Gamma Knife Stereotactic Radiosurgery for Brain Metastases Using Only 3 Pins

Background Removal of a pin during Gamma Knife stereotactic radiosurgery (GK-SRS) may be necessary to prevent collision and allow treatment. Objective To investigate outcomes after GK-SRS for treatment of brain metastases using a head frame immobilized to the skull with only 3 pins. Methods Between 2009 and 2014, we retrospectively reviewed the records of 1971 patients and identified 20 patients with multiple brain metastases treated with GK-SRS in which 1 anterior pin was removed immediately before treatment of a single posterior lesion. GK-SRS was also delivered to 116 other lesions in these 20 patients using the standard 4 pins during the same session, serving as an internal control for comparison. Endpoints included local control, dosimetric parameters, toxicity, and overall survival. Results The median number of lesions treated per session was 6 (range, 2-14). The lesions treated using 3 pins were located in the occipital lobe (n = 14) or the cerebellum (n = 6). Median follow-up was 12.3 months. There was 1 local failure involving a control lesion. Lesions treated using 3 pins had a lower prescription isodose line. GK-SRS of a lesion using 3 pins did not cause any clinical toxicities or increase in radiographic edema or hemorrhage. Conclusion Treating posteriorly located brain metastases with GK-SRS using only 3 pins provided excellent local control and no difference in treatment toxicity, which may make it a safe and reasonable option for lesions that may otherwise be difficult to treat.