Background and Aims

Laser-plasma accelerators (LPA) are a viable addition to the ultra-high dose rate accelerator portfolio, as they generate extremely intense proton bunches of several 10 MeV kinetic energy. Efficiently transported and spectrally shaped, a single LPA proton bunch enables homogeneous dose delivery above 20 Gy to mm-scale volumes with a dose rate well above 10⁸ Gy/s. At Draco PW we have recently shown the successful establishment of a proton LPA research platform for small animal studies employing a multi-shot accumulated dose delivery for a mouse model pilot study. [Kroll et al, Nature Physics 2022].

Methods

Reaching the range of FLASH-associated parameters at an LPA proton source requires single-shot irradiation. We performed such irradiations with zebrafish embryos and dosimeters using the pulsed beamline at Draco PW. Since LPA based accelerators are prone to inherent fluctuations of the source, to measure the applied dose, a minimally invasive, online spectral characterization of the delivered proton bunches is necessary. Clinically used ionization chambers saturate under LPA beam conditions. Therefore, we present a scintillator-based time-of-flight (ToF) beam monitoring system for the recording of kinetic energy spectra of single LPA proton bunches. The deduced spectra are used as an input for Monte-Carlo simulations to predict the delivered dose to the irradiated sample.

Results

The ToF ansatz enabled the reconstruction of the kinetic energy spectrum of the transported protons with a relative energy uncertainty down to ca. 11% (2σ). Subsequent Monte-Carlo simulations predict the applied depth dose distribution with an uncertainty of ca. 6% (2σ).

Conclusions

We present a laser-based proton irradiation platform at the Draco PW facility that enables systematic radiobiological studies within an unprecedented range of beam parameters and demonstrate a solution for minimally invasive volumetric dosimetry at ultra-high dose rates.

Background and Aims

Accurate dosimetry is paramount for the study of biological effects since dose and dose-rate are critical parameters governing the underlying interaction mechanisms. With the goal of evaluating the suitability of innovative dosimeters in a laser-plasma accelerated electron beam and experimental setup dedicated to radiobiological studies, we evaluated and compared the response of several of these passive and active detectors.

Methods

New developments in compact laser-driven electron beam technologies enable allow to consider the use of very high energy electron (VHEE) beams for radiation therapy and radiobiology applications. Laser-plasma accelerated electron beams with energy up to 300 MeV, large dose per pulse (>1Gy) and ultrashort pulse duration were used to characterise the response of the considered detectors in a large energy/dose rate range. Measurements were simultaneously carried out with EBT-XD radiochromic films, alanine pellets (readout performed with an X-band electron paramagnetic resonance spectrometer equipped with a high Q resonant cavity), a commercial dosimetry solution based on plastic scintillators (Medscint) as well as the new small ionization chamber Razor Nano Chamber (IBA).

Results

Dose rate independent detectors such as the alanine, film and the scintillator were used to cross calibrate the ionization chamber whose ion recombination efficiency was estimated. Mean dose rates and instantaneous dose rates ranging from 1 mGy/s to 0.5 Gy/s and from 1e10 Gy/s to 5e11 Gy/s, respectively, were explored. The dose values obtained with the four dosimeters were compared for various beam configurations.

Conclusions

Several detectors seem to be suitable and reliable for laser-plasma accelerated VHEE irradiation. Promising results in the small number of conditions tested were found and will support the analysis of radiobiological experiments for preclinical research.

Background and Aims

Very High Energy Electrons (VHEE) are a promising modality for radiation therapy including the use for FLASH. They are capable of penetrating further hence being able to treat deep-seated tumours whilst not requiring the larger and currently expensive accelerators used for hadron therapy. One of the key challenges of delivering RT including FLASH modality is the possibility of performing conformal irradiation of the tumour from different angles. This would require extremely precise angle change at FLASH timescales (<0.1s), which is very complex for a conventional mechanically rotating gantry.

A proposed solution to this is the novel GaToroid concept. This is based around the use of circularly symmetric toroidal magnets to allow treatment from different angles in a static gantry. A GaToroid gantry for 200MeV VHEE would be achievable with normal conducting magnets, and make use of novel toroidal quadrupoles and dipoles. The angle of treatment could be selected using a single variable kicker magnet to direct the beam path through the toroidal magnet gaps to the patient. This kicker can be designed to vary within FLASH timescales and thus allow multidirectional treatment.

The aim of this work is to carry out a beam optics design study for VHEE GaToroid.

Methods

Nelder-Mead techniques were used in the tracking codes to design the toroidal magnet configuration.

Results

Multivariable optimisation was carried out to minimise the required magnet strengths and physical dimensions of the full gantry system, whilst magnifying the beam to 75mm radius and ensuring a constant transverse dose distribution at the patient. Dispersion in the bending axis of the transfer line was minimised to achieve symmetry in the treatment beam.

Conclusions

Future work on this design is envisaged to examine the implementation of the circularly symmetric toroidal magnets themselves, the initial kicker magnet and requirements for potential clinical integration.

Background and Aims

There is growing evidence of the potential advances of FLASH radiotherapy for each of the available particle species: photons, electrons, protons and light ions. Alongside the ongoing efforts to fully characterise the FLASH effect, understand the underlying radiobiological processes and set limits on the beam conditions needed to induce the healthy-tissue sparing that is the predominant feature of FLASH, improvements in the accelerator and beam delivery technology are needed in order to deliver beams that meet these parameters.

Methods

While the specific challenges for each type of system are dependent on the particular particle species, the difficulty in delivering the required dose safely and accurately almost a thousand times faster than is currently possible is common to all.

Results

Accelerators capable of producing the necessary currents and dose rates are already in use in experimental facilities but significant technical hurdles must be overcome before clinical FLASH systems can be realised.

Conclusions

This contribution covers the current landscape of FLASH beam delivery and the efforts that are currently being made to deliver FLASH beams. Alongside the state-of-the-art for accelerator systems for each of the particle species under investigation, potential roadmaps to future clinical systems are discussed. In particular, areas of greatest concern — such as sufficient beam charge acceleration, dosimetry and dose delivery control, challengers connected to hypofractionation, alignment and adaptation to tumour motion, etc. — for each of the technologies is highlighted along with the technologies and delivery strategies most likely to provide the first clinical systems.

Background and Aims

The Laser-Hybrid Accelerator for Radiobiological Applications (LhARA) programme aims to reduce the costs associated with hadron radiotherapy by replacing a conventional accelerator with a laser-source capable of producing protons and ions and a Gabor lense for capturing before acceleration. This approach will allow the response of ultra high dose rates and tightly focused beams to be studied both in vivo and in vitro.

Methods

LhARA will use a high intensity laser as the ion source, which will be captured by a novel gabor lense before further acceleration. Phase one of LhARA will allow in-vitro radiobiological experiments with 15 MeV protons. Phase two will use an FFA to accelerate the beam up to 127 MeV protons for in-vivo and in-vitro experiments. In addition, ions will be studied in phase two up to 34 MeV/u.

Results

Initial funding for Phase one has been secured through the UK Research and Innovations Infrastructure Fund for the Ion Therapy Research Facility (ITRF) in the UK which will allow the LhARA programme to investigate the laser-source, the Gabor lense, shot-by-shot dosimetry using ion-acoustic imaging, novel end-stations and beam monitoring, as well as facility integration.

Conclusions

We will present the current LhARA concept as well as the outline of the initial two year design phase of the programme and the role of LhARA within ITRF, culminating in the LhARA Conceptual Design Report in 2024.

Background and Aims

Recent studies suggested that ultra-high dose rates (FLASH) radiation decreased damage to normal tissue while preserving the anti-tumor activity compared with conventional dose rates (CONV) radiation. High-energy X-ray (HEX) is the most widely used radiation in clinic radiotherapy, but its corresponding FLASH effect and mechanism were hardly ever reported due to the lack of research platform. Here, we described the first HEX platform for FLASH research, including the implementation of FLASH HEX, dosimetry and irradiation process in vitro and in vivo experiments.

Methods

A Platform for Advanced Radiotherapy Research (PARTER) was set up based on the superconducting linac at China Academy of Engineering Physics THz Free Electron Laser (CTFEL) facility, to produce high quality HEX of ultra-high dose rates (around 2000 Gy/second of maximum) for FLASH research. The high current electron beam (8 mA in maximum) is accelerated to 6-8 MeV then produce bremsstrahlung HEX by bombarding a rotating tungsten target. Carefully designed collimators, flatten filter, monitors and other auxiliary facilities are mounted to control the FLASH HEX and provide a qualified irradiation field to users. A dosimetry system consist of passive and active dosimeters is applied on PARTER platform to ensure the dose traceability.

Results

The FLASH irradiation platform was finished on PARTER and the corresponding performances showed agreement with the requirement of FLASH preclinical experiments. Over 10 biological experiments have been carried out in the last two years and significant FLASH effect of HEX was observed.

Conclusions

The PARTER platform based on the accelerator at CTFEL, China can provide high intensity MVs X-rays and corresponding dosimetry for FLASH irradiaion. High energy X-rays can trigger FLASH efffect in vivo experiment.