组织中气腔(Air Cavities)的存在产生非均质体界面效应,除导致剂量分布畸变外,还导致气腔邻接组织表浅层剂量降低,即欠剂量区,最终可能导致上呼吸道肿瘤如鼻咽癌、喉癌放疗失控。气腔邻接组织表层欠剂量是两种效应的影响:一是X线由组织内出射时表面剂量的跌落效应(buildpown);另一个则是X线由气腔入射到对侧组 The presence of air cavities in the tissue produces an asymmetric interface effect that, in addition to causing a dose distribution distortion, also results in a decrease in the dose of the superficial layer of the air cavity adjacent to the tissue, ie, an under-dose area, which may eventually lead to upper respiratory tract tumors such as nasal Pharyngeal cancer, laryngeal cancer radiotherapy out of control. The under dose of the air cavity adjacent to the tissue surface is the effect of two effects: one is the build-up of the surface dose when the X-ray is emitted from the tissue; the other is that the X-ray is incident on the contralateral group from the air cavity.