Abstract
We introduce a pharmacodynamic model that describes the tumor volume evolution during and after treatment with radiation and radiosensitizing agents. A key contribution is the inclusion of a long-term radiation effect, which allows the model to describe distinct tumor behaviors including tumor eradication and tumor regrowth with different growth rates. The model also accounts for the effects of combining radiation therapy with radiosensitizing treatment. The was model fitted to data from xenograft experiments using a clinically-relevant administration schedule.