A system to monitor patient setup in conformal radiotherapy of prostate cancer

In conformal radiotherapy dosimetry and ballistics of the rays to apply to irradiate the tumour are calculated before the treatment, using images provided by tomographic imaging. The treatment may lasts several meetings during several weeks. At the beginning of each session, the patient has to be positioned on the treatment couch under the linear accelerator in the same position as during MR or CT imaging and planning, and the organs are assumed to be in the same place. Currently, the methods used for this repositioning are based on the external anatomy and suppose an immobility of the internal bodies. In this study, we present a method, adapted to the clinical conditions, for the automatic set up of patient for prostate cancer radiotherapy. It is based on localisation by ultrasonic images and stereovision and a matching with planning images. The method exploits a statistical modelling of the prostate to automatically extract its contours