Ballisat Laura, De Sio Chiara, Guatelli Susanna, Sakata Dousatsu, Sabah Lujin Abu, Duan Jinyan, Shi Yuyao, Velthuis Jaap, Rosenfeld Anatoly
School of Physics, University of Bristol, Bristol, UK.
School of Physics, University of Bristol, Bristol, UK.
Phys Med. 2025 Jul;135:105005. doi: 10.1016/j.ejmp.2025.105005. Epub 2025 Jun 10.
Recent in-vivo experimental measurements of DaRT seeds have shown that the spread of Rn away from the DaRT seed is greater than expected. This has implications for accurate treatment planning.
Geant4 and Geant4-DNA have been used to simulate the additional spread of Rn and study the impact on particle and RBE (relative biological effectiveness) weighted dose distribution from the whole DaRT decay chain. A percentage of Rn is assumed to migrate with a higher effective diffusion constant due to transport in the blood flow in the surrounding vasculature. The DNA damage was simulated for the fit to the measurement showing the greatest additional spread.
Good agreement was found between the simulation and experimental in-vivo results. The additional spread of Rn increases the number of α-particles from these decays distally from the DaRT seed. However, the distribution of α-particles emitted from later stages of the decay chain is not as significantly affected. There is an increase in DSB yield and the RBE weighted dose extends further from the DaRT seed with the additional spread. The distance of the 1 Gy RBE weighted isodose from the DaRT seed surface moves from 4.4 mm without the additional spread to 5.7 mm including it.
The increase DSB induction distally from the DaRT seed has the potential to increase treatment efficacy. However, this additional spread cannot easily be predicted. Understanding this uncertainty is important for the dose calculations in treatment planning for tumours and normal tissues.
近期对达特种子的体内实验测量表明，氡从达特种子扩散的范围比预期的要大。这对精确的治疗计划有影响。
已使用Geant4和Geant4-DNA来模拟氡的额外扩散，并研究整个达特衰变链对粒子和相对生物效应（RBE）加权剂量分布的影响。假设一定比例的氡由于在周围脉管系统中的血流中传输而以更高的有效扩散常数迁移。针对显示出最大额外扩散的测量结果进行了DNA损伤模拟。
模拟结果与体内实验结果吻合良好。氡的额外扩散增加了来自这些衰变的α粒子在达特种子远端的数量。然而，衰变链后期发射的α粒子分布受影响不那么显著。双链断裂（DSB）产率增加，且随着额外扩散，RBE加权剂量从达特种子延伸得更远。从达特种子表面起1 Gy RBE加权等剂量线的距离从无额外扩散时的4.4毫米变为包括额外扩散时的5.7毫米。
达特种子远端DSB诱导的增加有可能提高治疗效果。然而，这种额外扩散不容易预测。了解这种不确定性对于肿瘤和正常组织治疗计划中的剂量计算很重要。
