Study of tissue temperature distribution during laser-immunotherapy for cancer treatment

Abstract

Scope and Method of Study: The ideal cancer treatment modality should not only cause primary tumor suppression but also induce an anti-tumor immunity, which is essential in controlling metastatic tumors. Motivation of this work is to monitor temperature during laser-cancer treatment. A Monte Carlo method for the light transport in tissue and a finite difference method for the solution of heat diffusion equation were performed to estimate the laser dose parameters, and concentration levels of dye and immunoadjuvant. The specimens used were gelatin phantom, rats and mice. Magnetic Resonance Imaging thermometry (MRT) and infrared thermography (IRT) have been used for the measurement of temperature in the biological tissues during treatment of the primary tumors. Thermal imaging is used to estimate the laser-dose in application to cancer treatment. The thermal imaging and dose calculation can increase the level of safety in the treatment by providing information on target tissue and also on surrounding normal tissue.

Findings and Conclusions: Magnetic Resonance Imaging (MRI) has been applied to measure the thermal distribution in gel phantom and tumor-bearing rats during laser treatment. Infrared thermography has been applied to measure the surface temperature under the same conditions in tumor-bearing mice. Intratumoral injection of both indocyanine green (ICG) and glycated chitosan (GC) followed by 805-nm laser irradiation has been found efficacious in the cancer treatment. The temperature rise with ICG and laser combination therapy was about 25 °C and with the ICG, GC, and laser combination therapy, the temperature increased by 30 °C. This infers that ICG and GC injection potentiates the laser-immunotherapy. In both the cases, the tumor temperature attains the cancer cell damage temperature range of 60 °C - 70 °C resulting in an increase in the survival time of the treated mice. More importantly, the temperature profiles in this study agree with the Monte Carlo simulation results. In summary, a combination therapy using a laser, a laser-absorbing dye, and an immunoadjuvant guided by temperature measurement probes, such as MRT and IRT, is an effective treatment modality.