Accurate surface-dose measurements in proton therapy are challenging and often of poor spatial resolution for most dosimeter types. However, optically stimulated luminescence (OSL) based 2D dosimeters could provide the required spatial dose resolution. The aim of this study was to investigate the dosimetric precision and energy dependence of an in-house made reusable dosimeter composed of a silicone-film containing OSL-active nanoparticles. The dosimeter was irradiated with a clinical proton therapy field and the readout dose was compared to the results from a commercial dosimeter. The pixelwise noise-to-signal ratio for the OSL dosimeter remained below 2% for doses above 1 Gy, and the energy dependence was negligible in the investigated energy range.