A theoretical design of a flattening filter to improve field uniformity of a superficial therapeutic X-ray beam

الملخص EN

A Monte Carlo model has been developed using the EGS4 code to aid the design of a flattening filter, to improve field uniformity of a superficial X-ray machine.

The machine is operating at 90 kV and filtered with a 1.1 mm aluminium filter.

In the theoretical simulation the original flat filter was replaced by a varying thickness filter to improve the uniformity across field sizes 20, 5 and 2 cm diameter as well as hardening the beam.

Simulation results showed that flatness of the beam profile was improved for the 20 cm field size from ±7.3 % to ±1.1 % across the anode/cathode direction, and from ±7.7 % to ±3.2% in the anode/cathode direction.

For the 5 cm field size the improvement was from ±4.6% to ±3.1% and from ±5.5% to ±3.4 %, and for the 2 cm field size from ± 3.1 % to ±2.4 % and from ±10.2 % to ±9.5%, in the same directions, respectively.

Beam quality simulations were made and the original half-value layer was reduced from 2.21 ± 0.09 mm aluminium to 2.04 ± 0.09 mm aluminium.

The study demonstrated that it was possible to build a filter capable of flattening the beam profile for different sized applicators without significantly changing the penetrating ability of the beam.