Lühr Armin, von Neubeck Cläre, Helmbrecht Stephan, Baumann Michael, Enghardt Wolfgang, Krause Mechthild
a OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus , Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf , Dresden , Germany.
b Helmholtz-Zentrum Dresden ? Rossendorf , Institute of Radiooncology - OncoRay , Dresden , Germany.
Acta Oncol. 2017 Nov;56(11):1392-1398. doi: 10.1080/0284186X.2017.1356468. Epub 2017 Aug 29.
The relative biological effectiveness (RBE) of particle therapy compared to photon radiotherapy is known to be variable but the exact dependencies are still subject to debate. In vitro data suggested that RBE is to a large extend independent of ion type if parametrized by the beam quality Q. This study analyzed the RBE dependence of pre-clinical data on late toxicity with an emphasis on the beam quality.
Published pre-clinical RBE dose-response data of the spinal cord following one and two fractions of photon and carbon ion irradiation were compiled. The beam quality for each treatment condition was obtained from Monte Carlo simulations. The α and β parameters of the linear-quadratic (LQ) model for particle irradiation were determined from the pre-clinical data and was provided as a function of Q. An introduced model proposed α to increase linearly with Q and β to remain constant. RBE values predicted by the model were compared to the published data.
The α parameter was highly correlated with Q (R = 0.96) with a linear slope of 0.019 Gy. No significant variation of β with Q was found. RBE and Q were also highly correlated (R = 0.98) for one and two fractions. The (extrapolated) RBE at Q = 0 (theoretical photon limit) for one and two fractions was 1.22 and significantly larger than 1 (p = .004). The model reproduced the dependence of RBE on fractionation well.
Fraction dose and beam quality Q were sufficient to describe the RBE variability for a late toxicity model within a carbon ion treatment field. Assuming the independence of the identified RBE parameters on the ion type might suggest the translation of variable (pre-) clinical RBE data from carbon ion to proton therapy.
与光子放疗相比，粒子治疗的相对生物有效性（RBE）是可变的，但其确切的相关因素仍存在争议。体外数据表明，如果通过射束质量Q进行参数化，RBE在很大程度上与离子类型无关。本研究分析了临床前数据中RBE对晚期毒性的依赖性，重点关注射束质量。
收集已发表的关于脊髓在单次和两次光子及碳离子照射后的临床前RBE剂量反应数据。每种治疗条件下的射束质量通过蒙特卡罗模拟获得。从临床前数据中确定粒子照射的线性二次（LQ）模型的α和β参数，并将其作为Q的函数给出。引入的模型提出α随Q线性增加，β保持不变。将该模型预测的RBE值与已发表的数据进行比较。
α参数与Q高度相关（R = 0.96），线性斜率为0.019 Gy。未发现β随Q有显著变化。对于单次和两次照射，RBE与Q也高度相关（R = 0.98）。单次和两次照射在Q = 0（理论光子极限）时的（外推）RBE分别为1.22，显著大于1（p = 0.004）。该模型很好地再现了RBE对分次照射的依赖性。
分次剂量和射束质量Q足以描述碳离子治疗野内晚期毒性模型的RBE变异性。假设所确定的RBE参数与离子类型无关，这可能意味着将碳离子可变的（临床前）RBE数据转化为质子治疗。
