A noninvasive localization and immobilization technique that facilitates planning and accurate delivery of both intensity modulated radiotherapy (IMRT) and linac based stereotactic radiotherapy (SRT) of intracranial tumors has been developed and clinically tested. Immobilization of a patient was based on a commercially available Gill-Thomas-Cossman (GTC) relocatable frame. A stereotactic localization frame (LF) with the attached NOMOS localization device (CT pointer) was used for CT scanning of patients. Thus, CT slices contained fiducial marks for both IMRT and SRT. The patient anatomy and target(s) were contoured on a stand-alone CT-based imaging system. CT slices and contours were then transmitted to both IMRT and SRT treatment planning systems (TPSs) for concurrent development of IMRT and SRT plans. The treatment method that more closely approached the treatment goals could be selected. Since all TPSs used the same contour set, the accuracy of competing treatment plans comparison was improved. SRT delivery was done conventionally. For IMRT delivery patients used the SRT patient immobilization system. For the patient setup, the IMRT target box was attached to the SRT LF, replacing the IMRT CT Pointer. A modified and lighter IMRT target box compatible with SRT LF was fabricated. The proposed technique can also be used for planning and delivery of 3D CRT, thus improving its accuracy. Day-to-day reproducibility of the patient setup can be evaluated using a SRT Depth Helmet.