Group of Medical Physics and Biomathematics, Instituto de Investigación Sanitaria de Santiago (IDIS), Santiago de Compostela, Spain.
Department of Medical Physics, Complexo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela, Spain.
Med Phys. 2023 Nov;50(11):7304-7312. doi: 10.1002/mp.16783. Epub 2023 Oct 11.
In treatment planning for proton therapy a constant Relative Biological Effectiveness (RBE) of 1.1 is used, disregarding variations with linear energy transfer, clinical endpoint, or fractionation.
To present a methodology to analyze the variation of RBE with fractionation from clinical data of tumor control probability (TCP) and to apply it to study the response of prostate cancer to proton therapy.
We analyzed the dependence of the RBE on the dose per fraction by using the LQ model and the Poisson TCP formalism. Clinical tumor control probabilities for prostate cancer (low and intermediate risk) treated with photon and proton therapy for conventional fractionation (2 Gy(RBE)×37 fractions), moderate hypofractionation (3 Gy(RBE)×20 fractions) and hypofractionation (7.25 Gy(RBE)×5 fractions) were obtained from the literature and analyzed aiming at obtaining the RBE and its dependence on the dose per fraction.
The theoretical analysis of the dependence of the RBE on the dose per fraction showed three distinct regions with RBE monotonically decreasing, increasing or staying constant with the dose per fraction, depending on the change of (α, β) values between photon and proton irradiation (the equilibrium point being at (α /β ) = (α /β )(α /α )). An analysis of the clinical data showed RBE values that decline with increasing dose per fraction: for low risk RBE≈1.124, 1.119, and 1.102 for 1.82 Gy, 2.73 Gy and 6.59 Gy per fraction (physical proton doses), respectively; for intermediate risk RBE≈1.119 and 1.102 for 1.82 Gy and 6.59 Gy per fraction (physical proton doses), respectively. These values are nonetheless very close to the nominal 1.1 value.
In this study, we have presented a methodology to analyze the RBE for different fractionations, and we used it to study clinical data for prostate cancer and evaluate the RBE versus dose per fraction. The analysis shows a monotonically decreasing RBE with increasing dose per fraction, which is expected from the LQ formalism and the changes in (α, β) values between photon and proton irradiation. However, the calculations in this study have to be considered with care as they may be biased by limitations in the modeling assumptions and/or by the clinical data set used for the analysis.
在质子治疗计划中，一直使用相对生物学效应（RBE）为 1.1，而不考虑与线性能量传递、临床终点或分割的变化。
提出一种从肿瘤控制概率（TCP）的临床数据中分析 RBE 随分割变化的方法，并将其应用于研究前列腺癌对质子治疗的反应。
我们使用 LQ 模型和泊松 TCP 公式来分析 RBE 与剂量分割的依赖性。从文献中获得了前列腺癌（低危和中危）接受光子和质子治疗的临床肿瘤控制概率，常规分割（2 Gy（RBE）×37 次分割）、中低分割（3 Gy（RBE）×20 次分割）和低分割（7.25 Gy（RBE）×5 次分割），并对其进行了分析，旨在获得 RBE 及其与剂量分割的依赖性。
对 RBE 与剂量分割依赖性的理论分析表明，根据光子和质子照射时（α/β）值的变化，存在三个不同的区域，RBE 单调递减、递增或保持不变，取决于（α/β）值的变化（平衡点为（α/β）=（α/β）（α/α））。对临床数据的分析表明，RBE 值随剂量分割的增加而下降：对于低危，RBE≈1.124、1.119 和 1.102，分别对应于 1.82 Gy、2.73 Gy 和 6.59 Gy 每分割（物理质子剂量）；对于中危，RBE≈1.119 和 1.102，分别对应于 1.82 Gy 和 6.59 Gy 每分割（物理质子剂量）。然而，这些值非常接近名义值 1.1。
在这项研究中，我们提出了一种分析不同分割 RBE 的方法，并将其用于研究前列腺癌的临床数据和评估 RBE 与剂量分割的关系。分析表明，RBE 随剂量分割的增加而单调下降，这与 LQ 公式和光子与质子照射时（α，β）值的变化一致。然而，由于建模假设的限制和/或分析中使用的临床数据集，本研究的计算结果需要谨慎考虑。
