3D conformal radiation therapy

3D conformal radiation therapy (3D-CRT) is a radiation therapy technique that involves CT planning where the volume to be treated is defined on a 3D data set. Therefore, organs at risk can also be delineated to shield these and reduce treatment side effects. Radiotherapy planning software is used to design complicated beam arrangements and to assess dose-volume histograms for the tumor and organs at risk.

In its simplest form, 3D-CRT uses a multileaf collimator (MLC) in a step-and-shoot technique. A multileaf collimator typically consists of 40-80 tungsten leaves, which can move independently into the beam path and thus create nearly limitless beam shapes.  Several of these 'conformal' beams would then be delivered from different angles to treat the tumor volume.