醫用直線加速器是現今應用於臨床放射治療最廣泛之放射治療儀器，其所產生之光子與電子束為進行腫瘤治療之主要射束。對高能量之直線加速器而言，其所產生之輻射不僅包括光子或電子，還可能含有中子輻射(當能量大於10 MV 時愈加明顯)，這些中子輻射會造成治療機頭屏蔽被活化，除了增加病人接受劑量的不確定度外，亦會造成放射腫瘤科工作人員(放射師)在病人治療前後於協助病人擺位時可能額外曝露不同程度之劑量。本研究針對國內放射腫瘤治療部門使用之加速器能量設備進行評估；評估不同能量之光子照射下，機頭活化之影響。對於常使用高能量直線加速器進行光子放射治療及每日治療病人數較多之醫院而言，對中子活化之劑量與相關活化特性評估，乃是這些醫院放射腫瘤治療部門必須面對的重要課題；本研究計畫之調查結果將提供予臨床放射治療部門之參考。

The medical linear accelerator (Linac) is the most popular unit in clinical radiotherapy. Photon and electron beams produced by Linac are the major considered radiations in tumor treatments. As the photon energy is higher (especially beyond 10 MV), probabilities of photonuclear reactions are increased; secondary particles such as neutrons are then following emitted. Thereby, the particles produced by a high energy Linac would activate the shielding materials in treatment head. This would increase the uncertainty of delivered dose, and may cause different level of radiation exposure for the radiological technologists as they position the patient before and after the treatment. This study investigated the neutron activation characteristics of the treatment head for the high-energy medical Linac using in radiotherapy. Activation products in the treatment head will be also investigated. Results and findings of this research will be provided to the department of radiation oncology or radiotherapy. For the departments of radiation oncology in hospitals which use beam energy above 10MV of photons frequently and treat large number of patients per day, assessment of the increased dose and relative characteristics due to neutron activation is an important issue.