**2. Three-dimensional conformal radiotherapy (3DCRT)**

Three-Dimensional Conformal Radiation Therapy (3DCRT) means conformal dose distribution in terms of adequate dose to the tumor and minimum possible dose to normal tissue based on 3D anatomic information. The main distinction between treatment planning of 3DCRT and that of conventional radiation therapy is that treatment planning system optimizes dose distribution in accordance with the clinical objectives using anatomic information. Depending on imaging modality, visible tumor, the suspected tumor spread, patient motion uncertainties, critical structures, and relevant landmarks are outlined slice by slice by the radiation oncologist. This technique, however, fails in achieving conformal dose distribution for patient geometries where Organ at Risks (OARs) are located in close proximity to or are even embedded within complicated tumor shapes. Due to lesser conformity of dose distribution in Three-Dimensional Conformal Radiation Therapy (3DCRT), it may be insufficient to allow adequate escalation of tumor dose and there is a need for further improvement. It is possible only with intensity-modulated radiotherapy.
