A first dose calculated using a first set of fluence maps and a first (faster) dose prediction model is accessed 602. A second fluence map is accessed 604. The second fluence map is projected onto the first set of fluence maps to determine a set of scalars and a residual value 606. When the residual value satisfies a criterion, a second dose is calculated using the first dose prediction model, the set of scalars, and the second fluence map 608. When the residual value does not satisfy the criterion, the second dose is calculated using a second (more accurate) dose prediction model and the second fluence map 608.
