Automatic detection of three radio-opaque markers for prostate targeting using EPID during external radiation therapy

External radiotherapy is an option used for the treatment of the prostate cancer. In order to achieve the best results, radiation must be precisely delivered to the target volume while preserving healthy tissues and protecting organs at risk. Electronic portal imaging devices (EPID) are now available to verify the dose delivery by using the treatment radiation to obtain a portal image. The localization of the prostate, usually not visible on portal images, is performed by inserting up to three radio-opaque markers into the prostate. The identification and position of the markers relative to bone structures and beam field are used to insure the proper delivery of radiation to the prostate. We present a sequence of algorithms optimized for the automatic detection of the three radio-opaque markers on images obtained with EPID during prostate radiotherapy. A neural network is used to validate the detection of true markers in images