We have investigated the elastic backscattering which occurs during ion implantation, and its impact on the retained implantation dose. A series of Si_1-xGe_x (0 ≤ x ≤ 1) alloy films were implanted with 5 × 10¹⁴ atoms/cm² of ¹¹B at an energy of 10 keV. Nuclear reaction analysis (NRA) was used to characterize the retained boron dose within the Si_1-xGe_x (0 ≤ x ≤ 1) samples by means of the ¹¹B(p,α1)2α12 nuclear reaction. The experimental results show that the elastic backscattering effect is significant in this case, with the retained boron dose decreasing linearly as the target matrix varies from pure silicon to pure germanium. Our findings are in good agreement with simulations carried out using the SRIM-2013 software. Our study indicates that the backscattering effect during implantation must be accounted for when a specific concentration is targeted, or when adopting an implanted film as a reference standard, for example, in secondary ion mass spectrometry.