Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1881986 | Medical Dosimetry | 2013 | 8 Pages |
Abstract
The electron benefit transfer (EBT) GAFCHROMIC films possess a number of features making them appropriate for high-quality dosimetry in intensity-modulated radiation therapy (IMRT). Compensators to deliver IMRT are known to change the beam-energy spectrum as well as to produce scattered photons and to contaminate electrons; therefore, the accuracy and validity of EBT-film dosimetry in compensator-based IMRT should be investigated. Percentage-depth doses and lateral-beam profiles were measured using EBT films in perpendicular orientation with respect to 6 and 18Â MV photon beam energies for: (1) different thicknesses of cerrobend slab (open, 1.0, 2.0, 4.0, and 6.0Â cm), field sizes (5Ã5, 10Ã10, and 20Ã20Â cm2), and measurement depths (Dmax, 5.0 and 10.0Â cm); and (2) step-wedged compensator in a solid phantom. To verify results, same measurements were implemented using a 0.125Â cm3 ionization chamber in a water phantom and also in Monte Carlo simulations using the Monte Carlo N-particle radiation transport computer code. The mean energy of photons was increased due to beam hardening in comparison with open fields at both 6 and 18Â MV energies. For a 20Ã20Â cm2 field size of a 6Â MV photon beam and a 6.0Â cm thick block, the surface dose decreased by about 12% and percentage-depth doses increased up to 3% at 30.0Â cm depth, due to the beam-hardening effect induced by the block. In contrast, at 18Â MV, the surface dose increased by about 8% and depth dose reduced by 3% at 30.0Â cm depth. The penumbral widths (80% to 20%) increase with block thickness, field size, and beam energy. The EBT film results were in good agreement with the ionization chamber dose profiles and Monte Carlo N-particle radiation transport computer code simulation behind the step-wedged compensator. Also, there was a good agreement between the EBT-film and the treatment-planning results on the anthropomorphic phantom. The EBT films can be accurately used as a 2D dosimeter for dose verification and quality assurance of compensator-based C-IMRT.
Related Topics
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Authors
Seyedali Ph.D., Mahmoud Ph.D., Hasan A. Ph.D., Mohammadreza Ph.D., Alireza Ph.D., Mehran Ph.D.,