A radiation therapy system includes a treatment couch positioning assembly that is directly coupled to a fixed structure supporting the linear accelerator of the radiation therapy system. The radiation therapy system can be installed in a radiation therapy facility without the floor of the facility being excavated and a sub-floor structure, such as a base frame, being installed. To laterally position a patient relative to the linear accelerator, the treatment couch positioning assembly of the radiation therapy system is laterally translated via a linear motor, and laterally translates with the treatment couch, rather than cantilevering the treatment couch to either side of the couch positioning assembly.