Beyond Liquid Nitrogen Coolant: Extreme Freezing to Maximize Cryosurgical Ablation of Tumor

As a minimally invasive physical therapy for targeted tumor treatment, cryosurgery is increasingly used in a wide variety of clinical situations such as for freezing ablation of skin cancers, glaucoma, lung tumor etc. owing to its outstanding virtues like quick, clean, relatively painless, good homeostasis, and satisfactory of little scar. A most important issue in performing such a surgical operation is to guarantee a strong enough freezing while minimizing the mechanical insertion trauma. Among the many freezing protocols ever developed, using a needle to deliver liquid nitrogen to the target tissues has been the most popular way to ablate the tumor. A critical need from the clinical aspect is that the size of the freezing needle should be as small as possible while supplying extremely large amount of cold to the target so as to take full use of the unique minimally invasive merit of the cryosurgery. This paper evaluated the freezing performance of different working fluids including liquid helium (He), liquid nitrogen (N₂), alcohol (Alc), dichlorodifluoromethane (R12) and 1,1,1,2-Tetrafluoroethane (R134a). The freezing capabilities inside the biological tissues of several most promising coolant candidates were comparatively evaluated through the three-dimensional phase change bioheat transfer simulation. Future applications were suggested. It is expected that the present freezing strategy would offer new opportunities for realizing a better tumor cryosurgical ablation over existing coolants.