1.4 Evolution of Stereotactic conformal radiotherapy (SCRT) Conventional radiotherapy techniques generally involve the use of 2-3 radiation beams covering the tumour and a margin of 1-3 cms for any subclinical disease and physical inaccuracies in the daily treatment delivery. The last decade has seen tremendous technological advances in radiotherapy planning and accurate treatment delivery. Stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) techniques involve firm and accurate immobilisation with fixed or relocatable frames, high precision three-dimensional (3-D) target localisation with CT/CT-MRI fusion and focused radiation delivery. This is achieved either with a multiple source cobalt unit (gamma knife) or with multiple arcs using a modified conventional linear accelerator. Such conventional stereotactic irradiation techniques typically produce spherical high dose volumes and are therefore suitable only for small spherical lesions. A majority of the brain tumours considered for radiotherapy however are not spherical and frequently extend to adjacent structures. To treat large non-spherical volumes with conventional SRS requires the addition of multiple small spherical high dose volumes described as multiple isocentre treatment. The overlap of high dose spheres results in dose inhomogeneity, which has been associated with a higher incidence of radiation induced complications. It has been previously demonstrated that the optimum way of delivering high precision localised irradiation to larger non-spherical targets is with the use of multiple conformal fixed fields with individualised shielding of each radiation field conforming to the shape of the target. This principle of conformal therapy combined with the precision of stereotactic localisation and focused radiation delivery is described as stereotactic conformal radiotherapy (SCRT).