A therapy system comprises a therapy module to direct a therapeutic action to a target along successive trajectories in a target zone that includes the target. A thermometry module is provided to measure temperature in a measurement field and to compute a thermal dose. The measurement field at least partially covers the target zone. A control module controls the therapy module to switch the therapeutic action to a next successive trajectory on the basis of the measured temperature or thermal dose. The successive trajectories are located inside of or outside of one another within the target zone. The therapeutic action comprises application of a focused ultrasound beam to the target. Temperature measurement is done on the basis of magnetic resonance signals.
