Dose solutions

 When the PTV and normal organs have been defined in 3D, the optimal dose distribution for treating the tumour is sought. Consultation with a dosimetrist is vital to select the best parameters. For example, a treatment machine must be chosen according to percentage depth dose characteristics and build up depth which will vary with energy and beam size as shown in Table 2.1. These can be used to calculate doses for treatment using single fields and to learn the construction of isodose distributions using computer modelling. Other factors to be considered in the choice of machine are the effect of penumbra on beam definition, the availability of independent or multi-leaf collimators, facilities for beam modification and portal imaging.




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