Systems and methods can include a system for positioning an ultrasound probe proximal to anatomy of a patient on a radiation couch including a substantially planar base including engagement features to directly or indirectly index the substantially planar base to the radiation couch and a centrally located guide extending longitudinally along a top side of the base, a probe holder, configured to be coupled to, to translate longitudinally, and to be user-accessed and user-controlled from within, a central region of the substantially planar base, a clamp, configured to localize the probe holder at a specified location along a translation path in the central region of the substantially planar base, leg supports shaped to accommodate a patient's legs from behind, the pair of leg supports being shaped and arranged to provide a space therebetween that can accommodate an ultrasound probe holder.