A method of tumor ablation using injectable thermal-sensing balls. A catheter system (115) is used to inject a slurry (134) of thermal-sensing balls (136) into a tumor (122) located in, for example, a liver (120). The catheter system (115) comprises a catheter (128) and a specialized syringe (129) consisting of a housing (130) and a plunger (132). The housing (130) includes a cylindrical chamber having the slurry (134) of thermal-sensing balls (136). The catheter (128) is inserted retrograde into the femoral artery and passed to the site of the tumor (122). The hepatic artery (124) branches into smaller vessels, one of which is a tumor artery (126) which feeds the tumor (122). The tip of the catheter (128) is placed in the tumor artery (126) guided by conventional fluoroscopy. The injected balls (136) then receive energy from an external control system (110). The system (110) comprises a control panel (114) as an operator interface for controlling the system (110) and reading data therefrom. A CPU (112) is used for control and monitor of the operation, and transmits power and signals to the injected balls (136) via a radiating antenna (118), which energy is converted into heat to increase the temperature of the tumor (122). The temperature of the balls (136) can then be read from one or more onboard temperature sensors, and displayed to the operator for accurate control of the tumor temperature.