The implementation of IMRT methods including the assessment of a new calculation algorithm The development of intensity modulated radiotherapy (IMRT) planning techniques has introduced new possibilities for improving the treatment of cancer. However, as just one step in the radiotherapy process its potential cannot be fully realised without the continuing development of other steps such as dose calculation accuracy and imaging. The aims of this were threefold. The first aim was to investigate the use ofIMRT in the treatment of tumours of the parotid and non-small cell lung cancer (NSCLC). Secondly, the potential for improving the planning of IMRT NSCLC treatments through the incorporation of lung function information derived from hyperpolarised 3-helium magnetic resonance imaging eHe-MRI) was .studied. The final aim was to investigate the impact of a new convolution-superposition dose calculation algorithm, the Analytical Anisotropic Algorithm (AAA), on the planning and pretreatment verification ofIMRT treatments for a range of sites. Class solutions were developed for the IMRT treatment of parotid and NSCLC. Improved sparing of normal lung tissue was found to be possible by the inclusion oflung ventilation information from 3He-MRI in the IMRT planning process, without detriment to target coverage. A detailed dosimetric assessment of the performance of the AAA in less challenging situations than those posed by IMRT showed its accuracy to be excellent in situations ranging from heterogeneous phantoms to simulated treatment plans. AAA calculations of IMRT plans agreed with measurement generally to within 3% or 3mm distance to agreement, an improvement in accuracy over the previous pencil beam algorithm, particularly in regions of low density. Reassessment of NSCLC plan acceptance criteria is necessary in the light of this.