Department of Molecular and Clinical Cancer Medicine, Institute of Translational Medicine, University of Liverpool, The Sherrington Building, Ashton Street, Liverpool L69 3BX, United Kingdom. Department of Physics, Clatterbridge Cancer Centre, Clatterbridge Road, Wirral CH63 4JY, United Kingdom. Author to whom any correspondence should be addressed.
Phys Med Biol. 2018 Oct 3;63(19):198002. doi: 10.1088/1361-6560/aae0e4.
Andreo and Benmakhlouf (2017 Phys. Med. Biol. 62 1518-32) have disputed a finding of Scott et al (2012 Phys. Med. Biol. 57 4461-76) that the variation with field-size of the response of small ion chambers and solid-state dosimeters in small megavoltage photon radiation fields can largely be attributed to density. Further evidence for this finding was provided by Fenwick et al (2018 Phys. Med. Biol. 63 125003), but Andreo and Benmakhlouf (2018 Phys. Med. Biol. 63 125003) have now challenged the methodology used in that study. Specifically, Andreo and Benmakhlouf suggest that mass stopping-powers of fictitious materials used in Monte Carlo radiation transport calculations should be adjusted with material density according to the polarization effect, as if the materials were real and created by compressing other real materials. In this reply, we observe that fictitious materials are not real, and therefore their densities, mass stopping-powers and microscopic radiation interaction cross-sections can be freely and independently chosen to provide the clearest answers to the questions being studied. And we note that the key role played by density in small field detector response was further confirmed by our group back in 2013, using fictitious materials in which mass stopping-powers were adjusted with density, as preferred by Andreo and Benmakhlouf, as well as being held fixed, with very similar results being obtained in both circumstances (Underwood et al 2013a Med. Phys. 40 082102).
安德烈奥和本马克卢夫（2017 年《物理医学与生物学》62 卷 1518-32 页）对斯科特等人（2012 年《物理医学与生物学》57 卷 4461-76 页）的发现提出质疑，即小离子室和固态剂量计在小兆伏光子辐射场中随射野大小变化的响应，很大程度上可以归因于密度。费恩威克等人（2018 年《物理医学与生物学》63 卷 125003 页）提供了这一发现的进一步证据，但安德烈奥和本马克卢夫（2018 年《物理医学与生物学》63 卷 125003 页）现在对该研究中使用的方法提出了质疑。具体来说，安德烈奥和本马克卢夫认为，在蒙特卡罗辐射传输计算中用于虚构材料的质量阻止本领应根据极化效应根据材料密度进行调整，就好像这些材料是真实的，并通过压缩其他真实材料而产生。在这篇回复中，我们观察到虚构材料不是真实的，因此它们的密度、质量阻止本领和微观辐射相互作用截面可以自由和独立地选择，以最清晰地回答正在研究的问题。我们注意到，密度在小射野探测器响应中的关键作用早在 2013 年就被我们小组进一步证实，当时我们使用了质量阻止本领根据密度进行调整的虚构材料，正如安德烈奥和本马克卢夫所偏好的那样，或者保持固定，在这两种情况下都得到了非常相似的结果（安德伍德等人，2013a《医学物理学》40 卷 082102 页）。
