Baghani Hamid Reza, Shiri Ali, Gholamhosseinian Hamid
Physics Department, Hakim Sabzevari University, Sabzevar, Iran.
Medical Physics Department, Mashhad University of Medical Sciences, Mashhad, Iran.
Int J Radiat Biol. 2024;100(1):46-60. doi: 10.1080/09553002.2023.2242931. Epub 2023 Aug 9.
Employing electron beam for radiotherapy purposes now has been established as one of the standard cancer treatment modalities. Both dedicated intraoperative and conventional electron beams can be employed in patient irradiation. Due to the differences between accelerating structure and electron beam delivery of dedicated intraoperative radiotherapy (IORT) machines and conventional ones, the initial energy spectra of the produced electron beam by these machines may be different. Accordingly, this study aims to evaluate whether these spectral differences can affect the relevant relative biological effectiveness (RBE) values of intraoperative and conventional electron beams.
A hybrid Monte Carlo simulation approach was considered. At first, the head LIAC12 machine (as an IORT accelerator) and Varian 2100C/D (as a conventional accelerator) were simulated by MCNPX code and electron energy spectra at different depths and off-axis distances were scored for two nominal electron energies of 6 and 12 MeV at the field sizes of 6 and 10 cm. Then, the calculated spectra were imported to MCDS code to estimate the induced DNA-damage RBE values. Finally, the obtained RBE values for intraoperative and conventional electron beams were compared together.
The results showed that the RBE values of the intraoperative electron beam are superior to those obtained for conventional electron beam at the same energy/field size combination. Variations of the depth can regularly affect the RBE value for both conventional and intraoperative electron beams, while no ordered variation trend was observed for RBE with changing the off-axis distance. Variations of electron energy and field size can also influence the RBE value for both types of studied electron beams.
From the results, it can be concluded the structural differences between the dedicated IORT and conventional Linacs can lead to distinct initial electron energy spectra for intraoperative and conventional electron beams. These physical differences can finally lead to different RBE values for intraoperative and conventional electron beams at the same energy and field size.
利用电子束进行放射治疗现已成为标准的癌症治疗方式之一。专用术中电子束和传统电子束均可用于患者照射。由于专用术中放射治疗（IORT）机器与传统机器在加速结构和电子束传输方面存在差异，这些机器产生的电子束的初始能谱可能不同。因此，本研究旨在评估这些能谱差异是否会影响术中及传统电子束的相关相对生物效应（RBE）值。
采用混合蒙特卡罗模拟方法。首先，使用MCNPX代码对LIAC12机头（作为IORT加速器）和Varian 2100C/D（作为传统加速器）进行模拟，并在6和10 cm的射野尺寸下，针对6和12 MeV两种标称电子能量，对不同深度和离轴距离处的电子能谱进行评分。然后，将计算得到的能谱导入MCDS代码，以估计诱导DNA损伤的RBE值。最后，将术中及传统电子束获得的RBE值进行比较。
结果表明，在相同能量/射野尺寸组合下，术中电子束的RBE值优于传统电子束。深度变化会规律性地影响传统和术中电子束的RBE值，而随着离轴距离的变化，RBE未观察到有序的变化趋势。电子能量和射野尺寸的变化也会影响两种研究电子束的RBE值。
从结果可以得出结论，专用IORT与传统直线加速器之间的结构差异可导致术中及传统电子束具有不同的初始电子能谱。这些物理差异最终可导致术中及传统电子束在相同能量和射野尺寸下具有不同的RBE值。
