Comparison and estimation of photoneutron dose produce between 10 MV flattened and unflattened beam in Elekta Versa HD? medical linac

Background: In a high-energy medical linear accelerator (linac), if the interaction of photon energy is higher than the neutron binding energy of high atomic material, it emits a neutron field through photonuclear (gamma, n) reaction.Aim: The current study, evaluates the photoneutron dose equivalent (PNDE) produced between the 10 MV flattened and unflattened beams as a function of field sizes in the Elekta Versa HD (TM) linac.Materials and Methods: The PNDE produced from Versa linac was recorded along the patient plane using the bubble detector personal neutron dosimeter and from the measured PNDE values, the theoretical PNDE values were simulated for various field sizes using nonlinear least-squares curve-fitting as a function of a polynomial. The percentage of deviation (PoD) and Chi-square (chi 2) tests were performed between the measured and simulated PNDE values to study the reliability and validity.Results: The results show that the mean PoD between the measured and simulated PNDE values for respective positions of a field size of FF beam was found to be -1.99% for 0.3x0.3, -4.39% for 5x5, -3.868% for 10x10, 0.590% for 15x15, 9.18% for 20x20, -4.133% for 25x25, and 0.467% for 30x30 cm(2). Similarly, the mean PoD between the measured and simulated PNDE values for flattening filter-free (FFF) beam was found to be 1.36% for 0.3x0.3, -1.39% for 5x5, -5.38% for 10x10, 4.41% for 15x15, 3.84% for 20x20, 5.69% for 25x25, and -1.75% for 30x30 cm2. The maximum deviation between the measured and simulated PNDE values lies within the range +/- 5%.Conclusions: From the study, it is observed that the FFF beam produces lesser neutron contamination than the FF beam.