Photoneutron dose in soft tissue phantoms irradiated by 25 MV X-rays

Abstract

The photoneutron production and the absorbed dose in two soft tissue phantoms irradiated with 25 MV X-ray beams were estimated by means of the MCNP4 Monte Carlo code. Both single-beam and four-field box irradiations were considered. The neutron and photon therapy dose was calculated in various regions of the phantoms. An experimental verification of the photoneutron yield as a function of depth in a water phantom was also carried out by means of photoactivation reactions on 16O. An average photoneutron and X-ray integral dose ratio of 3.7*10-5 (photoneutron Gy kg-1)/(X-ray therapy Gy kg-1) was estimated inside the target volume of the four-field box irradiation phantom, whilst outside the integral dose ratio is 9.2*10-6 (photoneutron Gy kg-1)/(X-ray therapy Gy kg-1).