Boron Neutron Capture Therapy is dependent on localized energy deposition of alpha particles and lithium nuclei. However, deviations and inconsistencies in cellular responses to neutron beams are frequently reported in radiobiological studies. This technical note investigates dosimetric impact of the overlying medium thickness on a \(3\times 3\) cellular array using Monte Carlo method. \(^{10}\) B concentrations ranging from 0 to 80 ppm were evaluated to explicitly quantify energy partitioning between the cytoplasm and nucleus. Our findings demonstrate that minor variations in the aqueous medium layer severely attenuate the thermal neutron flux, leading to a marked decrease in the absolute dose deposited in the cellular targets. Specifically, increasing the medium thickness from 100 \(\mu \) m to 800 \(\mu \) m resulted in a \(9.8 \pm 1.8\%\) reduction in the total cellular dose at 80 ppm. These results highlight the critical necessity of controlling and reporting fluid levels in BNCT in vitro experiments to prevent dosimetric variations and ensure reproducible biological outcomes.
