Abstract

Purpose

In the modern era of radiotherapy, use of conventional radiation modalities (based on γ-rays) is being replaced by high-energy linear accelerator-based X-rays. As a result of mishandling of equipment or mechanical errors, health workers can be exposed to these high-energy X-rays. Especially in the absence of personnel monitoring devices, biodosimetry with a lower energy X-ray calibration curve may not provide an acceptable dose estimate. Moreover, the relative biological effectiveness (RBE) value assigned for X-rays is the same (ONE) regardless of beam energy (V), employed in diagnosis, interventional medicine, and radiotherapy. Therefore, the purpose of the study is to examine the induced biological effects, measured through micronucleus (MN) formation, of X-rays of different energies (3 and 6 MV X-rays), and to investigate the RBE relative to 225 kVp X-rays.

Materials and methods

Peripheral blood lymphocytes (PBLs) from healthy donors (n = 6), were irradiated with 225 kVp, 3 MV, and 6 MV energy X-rays and induced biological damage was quantified as MN formation using the cytokinesis blocked MN (CBMN) assay.

Results

The MN per cell in the X-irradiated samples for the three different X-ray energies showed a significant (p<.0001) dose-dependent increase, when compared to unexposed samples. Aberration frequencies obtained at the same dose for the three different energies showed significant (p<.05) difference for the MN per cell among the energy levels; however, the in vitro dose–response curve parameters (slope, intercept, and coefficient) did not show any significant differences. The estimated dose in the blinded sample was within the 95% confidence intervals of each of the calibration curves. However, overall, the 6 MV dose–response curve coefficients yielded the closest dose estimate to that of the true dose. The calculated RBE values at 5% induced MN for 3 and 6 MV LINAC X-rays were 2.0 ± 0.04 and 0.70 ± 0.01, respectively, and the average RBE for the complete dose–response curves were 1.13 ± 0.04 and 0.80 ± 0.02 relative to 225 kVp X-rays as standard radiation.

Conclusion

The established dose–response curves obtained for PBL exposed to different energy levels of X-rays of 225 kVp, 3 MV, and 6 MV are ready to use for biological dosimetry purposes. The calculated RBE values for the higher energies of X-rays relative to 225 kVp X-rays in this study suggest that RBE of X-rays may not be equal to one, with the true value dependent on the beam energy, the dose and dose rate, and the endpoint investigated.

中文翻译：

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高能临床 3 MV 和 6 MV X 射线对人淋巴细胞微核诱导的相对生物学有效性

 抽象的

 目的

在现代放射治疗时代，传统放射方式（基于 γ 射线）的使用正在被基于高能直线加速器的 X 射线所取代。由于设备操作不当或机械错误，卫生工作者可能会接触到这些高能 X 射线。特别是在没有人员监测设备的情况下，使用较低能量 X 射线校准曲线的生物剂量测定可能无法提供可接受的剂量估计。此外，无论束能量 (V) 如何，X 射线的相对生物有效性 (RBE) 值都是相同的 (1)，用于诊断、介入医学和放射治疗。因此，本研究的目的是检查不同能量 X 射线（3 和 6 MV X 射线）的诱导生物效应（通过微核 (MN) 形成测量），并研究相对于 225 kVp X 的 RBE -射线。

 材料和方法

使用 225 kVp、3 MV 和 6 MV 能量 X 射线照射健康供体 ( n = 6) 的外周血淋巴细胞 (PBL)，并使用胞质分裂阻断 MN (CBMN) 测定将诱导的生物损伤量化为 MN 形成。

 结果

与未暴露的样品相比，三种不同 X 射线能量的 X 射线照射样品中每个细胞的 MN 显示出显着 ( p <.0001) 剂量依赖性增加。在三种不同能量的相同剂量下获得的畸变频率显示能量水平之间每个细胞的 MN 存在显着差异 ( p <.05)；然而，体外剂量反应曲线参数（斜率、截距和系数）没有显示出任何显着差异。盲样中的估计剂量在每条校准曲线的 95% 置信区间内。然而，总体而言，6 MV 剂量反应曲线系数产生了最接近真实剂量的剂量估计值。 3 MV 和 6 MV LINAC X 射线在 5% 诱发 MN 时计算的 RBE 值分别为 2.0 ± 0.04 和 0.70 ± 0.01，完整剂量反应曲线的平均 RBE 相对于 1.13 ± 0.04 和 0.80 ± 0.02 225 kVp X 射线作为标准辐射。

 结论

暴露于 225 kVp、3 MV 和 6 MV 不同能级 X 射线的 PBL 所获得的已建立的剂量响应曲线可用于生物剂量测定目的。本研究中相对于 225 kVp X 射线的较高能量 X 射线的计算 RBE 值表明，X 射线的 RBE 可能不等于 1，真实值取决于束流能量、剂量和剂量率和调查的终点。