Thermal Assessment of Ablation Limit of Subsurface Tumor During Focused Ultrasound and Laser Heating

Theoretical study on the thermal assessment of two types of tumor ablation techniques, viz., focused laser for ablating skin lesion and focused high-frequency ultrasound for ablating breast tumor has been presented in this article. Estimation of temperature rise and the induced thermal damage in the skin using laser heating have been done by integrating the bioheat transfer, the laser-light attenuation, and the thermal damage models. Further, ultrasound heating of deep seated tumor within the breast has been implemented to estimate the temperature rise and the induced thermal damage by combining the bioheat transfer, the vascularized, the pressure wave, and the thermal damage models. The theoretical models for skin, breast, and blood vessels have been constructed based on the anatomical details, thermophysical, optical, and acoustic properties available in the literature. The study indicates that the focused ultrasound heating can selectively raise the temperature of the tissue above the ablation limit sparing the surrounding healthy ones and imposes sufficient thermal damage to the entire tumor volume in a relatively short exposure time and longer cooling period. Whereas the laser-based heating would lead to collateral damage of the surrounding tissues and demands longer exposure time in order to achieve complete heating of the tumor volume. Heating of tumor at a uniform rate is a major issue in both the cases, and in the course of heating, the entire tumor volume in certain regions may experience irregular necrosis rate and char formation. Based on the comprehensive modeling efforts, the study further suggests two important thermal ablation criteria for complete and uniform heating of tumor volume at relatively short exposure time.