RESUMO
Photoneutron production, and the dose equivalent, in the head assembly of the 15â¯MV Elekta Precise medical linac; operating in the faculty of Medicine at Alexandria University were estimated with the MCNP5 code. Photoneutron spectra were calculated in air and inside a water phantom to different depths as a function of the radiation field sizes. The maximum neutron fluence is 3.346×10-9 n/cm2-e for a 30×30â¯cm2 field size to 2-4â¯cm-depth in the phantom. The dose equivalent due to fast neutron increases as the field size increases, being a maximum of 0.912 ± 0.05â¯mSv/Gy at depth between 2 and 4â¯cm in the water phantom for 40×40â¯cm2 field size. Photoneutron fluence and dose equivalent are larger to 100â¯cm from the isocenter than to 35â¯cm from the treatment room wall.