Multiple cryoprobe placement strategy for a single freeze cryosurgery planning

The present work is concerned with the development of a numerical methodology for the placement of cryoprobes inside three-dimensional irregular-shaped tumors. A set of discrete regions enclosed by lethal temperature are superposed using the algorithm to predict the required number of cryoprobes, their placement, operation time, and resulting thermal damage to the tumor and surrounding healthy tissues. The algorithm developed is characterized using the parameter called cryoprobe-core using three values viz. 14, 12, and 10 mm2. It is found that the value of the cryoprobe-core affects the operation time, defect region, and invasiveness of the treatment. The efficacy of the present algorithm is tested using three hypothetical cases of irregular tumors. For the first case, the cryoprobe-core of 12 mm2 is found most optimum with a lethal temperature criterion of -50 °C. Based on the simulation results, an internal defect of less than 2% (i.e., treating >98% of the tumor volume) is predicted using five cryoprobes in a single bioheat simulation. The implementation of Stage-4 planning successfully reduced the internal defect to almost zero and cut down the operation time by almost 10 min without requiring any additional cryoprobe. The step-by-step methodology of the present work could assist the clinicians in the pre-planning stage of cryosurgery.