Computer assisted simulation model for cryoablation of prostate cancer including the possible injury of rectum

This study is to establish a preliminary computer assisted simulation model for cryoablation of a prostate cancer. It is hoped that the results from this study can supply valuable data for the clinician to refer to before a real cryosurgery or cryotherapy. In order to reach the goal of real implementation, a radiologist and an urologist in a medical center in addition to the engineering specialist from the university participated in this interdisciplinary research program. Firstly, hundreds of the two-dimensional medical imaging photos for the patient are obtained from the magnetic resonance imaging (MRI) in the imaging department of hospital. Through the imaging reconstructive software, these photos are trimmed into building a three-dimensional solid modeling. In this step, the urethra, bladder, prostate and rectum are segmented separately into an engineering graphic solid model with high resolution. Secondly, the number of probes, the position of each probe, and the operating time duration of each probe are determined in advance according to the clinical experience from a surgeon. Meanwhile, these data are transferred into the software package of thermal calculation for numerical simulations. Thirdly, the energy equation in the commercial software is modified to behave bio-heat transfer model by the input of user subroutines. Moreover, the occurrence of phase change during some specified temperature range and the latent heat of fusion are also incorporated into bio-heat transfer model to simulate the clinical situation for cryoablation of prostate cancer. In the simulation model, the three-dimensional transient temperature distributions based on cryosurgery for prostate cancer have been demonstrated precisely. The cryoprobes with various freezing time are considered to observe the temperature distribution. In addition, the frozen rectum is displayed in a region enclosed by a critical isotherm of 0°C. The simulated results for cryosurgery of prostate cancer can be supplied for practicing physicians as reference to greatly improve the effectiveness of cryosurgery.