Winter Johanna, Dimroth Anton, Roetzer Sebastian, Zhang Yunzhe, Krämer Karl-Ludwig, Petrich Christian, Matejcek Christoph, Aulenbacher Kurt, Zimmermann Markus, Combs Stephanie E, Galek Marek, Natour Ghaleb, Butzek Michael, Wilkens Jan J, Bartzsch Stefan
Department of Radiation Oncology, School of Medicine and Klinikum Rechts der Isar, Technical University of Munich (TUM), Munich, Germany.
Institute of Radiation Medicine (IRM), Helmholtz Zentrum München GmbH, German Research Center for Environmental Health (HMGU), Neuherberg, Germany.
Med Phys. 2022 May;49(5):3375-3388. doi: 10.1002/mp.15611. Epub 2022 Apr 7.
Microbeam and x-ray FLASH radiation therapy are innovative concepts that promise reduced normal tissue toxicity in radiation oncology without compromising tumor control. However, currently only large third-generation synchrotrons deliver acceptable x-ray beam qualities and there is a need for compact, hospital-based radiation sources to facilitate clinical translation of these novel treatment strategies.
We are currently setting up the first prototype of a line-focus x-ray tube (LFxT), a promising technology that may deliver ultra-high dose rates (UHDRs) of more than 100 Gy/s from a table-top source. The operation of the source in the heat capacity limit allows very high dose rates with micrometer-sized focal spot widths. Here, we investigate concepts of effective heat management for the LFxT, a prerequisite for the performance of the source.
For different focal spot widths, we investigated the temperature increase numerically with Monte Carlo simulations and finite element analysis (FEA). We benchmarked the temperature and thermal stresses at the focal spot against a commercial x-ray tube with similar power characteristics. We assessed thermal loads at the vacuum chamber housing caused by scattering electrons in Monte Carlo simulations and FEA. Further, we discuss active cooling strategies and present a design of the rotating target.
Conventional focal spot widths led to a temperature increase dominated by heat conduction, while very narrow focal spots led to a temperature increase dominated by the heat capacity of the target material. Due to operation in the heat capacity limit, the temperature increase at the focal spot was lower than for the investigated commercial x-ray tube. Hence, the thermal stress at the focal spot of the LFxT was considered uncritical. The target shaft and the vacuum chamber housing require active cooling to withstand the high heat loads.
The heat capacity limit allows very high power densities at the focal spot of the LFxT and thus facilitates very high dose rates. Numerical simulations demonstrated that the heat load imparted by scattering electrons requires active cooling.
微束和X射线FLASH放射治疗是创新概念，有望在不影响肿瘤控制的情况下降低放射肿瘤学中正常组织的毒性。然而，目前只有大型第三代同步加速器才能提供可接受的X射线束质量，因此需要紧凑的、基于医院的放射源，以促进这些新型治疗策略的临床转化。
我们目前正在建立线聚焦X射线管（LFxT）的首个原型，这是一项很有前景的技术，可从桌面源提供超过100 Gy/s的超高剂量率（UHDR）。在热容量极限下运行该源可实现具有微米级焦斑宽度的非常高的剂量率。在此，我们研究LFxT的有效热管理概念，这是该源性能的一个先决条件。
对于不同的焦斑宽度，我们通过蒙特卡罗模拟和有限元分析（FEA）对温度升高进行了数值研究。我们将焦斑处的温度和热应力与具有相似功率特性的商用X射线管进行了基准对比。我们在蒙特卡罗模拟和FEA中评估了由散射电子引起的真空腔室外壳的热负荷。此外，我们讨论了主动冷却策略并提出了旋转靶的设计。
传统的焦斑宽度导致温度升高以热传导为主，而非常窄的焦斑导致温度升高以靶材料的热容量为主。由于在热容量极限下运行，焦斑处的温度升高低于所研究的商用X射线管。因此，LFxT焦斑处的热应力被认为不严重。靶轴和真空腔室外壳需要主动冷却以承受高热负荷。
热容量极限允许LFxT的焦斑处具有非常高的功率密度，从而有利于实现非常高的剂量率。数值模拟表明，散射电子施加的热负荷需要主动冷却。
