A treatment system comprising: a treatment apparatus for treating a patient; a mechanical couch for positioning a patient relative to the treatment apparatus; and a treatment monitoring system for monitoring the relative positioning of the treatment apparatus relative to a patient to which radiation treatment is being applied, the treatment monitoring system comprising: a stereoscopic camera system comprising a projector operable to project a speckled pattern of light or structured light onto the surface of a patient, the stereoscopic camera system being operable to obtain images of the projection of a speckled pattern of light or a projection of structured light onto the surface of a patient to which radiation treatment is being applied; a modeling unit operable to process images of the projection of a speckled pattern of light or structured light onto the surface of a patient obtained by the stereoscopic camera system and generate a 3D wire mesh computer model of the surface of a patient being monitored on the basis of the appearance of the patient corresponding to part of the images obtained by the stereoscopic camera system; and an apparatus position determination module operable to determine the positioning of the treatment apparatus; characterized in that: the treatment apparatus further comprises a plurality of markers attached to the surface of the treatment apparatus wherein the apparatus position determination module is arranged to process images of the markers contained in portions of the images obtained by the stereoscopic camera system which are not utilized to generate the 3D wire mesh computer model of the surface of a patient to determine the relative positioning of the treatment apparatus relative to the 3D wire mesh model of the patient. a treatment apparatus for treating a patient; a mechanical couch for positioning a patient relative to the treatment apparatus; and a treatment monitoring system for monitoring the relative positioning of the treatment apparatus relative to a patient to which radiation treatment is being applied, the treatment monitoring system comprising: a stereoscopic camera system comprising a projector operable to project a speckled pattern of light or structured light onto the surface of a patient, the stereoscopic camera system being operable to obtain images of the projection of a speckled pattern of light or a projection of structured light onto the surface of a patient to which radiation treatment is being applied; a modeling unit operable to process images of the projection of a speckled pattern of light or structured light onto the surface of a patient obtained by the stereoscopic camera system and generate a 3D wire mesh computer model of the surface of a patient being monitored on the basis of the appearance of the patient corresponding to part of the images obtained by the stereoscopic camera system; and an apparatus position determination module operable to determine the positioning of the treatment apparatus; characterized in that: the treatment apparatus further comprises a plurality of markers attached to the surface of the treatment apparatus wherein the apparatus position determination module is arranged to process images of the markers contained in portions of the images obtained by the stereoscopic camera system which are not utilized to generate the 3D wire mesh computer model of the surface of a patient to determine the relative positioning of the treatment apparatus relative to the 3D wire mesh model of the patient. a stereoscopic camera system comprising a projector operable to project a speckled pattern of light or structured light onto the surface of a patient, the stereoscopic camera system being operable to obtain images of the projection of a speckled pattern of light or a projection of structured light onto the surface of a patient to which radiation treatment is being applied; a modeling unit operable to process images of the projection of a speckled pattern of light or structured light onto the surface of a patient obtained by the stereoscopic camera system and generate a 3D wire mesh computer model of the surface of a patient being monitored on the basis of the appearance of the patient corresponding to part of the images obtained by the stereoscopic camera system; and an apparatus position determination module operable to determine the positioning of the treatment apparatus; characterized in that: the treatment apparatus further comprises a plurality of markers attached to the surface of the treatment apparatus wherein the apparatus position determination module is arranged to process images of the markers contained in portions of the images obtained by the stereoscopic camera system which are not utilized to generate the 3D wire mesh computer model of the surface of a patient to determine the relative positioning of the treatment apparatus relative to the 3D wire mesh model of the patient.