Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin.
Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin.
Radiat Res. 2023 May 1;199(5):429-438. doi: 10.1667/RADE-22-00112.1.
Low-energy X-ray sources that operate in the kilovoltage energy range have been shown to induce more cellular damage when compared to their megavoltage counterparts. However, low-energy X-ray sources are more susceptible to the effects of filtration on the beam spectrum. This work sought to characterize the biological effects of the Xoft Axxent® source, a low-energy therapeutic X-ray source, both with and without the titanium vaginal applicator in place. It was hypothesized that there would be an increase in relative biological effectiveness (RBE) of the Axxent® source compared to 60Co and that the source in the titanium vaginal applicator (SIA) would have decreased biological effects compared to the bare source (BS). This hypothesis was drawn from linear energy transfer (LET) simulations performed using the TOPAS Monte Carlo user code as well a reduction in dose rate of the SIA compared to the BS. A HeLa cell line was maintained and used to evaluate these effects. Clonogenic survival assays were performed to evaluate differences in the RBE between the BS and SIA using 60Co as the reference beam quality. Neutral comet assay was used to assess induction of DNA strand damage by each beam to estimate differences in RBE. Quantification of mitotic errors was used to evaluate differences in chromosomal instability (CIN) induced by the three beam qualities. The BS was responsible for the greatest quantity of cell death due to a greater number of DNA double strand breaks (DSB) and CIN observed in the cells. The differences observed in the BS and SIA surviving fractions and RBE values were consistent with the 13% difference in LET as well as the factor of 3.5 reduction in dose rate of the SIA. Results from the comet and CIN assays were consistent with these results as well. The use of the titanium applicator results in a reduction in the biological effects observed with these sources, but still provides an advantage over megavoltage beam qualities. © 2023 by Radiation Research Society.
低能量 X 射线源在千伏能量范围内工作时，已被证明比兆伏 counterparts 更能引起细胞损伤。然而，低能量 X 射线源更容易受到光束谱过滤的影响。本工作旨在表征 Xoft Axxent®源的生物学效应，该源为低能治疗性 X 射线源，既有钛阴道应用器又无。据假设，与 60Co 相比，Axxent®源的相对生物学效应（RBE）会增加，并且与裸源（BS）相比，钛阴道应用器（SIA）中的源的生物学效应会降低。这一假设来自于使用 TOPAS 蒙特卡罗用户代码进行的线性能量转移（LET）模拟，以及与 BS 相比，SIA 的剂量率降低。维持 HeLa 细胞系并用于评估这些效应。使用 60Co 作为参考束质量，进行克隆存活测定，以评估 BS 和 SIA 之间的 RBE 差异。中性彗星测定法用于评估每种光束诱导的 DNA 链损伤，以估计 RBE 差异。有丝分裂错误的定量用于评估三种光束质量诱导的染色体不稳定性（CIN）差异。BS 导致的细胞死亡数量最多，因为观察到的细胞中 DNA 双链断裂（DSB）和 CIN 的数量更多。BS 和 SIA 存活分数和 RBE 值观察到的差异与 LET 的 13%差异以及 SIA 剂量率降低 3.5 倍的因素一致。彗星和 CIN 测定的结果也与这些结果一致。钛应用器的使用导致观察到的这些源的生物学效应降低，但与兆伏束质量相比仍具有优势。
