Department of Radiation Oncology, Technische Universität München, Germany.
Phys Med Biol. 2012 Oct 7;57(19):5889-907. doi: 10.1088/0031-9155/57/19/5889. Epub 2012 Sep 7.
This study shows that enhanced radiobiological effectiveness (RBE) values can be generated focusing low linear energy transfer (LET) radiation and thus changing the microdose distribution. 20 MeV protons (LET = 2.65 keV µm(-1)) are focused to submicrometer diameter at the ion microprobe superconducting nanoprobe for applied nuclear (Kern) physics experiments of the Munich tandem accelerator. The RBE values, as determined by measuring micronuclei (RBE(MN) = 1.48 ± 0.07) and dicentrics (RBE(D) = 1.92 ± 0.15), in human-hamster hybrid (A(L)) cells are significantly higher when 117 protons were focused to a submicrometer irradiation field within a 5.4 × 5.4 µm(2) matrix compared to quasi homogeneous in a 1 × 1 µm(2) matrix applied protons (RBE(MN) = 1.28 ± 0.07; RBE(D) = 1.41 ± 0.14) at the same average dose of 1.7 Gy. The RBE values are normalized to standard 70 kV (dicentrics) or 200 kV (micronuclei) x-ray irradiation. The 117 protons applied per point deposit the same amount of energy like a (12)C ion with 55 MeV total energy (4.48 MeV u(-1)). The enhancements are about half of that obtained for (12)C ions (RBE(MN) = 2.20 ± 0.06 and RBE(D) = 3.21 ± 0.10) and they are attributed to intertrack interactions of the induced damages. The measured RBE values show differences from predictions of the local effect model (LEM III) that is used to calculate RBE values for irradiation plans to treat tumors with high LET particles.
这项研究表明，通过聚焦低线性能量传递（LET）辐射并改变微剂量分布，可以产生增强的放射生物学效应（RBE）值。20 MeV 质子（LET = 2.65 keV µm(-1)) 在慕尼黑串列加速器的离子微探针超导纳米探针下聚焦到亚微米直径，用于进行应用核（Kern）物理实验。通过测量微核（RBE(MN) = 1.48 ± 0.07) 和双着丝粒（RBE(D) = 1.92 ± 0.15)，在人仓鼠杂种（A(L)) 细胞中，当 117 个质子聚焦到一个亚微米照射场中时，与在相同平均剂量 1.7 Gy 下应用于 1×1 µm(2) 矩阵的准均匀质子相比，RBE 值显著更高（RBE(MN) = 1.28 ± 0.07; RBE(D) = 1.41 ± 0.14)。RBE 值相对于标准 70 kV（双着丝粒）或 200 kV（微核）X 射线照射进行归一化。每个点应用的 117 个质子沉积的能量与具有 55 MeV 总能量（4.48 MeV u(-1)) 的 (12)C 离子相同。增强约为获得的 (12)C 离子的一半（RBE(MN) = 2.20 ± 0.06 和 RBE(D) = 3.21 ± 0.10)，这归因于诱导损伤的轨道间相互作用。所测量的 RBE 值与用于计算用高 LET 粒子治疗肿瘤的照射计划的 RBE 值的局部效应模型（LEM III）的预测值存在差异。
