| The purpose of this dissertation was to evaluate the accuracy of the measurement of beam output factors (OFs) using a new American Rotating Gamma System (RGSA) GammaART-6000(TM), for stereotactic radiosurgery. The Monte Carlo simulation technique FOTELP code and GafChromic MD-55 films were employed to determine the output factors along the x-z plane, with a single shot. The (RGSA) GammaART-6000(TM) consists of 30 Cobalt-60 gamma radiation sources distributed asymmetrically around a hemisphere, confined within a sector of 72 degree, and delivers the radiation through a concentric collimating hemisphere is co-rotating with the sources [1]. This collimated the beam to be confined at the focal point by using different collimators with varying nominal diameters of 4, 8, 14 and 18 mm. Experiments were performed on a simulated spherical water equivalent phantom with a diameter of 160 mm. The output factors measurement with GafChromic films from the 4, 8 and 14 mm collimators relative to the 18 mm collimator are in good agreement with the values computed, from the Monte Carlo simulation program. |
