  We argue that the so-called "Pioneer Anomaly" is related to the quantum
vacuum fluctuations. Our approach is based on the hypothesis of the
gravitational repulsion between matter and antimatter, what allows considering,
the virtual particle-antiparticle pairs in the physical vacuum, as
gravitational dipoles. Our simplified calculations indicate that the anomalous
deceleration of the Pioneer spacecrafts could be a consequence of the vacuum
polarization in the gravitational field of the Sun. At the large distances, the
vacuum polarization by baryonic matter could mimic dark matter what opens
possibility that dark matter do not exist, as advocated by the Modified
Newtonian Dynamics (MOND).
