Background: Nowadays, radiotherapy has an important role in the treatment of cancer. The use of medical linacs in radiotherapy can have risks for patients. When radiotherapy is performed with photons with energies higher than 8 MeV, due to the photonuclear reaction of photons with various components in the head of the accelerator, the neutron is produced. This imposes an unwanted neutron dose to the patient. The purpose of this study is evaluation and comparison of fast-neutron contamination with increasing of field size and depth for Siemens Primus (15 MV), Siemens Primus Plus (18 MV), and Siemens Artiste (15 MV) linacs.
Materials and Methods: Neutron dosimetry was carried out with CR-39 films, as a fast-neutron dosimeter, using chemical etching technique. Measurements were performed in depths of 0.5, 2, 3, and 4 cm and source-to-surface distance of 100 cm. Field sizes were 10 cm × 10 cm and 30 cm × 30 cm.
Results: The results of measurements showed that, with increasing depth, equivalent dose is reduced. In addition, fast-neutron equivalent dose decreases with increasing the field size.
Conclusion: Siemens Primus Plus had the highest neutron contamination in comparison with the two other linacs. Deeper tissues receive less fast-neutron doses. In radiation therapy with high-energy photon beams, neutron dose delivered to the patients should be taking into account.


中文翻译：

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不同型号西门子医用直线加速器与CR-39薄膜的快中子污染比较


背景：如今，放射治疗在癌症治疗中发挥着重要作用。在放射治疗中使用医用直线加速器可能会给患者带来风险。当使用能量高于 8 MeV 的光子进行放射治疗时，由于光子与加速器头部的各种组件发生光核反应，会产生中子。这将不希望的中子剂量强加给患者。本研究的目的是评估和比较 Siemens Primus (15 MV)、Siemens Primus Plus (18 MV) 和 Siemens Artiste (15 MV) 直线加速器的快中子污染随射野大小和深度的增加。
材料和方法：使用化学蚀刻技术对 CR-39 薄膜作为快中子剂量计进行中子剂量测定。在 0.5、2、3 和 4 厘米的深度和 100 厘米的源到表面距离进行测量。视野大小为 10 cm × 10 cm 和 30 cm × 30 cm。
结果：测量结果表明，随着深度的增加，当量剂量减少。此外，快中子当量剂量随着射野大小的增加而降低。
结论：与其他两个直线加速器相比，Siemens Primus Plus 的中子污染最高。较深的组织接受较少的快中子剂量。在使用高能光子束进行放射治疗时，应考虑输送给患者的中子剂量。