Assessment of secondary neutron dose due to dental restorations in head and neck radiation therapy

Introduction: One of scientific concern is increasing of unwanted neutron dose to the patient, in head and neck radiation therapy due to the presence of some isotopes in dental restorations and head of medical linac. The aim of this study is to measure the equivalent dose of thermal and fast neutron due to head of Siemens Primus Linac and a healthy tooth, Amalgam, Ni-Cr alloy and Ceramco irradiated by 15 MV photon beams.   Materials and Methods: To evaluation of production of secondary neutrons due to the various dental restorations and head of medical linac in in 15 MV photon beam of Siemens Primus linac (Siemens AG, Erlangen, Germany), three commercial dental materials were used. This dental phantom configuration was consisted of combination of two healthy teeth, a tooth filled with Amalgam, a Ni-Cr alloy and Ceramco which they were collected randomly from dentistry clinics. The dental phantom was placed in depth of 1 cm in PMMA. In order to score of thermal and fast neutron equivalent doses, CR-39 detector was used. All the results of equivalent dose are considered to the delivery of 100 cGy dose at the maximum depth of 3.1 cm in the PMMA phantom with 15 MV photon beam and 10 × 10 cm2 field. Results: It is found out the maximum fast neutron dose was scored on the phantom surface which is related to head of Siemens primus linac. About the dental restorations, maximum fast neutron equivalent dose is related to amalgam, Ceramco and Ni-Cr alloy with amount of 0.19 mSv, 1.04 mSv, and 0.97 mSv at depth of 1.8 cm, respectively and then they decrease as the depth increases. The minimum amount of thermal neutron dose was measured on the surface of phantom. In case of denture samples, after dental phantom, the trend of the thermal neutron dose is reduced. The results indicated that maximum amount of thermal equivalent dose is related to Amalgam, Ceramco and Ni-Cr alloy and is equal to 1.45 mSv, 1.38 mSv, and 1.32 mSv, respectively. Conclusion: This study indicates an interpretation about photoneutron production in presence of the various dental restorations and head of Siemens primus medical linac. Presence of some elements in metallic dentures and head of medical linac, on the path of high photon beam can leads to the additional dose in the patient body. According to these results, thermal and fast neutron equivalent dose are started with an increase then they are reduced at depths after the dental restorations. Therefore, according to these results, it is recommended that some attempt should be carried out to make sure that the dental restorations are not in the path of primary photon beam with high energy.