Novel systems for and methods of delivering therapeutic agents to target tissues are disclosed. The method of delivering a therapeutic agent to a target tissue involves identifying a target tissue via an imaging modality and then using a guidewire capable of anchoring in tissue to advance a cannula to the target tissue. The guidewire and novel cannula configurations enable rapid and repeated treatments of the target tissue without the need for subsequent imaging. The cannula is coupled to a source of ultrasound, radiation, radiofrequency energy, or chemotherapeutic agents which can then be delivered to from the cannula the target tissue. The system and method can be used to treat tumors that are small or surgically inoperable. In addition, the system can be used to treat lymphatic tissue that may contain metastases from the tumors.