Bonfrate Anthony, Ronga Maria Grazia, Patriarca Annalisa, Heinrich Sophie, De Marzi Ludovic
Institut Curie, PSL Research University, Radiation Oncology Department, Proton Therapy Centre, Centre Universitaire, Orsay, France.
Institut Curie, PSL Research University, Inserm LITO, U1288, University of Paris Saclay, Orsay, France.
Med Phys. 2025 Feb;52(2):1224-1234. doi: 10.1002/mp.17492. Epub 2024 Nov 6.
Ultra-high dose rate (UHDR/FLASH) irradiations, along with particle minibeam therapy (PMBT) are both emerging as promising alternatives to current radiotherapy techniques thanks to their improved healthy tissue sparing and similar tumor control.
Monte Carlo (MC) modeling of a commercial machine delivering 5-7 MeV electrons at UHDR. This model was used afterward to compare measurements against simulations for an experimental setup combining both FLASH and PMBT modalities.
We modeled the main accelerator elements with TOPAS3.8/Geant4.10.07.p03, optimized the electron source parameters, and subsequently benchmarked this geometry against measurements. Minibeam experiments were performed by delivering 7 MeV electrons at UHDR on three different 65-mm thick brass collimators as manufactured for protons with a 400-µm slit width: single slit, 5 slits with a center-to-center (CTC) distance of 4 mm and 9 slits with CTC of 2 mm. Finally, complementary simulations were run by changing critical PMBT collimator parameters to assess their specific impact on peak-to-valley dose ratio (PVDR) as well as on the Bremsstrahlung photon contribution to the total dose.
Percentage depth dose (PDD) distributions and lateral dose profiles showed a good agreement between simulations and measurements, with a maximum discrepancy of less than 4%. With the PMBT collimators in place, discrepancies between simulated and measured dose profiles, lateral and in-depth in peaks and valleys, were within 3%. High PVDR between 5 and 26 were observed until 4 mm in the phantom. During the experiments, a mean dose rate of 167 Gy/s and an instantaneous dose rate of 1.2 × 10 Gy/s were obtained for the FLASH-minibeam setup. PMBT collimator parameters need to be optimized to maximize PVDR while limiting Bremsstrahlung photon contribution to the total dose.
The validation of the MC model and the configuration of an electron FLASH-minibeam setup were successfully completed, paving the way for future radiobiological investigations.
超高剂量率（UHDR/FLASH）照射以及粒子微束疗法（PMBT）作为当前放射治疗技术的有前景的替代方法正在兴起，这得益于它们对健康组织更好的保护以及相似的肿瘤控制效果。
对一台能以超高剂量率提供5-7兆电子伏电子的商用机器进行蒙特卡罗（MC）建模。之后该模型被用于将测量结果与结合了FLASH和PMBT两种模式的实验装置的模拟结果进行比较。
我们使用TOPAS3.8/Geant4.10.07.p03对主要加速器元件进行建模，优化电子源参数，随后将此几何结构与测量结果进行基准比对。微束实验是通过在超高剂量率下向三个不同的65毫米厚的黄铜准直器输送7兆电子伏电子来进行的，这些准直器是为质子制造的，狭缝宽度为400微米：单狭缝、中心距（CTC）为4毫米的5个狭缝以及CTC为2毫米的9个狭缝。最后，通过改变关键的PMBT准直器参数进行补充模拟，以评估它们对峰谷剂量比（PVDR）以及轫致辐射光子对总剂量贡献的具体影响。
百分深度剂量（PDD）分布和侧向剂量剖面显示模拟结果与测量结果吻合良好，最大差异小于4%。安装PMBT准直器后，模拟和测量的剂量剖面在侧向以及峰谷处的深度方向上的差异在3%以内。在模体中直至4毫米处观察到5至26之间的高PVDR。在实验期间，FLASH-微束装置的平均剂量率为167戈瑞/秒，瞬时剂量率为1.2×10戈瑞/秒。需要优化PMBT准直器参数以最大化PVDR，同时限制轫致辐射光子对总剂量的贡献。
成功完成了MC模型的验证以及电子FLASH-微束装置的配置，为未来的放射生物学研究铺平了道路。
