Finite element heat transfer models of ferromagnetic thermoseeds and catheters were developed for computerized pretreatment planning of ferromagnetic hyperthermia. These models were implemented into a general purpose finite element program to solve the bioheat transfer equation. In simulations with a 4×4 array of thermoseeds in a twodimensional tissue model, the heat transfer model predicted that fractions of tumor greater than 43"C were between 8 and 40% lower when thermoseed temperature depended on power versus models which assumed a constant thermoseed temperature. The modeling of catheters was found to be necessary since the fractions of tumor greater than 420C in simulations using thermoseed and catheter models were between 1 and 45.3% lower than in simulations with bare thermoseeds.

An objective function was developed to aid in selecting optimal thermoseed temperatures and seed spacings a priori. The objective function has a physiological basis and considers increased cell killing at temperatures above 42 to 430C (= T_min,thera.). There is a penalty term in the objective function to account for heating of normal tissues above T_min,thera.. The objective function is independent of the size and shape of normal tissues included in the model. There is a scalar weighting factor γ in the objective function that has treatment implications. In a simple tissue model, it was shown that the uncertainties associated with cell survival above T_min,thera.. had a small effect on the fraction of tumor killed and on the objective function. It was also shown that the objective function identifies optimal thermoseed spacings that maximize the fraction of tumor killed. In a model of a tumor in the human prostate, it was shown that if a compromise was sought between maximizing the minimum tumor temperature (= T_min,tumor) and minimizing the maximum temperature in normal tissues (= T_max,normal) the objective function was an effective method to optimize the treatment plan. Additionally, it was shown in simulations that fractions of tumor above temperatures between 42 and 50 0C were between 0 and 60% higher with a temperaturedependent versus a constant blood flow model.