A component of a microwave hyperthermia system designed to be placed inside the body to deliver microwave energy to produce a systemic or local heating effect. It is also referred to as an interstitial applicator or probe and is typically a catheter-enclosed conductor of microwave energy that is introduced into the body either manually or endoscopically. It typically includes a thermometry component that monitors the temperature of the device during operation. This is a single-use device.