2Department of Medical Physics, Dokuz Eylül University, Institution of Health Science, İzmir-Türkiye
3İzmir Tınaztepe University, Vocational School of Health Services, İzmir-Türkiye
4Department of Atomic and Molecular Physics, Dokuz Eylül University, Faculty of Science, İzmir-Türkiye DOI : 10.5505/tjo.2023.4183 OBJECTIVE
This study aims to contribute to the literature the broadened demonstration of energy-related and field size-related responses of three different cylindrical ionization chambers, commonly used for clinical applications of the therapeutic photon beams, using GEANT4 code.
METHODS
GEANT4 simulation of Varian TrueBeam STx was compared with the real-time measurements. The
variations in the output factor (OF) measurements depending on field sizes ranging from 0.6×0.6 cm2
to 30×30 cm2 and photon energies of 6MV, 6MV-FFF, 10MV, 10MV-FFF, and 15MV were recorded for
each chamber and compared with the GEANT4 simulations. Response of the chambers was analyzed
depending on those OFs.
RESULTS
The GEANT4 simulation model was validated. All the chambers were in a good agreement within 1.5%
for field sizes between 4×4 cm2 and 30×30 cm2. The farmer chamber presented a major deviation up to
22% for the field sizes smaller than 4×4 cm2. Semiflex and pinpoint chambers have an agreement within
2% and 5.5% for 3×3cm2 and 2×2 cm2, respectively.
CONCLUSION
The chambers evaluated in this study can be used reliably for all photon energies and field sizes between
4×4 cm2 and 30×30 cm2. To obtain accurate measurements for field sizes smaller than 3×3 cm2, it is recommended
to use detectors with a smaller sensitive volume instead of the detectors used in this study.