[en] This work investigates the change in shape of optically stimulated luminescence (OSL) curves from carbon-doped aluminum oxide (Al₂O₃:C) dosimeters as a function of ionization density. The dosimeters were exposed to Ne 371.9 MeV/u and Fe 120.4 MeV/u heavy charged particle (HCP) beams, and ⁹⁰Sr/⁹⁰Y beta radiation in the interval of absorbed dose to water from 2 mGy up to 8.5 kGy. The change in the shape of the OSL curves occurs for absorbed doses higher than 10 Gy for beta radiation and higher than 50 Gy for the HCP beams. Based on the HCP fluences corresponding to the absorbed dose of 50 Gy and analytical models of radial dose distribution, we estimated that the dose level in the overlapping track region is comparable to the beta dose in which the OSL curve start to change. This is an indication that track overlap is responsible for changes in shape of the OSL curves of Al₂O₃:C Luxel^TM dosimeters as the HCP fluence increases