Characterisation of MCP-600D and MCP-700D thermoluminescence detectors and their applicability for photoneutron detection

Experimental study of the influence of dental restorations on thermal and fast photo-neutron production in radiotherapy with a high-energy photon beam

In head and neck radiation therapy, the presence of dental restorations can increase unwanted neutron dose to the patient. This study aimed at the measurement of secondary neutron production induced by irradiation of a healthy tooth, Amalgam, Ni-Cr alloy and Ceramco with a photon beam generated in the treatment head of a Siemens Primus linac at a voltage of 15 MV. The irradiation field amounted to 10 × 10 cm². The measurements of thermal and fast-neutron equivalent doses were performed by means of CR-39 detectors positioned in various depths of a Perspex (polymethyl methacrylate) phantom as at open field as at presence of corresponding dental restorations. The general trend of thermal neutron as well as fast-neutron equivalent dose behind the denture samples reveals their reduction with increasing depth. The maximum values of thermal-neutron dose related to Amalgam, Ceramco and Ni-Cr alloy amount to 1.45 mSv/100 MU, 1.38 mSv/100 MU and 1.32 mSv/100 MU, whereas the corresponding maximum values of fast-neutron dose at the depth of 1.8 cm amount to 0.19 mSv/100 MU, 1.04 mSv/100 MU and 0.97 mSv/100 MU, respectively. The present study investigates the neutron dose accompanied with radiotherapy. It is recommended that attempts have to be made to ensure that dental restorations are not in the path of the primary high-energy photon beam. Considering treatment planning, the guidelines of radiation protection should be improved.

Photoneutron contamination from an 18 MV Saturne medical linear accelerator in the treatment room

Dose escalation with high-energy X rays of medical linear accelerators (linacs) in radiotherapy offers several distinct advantages over the lower energy photons. However, owing to photoneutron reactions, interaction of high-energy photons (>8 MV) with various high-Z nuclei of the materials in the linac head components produces unavoidable neutrons. The aim of this study was to evaluate the photoneutron dose equivalent per unit therapeutic X-ray dose of 18 MV, GE Saturne 20 linac in the treatment room using Monte Carlo (MC) MCNP linac head full simulation as well as thermoluminescence dosemeter measurements. This machine is one of the old linac models manufactured by General Electric Company; however, it is widely used in the developing countries because of low cost and simple maintenance for radiotherapy applications. The results showed a significant photoneutron dose from Saturne 20 linac head components especially at distances near the linac head (<150 cm). Results of this work could be used in several applications, especially designing bunker and entrance door shielding against neutrons produced by photoneutron reactions in GE Saturne 20. However, a detailed cost optimisation for a specific room would require a dedicated calculation.