West German Proton Therapy Centre Essen (WPE), Essen, D-45147, Germany.
West German Cancer Center (WTZ), Essen, D-45147, Germany.
Radiat Oncol. 2019 Jan 11;14(1):6. doi: 10.1186/s13014-018-1186-8.
The availability of photon and electron spectra in digital form from current accelerators and Monte Carlo (MC) systems is scarce, and one of the packages widely used refers to linacs with a reduced clinical use nowadays. Such spectra are mainly intended for the MC calculation of detector-related quantities in conventional broad beams, where the use of detailed phase-space files (PSFs) is less critical than for MC-based treatment planning applications, but unlike PSFs, spectra can easily be transferred to other computer systems and users.
A set of spectra for a range of Varian linacs has been calculated using the PENELOPE/PRIMO MC system. They have been extracted from PSFs tallied for field sizes of 10 cm × 10 cm and 15 cm × 15 cm for photon and electron beams, respectively. The influence of the spectral bin width and of the beam central axis region used to extract the spectra have been analyzed.
Spectra have been compared to those by other authors showing good agreement with those obtained using the, now superseded, EGS4/BEAM MC code, but significant differences with the most widely used photon data set. Other spectra, particularly for electron beams, have not been published previously for the machines simulated in this work. The influence of the bin width on the spectrum mean energy for 6 and 10 MV beams has been found to be negligible. The size of the region used to extract the spectra yields differences of up to 40% for the mean energies in 10 MV beams, but the maximum difference for TPR values derived from depth-dose distributions does not exceed 2% relative to those obtained using the PSFs. This corresponds to k differences below 0.2% for a typical Farmer-type chamber, considered to be negligible for reference dosimetry. Different configurations for using electron spectra have been compared for 6 MeV beams, concluding that the geometry used for tallying the PSFs used to extract the spectra must be accounted for in subsequent calculations using the spectra as a source.
An up-to-date set of consistent spectra for Varian accelerators suitable for the calculation of detector-related quantities in conventional broad beams has been developed and made available in digital form.
当前加速器和蒙特卡罗（MC）系统提供的光子和电子能谱以数字形式呈现的情况较为少见，其中一个广泛使用的软件包是指现在临床应用较少的直线加速器。这些能谱主要用于传统宽束中与探测器相关的量的 MC 计算，在这种情况下，详细的相空间文件（PSF）的使用不如 MC 治疗计划应用程序那么关键，但与 PSF 不同的是，能谱可以轻松地转移到其他计算机系统和用户。
使用 PENELPE/PRIMO MC 系统为一系列瓦里安直线加速器计算了一套能谱。它们是从光子和电子束的 10cm×10cm 和 15cm×15cm 射野的 PSF 中提取出来的。分析了光谱-bin 宽度和用于提取光谱的束中轴线区域的影响。
与其他作者的能谱进行了比较，结果与使用现已过时的 EGS4/BEAM MC 代码获得的能谱吻合良好，但与最广泛使用的光子数据集存在显著差异。对于在这项工作中模拟的机器，其他的能谱，特别是电子束的能谱，以前没有发表过。对于 6MV 和 10MV 束，发现光谱平均能量对 bin 宽度的影响可以忽略不计。用于提取光谱的区域大小会导致 10MV 束平均能量的差异高达 40%，但从深度剂量分布得出的 TPR 值的最大差异相对于使用 PSF 获得的值不超过 2%。这对应于典型的 Farmer 型剂量计的 k 差异低于 0.2%，对于参考剂量学来说可以忽略不计。对于 6MV 束，比较了使用电子能谱的不同配置，得出结论：必须考虑用于提取光谱的 PSF 计数的几何形状，以便在后续使用能谱作为源的计算中进行考虑。
开发了一套适用于传统宽束中与探测器相关的量的 MC 计算的瓦里安加速器的最新、一致的能谱，并以数字形式提供。
