Traceable dosimetry for FLASH radiotherapy

More than 1 million cancer patients are treated with radiotherapy in the EU each year. In this, ionising radiation is delivered to a tumour site to kill cancerous cells. Whilst effective, some radiation dose is unavoidably delivered to healthy, surrounding tissue and many patients experience severe toxicity. To reduce ill-effects the adiation is often delivered in small, fractionated doses, typically at a rate of 0.1 Gy/s in several treatments over the course of 5 – 6 weeks.

Recently a new form of treatment, termed “FLASH” radiotherapy, has emerged that delivers radiation at ultra-high dose-rates (UHDR) (> 40 Gy/s) or ultra-high dose-per-pulse (UHDPP) (>0.6 Gy/pulse). This has demonstrated the capability to spare healthy tissue up to 40%, while still suppressing tumour growth.

However, the code of practice (CoP) used for calibrating conventional beam monitors, IAEA TRS-398, cannot be used in FLASH therapy as this uses ionisation chambers as calibration standards which do not function correctly under UHDR/UHDPP conditions.

This project will address these issues and develop three new portable primary standards suitable for FLASH therapy conditions and, based on simulations and clinical-like reference fields, will make recommendations on how to extend existing CoPs to UHDR proton and UHDPP electron beams. The work performed is expected to positively impact the FLASH treatment facilities already installed in Europe and will enhance the speed of clinical implementation of FLASH therapy.

It will also enable manufacturers of FLASH systems to demonstrate that their products meet regulatory criteria, thereby enhancing their pace of innovation and provide a better treatment outcome for millions of European citizens.