Temperature control in deep tumor treatment

摘要

Tumor cells are more sensitive to temperature increase than normal tissue. Hyperthermia has been used as a potential modality for cancer treatment. Another benefit from the thermal interruption of tumor cells is the immunological reactions, caused by inflammation and other mechanisms, and more interestingly caused by antigen(s) release. The temperature control is crucial both in direct tumor destruction through acute thermal effect and in immune reactions. Low temperature may not achieve the desired tumor cell killing. High temperature could result in over heating of the tumor, hence introducing undesirable damage to surrounding normal tissue. High temperature could completely denature the cell proteins, hence rendering tumor antigen(s) useless in immunological stimulation. A combination of an 805-nm, laser and in-situ indocyanine green (ICG) solutions were used in treating rat tumors. Temperature measured at different locations showed that the effective photothermal interaction could reach as deep as 1 cm below the treatment surface and the temperature inside the tumor can be controlled by the laser and dye parameters. Multiple beams were also used to irradiate the tumor. When the tumor is free of ICG, the temperature increase of the tumor was less significant under the laser irradiation with a power density of 0.33 W/cm~2; tumor tissue at a depth of 1 cm only experienced a 7°C-temperature increase. However, when the tumor contained ICG solution, the temperature at 1-cm depth experienced more than 15°C-temperature increase. Multiple-fiber irradiation further enhanced the photothermal selectivity. Furthermore, when one fiber was used, the edge of the tumor experienced less impact by the laser beam, while multiple beams resulted in an almost uniform temperature increase over the entire tumor.