A therapeutic apparatus comprising: - a high intensity focused ultrasound system (100, 200, 504) for treating a target region of a subject, wherein the high intensity focused ultrasound system comprises an ultrasound transducer (112, 212, 530) having a mechanical structure, wherein the high intensity focused ultrasound system further comprises a mechanical positioning system (532, 534) adapted to mechanically position the ultrasound transducer; - a processor for controlling the therapeutic system; - a display for displaying treatment planning data; - a memory containing machine executable instructions (580, 582, 584, 586, 588) for execution by the processor, wherein the memory further contains a geometric model of the high intensity focused ultrasound system, wherein the geometric model is descriptive of a three-dimensional shape of the mechanical structure of the ultrasound transducer and the mechanical positioning system, wherein the geometric model comprises a geometric representation (114, 118, 214, 216, 218) of the path of focused ultrasound generated by the ultrasound transducer, wherein execution of the instructions causes the processor to: - receive (300, 400) the treatment planning data, wherein the treatment planning data comprises a geometric representation of the target region; - render (302, 402) the geometric representation of the target region on the display; - calculate (304, 404, 406) an achievable target region in accordance with the geometric model by calculating possible locations and positions of the ultrasound transducer, wherein the achievable target region is representative of a region treatable by the high intensity focused ultrasound system; and - render (306, 408) the achievable target region on the display. - a high intensity focused ultrasound system (100, 200, 504) for treating a target region of a subject, wherein the high intensity focused ultrasound system comprises an ultrasound transducer (112, 212, 530) having a mechanical structure, wherein the high intensity focused ultrasound system further comprises a mechanical positioning system (532, 534) adapted to mechanically position the ultrasound transducer; - a processor for controlling the therapeutic system; - a display for displaying treatment planning data; - a memory containing machine executable instructions (580, 582, 584, 586, 588) for execution by the processor, wherein the memory further contains a geometric model of the high intensity focused ultrasound system, wherein the geometric model is descriptive of a three-dimensional shape of the mechanical structure of the ultrasound transducer and the mechanical positioning system, wherein the geometric model comprises a geometric representation (114, 118, 214, 216, 218) of the path of focused ultrasound generated by the ultrasound transducer, wherein execution of the instructions causes the processor to: - receive (300, 400) the treatment planning data, wherein the treatment planning data comprises a geometric representation of the target region; - render (302, 402) the geometric representation of the target region on the display; - calculate (304, 404, 406) an achievable target region in accordance with the geometric model by calculating possible locations and positions of the ultrasound transducer, wherein the achievable target region is representative of a region treatable by the high intensity focused ultrasound system; and - render (306, 408) the achievable target region on the display. - receive (300, 400) the treatment planning data, wherein the treatment planning data comprises a geometric representation of the target region; - render (302, 402) the geometric representation of the target region on the display; - calculate (304, 404, 406) an achievable target region in accordance with the geometric model by calculating possible locations and positions of the ultrasound transducer, wherein the achievable target region is representative of a region treatable by the high intensity focused ultrasound system; and - render (306, 408) the achievable target region on the display.