In three inhomogeneous mediums, the performance of different algorithms for Flattening Filter Free (FFF) photon beams and Flattening Filter (FF) photon beams was evaluated. The three CT image sets of the CIRS phantom, each including an ionization chamber in the lung, bone, and tissue locations, were collected using the SAD configuration. For flattened and non-flattened photon beams, the corresponding Treatment Planning System (TPS) calculated and ionization chamber measured doses in the centre of chamber (in the three mediums) were compared. In lung structure, higher deviation was recorded in 10X10 cm2 field by all the three algorithms. These deviations are larger in magnitude, both FF and FFF, compared to water and bone mediums. Thus, both FF and FFF beams performed differently in lung, water, and bone mediums. Algorithms contribute to one of the potential sources of radiation delivery uncertainty.
Aim:
The present study was undertaken to evaluate the performance of different algorithms for flattening filter-free (FFF) and flattened (FF) photon beams in three different in-homogeneities.
Materials and Method:
Computed tomography (CT) image sets of the CIRS phantom maintained in the SAD setup by placing the ionization chamber in the lung, bone, and tissue regions, respectively, were acquired. The treatment planning system (TPS) calculated and the ionization chamber measured the doses at the center of the chamber (in the three mediums) were recorded for the flattened and non-flattened photon beams.
Results:
The results were reported for photon energies of 6 MV, 10 MV, 15 MV, 6 FFF, and 10 FFF of field sizes 5 × 5 cm2, 10 × 10 cm2, and 15 × 15 cm2. In the bone inhomogeneity, the pencil beam algorithm predicted that the maximum dose variation was 4.88% of measured chamber dose in 10-MV photon energy for the field size 10 × 10 cm2. In water inhomogeneity, both the collapsed cone and Monte Carlo algorithm predicted that the maximum dose variation was ± 3% of measured chamber dose in 10-MV photon energy for the field size 10 × 10 cm2 and in 10-MV FFF photon energy for the field size 5 × 5 cm2, whereas in lung inhomogeneity, the pencil beam algorithm predicted that the highest dose variation was - 6.9% of measured chamber dose in 10-MV FFF photon energy for the field size 5 × 5 cm2.
Conclusion:
FF and FFF beams performed differently in lung, water, and bone mediums. The assessment of algorithms was conducted using the anthropomorphic phantom; therefore, these findings may help in the selection of appropriate algorithms for particular clinical settings in radiation delivery.
The focus of this research was to calculate initial beam characteristics of a 6 MV X-rays with flattening filter (FF) from Elekta Versa-HD linear accelerator (Linac) using the Tool for Particle Simulation (TOPAS) Monte Carlo (MC) simulation code. TOPAS 3.6 simulated data was compared with the measured data. During simulation, all the main component were simulated including Linac head, Multi-Leaf Collimators (MLCs), and uniform water phantom, while the SNC 3D scanner phantom and SNC125c Chamber were used for measurements. At collimator sizes of 5x5, 10x10, and 20x20 cm2, the depth dose scans (PDD) distribution and beam profiles (BP) were measured. The estimated tissue phantom ratio (TPR20,10) was 0.669, which was -1.1 percent lower than the measured TPR20,10 of 0.681. The obtained results show that the simulated and measured data were in good agreement, with gamma rate analysis of 3%/3 mm criteria reaching 95% and 99 % for PDD and BP respectively.
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