A high-intensity focused ultrasound (HIFU) therapy system comprises an ultrasound transduce to emit a focused ultrasound beam along a beam path. An ultrasound transparent window is positioned in the beam path. A fluid cooling system to provide cooling of an object to which the focused ultrasound beam is directed. The fluid cooling system includes a fluid receptacle mounted adjacent to the ultrasound transparent window and a cooling unit to cool a coolant and pass the coolant trough the fluid receptacle to and from the fluid receptacle. A degassing module and preferably also a filter to remove volatile components from the coolant. Dissolved air or other gases are removed from the coolant, so that the formation of bubbles in the coolant is avoided or at least suppressed.