Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany; National Center for Radiation Research in Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Germany; Faculty of Biosciences, Heidelberg University, Germany.
Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany; National Center for Radiation Research in Oncology (NCRO), Heidelberg Institute for Radiation Oncology (HIRO), Germany; Department of Radiation Oncology and Radiotherapy, University Hospital Heidelberg, Germany.
Radiother Oncol. 2022 May;170:224-230. doi: 10.1016/j.radonc.2022.03.017. Epub 2022 Mar 31.
Determination of the relative biological effectiveness (RBE) of helium ions as a function of linear energy transfer (LET) for single and split doses using the rat cervical spinal cord as model system for late-responding normal tissue.
The rat cervical spinal cord was irradiated at four different positions within a 6 cm spread-out Bragg-peak (SOBP) (LET 2.9, 9.4, 14.4 and 20.7 keV/µm) using increasing levels of single or split doses of helium ions. Dose-response curves were determined and based on TD-values (dose at 50% effect probability using paresis II as endpoint), RBE-values were derived for the endpoint of radiation-induced myelopathy.
With increasing LET, RBE-values increased from 1.13 ± 0.04 to 1.42 ± 0.05 (single dose) and 1.12 ± 0.03 to 1.50 ± 0.04 (split doses) as TD-values decreased from 21.7 ± 0.3 Gy to 17.3 ± 0.3 Gy (single dose) and 30.6 ± 0.3 Gy to 22.9 ± 0.3 Gy (split doses), respectively. RBE-models (LEM I and IV, mMKM) deviated differently for single and split doses but described the RBE variation in the high-LET region sufficiently accurate.
This study established the LET-dependence of the RBE for late effects in the central nervous system after single and split doses of helium ions. The results extend the existing database for protons and carbon ions and allow systematic testing of RBE-models. While the RBE-values of helium were generally lower than for carbon ions, the increase at the distal edge of the Bragg-peak was larger than for protons, making detailed RBE-modeling necessary.
使用大鼠颈椎脊髓作为迟发性正常组织模型系统，确定氦离子作为单次和分割剂量的相对生物效应（RBE）与线性能量传递（LET）的关系。
在 6cm 扩展布拉格峰（SOBP）内的四个不同位置用氦离子照射大鼠颈椎脊髓，LET 分别为 2.9、9.4、14.4 和 20.7keV/μm。用增加的单次或分割剂量的氦离子确定剂量反应曲线，并基于 TD 值（以 II 级瘫痪为终点的 50%效应概率的剂量），推导出用于放射性脊髓病终点的 RBE 值。
随着 LET 的增加，RBE 值从 1.13±0.04 增加到 1.42±0.05（单次剂量）和 1.12±0.03 增加到 1.50±0.04（分割剂量），而 TD 值从 21.7±0.3Gy 降低到 17.3±0.3Gy（单次剂量）和 30.6±0.3Gy 降低到 22.9±0.3Gy（分割剂量）。RBE 模型（LEM I 和 IV、mMKM）对单次和分割剂量的偏差不同，但足以准确描述高 LET 区域的 RBE 变化。
本研究建立了氦离子单次和分割剂量后中枢神经系统迟发效应的 LET 依赖性 RBE。研究结果扩展了质子和碳离子的现有数据库，并允许对 RBE 模型进行系统测试。虽然氦离子的 RBE 值通常低于碳离子，但在布拉格峰的远端边缘的增加大于质子，因此需要详细的 RBE 建模。
