Measurements of photoneutron dose rate for 15 MV photon beam from medical linear accelerator using neutron survey meter

Abstract

High-energy medical linear accelerators (>10MV) are increasingly used in the medical field to treat cancer patients depending on the treatment organ and patient physic. Medical linear accelerators (Linacs) operating above 10 MV photon beam produce unwanted neutrons (photoneutron) by means of photonuclear reaction (γ, n) between bremsstrahlung photon beams and constituent materials of Linac head. This study involved the measurement of the neutron dose rate from photon beam of medical linear accelerator (Elekta Synergy) operated at 15 MV photon. For the measurement of dose rate, a neutron survey meter LB 6411 probe was used. Neutron dose rate was obtained as a function of delivered dose, field size and detector position. In the study neutron dose rate was found 13.14 mSv/h at a field size of 10 × 10 cm2

at position (0, 90, 0) cm for 350 cGy and 9.26 mSv/h at 5 × 5 cm2

field size at position (0, 80, 0) cm for 200 cGy photon dose delivery. The dose rate varied with respect to detector position in an irregular manner; 2.95 mSv/h at position (-100, 0, 0) cm -on the side of maze entrance and 4.85 mSv/h at position (100, 0, 0) cm -off side of maze entrance.