The
therapy operating characteristic (TOC) curve, developed in the context of
radiation therapy, is a plot of the probability of
tumor control versus the probability of normal-tissue complications as the overall radiation dose level is varied, e.g., by varying the beam current in external-beam
radiotherapy or the total injected activity in
radionuclide therapy. This paper shows how TOC can be applied to
chemotherapy with the administered drug dosage as the variable. The area under a TOC curve (AUTOC) can be used as a figure of merit for therapeutic efficacy, analogous to the area under an ROC curve (AUROC), which is a figure of merit for diagnostic efficacy. In
radiation therapy, AUTOC can be computed for a single patient by using image data along with radiobiological models for
tumor response and adverse side effects. The mathematical analogy between response of observers to images and the response of
tumors to distributions of a
chemotherapy drug is exploited to obtain linear discriminant functions from which AUTOC can be calculated. Methods for using mathematical models of drug delivery and
tumor response with imaging data to estimate patient-specific parameters that are needed for calculation of AUTOC are outlined. The implications of this viewpoint for clinical trials are discussed.