We describe an optimization process specially designed for regional hyperthermia of deep seated tumors in order to achieve desired steady-state temperature distributions. A nonlinear three-dimensional heat-transfer model based on temperature-dependent blood perfusion is applied to predict the temperature. Optimal heating is obtained by minimizing an integral object function which measures the distance between desired and model predicted temperatures. Sequential minima are calculated from successively improved constant-rate perfusion models employing a damped Newton method in an inner iteration. Numerical results for a Sigma 60 applicator are presented.