This is the first report of prolonged antitumor response to and radiographic complete remissions as a result of CAPTEM in patients with aggressive pituitary tumors who had exhausted all other therapies.

T he high dose of radiation delivered via stereotactic radiosurgery (SRS) requires accurate and reproducible immobilization of the head. 7 Accuracy within a range of 1-2 mm is essential to limit irradiation of surrounding anatomical structures. A rigid stereotactic head frame has traditionally been used for fixation in Gamma Knife (GK) radiosurgery. 20 Frame-based fixation allows for precise delivery of a single high-dose fraction of radiation treatment. Motion error associated with frame-based fixation is estimated to be ≤ 1-1.5 mm. 12 New SRS strategies for the treatment of large intracranial lesions have trended toward the use of multifractionation stereotactic radiotherapy (SRT) treatments. But head frame placement is invasive, involving 4-point fixation us-ABBREVIATIONS CBCT = cone-beam computed tomography; GK = Gamma Knife; IR = infrared; LINAC = linear accelerator; SRS = stereotactic radiosurgery; SRT = stereotactic radiotherapy. OBJECTIVE The Leksell Gamma Knife Icon (GK Icon) radiosurgery system can utilize cone-beam computed tomography (CBCT) to evaluate motion error. This study compares the accuracy of frame-based and frameless mask-based fixation using the Icon system. METHODS A retrospective cohort study was conducted to evaluate patients who had undergone radiosurgery with the GK Icon system between June and December 2017. Patients were immobilized in either a stereotactic head frame or a noninvasive thermoplastic mask with stereotactic infrared (IR) camera monitoring. Setup error was defined as displacement of the skull in the stereotactic space upon setup as noted on pretreatment CBCT compared to its position in the stereotactic space defined by planning MRI for frame patients and defined as skull displacement on planning CBCT compared to its position on pretreatment CBCT for mask patients. For frame patients, the intrafractionation motion was measured by comparing pretreatment and posttreatment CBCT. For mask patients, the intrafractionation motion was evaluated by comparing pretreatment CBCT and additional CBCT obtained during the treatment. The translational and rotational errors were recorded. RESULTS Data were collected from 77 patients undergoing SRS with the GK Icon. Sixty-four patients underwent frame fixation, with pre-and posttreatment CBCT studies obtained. Thirteen patients were treated using mask fixation to deliver a total of 33 treatment fractions. Mean setup and intrafraction translational and rotation errors were small for both fixation systems, within 1 mm and 1° in all axes. Yet mask fixation demonstrated significantly larger intrafraction errors than frame fixation. Also, there was greater variability in both setup and intrafraction errors for mask fixation than for frame fixation in all translational and rotational directions. Whether the GK treatment was for metastasis or nonmetastasis did not influence motion uncertainties between the two fixation types. Additionally, monitoring IR-based intrafraction motion for mask fixation-i.e., the number of treatment stoppages due to re...