 Computerised treatment planning systems began to be used in the 1970s to improve the accuracy and speed of dose calculations.By the 1990s CT scans, more powerful computers, improved dose calculation algorithms and Multileaf collimators (MLCs) lead to 3D conformal planning (3DCRT), categorised as a Level 2 technique by the European Dynarad consortium.3DCRT uses MLCs to shape the radiotherapy beam to closely match the shape of a target tumour, reducing the dose to healthy surrounding tissue.