1. A tumor-growth prediction system comprising: one or more electronic computational processors; one or more electronic memories; a computational model, stored in one or more of the electronic memories, that provides estimated tumor-cell concentrations at points within a tumor-containing tissue, the computational model parameterized by a tumor-cell proliferation coefficient and a tumor-cell migration coefficient; a parameter-estimation component, implemented by computer instructions that execute on the one or more electronic computational processors, that uses one or more images of a tumor and stored parameter-estimation data to estimate a specific tumor-cell proliferation coefficient and a specific tumor-cell migration coefficient for a specific tumor within a specific tissue of a patient; and a tumor-growth prediction component, implemented by computer instructions that execute on the one or more electronic computational processors, that, upon receiving a specified time and specified location within the specific tissue, uses the computational model, parameterized by the specific tumor-cell proliferation coefficient and the specific tumor-cell migration coefficient to estimate the concentration of tumor cells at the specified time and specified location within the specific tissue.