MedAustron is a synchrotron-based cancer therapy center located in Lower Austria. Patients are treated with proton and carbon ion beams in an energy range of 62-252 MeV/u and of 120-400 MeV/u respectively. The facility features three clinical irradiation rooms, among which horizontal and vertical beam lines as well as a proton gantry are available for treatment. A fourth irradiation room (IR1) is dedicated to non-clinical research activities among which helium ion beams are currently under commissioning. Helium ions are also promising future candidates for clinical treatment due their favorable physical and biological properties. At MedAustron the beam commissioning up to IR1 is near completion. A large energy range (i.e. 39-402 MeV/u) has been commissioned with the support of Monte Carlo simulations performed by the future users. The beam properties in terms of spot size and beam roundness obtained at the isocenter fulfill the user requirements. In this work we present the helium commissioning status with the main focus on the recent results obtained from the commissioning of the synchrotron and transfer line up to the isocenter in IR1.

With a very low relative charge-to-mass ratio offset of approximately 0.065%, helium (⁴He²⁺) and carbon ions (¹²C⁶⁺) are interesting candidates for being simultaneously accelerated in hadron therapy accelerators. At the same energy per nucleon, helium ions exhibit a stopping range approximately three times greater than that of carbon ions. They can therefore be exploited for online range verification in a detector downstream of the patient during carbon ion therapy. The synchrotron-based MedAustron Ion Therapy Center provides the opportunity to study the feasibility of such a mixed beam-based in-vivo range verification system due to the availability of 120-402.8 MeV/u carbon beams and the ongoing commissioning of 39.8-402.8 MeV/u helium beams. One possibility for creating this mixed beam is accelerating ⁴He²⁺ and ¹²C⁶⁺ sequentially through the LINAC and subsequently “mixing” the ion species at injection energy in the synchrotron with a double injection scheme. This contribution introduces this newly proposed injection scheme, outlines challenges and presents first feasibility estimates obtained through measurements and particle tracking simulations.

In recent years, mixed helium and carbon ion irradiation schemes have been proposed to facilitate in-vivo range verification in ion beam therapy. Such a scheme proposes to deliver both ion species simultaneously, with the idea of performing the treatment with carbon ions, while exploiting helium for online dosimetry downstream of the patient. The center for ion beam therapy and research MedAustron supplies protons and carbon ions for clinical treatment. It is currently being commissioned to additionally provide helium ions for non-clinical research, opening the opportunity for exploring the feasibility of mixed beam irradiation. A key aspect in this context is the slow extraction of the ion mix, which is affected by the relative charge-to-mass ratio offset between the two ions of approximately 6e-4. This contribution analyses differences in the transverse phase space and tune distributions of the two ion species and subsequently discusses first simulation results of the extraction process.