Intensity-modulated radiation therapy

Over the last decades, constant development of radiotherapy techniques led to more and more conformal dose distributions for better restricting the high dose area inside the patient to the tumor target volume and sparing adjacent critical organs at risk. For external photon beams, the most frequently used modality in radiotherapy by far, the most advanced technique currently available is intensity-modulated radiation therapy (IMRT). As the name implies, the intensity of each beam is no longer constant over the whole aperture, but can be varied to a great extend. Due to the large number of degrees of freedom, IMRT planning must be modelled as an optimization problem where the computer varies the intensities with respect to an objective function based on predefined dose prescriptions. While the plan quality and also the clinical outcome could be improved, even IMRT cannot achieve the ideal dose distribution of 100% dose to the tumor and 0% everywhere else, so often compromises still have to be made. One field of current research is multicriteria optimization where all relevant compromises for a specific patient are calculated and explored interactively. Also biologically motivated objective functions that are more relevant for the clinical outcome than the pure physical dose are being investigated. Potentially these are major next steps towards a radiotherapy that further maximizes the benefit and minimizes the risk of the treatment for a large number of cancer patients