Cooled antennas for spherical ablation

A system, comprising:

• an energy delivery device including an antenna operable to deliver energy to tissue of a patient, the antenna including:
• an outer conductor;
• a dielectric tube extending within the outer conductor;
• an inner conductor extending within the dielectric tube;
• and
• a coolant tube extending within the dielectric tube to convey a coolant to the antenna;
• and
• a controller operable to control a flow of coolant from a coolant supply through the coolant tube and to the antenna.

A method, comprising:

• advancing an antenna of an energy delivery device toward the tissue, the antenna including:
• an outer conductor;
• a dielectric tube extending within the outer conductor;
• an inner conductor extending within the dielectric tube;
• and
• a conductive sleeve arranged about the dielectric tube and offset from the outer conductor such that an axial gap is defined therebetween;
• conveying a current distally to the antenna via the inner conductor;
• preventing a return current from travelling proximally on the outer conductor with the conductive sleeve and thereby preventing back heating of the tissue along the outer conductor;
• and
• generating a substantially spherical ablation zone in the tissue by preventing the return current from travelling proximally on the outer conductor.