Abstract: The invention relates to a phantom for the quality control of a radiotherapy treatment virtual simulation system which comprises a medical imaging device, characterized in that it comprises: a support casing (1), a core (4) which is arranged in the support casing (1) and which is constituted by a plurality of elements (5, 6, 7, 8, 11, 12, 14, 15, 16, 17) of different shapes, dimensions and densities, the densities simulating the densities of various organs and media of the human body, two of these elements (11, 12) being constituted by two truncated pyramids of different densities which are fitted one inside the other, at least one of them not being completely symmetrical relative to the longitudinal axis thereof, balls (9, 10, 13) of a non-radiotransparent material arranged in the core (4), at least two removable lateral faces (18, 21) which face each other and which comprise metal wires which define geometric figures.