Instead of an objective function based on penalizing deviations from a prescribed dose, one might wish for an objective function that attempted to explicitly model the probability of controlling the tumor without inducing serious complications in normal tissue. Most current theoretical models of tumor control probability (TCP) and normal tissue complication probability (NTCP) are based on dose histograms, largely since more complicated models would require more data than currently available. Thus, a histogram-based approach such as the one above would be sufficient to implement a biological-response-based objective function.