Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen, Giessen, Germany. University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, Germany.
Phys Med Biol. 2018 Aug 1;63(15):155015. doi: 10.1088/1361-6560/aad148.
In 2016 the ICRU published a new report dealing with key data for ionizing radiation dosimetry (ICRU Report 90). New recommendations have been made for the mean excitation energies I for air, graphite and liquid water as well as for the graphite density to use when evaluating the density effect. In addition, the ICRU Report 90 discusses renormalized photoelectric cross sections, but refuses to give a recommendation on the use of renormalization factors. However, the Consultative Committee for Ionizing Radiation recommends to use renormalized photoeffect cross sections. Goal of the present work is to evaluate the impact of these new recommendations on clinical reference dosimetry for high energy photon and electron beams. The beam quality correction factor k was calculated by Monte Carlo simulations for compact and parallel plate ionization chambers. In case of photons seven phase space files from clinical accelerators and twelve spectra taken from literature from 4 MV to 24 MV and additionally a Co source were applied. As electron source thirteen electron spectra available in literature were used in the range of 4 MeV-21 MeV. The new ICRU recommendations have a small impact on Monte Carlo calculated k values for the chosen ionization chambers in the range of 0.1%-0.35% only-the difference increases for higher photon energies. The impact of the ICRU Report 90 recommendations on Monte Carlo calculated stopping power ratios s , perturbation factors p and beam quality correction factors k was investigated and confirmed a decrese of s by a fraction of a percent for photon and electron beams. This study indicates that the impact of the new ICRU recommendation is within 0.35%. The determined deviations should be taken into account, when widely published Monte Carlo calculated values are examined.
2016 年，ICRU 发布了一份新的报告，涉及离子辐射剂量学的关键数据（ICRU 报告 90）。该报告对空气、石墨和液态水的平均激发能 I 以及评估密度效应时使用的石墨密度提出了新的建议。此外，ICRU 报告 90 还讨论了归一化光电截面，但拒绝就使用归一化因子提出建议。然而，电离辐射咨询委员会建议使用归一化光电效应截面。本工作的目的是评估这些新建议对高能光子和电子束临床参考剂量学的影响。通过蒙特卡罗模拟为紧凑型和平行板电离室计算了束品质修正因子 k。对于光子，从临床加速器中应用了七个相空间文件和从文献中获取的十二个谱线，从 4MV 到 24MV，另外还有一个 Co 源。对于电子源，从文献中获取了 13 个电子谱线，应用范围为 4MeV-21MeV。对于所选的电离室，新的 ICRU 建议对 Monte Carlo 计算的 k 值的影响仅在 0.1%-0.35%之间，随着光子能量的增加，这种差异会增大。对 ICRU 报告 90 建议对 Monte Carlo 计算的阻止本领比 s 、微扰因子 p 和束品质修正因子 k 的影响进行了研究，并证实光子和电子束的 s 会降低几个百分点。这项研究表明，新的 ICRU 建议的影响在 0.35%以内。在检查广泛发布的 Monte Carlo 计算值时，应考虑到确定的偏差。
