Patent ID: 7564950
Filing Date: 2009-07-21
Classification: A61N,G21K

Abstract:
1. A method for capturing a portal image using a linear accelerator having a multi-leaf collimator and an imager, comprising: positioning the imager; receiving portal image field information, the portal image field information including a planned portal image field size for defining a portal image field; comparing the portal image field to an allowed image area of the imager that is suitable for being irradiated to determine if a maximum size of the portal image field exceeds the allowed image area of the imager, wherein the maximum size of the portal image field is inversely proportional to a distance between a radiation source of the linear accelerator and the imager; calculating a leaf position for at least one leaf of the multi-leaf collimator for clipping the portal image field, wherein the clipped portal image filed does not include a portion of the maximum size of the portal image field that exceeds the allowed image area of the imager so that a projection of the portal image field onto the imager falls within the allowed image area of the imager, wherein the clipped portal image field prevents irradiation of radiation-sensitive electronics of the imager; controlling the multi-leaf collimator to move the at least one leaf of the multi-leaf collimator to the calculated leaf position; and