Paper detail

Development of a 3-Dimensional Dosimetry System for Leksell Gamma Knife-Perfexion

The purpose of our study is to develop a new, 3-dimensional dosimetry system to verify the accuracy of dose deliveries in Leksell Gamma Knife-Perfexion TM (LGKP) (Elekta, Norcross, GA, USA). The instrument consists of a moving head phantom, an embedded thin active layer and a CCD camera system and was designed to be mounted to LGKP. As an active material concentrically located in the hemispheric head phantom, we choose Gafchromic EBT3 films and Gd2O2S;Tb phosphor sheets for dosimetric measurements. Also, to compensate the lack of backscatter, we located a 1 cm thick PMMA plate downstream of the active layer. The PMMA plate was transparent for scintillation lights to reach the CCD with 1200x1200 pixels by a 5.2 um pitch. Using this system, three hundred images by a 0.2 mm slice gap were acquired under each of three collimator setups, i.e. 4 mm, 8 mm, and 16 mm, respectively. The 2D projected images taken by CCD camera were compared with the dose distributions measured by EBT3 films in the same conditions. All 2D distributions were normalized by the maximum values derived by fitting peaks for each collimator setup. The FWHM differences of 2D profiles between of CCD images and of film doses were measured to be less than 0.3 mm. The scanning task for whole peak regions took less than three minutes with the new instrument. It could be utilized as a QA tool for the Gamma Knife radiosurgery system instead of film dosimetry, the use of which requires much more time and resources.