Monte Carlo study on beam hardening effect of physical wedges

Background: Physical wedges are still widely used as beam modifiers in external beam radiotherapy. However the presence of them in the beam trace may cause beam hardening which may not be considered in many treatment planning systems. The aim of this study is to investigate the beam hardening effect generated by physical wedges via different beam quality indexes as photon spectrum, half value layer, mean energy and tissue–phantom ratio. Materials and Methods: The effect of physical wedges on the photon beam quality of a 6-18MV Varian 2100C/D accelerator was studied with the BEAMnrc Monte Carlo code. Good agreements were obtained between measured and calculated depth doses and beam profiles for open and wedged photon beams at both energies. Results: It was noticed that for 6 MV photon beams, physical wedges have more significant effects on beam quality than for 18 MV. Also it was obtained that at 18 MV photon beam as the wedge angle increased, the effect of wedge on beam quality becomes reversed and beam softening occurred. Conclusion: According to these results, it is recommended that beam hardening and softening of physical wedges should be considered in treatment planning systems in order to increase the accuracy in dose delivery.