When an accelerator is used to treat tumour of illness, the distribution of doses is changed by commonly inserting a wedge into the path of radial beam.
利用加速器治疗肿瘤时，通常要在射线束的路径上加入楔形板以改变平野的剂量分布。
2
The formula of wedge angle is deduced under the condition of two-beam interference.