PENUMBRA AND OUTPUT FACTORS MEASUREMENTS FOR SMALL AND NON-SMALL FIELDS IN RADIOTHERAPY
DOI:
https://doi.org/10.17656/jsmc.10156Keywords:
Small field, penumbra, Output factor, Ionizing chambers, Intensity modulated radiation therapyAbstract
Background
The use of radiotherapy linear accelerators in special procedures require strict quality assurance procedures to ensure the level of confidence in the accuracy of dose delivered. The radiation beam needs to be precisely targeted to maximize the dose to the target volume cancer, and minimize the dose to the surrounding healthy tissue.
Objectives
The aim of this study was to measure the penumbra and output factors of different ionization chambers for small and non-small fields using two photon energies.
Methods
The penumbra and output factors were measured using PinPoint, Roos, Farmer and Semiflex chambers at a depth of 10 cm and photon beam energies of 6 MV and 10 MV for both small (1×1, 2×2, 3×3) cm2 and non-small fields (4×4, 5×5, 10×10) cm2 defined by conventional multi-leaf collimators. As the same detectors, field sizes, photon energies were used to measure the output factors. The Percentage dose depth of the beam measured for all field sizes and beam energies.
Results
Our results showed that the extension of the Roos chamber was less than the other chambers and the output factors corresponding to non-small field 5×5 cm2 and above had identical values and exhibited similar Percentage dose depth (PDD) curves, while in those corresponding to small field 3×3 cm2 and below exhibited different output factors and PDD curves.
Conclusion
We conclude that the size of the chamber has a significant effect on the output factor and penumbra and the PinPoint chamber is the most suitable choice of chambers for use as an output detector from those available in Zhianawa cancer center.
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