Biological optimization can be based on the possible risk characteristics for local recurrence in tumor sub-volumes rather than individual tumor voxels and treatment plans may be optimized using biological objective functions that are region-specific. To this end, risk characteristics for local recurrence should be identified and quantified using functional imaging or functional imaging in combination with biopsy data. However, the diagnostic accuracy (sensitivity and specificity) of these functional imaging techniques will have a definite impact on any optimization strategy that uses such imaging information as input. Therefore, a detailed understanding of the effects of theragnostic accuracy (i.e., sensitivity and specificity) on tumor control and normal tissue complications is crucial to achieve optimum clinical outcome.