A mathematical model to predict tissue temperatures and necrosis during microwave thermal ablation of the prostate

Benign prostatic hyperplasia (BPH) is a condition commonly encountered in elderly men. It involves proliferative (but benign) growth of tissue in the prostate leading to a complex of bothersome urinary symptoms. Transurethral ablation of prostatic tissue by microwave radiation is now an accepted modality for the treatment of BPH and is oered as an alternative to a lifelong regimen of drugs or invasive surgery [1]. e procedure involves heating prostatic tissue by means of a microwave delivery catheter inserted into the prostate via the urethra. Figure 10.1 shows a cross-sectional view of the Targis microwave catheter CONTENTS 10.1 Introduction 345 10.1.1 Previous Modeling Eorts 348 10.1.2 Factors Inuencing Model Accuracy 349 10.2 Temperature Measurements in Human Subjects 350 10.3 e Mathematical Model 351 10.3.1 ermophysical Properties 353 10.3.2 Blood Perfusion Values 353 10.4 Studies in Tissue-Equivalent Phantom Gel 355 10.5 Prediction of Interstitial Temperatures in Human Subjects 357 10.6 Comparison of Observed and Predicted Zones of Tissue Necrosis 362 10.6.1 Prostate 362 10.7 Extension of the Model to Account for Phase Change 364 10.8 Conclusions 368 References 370 (Urologix, Inc., Minneapolis, Minnesota), one of several commonly used types. e catheter contains a microwave antenna surrounded by coolant channels, the latter serving to reduce the temperature elevation of the urethral surface. e catheter is positioned in the prostatic urethra, as shown in Figure 10.2. A balloon at the tip of the catheter is inated once the catheter is passed into the prostate. e catheter is then gently retracted to seat the balloon at the bladder neck, thus accurately locating the microwave antenna within the prostate. e ow of coolant through the catheter as well as the distribution of microwave heating within the prostate are depicted pictorially in Figure 10.3.