ESTRO 2023 - Abstract Book

S1567

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ESTRO 2023

Results All simulated geometries exhibited non-uniform amplification across the bandwidth of f , with amplification factors approaching a plateau at higher frequencies (Fig 2). Decreasing r in , increasing r out , and increasing ε r all increased amplification of the signal, although the frequency-dependence of this effect was unique to each parameter. Additional study is needed to understand the interplay between the parameters, and to further quantify the frequency-dependence of the responses. Changing d had no effect on G .

Conclusion Decreasing the inner radius, increasing the outer radius, and increasing the relative permittivity of the waveguide all led to increased amplification across the frequencies studied. This information can be used in conjunction with external factors in the accelerator design (particle bunch stability, material cost/availability, size/weight of the device, etc.) to select an appropriate waveguide geometry and composition. These results also inform the power output and pulse shaping requirements of the upstream circuit design as they provide an important bridge between the strength and temporal profile of the injected pulses and those of the accelerating fields.

PO-1834 Conventional and minibeam LIGHT proton linac for conformal FLASH treatment of brain metastases

A.M. Kolano 1 , T. Gray 2 , C. Liu 2 , P. Xia 2 , J.B. Farr 3

1 ADAM. S.A., Advanced Oncotherapy Plc, Clinical Office, Geneva, Switzerland; 2 Cleveland Clinic Foundation, Medical Physics, Cleveland, OH, USA; 3 ADAM. S.A., Advanced Oncotherapy Plc, Clinical Office, Geneva, Switzerland Purpose or Objective To investigate the LiGHT proton linac (Advanced Oncotherapy plc, London, UK; model: LiGHT) and proton minibeam linac used for delivering Stereotactic Radiosurgery (SRS) conformal FLASH to patients with multiple brain metastasis, as an alternative to photon and standard proton treatments. Materials and Methods Current proton systems can deliver ultra-high dose rates (UHDRs) only at the highest energy, where single energy layer Bragg peaks lie outside of the patient. Proton linacs, such as LiGHT, however, have output invariant on energy which, combined with a fast spot and energy switching time of 5 ms, allows for multi-energy FLASH irradiation of targets within 0.5 s. Additionally, proton linacs can generate a smaller beam, in the order of 1/3rd of the nominal spot. Brain metastasis treatment plans were created using a commercial treatment planning system, with beam parameters of LiGHT. The FLASH-optimised plans were compared to photon SRS plans and LiGHT FLASH SRS plans in terms of the target coverage, dose to Organs at Risk (OARs), and Dose-Rate average (DRav). Each target was treated with a dedicated single field. Results FLASH dose rates up to 200 Gy/s were achieved, depending on the target. FLASH-plan spot counts were reduced to maximise UHDRs. Flash standard and minibeam plan quality was found to be superior to nominal photon plans, with comparable