| NUKLEONIKA 2011, 56(1):49-51
THE EFFECT OF EXTERNAL WEDGE ON THE PHOTONEUTRON DOSE EQUIVALENT AT A HIGH ENERGY MEDIC LINACSeyed M. Hashemi1, Gholamreza Raisali2, Mehran Taheri3, Abbas Majdabadi1, Mostafa Ghafoori1 1 Dosimetry and Radiation Monitoring Research Group, Agricultural, Medical and Industrial Research School (AMIRS), Nuclear Science and Technology Research Institute (NSTRI), P. O. Box 31485-49, Karaj, Tehran, Iran 2 Radiation Applications Research School, Nuclear Science and Technology Research Institute (NSTRI), Atomic Energy Organization of Iran, End of Kargare Shomali, Tehran, Iran 3 National Radiation Protection Department, Iranian Nuclear Regulatory Authority, P. O. Box 14155-4494, Tehran, Iran Medical linacs used in radiotherapy produce bremsstrahlung spectra. In the energy range from 8 to 25 MV medical linacs produce, besides the clinically useful electron and photon beams, secondary neutrons. The aim of this study was to investigate the effect of an external wedge filter on the photoneutron dose equivalent produced by a medical linac at patient plane. Polycarbonate (PC) films were used for the determination of photoneutron dose equivalent produced by a Varian 2100 C/D linac working at 18 MV photon mode. Neutron dose equivalent was measured at distances 0, 10, 20 and 50 cm from the center of the X-ray beam for open field and after inserting a wedge filter. It was noted that by inserting the external wedge in the path of the X-ray beam, the photoneutron dose equivalent was increased compared to open field. It can be concluded that an external wedge, made from heavy materials may act like the other components of linac head, producing undesired photoneutrons and thus increasing patient dose. Close X |