Progress Toward Beam Diagnostics for FLASH Proton Therapy

A new publication from the University of Liverpool’s QUASAR Group reports the design and characterization of an advanced extraction system for a Supersonic Gas Curtain–based Ionization Profile Monitor (SGC-IPM), contributes to the development of beam diagnostics for FLASH proton therapy.

Schematic of SGC-IPM (Extraction system highlighted in green box). (Image credit: Parambil, F. T. M., et al, Instruments, 10(1), 4, CC BY)

The work has been published in the open-access journal Instruments under the title “Characterization of the Extraction System of Supersonic Gas Curtain-Based Ionization Profile Monitor for FLASH Proton Therapy.”

Led by EuPRAXIA-DN Fellow and QUASAR member Farhana Thesni and QUASAR Dr Narender Kumar, the research presents the detailed CST simulations of the extraction system developed by our group (proceedings IPAC 2024) to verify the SGC-IPM’s capability to simultaneously measure two-dimensional transverse beam profiles and beam position. This dual functionality is a critical requirement for next-generation medical accelerators operating at ultra-high dose rates.

FLASH radiotherapy poses a major diagnostic challenge, as conventional beam monitoring techniques often fail or significantly perturb the beam under extreme dose-rate conditions. The Supersonic Gas Curtain Ionization Profile Monitor offers a promising non-perturbative solution, enabling real-time monitoring without compromising beam quality.

In the study, comprehensive electrostatic and particle-tracking simulations of the extraction system were benchmarked against experimental measurements using a 28 MeV proton beam at the University of Birmingham. The authors systematically investigated the impact of beam size on profile reconstruction, quantified electric-field uniformity, and demonstrated reliable beam position monitoring. Additional factors, such as the influence of the tilted gas curtain, gained ion energy and its spread, and microchannel plate (MCP) detection efficiency, are analysed and will inform future design advancements.

The results are highly encouraging. Simulations show robust reconstruction of transverse beam profiles across a wide range of beam sizes, along with a clear and linear response to intentional beam position offsets. The simulated characteristic drift induced by the supersonic gas flow was found to be in strong agreement with experimental measurements. These findings strengthen the case for the SGC-IPM as a powerful diagnostic tool for future medical and laser-driven accelerator facilities.

The study highlights the growing maturity of SGC-IPM technology and its potential to meet the stringent demands of next-generation radiotherapy.

Comparison of beam profile shift (Experimental (Left), Simualtions (Right)), caused by the flow of the supersonic gas curtain. (Image credit: Parambil, F. T. M., et al, Instruments, 10(1), 4, CC BY)

Dr Narender Kumar, who has led the development of this technology over the past five years, commented: “This marks further progress towards beam diagnostics for medical accelerators, particularly for FLASH proton therapy. The work aligns closely with clinical diagnostic requirements, enabling simultaneous two-dimensional transverse profile and beam position measurements over a wide range of beam sizes. Going forward, these results will help optimize the SGC-IPM design and facilitate its easier integration into medical accelerator systems.”

Further information:

‘Characterization of the Extraction System of Supersonic Gas Curtain-Based Ionization Profile Monitor for FLASH Proton Therapy’, Parambil, F. T. M., et al.,  Instruments, 10(1), 4 (2026). https://doi.org/10.3390/instruments10010004