  Most radiative transfer models assume that dust in spiral galaxies is
distributed exponentially. In this paper our goal is to verify this assumption
by analysing the two-dimensional large-scale distribution of dust in galaxies
from the DustPedia sample. For this purpose, we make use of Herschel imaging in
five bands, from 100 to 500{\mu}m, in which the cold dust constituent is
primarily traced and makes up the bulk of the dust mass in spiral galaxies. For
a subsample of 320 disc galaxies, we successfully perform a simultaneous
fitting with a single S\'ersic model of the Herschel images in all five bands
using the multiband modelling code GALFITM. We report that the S\'ersic index
$n$, which characterises the shape of the S\'ersic profile, lies systematically
below 1 in all Herschel bands and is almost constant with wavelength. The
average value at 250{\mu}m is $0.67\pm0.37$ (187 galaxies are fitted with
$n_{250}\leq0.75$, 87 galaxies have $0.75<n_{250}\leq1.25$, and 46 - with
$n_{250}>1.25$). Most observed profiles exhibit a depletion in the inner region
(at $r<0.3-0.4$ of the optical radius $r_{25}$ ) and are more or less
exponential in the outer part. We also find breaks in the dust emission
profiles at longer distances $(0.5-0.6)r_{25}$ which are associated with the
breaks in the optical and near-infrared. We assume that the observed deficit of
dust emission in the inner galaxy region is related to the depression in the
radial profile of the HI surface density in the same region because the atomic
gas reaches high enough surface densities there to be transformed into
molecular gas. If a galaxy has a triggered star formation in the inner region
(for example, because of a strong bar instability, which transfers the gas
inwards to the centre, or a pseudobulge formation), no depletion or even an
excess of dust emission in the centre is observed.
