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 by 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.