DESIGN OF FIELD FLATTENING FILTERS FOR A HIGH-POWER BREMSSTRAHLUNG CONVERTER BY FULL MONTE-CARLO SIMULATION

To compensate for off-axis dose reduction, biconical-shaped Pb held fl attening filters were constructed for a specific high-power static Ta- C bremsstrahlung target configuration, at end-point energies 5 and 10 MeV. The filter design was optimized by full Monte Carlo simulation. T he absolute dose calculation was compared to experimental ionization a nd Fricke measurements. Spectral data were analysed and the influence of incident electron beam parameters (diameter, oblique Incidence) was simulated. With the constructed filtered set-up we are able to produc e any required gamma-dose rate up to a maximum value of 35 kGy/h in a water phantom at SSD 25 cm. The accomplished homogeneity at this dista nce is better than a few per cent over a surface of 25 cm diameter per pendicular to the beam axis, for both energies. (C) 1997 Elsevier Scie nce Ltd.