Ion beam therapy (IBT) is the medical use of heavy charged particles to treat cancer due to their physical and biological properties, and damage the tumor at a given physical dose without causing damage to healthy tissues. The aim of this study was to investigate the ion track overlap (TO) from aluminium oxide doped with carbon and magnesium (Al2O3:C-Mg) dosimeters as a probability function. The dosimeters were exposed to proton 3 MeV u–1 and carbon 26 MeV u–1 heavy charged particle (HCP) beams-dosimeters in the interval of fluencies from 2.23 × 106 to 8.93 ×107 (ion cm–2). The TO occurs for fluencies higher than 106 cm2 for all radiation types. A model for the TO process was developed, considering the dependence of the quantity of TO on the number of simulated tracks by a probability function, also the number of total induced tracks was determined. As the particle fluence increases, TO also increases, leading to increasing the number of track per spot. Therefore, the HCP fluence or dose at which the histogram starts to change may be an indication of onset of TO. It was observed that, TO starts from the fluence above 106 cm2, also the number of track per spot was increased with the increase of the fluence and the probability of getting one track per spot is approximately 100% for the very low fluence.