Comparison of Relative Dose Factors of a 6 MV Beam Measured With Diode, Radiochromic Film and Ionization Chambers in Different Orientations

Abstract

In this research study the output factors of a 6 MV beam were measured by using Razor diode, Gafchromic EBT-3 film and small volume ionization chambers 0.13 cc ionization chamber, 0.01 cc Razor ionization chamber from IBA –dosimetry, BahnhofstraBe, Germany. Both perpendicular and parallel orientations of ionization chambers relative to the propagation of radiation beam were considered. Varian Unique medical system Linac was used to deliver a 6 MV beam. Detectors were placed at the stage attached to the water phantom full of water. The measurements of output factor (OF) were conducted at different clinical set ups for source to surface distances of 100 and 90 cm at depths of dmax and 10 cm, respectively. From the results, relative errors (%) calculated on field size of 1 × 1 cm2 between output factors of 0.13 cc chamber and EBT-3 film when the chamber was positioned parallelly with respect to the beam central axis were -2.23 and 0.57%, and -19.68 and -9.40% at SSD = 90 cm and SSD = 100 cm respectively when the chamber was set perpendicularly relative to the beam central axis. Relative errors (%) calculated on field size of 1 × 1 cm2 between OFs of Razor chamber and EBT-3 film when the chamber was positioned parallel with respect to the beam central axis were 8.45 and 12.53%, and -3.29 and 4.12% at SSD = 90 cm and at SSD = 100 cm respectively when the chamber was set perpendicularly relative to the beam central axis. Relative errors (%) were also calculated between 0.13cc chamber and Razor diode, of which the findings were -7.75 and -9.97% at SSD = 90 cm and at SSD = 100 cm when the chamber was set parallel to the central beam axis. The study has shown that 0.13 cc ionization chamber could be a good choice for measurement of output factor from small to large field sizes when the chamber was positioned parallel with respect to the beam central axis.