Evaluation of ambient dose equivalent for photoneutrons around linear accelerator and their radioprotection quantities

Abstract

The present work aims to assess in a first phase, different parameters influencing the creation and distribution of photoneutrons around Elekta Synergy medical linear accelerator.Field size and photon energy were investigated. The first parameter has allowed the evaluation of the intra and extra fraction of created neutrons. Thus, the ambient equivalent dose has attained in the isocenter, 0.198 ± 0.002 mSv/Gy of neutrons poisoning the therapeutic field, the extra field fraction didn't exceed 0.087 ± 0.001 mSv/Gy for all combinations of field sizes. The source of the current neutron dose is principally arising from the components of the linac head (target, flattening filter ….). The effect of photon energy assessed in the current work reaffirms the dependency of the photonuclear cross-section to photon energy. In fact, the bigger the photon energy is, the more neutron are created otherwise more dose delivered, a factor of 20 has been remarked between photons of 15 MV and 6 MV when comparing equivalent ambient dose H*(10) for both photon energies.In order to implement the optimization principle of radiation protection, the risk related to produced photoneutrons has been evaluated. The effective dose (E) is calculated according to methods established in ICRP 74 and ICRP 116 reports in addition ICRU publication 57, by making transition from the operational quantity H*(10) to the protection quantity E. Results has proved an additional exposition to unwanted dose resumed in an effective dose which could attain a value of 0.113 ± 0.002 mSv/Gy received by patient.