Department of Radiation Oncology and Radiotherapy, University Hospital Heidelberg, Germany; Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Germany; Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany.
Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Germany; Heidelberg Institute for Radiation Oncology (HIRO), National Center for Radiation Research in Oncology (NCRO), Heidelberg, Germany.
Radiother Oncol. 2021 May;158:131-137. doi: 10.1016/j.radonc.2021.01.038. Epub 2021 Feb 13.
To quantify the fractionation dependence of carbon (C) ions and photons in three rat prostate carcinomas differing in growth rate, differentiation and hypoxia.
Three sublines (AT1, HI, H) of syngeneic rat prostate tumors (R3327) were treated with six fractions of either C-ions or 6 MV photons. Dose-response curves were determined for the endpoint local tumor control within 300 days. The doses at 50% control probability (TCD) and the relative biological effectiveness (RBE) of C-ions were calculated and compared with the values from single and split dose studies.
Experimental findings for the three tumor sublines revealed (i) a comparably increased RBE (2.47-2.67), (ii) a much smaller variation of the radiation response for C-ions (TCD: 35.8-43.7 Gy) than for photons (TCD: 91.3-116.6 Gy), (iii) similarly steep (AT1) or steeper (HI, H) dose-response curves for C-ions than for photons, (iv) a larger fractionation effect for photons than for C-ions, and (v) a steeper increase of the RBE with decreasing fractional dose for the well-differentiated H- than for the less-differentiated HI- and AT1-tumors, reflected by (vi) the smallest α/β-value for H-tumors after photon irradiation.
C-ions reduce the radiation response heterogeneity between the three tumor sublines as well as within each subline relative to photon treatments, independently of fractionation. The dose dependence of the RBE varies between tumors of different histology. The results support the use of hypofractionated carbon ion treatments in radioresistant tumors.
定量分析三种不同生长速度、分化程度和乏氧程度的大鼠前列腺癌中碳离子和光子的分割依赖性。
采用同源大鼠前列腺肿瘤（R3327）的三个亚系（AT1、HI、H），用 6 个 C-离子或 6 MV 光子的剂量进行处理。在 300 天内确定局部肿瘤控制终点的剂量反应曲线。计算并比较 TCD（50%控制概率剂量）和 C-离子的相对生物效应（RBE）值与单次和分割剂量研究的值。
对三个肿瘤亚系的实验结果表明：（i）相对生物效应（RBE）明显增加（2.47-2.67）；（ii）与光子相比，C-离子的辐射反应变异较小（TCD：35.8-43.7 Gy）；（iii）C-离子的剂量反应曲线比光子陡峭（AT1）或更陡峭（HI、H）；（iv）光子的分割效应大于 C-离子；（v）随着分次剂量的减少，RBE 增加幅度在分化良好的 H-肿瘤中比在分化较差的 HI-和 AT1-肿瘤中更大，这反映在光子照射后 H-肿瘤的α/β 值最小；（vi）。
C-离子降低了三种肿瘤亚系之间以及每种亚系内部的辐射反应异质性，而与分割无关。RBE 的剂量依赖性在不同组织学类型的肿瘤之间存在差异。结果支持在放射性抵抗肿瘤中使用低分割碳离子治疗。
