ABSTRACT
The Elekta Corporation was founded in 1972 by Lars Leksell and his two sons Daniel and Laurent to market the Gamma Knife, the Leksell Model G stereotactic frame, and other surgical devices that the elder Leksell had invented. The first commercial Leksell Gamma Unit (later designated the Model U) was delivered to the University of Pittsburgh Medical Center (UPMC) in 1987 (Wu et al. 1990). The 22-ton unit delivered to UPMC contained 201 cobalt-60 sources of nominal activity 1.11 TBq (30 Ci) each with specially machined interchangeable helmets (approximately 200 kg each) with nominal beam diameters of 4, 8, 14, and 18 mm (Figure 2.1a and b). Unlike the original Gamma Knife, the collimators were circular, not elliptical, and were designed to create a nearly spherical irradiation volume. Wu reported beam alignment within 0.2 mm and an absorbed dose rate (at the center of a 16-cm diameter plastic phantom) of greater than 3 Gy/min. A simple computer program (KulaPlan) was provided to calculate the treatment time and provide two-dimensional isodose contours for a single isocenter or “shot” with a computation time of about 15 min. The X (lateral), Y (anterior-posterior), and Z (superior-inferior) coordinates were set by hand and then verified by the treatment team before each shot. A system of beam plugs was used
Contents 2.1 Introduction 39 2.2 First-generation commercial device characteristics 39 2.3 Gamma Knife Perfexion 43
2.3.1 Description and basic operation 43 2.3.2 Treatment planning 46 2.3.3 Radiation protection 47 2.3.4 Extracranial patient dose 47
2.4 Fractionated treatments and relocatable frames 48 2.5 Dosimetry and quality assurance 50 References 51
to shape the beam into different three-dimensional (3-D) shapes for individualized patient treatments (Flickinger et al. 1990b).
