Radiation therapy relies on energy deposition (absorbed dose) in the body tissues to stop the tumoral growth. Its effectivity depends on the uncertainties associated with the absorbed dose measurements. Using low-energy photon beams (<100 kV) presents several advantages in the treatment of certain diseases. However, those advantages come with a price: measurements with higher uncertainties. Historically, Monte Carlo (MC) simulations have been used to increase our understanding of this field. However, MC codes have issues with low-energy photons, which are related to different implementations in some of their libraries. In this seminar, we will analyze their effects on low-energy photon dosimetry applied in radiation therapy.