A method and device for accurately positioning patients for imaging and radiotherapy is disclosed. The device includes a support platform (such as a bed, a table, a couch, a chair, etc.) connected to a fixed base by at least two and preferably four offset supporting arms. The support arms are journaled into the support platform at passive-rotatable pivot joints and are journaled into the base at active-rotatable pivot points. The base contains actuators (manual or powered by motors, pneumatics or hydraulics) for articulating the support arms. The relative lengths of the support arms may be varied to create a pre-defined trajectory of the support platform, between a starting spatial position and orientation to an ending spatial position and orientation, and through a continuous range there between. This makes it possible to position a patient within a range from a low, standing up position to a high, forwarding, prone or supine position, or vice versa.