  Multi-slat prompt-gamma camera is a promising tool for range monitoring
during proton therapy. We report the results of a comprehensive simulation
study analyzing the precision which is possible to reach with this camera in
determination of the position of the distal edge of the Bragg peak. For the
first time we include simulation of optical photons. The proton beam (single
pencil beam, 130 MeV, 10 ns bunch period, total of 10^8 protons) is interacting
with a polymethyl methacrylate (PMMA) phantom, which is a cylinder of 200 mm in
diameter and length. The prompt gamma rays generated in the phantom are
collimated with a multi-slat collimator and detected using a combination of
yttrium aluminum perovskite (YAP) scintillators, installed in the collimator
apertures, and light sensors. Two scintillator packing schemes, with one and
with two scintillator plates per aperture, are considered. The collimator
configuration (the septal thickness, aperture and height), resulting in the
best precision, is determined using two methods of detector optimization.
Precision of 2.1 mm (full width at half maximum) in the edge position
determination is demonstrated.
