Radiation dosimetry in the Leksell Gamma Knife treatment room

The medical technology company Elekta is the manufacturer of the worldwide used Leksell Gamma Knife, LGK, an instrument specially designed for treating brain disorders. Sweden today has two LGKs treating patients, one of an older model and one newer. Both are owned by the Karolinska Hospital and placed in Stockholm. The radioactive sources of Cobalt in the machine lead to an enhanced radiation level in the treatment room and it is therefore important to have sufficient shielding in the surrounding walls. In this Master of Science Thesis the radiation in the LGK treatment room of both these machines has been measured, using a sodium iodide scintillator detector. The absorbed doses are calculated by integrating the resulting energy spectra from the detectorregistered particles. A Monte Carlo simulation program is used to simulate photon transport through the LGK machine. The absorbed doses and detector count rates are calculated and compared to the experimental values. The results show the differences between the photon transport in the two models, and that the radiation leakage is much higher in the older model. The comparison between the simulated results and the experimental results shows excellent agreement on the backside of the machine. This suggests a simulation method applicable for particle transport through the LGK.