An electrosurgical system comprising: an electrosurgical energy source; a feedline including an inner conductor, an outer conductor coaxially-disposed about the inner conductor, and a dielectric material disposed between the inner conductor and the outer conductor; a probe operably coupled to the electrosurgical energy source by the feedline, the probe including an antenna assembly having a radiating portion ("R") and defining a coolant chamber about the antenna assembly; a flexible, extendable/retractable fluid cooled shaft coupled in fluid communication with the coolant chamber, the shaft adapted to remove heat along the length of the feedline during delivery of energy to the antenna assembly, characterized in that the shaft includes: an inlet sleeve; an outlet sleeve; an inner tubular member coaxially disposed about and slideably coupled to the inlet sleeve, the inner tubular member disposed around a portion of the feedline to define a fluid inflow conduit between the inner tubular member and the antenna assembly, the fluid inflow conduit fluidly coupled to the coolant chamber; and an outer tubular member coaxially disposed about and slideably coupled to the outlet sleeve, the outer tubular member fluidly coupled to the coolant chamber and disposed around the inner tubular member to define a fluid outflow conduit between the outer tubular member and the inner tubular member; wherein the shaft is selectively adjustable relative to the feedline between a first length, where the shaft is in a retracted configuration, and a second length, where the shaft is in an extended configuration. an electrosurgical energy source; a feedline including an inner conductor, an outer conductor coaxially-disposed about the inner conductor, and a dielectric material disposed between the inner conductor and the outer conductor; a probe operably coupled to the electrosurgical energy source by the feedline, the probe including an antenna assembly having a radiating portion ("R") and defining a coolant chamber about the antenna assembly; a flexible, extendable/retractable fluid cooled shaft coupled in fluid communication with the coolant chamber, the shaft adapted to remove heat along the length of the feedline during delivery of energy to the antenna assembly, an inlet sleeve; an outlet sleeve; an inner tubular member coaxially disposed about and slideably coupled to the inlet sleeve, the inner tubular member disposed around a portion of the feedline to define a fluid inflow conduit between the inner tubular member and the antenna assembly, the fluid inflow conduit fluidly coupled to the coolant chamber; and an outer tubular member coaxially disposed about and slideably coupled to the outlet sleeve, the outer tubular member fluidly coupled to the coolant chamber and disposed around the inner tubular member to define a fluid outflow conduit between the outer tubular member and the inner tubular member; an outlet sleeve; an inner tubular member coaxially disposed about and slideably coupled to the inlet sleeve, the inner tubular member disposed around a portion of the feedline to define a fluid inflow conduit between the inner tubular member and the antenna assembly, the fluid inflow conduit fluidly coupled to the coolant chamber; and an outer tubular member coaxially disposed about and slideably coupled to the outlet sleeve, the outer tubular member fluidly coupled to the coolant chamber and disposed around the inner tubular member to define a fluid outflow conduit between the outer tubular member and the inner tubular member; wherein the shaft is selectively adjustable relative to the feedline between a first length, where the shaft is in a retracted configuration, and a second length, where the shaft is in an extended configuration.