The invention provides for a medical apparatus (400, 500, 600, 700, 800) comprising a magnetic resonance imaging system (402) for acquiring magnetic resonance thermometry data (442) from a subject (418). The magnetic resonance imaging system comprises a magnet (404) with an imaging zone (408). The medical apparatus further comprises a memory (432) for storing machine executable instructions (460, 462, 464, 466, 510, 660). The medical apparatus further comprises a processor (426) for controlling the medical apparatus, wherein execution of the machine executable instructions causes the processor to: acquire (100, 200, 300) the magnetic resonance thermometry data from multiple slices (421, 421', 421'') within the imaging zone by controlling the magnetic resonance imaging system； and interpolate (102, 202, 204, 302, 304) a three dimensional thermal dose estimate (444) in accordance with the magnetic resonance thermometry data.
