Dose distributions at extreme irradiation depths of gamma knife radiosurgery: EGS4 Monte Carlo calculations

The accuracy of the dose planning system (Leksell GammaPlan), used in Gamma Knife (type B) radiosurgery at extreme irradiation depths, was verified us ing the Monte Carlo technique. EGS4 Monte Carlo calculations were employed to calculate the dose distribution along the x, y and z axes for an irradia tion relatively shallow in a spherical bony cavity water phantom. Two diffe rent sizes of the collimator helmets, 8 and 18 mm, of the Leksell Gamma Kni fe Unit were studied. The results of GammaPlan showed good consistency with the Monte Carlo results. Furthermore, small dose enhancements were observe d in the skull bone where accurate dose measurements are difficult due to t he presence of the air-phantom interface. Therefore, the results of this pr oject can promote confidence to all Gamma Knife centres in the world when u sing the Leksell GammaPlan. (C) 2001 Elsevier Science Ltd. All rights reser ved.