Optimization of Multiprobe Cryosurgery

This paper describes a general technique for optimizing cryosurgical procedures. The method, which is based on the simplex minimization algorithm, minimizes unnecessary freezing by optimizing various surgical parameters. The optimization procedure is illustrated using a simplified model of prostatic cryosurgery. In this illustrative case, the function to be minimized, F, defined as the volume of healthy tissue destroyed during complete freezing of the prostate, is assumed to depend on three parameters: the number of cryoprobes used, the freezing length per cryoprobe, and the cryoprobe diameter. Using an iterative procedure, the optimization algorithm first alters these parameters, then calculates F by solving a three-dimensional bioheat transfer model of multiprobe cryosurgery, and finally determines whether F is minimized. The iterative procedure continues until unnecessary freezing is minimized. For the model considered here, the optimization code indicates that unnecessary freezing during cryoprostatectomy is minimized using approximately 5 cryoprobes, each 7.5 mm in length and 4 mm in diameter.