Measurement of the stopping power of water in condensed phase for carbon ions in the energy range between 1 MeV and 5 MeV

1 MeV 至 5 MeV 能量范围内凝相水对碳离子的阻止本领的测量

• 批准号: 311099672
• 负责人: Dr. Woon Yong Baek
• 金额: --
• 依托单位: Abteilung 6 - Ionisierende Strahlung
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2020-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/311099672?language=en
• 关键词: Measurement; stopping; power; water; condensed

The accurate knowledge of the stopping power of liquid water for carbon ions in the intermediate energy region is of paramount importance for heavy ion dosimetry. Not only the relative biological effectiveness but also the absorbed dose in the target volume directly depends on the stopping power but also the ratio of the stopping power of water to that of air is the crucial parameter in determining the absorbed dose by means of air-filled ionization chambers that are used in most particle therapy centers. At present, the conversion of the ionization-chamber measurements to absorbed dose is based on the results of Monte-Carlo simulations. These simulations employ semiempirical and theoretical stopping power data which are only approximate for intermediate ion energies prevailing in the Bragg peak area, with the consequence that the greatest contribution to the uncertainty of the calculated absorbed dose arises due to the inaccuracy of the stopping power ratio water-to-air [1]. It has been found that the stopping power of condensed and gaseous substances can differ up to 48% for heavy ions [2]. For carbon ions in the intermediate energy region, it is even not clear whether the stopping power of a substance in liquid phase is smaller or greater than that in gaseous phase. It cannot be excluded that stopping power ratios water-to-air calculated using Monte-Carlo simulations are subject to uncertainties higher than the maximal tolerance [1] for the deviation between the prescribed and delivered dose to the target volume. Therefore, the examination of the stopping power ratios by means of experimental data is mandatory. Despite this importance, there exist no experimental data for the stopping power of liquid water for carbon ions in the intermediate energy region. The reason for this lack of experimental data is that accurate direct measurement of the stopping power of liquid substances for intermediate ion energies is not feasible because of their very short ranges. The present project is aimed to experimentally determine the stopping power of liquid water for carbon ions in the energy range between 1 and 5 MeV for the first time by means of a sophisticated experimental technique, the so-called Inverted Doppler Shift Attenuation (IDSA) Method. The project will provide important data for clinical dosimetry and for a more accurate assessment of the relative biological effectiveness in carbon ion cancer therapy. Furthermore, it will help to clarify the uncertainties with respect to the sign and the magnitude of the condensed phase effect for carbon ions.

中能区液态水对碳离子的阻止本领的准确认识对于重离子剂量学是至关重要的。不仅相对生物有效性，而且目标体积中的吸收剂量直接取决于阻止能力，而且水的阻止能力与空气的阻止能力的比率也是通过大多数粒子治疗中心中使用的充气电离室确定吸收剂量的关键参数。目前，电离室测量值到吸收剂量的转换是基于蒙特-卡罗模拟的结果。这些模拟采用了半经验和理论阻止功率数据，这些数据仅近似于布拉格峰区域中占主导地位的中间离子能量，其结果是，由于水与空气的阻止功率比的不准确性，对计算的吸收剂量的不确定性的最大贡献[1]。 已经发现，凝聚态和气态物质的阻止本领对于重离子可以相差高达48%[2]。对于中能区的碳离子，甚至不清楚物质在液相中的阻止本领是小于还是大于气相。不能排除使用蒙特-卡罗模拟计算的水-空气阻止功率比的不确定性高于处方剂量与靶体积输送剂量之间偏差的最大容差[1]。因此，必须通过实验数据检查阻止本领比。 尽管如此重要，在中能区液态水对碳离子的阻止能力还没有实验数据。缺乏实验数据的原因是，由于液体物质的射程很短，因此直接精确测量液体物质对中等离子能量的阻止本领是不可行的。本项目的目的是通过一种复杂的实验技术，即所谓的反向多普勒频移衰减（IDSA）方法，首次通过实验确定液态水对能量范围在1至5 MeV之间的碳离子的阻止能力。该项目将为临床剂量学和更准确地评估碳离子癌症治疗的相对生物学有效性提供重要数据。此外，这将有助于澄清关于碳离子凝聚相效应的符号和大小的不确定性。