systemLeksellGamma Knife

Elekta Leksell Gamma Knife Perfexion

Manufacturer: Elekta Leksell · Modality: Gamma Knife

Fourth-generation Leksell Gamma Knife platform. Replaced the earlier Model 4C (and the U / B / C hemispherical-source predecessors) with a fundamentally new source geometry and collimation system. The dominant framed-SRS platform through the late 2000s and 2010s; installed base remains broad, and Perfexion is the immediate predecessor of the current Leksell Gamma Knife Icon.

Radiation source and collimator architecture

  • 192 sealed Cobalt-60 sources arranged in a cylindrical (not hemispherical) geometry across 5 rings, giving a source-to-focus distance range of 374–433 mm depending on ring position.
  • 8 motorized sectors — each sector carries 24 sources and moves independently to any of five collimator positions: 4 mm, 8 mm, 16 mm, blocked, or home.
  • Single tungsten collimator ring — the 120 mm-thick tungsten array replaced the primary + secondary collimator helmets used on previous generations. The three aperture sizes (4 / 8 / 16 mm) are selected by physical sector motion over the fixed collimator ring rather than by swapping helmets.
  • Shaped-beam delivery — mixing collimator sizes across sectors within a single shot creates a non-spherical dose distribution, useful for irregular target shapes (vestibular schwannoma, meningioma, AVM).

Automated patient positioning

  • Automatic Positioning System (APS) — submillimetric accuracy, replaced the Trunnions + manual-frame coordinate setting of prior Gamma Knife generations. Patient couch translates in three axes under computer control to place each shot's focus at the intended stereotactic coordinate.
  • Frame-based workflow — Perfexion uses the Leksell Coordinate Frame G (rigid frame pinned under local anesthesia) for stereotactic localization. Frameless workflows require the Icon.

Specs

  • 192 × Co-60 sealed sources · 8 sectors × 24 sources
  • Collimator apertures: 4, 8, 16 mm (plus blocked / home per sector)
  • Source-to-focus distance: 374–433 mm (5-ring cylindrical geometry)
  • APS submillimetric automated patient positioning
  • Leksell GammaPlan treatment planning
  • Leksell Coordinate Frame G (required)

Clinical positioning

  • Brain metastases — single-fraction SRS to multiple targets in one session.
  • Meningioma, vestibular schwannoma, pituitary — benign skull-base tumors.
  • AVM — arteriovenous malformation treatment, typically single-fraction.
  • Functional — trigeminal neuralgia, select functional indications.
  • Skull base and cranial-nerve-adjacent targets — mm-level accuracy is clinically consequential.

Regulatory and operational reality

  • NRC / state radiation license required for the Co-60 source inventory; Radiation Safety Officer oversight, source exchange logistics on ~5–7 year cadence depending on activity decay and clinical schedule. See NRC licensing.
  • Source decay — Co-60 half-life is 5.27 years. Treatment times lengthen progressively until reload; the reload economics drive the Perfexion-vs-Icon replacement conversation at many centers.
  • Dedicated shielded vault — siting requirements per lead shielding and national radiation-safety code.

Relationship to siblings

  • Leksell Gamma Knife Icon — successor. Same 192-source / 8-sector / 4-8-16 mm collimator architecture, plus integrated CBCT and frameless-mask capability.
  • Prior Gamma Knife generations (4C, C, B, U) — hemispherical-source helmet-collimator architectures, largely retired or operating through end-of-life.

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