The impact of flattening filter free (FFF) photon beams to ion recombination correction factor

Abstract This study aimed to evaluate ion recombination correction for ionization chamber in flattening filter free (FFF) photon beams and compare it to the flattened (with-flattening-filter) photon beams. The evaluation of ion recombination correction factor was performed for FC65-G, SNC600c, and CC13 ionization chambers. The measurements of three ionization chambers were performed using the water phantom and the Varian Trilogy linac with FFF capability. The ion recombination correction factor values for the three ionization chambers were obtained from the calculation using the simple two-voltage method and Jaffe plot curve fitting. The ion recombination correction factor value obtained from all three ionization chambers were higher for unflattened (FFF) photon beams than the flattened (WFF) photon beams with discrepancy less than 3%. The ion recombination correction value obtained from the linear Jaffe plot curve fitting had the highest discrepancy at about 7.67% when compared to the two-voltage method. On the contrary, the ion recombination correction value obtained from the Jaffe plot with quadratic and exponential quadratic curve fitting had discrepancies less than 2% when compared to the two-voltage method.