some forms of instantaneous dose rate limits are promulgated as regulations.  The NCRP 49 becomes inadequate because the above mentioned areas have not been addressed properly in the report. In this talk, the latest method of shielding calculations will be presented.  The method to handle high energy accelerators including the neutron components will be described.  The neutron and the capture gamma characteristics along the maze and the impact on door shielding will be discussed, and the method to estimate the dose equivalent for door shielding design purposes will be presented. The concept of Time Averaged Dose Rate (TADR) will be described.  The applications of the TADR concept to assure adequate shielding for extraordinarily low workload facilities will be illustrated with examples.  The impact of IMRT on shielding requirements will be summarized.  The Session will be conducted in Chinese using English terms.

TS32-高能加速器的机房屏蔽、考虑中子和调强放疗

Raymond K. Wu, PhD

OhioHealth Hospitals

3535 Olentangy River Road,

Columbus, OH 43214

放射治疗设施的屏蔽计算方法已经在NCRP49号报告中进行了充分的阐述。然而因为这个报告是在30年前发布的，并且被普遍采用的设计剂量限值已小至原来的十至四十分之一，许多加速器的光子能量也已经超过了10MV。放射治疗技术也变得更加复杂。在一些国家，某些形式的瞬时剂量率限制已写进法规。因为没有对上述问题给出适当地论述，NCRP 49报告变得不再合适。下面会给出最新的屏蔽计算方法，说明高能加速器（包括中子成分）的屏蔽设计方法，讨论中子和俘获伽玛射线的特征沿着迷路变化情况，并考虑它们对防护门设计的影响。讲座还将介绍门防护设计时等效剂量估算方法，描述时间平均剂量率的概念，举例描述时间平均剂量率概念应用于工作量特别低的设备的防护设计，总结调强对防护要求的影响。