Department of Physics, Noorul Islam Centre for Higher Education, Kumaracoil- 629 180, Kanyakumari District, Tamil Nadu, India.
Department of Medical Physics and Radiation Safety, MVR Cancer Centre & Research Institute, Calicut, India.
Biomed Phys Eng Express. 2020 Sep 8;6(5):055018. doi: 10.1088/2057-1976/abac90.
A complex neutron spectrum generated along with a useful photon beam imposes an additional radiation protection risk around medical linear accelerators (linac). The thermal neutron component of this complex neutron spectrum formed during different photon modes of operation of Elekta Versa HD linac has been quantified using Indium foil activation technique. The thermal neutron fluence (Φ ) at isocenter for 15 MV, 10 MV and 10 MV FFF beams was found to be 2.45 × 10, 4.35 × 10 and 3.2 × 10 neutrons cm Gy, respectively. The analysis shows a reduction in the Φ as the flattening filter is being taken out from the beam path. A negative correlation in Φ with respect to field size has been observed with an average 18% reduction in Φ per monitor units as field size changes from 10 cm × 10 cm to 40 cm × 40 cm. For particular field size and photon energy, Φ was found to be uniform across the patient plane. From the measured gamma ray spectrum inside the treatment room six major isotopes have been identified which were Sb, W, Br, Mn, Na and Al.
在医用直线加速器（linac）周围，伴随有用光子束产生的复杂中子谱会带来额外的辐射防护风险。使用铟箔活化技术对 Elekta Versa HD 直线加速器在不同光子工作模式下形成的复杂中子谱中的热中子分量进行了量化。在等中心处，15 MV、10 MV 和 10 MVFFF 束的热中子通量（Φ）分别为 2.45×10、4.35×10 和 3.2×10 中子 cm Gy。分析表明，随着滤光板从光束路径中取出，Φ 值会降低。观察到 Φ 值与射野大小呈负相关，随着射野大小从 10 cm×10 cm 变化到 40 cm×40 cm，Φ 值平均每监测器单位降低 18%。对于特定的射野大小和光子能量，在患者平面内，Φ 值是均匀的。从治疗室内测量的伽马射线谱中鉴定出了六种主要的同位素，分别为 Sb、W、Br、Mn、Na 和 Al。
