In recent years, the irruption of the image-guided radiotherapy (IGRT) has enabled the practice of non-invasive (frameless) radiosurgical treatments. 4Ĭlassically, SRS has relied on an invasive head frame for patient immobilization and target localization. Ideally, differences should be less than 1 mm to avoid important dose errors during the treatment delivery. The measured distances for all shots between the center of the ball shadow and the radiation field center reveal isocenter movements. The ball is then irradiated with several beams at different angulations of the gantry and couch, and each shot is imaged using a film placed perpendicular to the beam direction on a stand behind ball, or using the electronic portal imaging device (EPID) of the linac. The ball center is positioned at the linac isocenter defined by the lasers of the treatment room. 3 A small metallic ball phantom, which is representative of the planned target, is fixed to the linac couch by a locking mechanism. 2 The Winston-Lutz (WL) test is a well-described procedure developed for verification of the linac isocenter for cranial SRS. 1 Intracranial SRS was initially developed in the 1960s using a Gamma Knife platform, but a standard linear accelerator (linac) modified for stereotactic purposes has been an alternative approach to Gamma Knife SRS since the 1980s. Stereotactic radiosurgery (SRS) is a non-surgical radiotherapy procedure for the treatment of both benign and malignant lesions of the brain.
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