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Enhanced scanning electron micrograph image of cancer cells

Reference standards and codes of practice for ultra-high pulse dose rate cancer treatment

The project

FLASH radiotherapy is a promising cancer treatment under development. It involves an almost instantaneous delivery of the prescribed radiation dose with only a few radiation pulses of ultra-high dose rate. Such an approach has been found to dramatically reduce adverse side effects to healthy tissues yet is as effective for tumour control as conventional radiotherapies.

Before full implementation in clinical practice, a method to precisely measure radiation doses at these ultra-high pulse dose rates is required, to ensure reliable delivery of prescribed doses to patients.

Completed EMPIR project Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates (18HLT04, UHDpulse) has developed a measurement framework, encompassing reference standards traceable to the units of the International System of Units (the SI), and validated reference methods for dose measurements at ultra-high pulse dose rates. It also characterised detector systems, developed traceable and validated methods for relative dosimetry, characterised stray radiation, and contributed to codes of practice. The initial project partners published 46 articles in renowned scientific journals (peer reviewed, open access, with acknowledgement to EMPIR) and 44 other publications as well as giving 91 oral presentations.

Project outcomes will be promoted to standards organisations, international agencies, manufacturers, and end users. Ultimately, the aim is confidence that patients will receive their prescribed dose, for safer, cost effective, cancer treatments.

First human trials of FLASH radiotherapy

As one activity within the project, the world’s first in-human clinical trial with FLASH proton beams (FAST-01) was supported by the dosimetric characterisation of the beam in a hospital by means of a portable primary standard. This clinical trial was crucial for approval and provided the hospital with the confidence to commence clinical implementation of this new treatment modality. This was described in the paper Ultrahigh dose rate pencil beam scanning proton dosimetry using ion chambers and a calorimeter in support of first in-human FLASH clinical trial published in the journal Medical Physics.

The first human trials for FLASH radiotherapy with electron beams benefited from the UHDpulse activities on new radiation dose monitors for portable FLASH electron accelerators. This was described in EURAMET case study Monitoring of ultra-high dose rate electron beams for advanced cancer treatment. and published in the paper Implementation and validation of a beam-current transformer on a medical pulsed electron beam LINAC for FLASH-RT beam monitoring in the journal Applied Clinical Medical Physics. The first phase-1 FLASH trial on a skin cancer patient took place in 2021 and the first randomised trial comparing conventional radiotherapy with FLASH therapy with electron beams on patients with localised carcinomas in 2023.

The use of portable electron accelerators for FLASH radiotherapy has the potential to revolutionise point of care cancer treatment – improving patient outcomes whilst minimising side-effects in a cost-effective manner.

In addition, the outputs of the UHDpulse project will enable manufacturers to develop improved ultra-high dose rate instrumentation to benefit both European competitiveness and the health of its citizens.

As conventional dosimeters are saturated due to the ultra-high dose rates, a new type of dosimeter was developed in the framework of UHDpulse that can provide real time information on ultra-high dose rate FLASH beams, as described in the EURAMET case study Measurement of radiation dose at ultra-high dose rates for advanced radiotherapy and published in the papers Design, realization, and characterization of a novel diamond detector prototype for FLASH radiotherapy dosimetry and Application of a novel diamond detector for commissioning of FLASH radiotherapy electron beams, both in the journal Medical Physics. This new type of dosimeter has been commercially available since the end of the project in 2023 and has already found use in a lot of laboratories and hospitals that are working on implementation of FLASH radiotherapy.

By providing the metrological tools needed to perform traceable dosimetric measurements in clinical or preclinical ultra-high dose rate particle beams, the project has allowed improved comparability between studies carried out in different facilities with different radiation modalities.

In the long-term this work will ensure the safety and efficacy of FLASH radiotherapy for cancer patients.

Project coordinator Andreas Schüller from PTB said

‘The new possibilities to measure in real time the radiation doses of particle beams with ultra-high dose rates marks a major step for the establishment of the advanced radiotherapy modality FLASH for better cancer treatment.’

This EMPIR project is co-funded by the European Union's Horizon 2020 research and innovation programme and the EMPIR Participating States.

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