The various steps of treatment planning and delivery for intensity-modulated radiotherapy (IMRT)

Intensity-modulated radiation therapy (IMRT) with non-uniform beams delivered by planned dynamic multi-leaf collimators can provide a better dose distribution within a target volume compared with conventional radiotherapy with uniform beams. The first step of treatment planning for IMRT is to acquire volumetric CT data by scanning the patients in the treatment position. Then, the clinical target volume (CTV) and the organ at risk (OAR) are outlined interactively on these CT images and a 0.5-cm margin is added around the CTV to define the planning target volume (PTV). Dose distribution of IMRT is calculated by using inverse-planning (IP). The parameters of beam weight optimization based on the inverse planning technique include some factors such as dose limits for each critical anatomical structure relative to the target volume and the penalty for exceeding the relative dose limit values in the regions of overlap. The optimum plan should be verified clinically and physically prior to the actual treatment of the patient. (author)