A system for treating tissue of a passageway within a body, the system comprising: an energy source; wherein the energy source is a radio frequency generator; a medical device for delivering energy to a treatment site in the passageway within the body, the medical device including an elongate member having a proximal end and a distal end, the medical device being configured to receive an amount of energy from the energy source, a first portion of the amount of energy being transmitted through the distal end to tissue at the treatment site and a second portion of the amount of energy being reflected back towards the proximal end of the elongate member; wherein the medical device comprises an energy emitting portion; a dual directional coupler coupled to the medical device, the dual directional coupler being configured to detect a signal corresponding to one or both of the first portion of the amount of energy and the second portion of the amount of energy; and a controller configured to analyze the signal to determine the state of treatment, (i) wherein the signal corresponds to the first portion of the amount of energy, the signal has a power, and wherein the power decreases during delivery of energy to the tissue, and/or (ii) wherein the signal corresponds to the second portion of the amount of energy, the signal has a power, and wherein the power increases during delivery of energy to the tissue, and characterized in that the controller is configured to measure a rate of change of the power, to determine whether a change in the rate of change of the power passes a threshold value, and to terminate the supply of energy from the energy source when the change in the rate of change of the power falls under the threshold value. an energy source; wherein the energy source is a radio frequency generator; a medical device for delivering energy to a treatment site in the passageway within the body, the medical device including an elongate member having a proximal end and a distal end, the medical device being configured to receive an amount of energy from the energy source, a first portion of the amount of energy being transmitted through the distal end to tissue at the treatment site and a second portion of the amount of energy being reflected back towards the proximal end of the elongate member; wherein the medical device comprises an energy emitting portion; a dual directional coupler coupled to the medical device, the dual directional coupler being configured to detect a signal corresponding to one or both of the first portion of the amount of energy and the second portion of the amount of energy; and a controller configured to analyze the signal to determine the state of treatment, (i) wherein the signal corresponds to the first portion of the amount of energy, the signal has a power, and wherein the power decreases during delivery of energy to the tissue, and/or (ii) wherein the signal corresponds to the second portion of the amount of energy, the signal has a power, and wherein the power increases during delivery of energy to the tissue, (i) wherein the signal corresponds to the first portion of the amount of energy, the signal has a power, and wherein the power decreases during delivery of energy to the tissue, and/or (ii) wherein the signal corresponds to the second portion of the amount of energy, the signal has a power, and wherein the power increases during delivery of energy to the tissue,