A system (10) for monitoring ablation size is provided. The system (10) includes a power source (200) including a microprocessor (335) for executing at least one control algorithm. A microwave antenna (100) is configured to deliver microwave energy from the power source (200) to tissue to form an ablation zone ("A"). A series of thermal sensors (136) is operably disposed adjacent a radiating section of the microwave antenna (100) and extends proximally therefrom. The thermal sensors (136) corresponding to a radius of the ablation zone ("A"), wherein each thermal sensor (136) generates a voltage when a predetermined threshold tissue temperature is reached corresponding to the radius of the ablation zone ("A").
