Treatment or low-grade meningiomas with helium, proton and carbon ions: Optimization of treatment planning, establishment of study concepts and in vivo verification

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Treatment of benign and malignant brain tumors remains a challenge even in modern radiation oncology. Particle therapy offers distinct physical and biological characteristics potentially contributing to an improved risk-benefit-ratio for the treatment of brain tumors. In the previous funding period of the project studies on skull base chordomas and chondrosarcomas, as well as on primary glioblastomas have been planned, initiated, and are currently in the recruitment phase. All three entities are evaluated within randomized trials directly comparing protons and carbon ions (see Interim Report). Besides this work funded within the previous round of the project, the treatment of skull base meningiomas has been reviewed extensively including biological, physical and clinical aspects by the group. The goal of renewal project is to develop novel concepts for treatment with particle therapy as well as in-vivo verification of skull base tumors with special focus on low- and high grade meningiomas. The optimization of existing treatment options will be first of all investigated by means of treatment plan comparisons with the already existing proton and carbon ion beams as well as the helium beam modality which will be available at our facility. Special emphasis will be given to the possibility of reducing toxicities and radiation induced risks, which could in turn be connected to dose escalation studies. These comparisons will not only involve absorbed and biological RBE (relative biological effectiveness)-weighted dose as provided by available commercial or research treatment planning systems (TPSs), but will also include detailed comparison of relevant quantities such as dose-averaged linear energy transfer (LET) and neutron dose which may be provided by dedicated Monte Carlo simulations. Moreover, the clinical feasibility of high dose conformality with reduced burden to surrounding critical structures will be addressed via prospective application of post-irradiation Positron-Emission-Tomography (PET)-based treatment verification within the framework of the MIRANDA IRB-approved clinical study. Thus, the first clinical goal is to provide optimized treatment concepts with particle therapy for patients with meningiomas. The different workpackages address the important steps in radiation therapy starting from optimal treatment planning, especially when introducing novel beams such as the helium beam, target volume definition, retrospective evaluation of clinical data for a subsequent clinical study focusing on reduction of treatment times (hypofractionation) as well as minimization of toxicity.