First year experience with newly developed Leksell Gamma Knife Perfexion

Abstract

A new model of Leksell Gamma Knife(R) (LGK), known as Perfexion (LGK PFX), was introduced by Elekta Instrument, AB, Sweden, in 2006. This model has a radically different design from the earlier models U, B, C and 4C. Dosimetric characteristics of LGK PFX, technical differences between LGK PFX and LGK 4C, experience gained with acceptance testing and commissioning of the LGK PFX, and comparison between LGK PFX and LGK 4C are presented in this study. Excellent agreement is found between the manufacturers recommended values of absorbed dose rate, relative output factors for 4 and 8 mm collimators, coincidence of mechanical and dosimetric isocenter, FWHM for beam profiles for various collimators and those reported in the present study. Excellent agreement is also found between the dosimetric characteristics of LGK PFX and LGK 4C for the 4 and 8 mm collimators. Examples of clinical cases treated with LGK PFX and impact of LGK PFX on workflow and dosimetric conformity of treatment planning is also given. The set up and treatment of patients on the LGK PFX is much more efficient since it is a fully automated system. The system also provides more options to generate plan with high dosimetric conformity.

Keywords: Leksell Gamma Knife PERFEXION; Leksell Gamma Knife dosimetry; Leksell Gamma Knife treatment planning.

Figure 1

LGK PFX radiation unit and collimator system. A) Cross section of the LGK PFX radiation unit. B) Detailed view of sectors; each sector holds 24 ⁶⁰Co sources and can be moved independent of other sectors in desired position to define a collimator size or to block beams. C) Sector position which defines a 4 mm collimator. D) Sector position which defines a 8 mm collimator. E) Sector position which defines a 16 mm collimator. (With permission of Elekta Instrument AB, Stockholm, Sweden.)

Figure 2

Comparison of LGK PFX and LGK 4C profiles calculated for 4, 8, 14, 16, and 18 mm collimators for all stereotactic X, Y, Z axes. Profiles for LGK 4C are given as solid lines whereas those for LGK PFX are given as dotted lines

Figure 3

Example of using composite shots for the LGK PFX. To shape 50% isodose line and cover irregular target volume (meningioma) different combination of composite shots was used (see combination of eight sectors for each of eight different shots used). Different sector colors indicate different collimator size used: yellow – 4 mm, green – 8 mm, red – 16 mm and blue – blocked beams. Cross hatched sectors represent sectors that were automatically blocked by the treatment planning system to reduce dose to critical structures

Figure 4

Example of using dynamic shaping for the LGK PFX. To shape 50% isodose line and cover irregular target volume (meningioma) and minimize dose to brainstem different sectors were blocked for three shots located close to brainstem by dynamic shaping. Please see elongated shape of these three shots and blocking pattern of sectors. Different sector colors indicate different collimator size used: yellow – 4 mm, green – 8 mm and red – 16 mm. Cross hatched sectors represent sectors that were automatically blocked by the treatment planning system to reduce dose to critical structures

Figure 5

Comparison of patient distribution according to diagnosis between (A) LGK 4C and (B) LGK PFX treated during the first year after LGK PFX installation at the University of Pittsburgh Medical Center