Abstract: An ultrasound medical system includes an interstitial end effector. The interstitial end effector is interstitially insertable into patient tissue, includes at least one medical-treatment ultrasound transducer, and includes at least one end-effector-tissue-track ablation device. One method for ultrasonically treating a lesion in a patient includes the steps of obtaining the interstitial end effector and inserting it into the patient creating a tissue track which is surrounded by patient tissue and which ends at the distal end of the inserted interstitial end effector. Other steps include ultrasonically ablating the lesion using the at-least-one medical-treatment ultrasound transducer, using the at-least-one end-effector-tissue-track ablation device to ablate the patient tissue surrounding the tissue track along substantially the entire tissue track, and withdrawing the end effector from the patient.