Schweins Luisa, Kirchgässner Rebekka, Ochoa-Parra Pamela, Winter Marcus, Harrabi Semi, Mairani Andrea, Jäkel Oliver, Debus Jürgen, Martišíková Mária, Kelleter Laurent
Heidelberg Institute for Radiation Oncology (HIRO) and National Center for Radiation Research in oncology (NCRO), Heidelberg, Germany.
Division of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
Med Phys. 2025 Apr;52(4):2399-2411. doi: 10.1002/mp.17590. Epub 2024 Dec 23.
Carbon-ion radiotherapy provides steep dose gradients that allow the simultaneous application of high tumor doses as well as the sparing of healthy tissue and radio-sensitive organs. However, even small anatomical changes may have a severe impact on the dose distribution because of the finite range of ion beams.
An in-vivo monitoring method based on secondary-ion emission could potentially provide feedback about the patient anatomy and thus the treatment quality. This work aims to prove that a clinically relevant anatomical change in an anthropomorphic head phantom may be detected via charged-fragment tracking during a treatment fraction.
A clinically representative carbon-ion treatment plan was created for a skull-base tumor in an anthropomorphic head phantom. In order to imitate an inter-fractional anatomical change - for example, through tissue swelling or mucous accumulation - a piece of silicone was inserted into the nasopharynx. Fragment distributions with and without the silicone insert were subsequently acquired with a mini-tracker made of four hybrid silicon pixel detectors. Experimental irradiations were carried out at the Heidelberg Ion Beam Therapy Centre (HIT, Germany). FLUKA Monte Carlo simulations were performed to support the interpretation of the experimental results.
It was found that the silicone causes a significant change in the fragment emission that was clearly distinguishable from statistical fluctuations and setup uncertainties. Two regions of fragment loss were observed upstream and downstream of the silicone with similar amplitude in both the measurement and the simulation. Monte Carlo simulations showed that the observed signature is a consequence of a complex interplay of fragment production, scattering, and absorption.
Carbon-ion therapy monitoring with charged nuclear fragments was shown to be capable of detecting clinically relevant density changes in an anthropomorphic head phantom under realistic clinic-like conditions. The complexity of the observed signal requires the development of advanced analysis techniques and underscores the importance of Monte Carlo simulations. The findings have strong implications for the ongoing InViMo clinical trial at HIT, which investigates the feasibility of secondary-ion monitoring for skull-base cancer patients.
碳离子放射治疗可提供陡峭的剂量梯度，能在给予高肿瘤剂量的同时保护健康组织和放射敏感器官。然而，由于离子束射程有限，即使是微小的解剖结构变化也可能对剂量分布产生严重影响。
基于二次离子发射的体内监测方法可能会提供有关患者解剖结构及治疗质量的反馈。本研究旨在证明，在治疗分次过程中，可通过带电碎片追踪检测到人体头部模型中具有临床相关性的解剖结构变化。
针对人体头部模型中的颅底肿瘤制定了具有临床代表性的碳离子治疗计划。为模拟分次间的解剖结构变化，例如组织肿胀或黏液积聚，在鼻咽部插入一块硅胶。随后，使用由四个混合硅像素探测器组成的微型追踪器获取有或没有硅胶插入时的碎片分布。实验照射在德国海德堡离子束治疗中心（HIT）进行。进行了FLUKA蒙特卡罗模拟以辅助解释实验结果。
发现硅胶会导致碎片发射发生显著变化，这与统计波动和设置不确定性明显不同。在测量和模拟中，均在硅胶的上游和下游观察到两个幅度相似的碎片损失区域。蒙特卡罗模拟表明，观察到的特征是碎片产生、散射和吸收复杂相互作用的结果。
结果表明，在类似临床的实际条件下，利用带电核碎片进行碳离子治疗监测能够检测人体头部模型中具有临床相关性的密度变化。观察到的信号复杂性需要开发先进的分析技术，并凸显了蒙特卡罗模拟的重要性。这些发现对HIT正在进行的InViMo临床试验具有重要意义，该试验旨在研究二次离子监测用于颅底癌症患者的可行性。
