Intensity-modulated radiation therapy (IMRT) by a dynamic-jaws-only (DJO) technique in rotate-translate mode

In this note it is shown how the use of a rotate-translate methodology employing only jaws, which move dynamically with the beam continuously on, can lead to a delivery of a two-dimensional intensity-modulated beam wherein the modulation is spatially slowly varying. All that is necessary is that a pair of jaws sweep across the face of an accelerator with the aperture between them suitably varying in width and defined by a position-time trajectory function for each jaw. This is then repeated, at the same gantry angle, with the jaws rotated to a different head twist and with a different jaw-pair trajectory for a number of sequential head twists. The result of superposing the individual beams at the same gantry angle is a two-dimensional variation of fluence at this gantry angle. A powerful theorem is developed which shows that there is an infinity of jaw trajectories for some specified number of head twists, each of which corresponds to the same delivered two-dimensional modulated beam. (note)