隨著醫療品質要求的提高，放射治療不僅關心照野內腫瘤部位及其鄰近正常組織的劑量，照野外重要器官如生殖腺的劑量亦日漸受重視。由於放射治療能量超過10 MV，在治療中產生之(ˠ,n)，(ˠ,2n)，(ˠ,pn)，(ˠ,p)等反應會對病人產生不可忽略的中子劑量，且產生之中子能譜能量在keV~MeV 等級之快中子佔大部份，其輻射加權因數(WR)根據NCRP-116 號報告書為10 與20，平均值視其能譜分佈在10~20 之間，故其對重要器官所造成之等效劑量預期將極為可觀。以鼻咽癌和攝護腺癌為例，其治療劑量約70 Gy，當危急器官位於治療照野內、深度0 cm 時，由結果得知，接受的快中子等效劑量為1066.5±32.7 μSv/Gy x-ray，慢中子等效劑量為53.9±7.3 μSv/Gy x-ray，所以在完整的療程後約接受了0.21 Sv 的中子等效劑量。如深度在10 cm 時，接受的快中子等效劑量為389.8±19.7 μSv/Gy x-ray，慢中子等效劑量為31.0±5.6 Sv/Gy x-ray，一樣在完整的療程後約接受了0.08 Sv 的中子等效劑量。

Since the medical quality requirements increased, radioncologists concern not only about the dose distribution of tumor and normal tissue in the field, but also critical organs (ex: gonads) doses outside the field. Intensity modulated radiotherapy (IMRT) are the most advanced radiotherapy technique up to now, which give the maximum dose to tumors while sparing the minimum dose to adjacent normal tissue by multileaf collimator and virtual wedge controlled intensity modulated beams.

According to the higher photon energy, photonuclear reactions such as (ˠ,n), (ˠ,2n), (ˠ,pn), (ˠ,p) due to photon energy higher than 10 MeV will cause slightly a lot neutron dose. Besides, the fast neutrons of MeV level which the WR value defined by NCRP No 116 Report is 20 are dominant in photoneutron spectrum, it’s dose equivalent will expected significant in health physics. But the relative data in health physics field about this advanced technique is still lack, thus, this proposal will plan to measure it. After measuring the equivalent dose of fast neutrons and slow neutrons, it found that the neutron equivalent dose would change by the irradiated field and energy to 10MV photon, the equivalent dose at0 cm2 and 10 cm2 are 1066.5±32.7 and 389.8±19.7 μSv per Gy x-ray.