Biggs P J
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
Health Phys. 1998 Jan;74(1):96-8. doi: 10.1097/00004032-199801000-00012.
A dedicated electron-only intra-operative suite has just been completed at the Massachusetts General Hospital. This suite is located on the 3rd floor with the shielding consisting entirely of lead and borated polyethylene, except for concrete in the floor and ceiling to support the lead and on the finished floor. The radiation protection barriers for this facility were calculated on the basis of a maximum permissible dose of 10 microSv wk(-1) for photons and 10 microSv wk(-1) for neutrons, based on a quality factor of 10 (this factor is specified in the regulations of the Commonwealth of Massachusetts). This even split was predicated on the basis that, except for the primary beam, the neutron leakage from the machine was generally about the same as for x rays. The initial survey showed that the neutron dose equivalent outside all barriers, except below the floor, was within the calculated values, < 10 microSv wk(-1). However, the neutron dose equivalent measured directly below the floor was found to be 35 microSv wk(-1) for the highest electron energy, a difference of > 25 microSv wk(-1). The neutron dose equivalent, for neutrons produced by bremsstrahlung photon interactions in the lead and based on a 3% photon background in the electron beam, was calculated to be 25 microSv wk(-1), in good agreement with this difference.
麻省总医院刚刚建成了一间专门的术中仅电子设备手术室。该手术室位于三楼，屏蔽层完全由铅和含硼聚乙烯构成，不过地板和天花板中的混凝土用于支撑铅以及铺设完成的地面。该设施的辐射防护屏障是根据光子最大允许剂量10微希沃特/周和中子最大允许剂量10微希沃特/周计算得出的，质量因子为10（该因子在马萨诸塞州联邦法规中有规定）。这种均匀分配是基于以下前提：除了主束外，机器的中子泄漏通常与X射线大致相同。初步测量表明，除地板下方外，所有屏障外的中子剂量当量均在计算值范围内，即<10微希沃特/周。然而，对于最高电子能量，在地板正下方直接测量到的中子剂量当量为35微希沃特/周，相差>25微希沃特/周。基于电子束中3%的光子本底，由铅中轫致辐射光子相互作用产生的中子剂量当量经计算为25微希沃特/周，与这一差值吻合良好。
