1. A patient monitoring arrangement adapted for use in connection with a radiation system comprising a radiation gantry including a tubular opening and an associated patient couch, said patient monitoring arrangement comprises: a pattern projector configured to project a two or three dimensional pattern onto at least a portion of a patient positioned on said patient couch, said pattern extending at least partly into said tubular opening of said radiation gantry adapted for receiving said patient couch; a first pattern detector arranged on a front side of said radiation gantry including said tubular opening, for detecting at least a first portion of said pattern on said patient and generating first detection data based on said detected at least a first portion; a second pattern detector arranged on an opposite back side of said radiation gantry including said tubular opening, for detecting at least a second portion of said pattern on said patient and generating second detection data based on said detected at least a second portion; and a pattern analyzer connected to said first pattern detector and said second pattern detector for generating information representative of movement of said patient on said patient couch based on first detection data and said second detection data.