Abstract: A method and a system of determining respiratory particle deposition in a lung is described. A single conduit model having conduit generations corresponding to generations of the lung is generated. Computational fluid dynamics simulations of respiratory particle delivery to an N conduit generation and an N+1 conduit generation of the single conduit model are performed to determine a mass of respiratory particles leaving the N conduit generation and a mass of respiratory particles deposited in the N+1 conduit generation. The mass deposited in the N+1 conduit generation is scaled up by a scaling factor, the scaling factor being based on the mass of respiratory particles leaving the N conduit generation, to determine a total mass of respiratory particles deposited in a generation of the lung corresponding to the N+1 conduit generation. Other embodiments are also described and claimed.