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In our study basic dosimetric properties of a flattening filter free 6 MV photon beam shaped by multileaf collimators (MLC) is examined using the Monte Carlo (MC) method.
Methods and Materials
BEAMnrc code was used to make a MC simulation model for 6 MV photon beam based on Varian Clinic 600 unique performance linac, operated with and without a flattening filter in beam line. Dosimetric features including central axis depth dose, beam profiles, photon and electron spectra were calculated and compared for flattened and unflattened cases.
Dosimetric field size and penumbra were found to be smaller for unflattened beam, and the decrease in field size was less for MLC shaped in comparison with jaw-shaped unflattened beam. Increase in dose rate of >2·4 times was observed for unflattened beam indicating a shorter beam delivery time for treatment. MLC leakage was found to decrease significantly when the flattening filter was removed from the beam line. The total scatter factor showed slower deviation with field sizes for unflattened beam indicating a reduced head scatter.
Our study demonstrated that improved accelerator characteristics can be achieved by removing flattening filter from beam line.
This study was designed to study the variations in different geometrical and dosimetric parameters.
Materials and methods
In this study, two groups comprises 21 and 28 patients, who were treated with 9·5 Gy × 2 Fx and 7·5 Gy × 3 Fx, respectively, using microselectron high-dose rate (HDR) remote control unit. All patients were analysed using orthogonal radiographs to evaluate variations in different parameters.
Variations in different parameters are more in Group II patients than in Group I patients, which show that the variation in geometrical and dosimetrical parameters increases with increasing HDR number of fractions.
In the reporting of an outcome of multiple fractionation of HDR treatments resultant dosimetric parameters must be evaluated and must be used for clinical interpretation.
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