γ-刀环境辐射探测及防护措施初探

由于γ-刀使用的201个60Co放射源其活度最高可达223480GBq，使用时应考虑其安全性及可靠性。虽然γ-刀本身有较为严格的防护措施，然而背景辐射和辐射渗漏是不可避免的。因此，准确掌握治疗室内及周围环境的辐射状况及其变化具有重要意义。通过分步设计实验，测量出γ-刀立体定向放射治疗中，在开机与关机两种情况下，治疗室内及周围环境的背景辐射与辐射渗漏。在此基础上，进一步测量患者在接受γ-刀治疗的整个过程中，颈部所接受的漏射线的剂量，并探讨对颈部的防护措施。结果表明治疗室内的辐射率约在10～130000μGy/h；周围环境约为0.18～0.63μGy/h，符合我国现行的《放射防护条例》的规定。许多患者颈部所接受的漏射线的剂量超过50mSv，需对其进行防护。可选择铅和含铅材料作为防护材料。

Study on Environmental Radiation Exposure and ShieldingMethods of the Leksell Gamma Unit

For the radiation source of the Gamma Unit is Co-60 with a total activity of 223480 GBq, it is necessary to take account of its safety and reliability. Although the Gamma Unit is shielded, background radiation and radiation leakage are unavoidable. Therefore, it is essential to measure the exposure rates in both the treatment room and the surrounding as the exposure levels in the treatment room during operation of the Gamma Unit. In the step experiment, background radiation and radiation leakage in both the treatment room and the surrounding during the stereotactic radiotherapy were measured under the on-state and off-state of the Gamma Unit. Then, the received radiation dose at the neck of the patients was measured in the process of the treatment of Gamma Unit and the protective measures investigated. The results showed that the exposure rates ranged from 10 to 130 000 μGy/h in the treatment room and from 0.18 to 0.63 μGy/h in the surrounding area during operation of the Gamma Unit, respectively. None of the area outside the treatment room exceeded the Atomic Energy Council(AEC). All measured exposure levels were well below the limits established by the AEC. The exposure dose of most of patient's neck during operation exceeded 50 mSv, a shielding instrument containing lead for the patient's neck during operation was needed.