  Recently it has become apparent that event-by-event fluctuations in the
initial state of hydrodynamical modelling of ultrarelativistic heavy-ion
collisions are crucial in order to understand the full centrality dependence of
the elliptic flow coefficient v_2. In particular, in central collisions the
density fluctuations play a major role in generating the spatial eccentricity
in the initial state. This raises the question to what degree high P_T physics,
in particular leading-parton energy loss, which takes place in the background
of an evolving medium, is sensitive to the presence of the event-by-event
density fluctuations in the background. In this work, we report results for the
effects of fluctuations on the nuclear modification factor R_AA in both central
and noncentral sqrt(s_NN) = 200 GeV Au+Au collisions at RHIC. Two different
types of energy-loss models, a radiative and an elastic, are considered. In
particular, we study the dependence of the results on the assumed spatial size
of the density fluctuations, and discuss the angular modulation of R_AA with
respect to the event plane.
