# PEERing into the Future: Benchmarking the ANSTO Australian Synchrotron’s Very-High-Energy Electron Linac for Ultra-High Dose-Rate, In Vivo FLASH Radiotherapy Research

## TL;DR

A new Australian facility is benchmarked for high-speed cancer treatments that spare healthy tissue.

## Contribution

Demonstrates the PEER beamline's suitability for in vivo FLASH radiotherapy research using very-high-energy electrons.

## Key findings

- PEER cell survival results align with VHEE results from DESY's ARES beamline.
- VHEE produced more cell sparing compared to conventional X-ray treatments.
- Mouse cadaver experiments confirmed PEER's capability to irradiate small animals safely.

## Abstract

The field of radiotherapy is continually advancing, striving for ways in which to deliver a dose to a tumour while limiting the damage to nearby tissues. An increasingly common technique which is under intense development is that of FLASH radiotherapy, where doses are often delivered in fractions of seconds, rather than multiple deliveries over the span of weeks and months. Recent investigations have combined this technique with very-high-energy electrons to also target deep-seated tumours. There are a limited number of facilities available globally to undertake these investigations. This study demonstrates the successes of a new facility in Australia, suitable for such work.

Background/Objectives: The PEER beamline at the ANSTO Australian Synchrotron has been developed to enable VHEE FLASH radiotherapy studies, both dosimetric and biological. Featuring a 100 MeV electron linac, it delivers single or multi-pulse irradiations consisting of 100 ps bunches with a 2 ns spacing, resulting in average dose-rates and instantaneous dose-rates as high as 108 Gy/s and 109 Gy/s, respectively. Much work has been conducted to realise a stable accelerator facility, complete with the tooling and diagnostics required to undertake such studies. However, to truly confirm its suitability required a successful biological benchmarking. Methods: Three cell lines were irradiated utilising real-time dosimetry to compare linear quadratic cell survival curves with other facilities. Also, mouse cadavers were transported and irradiated, mimicking live animals, to assess the feasibility and logistics of small animal experiments. Results: By comparing the trends of the linear quadratic model, evident in the α and β parameters, the PEER cell survival results were shown to be in agreement with VHEE results from the ARES beamline at DESY, Hamburg, Germany. Evident in the survival trends, VHEE produced more cell sparing in all cell lines compared to 2 Gy/s X-rays delivered on the IMBL, another beamline at the Australian Synchrotron. The results of the mouse cadaver irradiations showed that PEER can safely and efficiently irradiate small animals. Conclusions: The PEER beamline is shown to possess suitable capabilities, including real-time dosimetry, repeatable alignment, and linac diagnostics, rendering it suitable for future in vivo VHEE UHDR FLASH radiotherapy investigations.