  The influence of a periodic landscape of pinning sites on the vortex dynamics
in Pb thin films is explored by ac-susceptibility measurements. For different
amplitudes h of the ac-drive, the ac-susceptibility x=x'+ix'' exhibits a
complex field dependence associated with different dynamic regimes. At very low
ac-drives where both, multiquanta vortices trapped by the antidots and
interstitial vortices oscillate inside the pinning potential (intra-valley
motion), a small kink in x'(H) together with a very low dissipation is
observed. At intermediate ac-excitations such that vortices in the antidots
remain pinned whereas interstices are driven out of the pinning well, a more
pronounced kink in the screening coinciding with the onset of dissipation
(x''(H) ~ 0) indicates the entrance of interstitial vortices. Eventually, at
high enough amplitudes all vortices are set in motion and the penetration of
interstitial vortices appears as a sudden reduction of the shielding power. We
show that these distinctive features allow us to clearly identify the maximum
number of flux quanta per hole regardless the vortex dynamic regime.
