Abstract: Apparatus for in situ radiotherapy has a flexible catheter having a proximal end for receiving a radiosotope and a distal end for positioning the flexible catheter within a patient to be treated. An anchor, which is permanently connectable to tissues deep inside the patient, has a sealing collar connected to it which seals the distal end of the catheter. The anchor has a penetration point connected to it to assist a surgeon in implanting the catheter within a tumor. A threaded fastener is connected to the anchor and screwed into the catheter. The flexible catheter can be released remotely from the anchor by unscrewing it. A suture eye is connected to the anchor. The suture eye may be sutured to healthy tissue within the patient when the apparatus is implanted to secure the anchor to the patient.