A study of flattening filter removal effect of 15 MV linac on photoneutron dose

In accelerators operating energies above 7 MV, photoneutrons are produced by the interaction of photonuclear interaction with the heavy metals that constructed the linear accelerator (linac) head. Photoneutrons have destructive biological effects and increase the risk of secondary cancer in healthy organs outside the treatment area. In this study, the effect of flattening filter removal on the spectrum and dose of photoneutrons from the Siemens Primus 15 MV linear accelerator was investigated using the MCNPX2.6 Monte Carlo code. The results showed that removing the flattening filter increased the photon and photoneutron flux at the isocenter. The absorbed doses of photons and photoneutrons dose equivalent per incident electron on the linac target were also increased, without a flattening filter. However, in this case, the photoneutron dose equivalent per 1Gy of the photon absorbed dose at the isocenter is reduced to 50% at different distances from the isocenter.