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首页> 外文期刊>Health Physics: Official Journal of the Health Physics Society >Depth dose-equivalent and effective energies of photoneutrons generated by 6-18 MV X-ray beams for radiotherapy.
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Depth dose-equivalent and effective energies of photoneutrons generated by 6-18 MV X-ray beams for radiotherapy.

机译：6-18 MV X射线束放射疗法产生的光中子的深度剂量当量和有效能量。

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摘要

Photoneutron production was investigated on Siemens KD 2 and Varian Clinac accelerators operating in the 6-18 MV range. Neutron dose equivalent rates were measured on the surface of a water phantom at the isocenter of the accelerators and also inside the phantom at depths of 1, 5, and 10 cm and off-axis distances of 0, 20, and 50 cm. Superheated drop detectors based on dichlorofluoromethane and etched-track detectors with boronated converters were employed in this study. The energy response of these detectors permits a direct measurement of dose equivalent without prior knowledge of the neutron energy spectra. Dose equivalent rates were assessed using the Q(L) relationship from ICRP publication 60, as well as using earlier data from ICRP publication 21. This permitted both a comparison with previously published data and an assessment of the impact of the recent ICRP recommendations--which were found to increase the dose equivalent levels by about 30%. In addition, the depth corresponding to 50% of maximum dose equivalent, dH50, was determined along the central axis of the beams and at 50 cm off-axis. Monte Carlo neutron transport calculations were performed to determine the depth-dose equivalent distributions in a phantom irradiated with monoenergetic neutrons. Effective energies of the photoneutron spectra were then estimated by comparing our measured dH50 values to those calculated for monoenergetic neutrons. It was found that the effective photoneutron energy is 1.8-2.1 MeV within the 10-18 MV x-ray beams, and it is 0.5-0.8 MeV for photoneutrons transmitted through the accelerator head. Data from this work cover most of the x-ray beam energies in clinical use and permit an assessment of integral dose values as well as specific organ doses to a radiotherapy patient.
机译：在6-18 MV范围内运行的Siemens KD 2和Varian Clinac加速器上研究了光中子的产生。在加速器的等中心处的水体模表面上以及在体模内部，深度分别为1、5和10 cm以及离轴距离为0、20和50 cm处，测量中子剂量当量率。在这项研究中使用了基于二氯氟甲烷的过热液滴检测器和带有硼化转换器的蚀刻轨迹检测器。这些检测器的能量响应可直接测量剂量当量，而无需事先了解中子能谱。使用ICRP出版物60中的Q（L）关系以及使用ICRP出版物21中的早期数据来评估剂量当量率。这可以与以前发布的数据进行比较，也可以评估最近的ICRP建议的影响-被发现可以将剂量当量水平提高约30％。另外，沿着束的中心轴并在离轴50cm处确定对应于最大剂量当量dH 50的50％的深度。进行蒙特卡洛中子输运计算，以确定用单能中子辐照的体模中的深度剂量当量分布。然后，通过将我们测得的dH50值与为单能中子计算出的dH50值进行比较，估算光中子谱的有效能量。已发现，在10-18 MV X射线束内，有效的光中子能量为1.8-2.1 MeV，对于通过加速器头传输的光中子，其有效光能为0.5-0.8 MeV。这项工作的数据涵盖了临床使用中的大多数X射线束能量，并允许评估放射治疗患者的整体剂量值以及特定器官剂量。

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