Assessment of Linear Accelerator for Radiotherapy Performance in RICK

Abstract

viii Abstract This Study was performed to evaluate the linear accelerator performance in radiation and isotopes center Khartoum (RICK) concerning the mechanical tests done according to AAPM protocol and Canadian protocol. The result showed that the collimator isocenter rotation was optimum at 0 mm shift, Gantryisocenter rotation was at 2 mm shift and the table rotation was optimum at 0 mm shift i.e. all parameters were within the tolerance.Also the light and radiation field congruence showed 2 mm shift, the laser beam coincidence showed 2mm shift, the variation of field size (20x20, 14x14, 12x12, 10x10, 8x8, 6x6, 4x4 and 2x2cm2) versus SSD was optimum and the correlation was so significant at R2 =0.998. The Dose rate increase with Field sizes increment due to scatter from collimator, in the other hand the dose decreases with SSD increment according to inverse square law which was verified for field size 10x10 cm2 and 2x2 cm2. The temperature effect causes change in the output measurement according to the following equation: Y = 0.0041X+1.093, where Y refers to output in Gy/MU and X refers to temperature, while the pressure leading to change in the output measurement according to the following equation: Y = 0.063X + 7.298, where Y refers to output and X refers to pressure.ix The effect (temperature and pressure correction factor) the output varies linearly according to the following equation: Y = 1.0129X + 0.2901, where Y refers to output and X refers to temperature pressure correction factor.