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Forschungsstelle
METAS
Projektnummer
F-5155.30115
Projekttitel
18HLT04 UHDpulse: Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates

Texte zu diesem Projekt

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Schlüsselwörter
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Kurzbeschreibung
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Projektziele
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Abstract
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Umsetzung und Anwendungen
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Publikationen / Ergebnisse
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Erfasste Texte


KategorieText
Schlüsselwörter
(Englisch)

Radiotherapy, dosimetry, detector characteristics, ultra-high pulse dose rate, laser-based particle accelerator, ultrashort radiation pulses.

Kurzbeschreibung
(Englisch)

Recently, in vivo radiobiological experiments have shown that irradiation with electron beams, with ultra-high dose per pulse, may dramatically reduce adverse side effects while being equally efficient for tumour control as conventional irradiation. Extreme dose rates are delivered by laser-based accelerators, which are the next generation of accelerators for radiotherapy. These accelerators may facilitate the development of more efficient therapeutic techniques and cost-effective healthcare. Pulses with dose rate orders of magnitudes higher than those in conventional radiotherapy present significant metrological challenges, which need to be addressed to enable the translation of these novel radiotherapy techniques into clinical practice.


This is a joint research project carried out in the framework of the European Metrology Programme for Innovation and Research (EMPIR) (see:http://www.euramet.org/research-innovation/empir/). The EMPIR initiative is co-funded by the European Unions's Horizon 2020 research and innovation programme and the participating states. METAS is one of the project partners in the project.

Projektziele
(Englisch)

The overall goal of the project is to provide the metrological tools needed to establish traceability in absorbed dose measurements of particle beams with ultra-high pulse dose rates (UHPDR), i.e. with ultra-high dose per pulse or with ultra-short pulse duration.

The specific objectives of the project are:

  1. To develop a metrological framework, including SI-traceable primary and secondary reference standards and validated reference methods for dosimetry measurements for particle beams with ultra-high pulse dose rates.
  2. To characterise the response of available detector systems in particle beams with ultra-high dose per pulse or with ultra-short pulse duration.
  3. To develop traceable and validated methods for relative dosimetry and for the characterisation of stray radiation outside the primary pulsed particle beams.
  4. Using the results from objectives 1-3, to provide the input data for Codes of Practice for absolute dose measurements in particle beams with ultra-high pulse dose rates.
  5. To facilitate the uptake of the project’s achievements by the measurement supply chain, standards developing organisations (e.g. those associated with International Atomic Energy Agency (IAEA) and International Commission on Radiation Units (ICRU) reports) and end users (clinical and academic laboratories, hospitals and radiotherapy manufacturers).
Abstract
(Englisch)

The Ionizing Radiation Laboratory participates in the activities in WP1 and WP2 and as WP Leader of WP2. All planned activities were carried out and completed.
The METAS accelerator for FLASH-RT was optimized on the basis of the beam parameters for FLASH radiotherapy (RT) compiled by the CHUV. The beam profile was characterized and compared with associated Monte Carlo simulations calculated at GUM. For these relative measurements, measurements with demonstrably dose rate-independent EBT3 films were introduced at METAS. 

When parameterizing the radiochemical yield factor of the Fricke dosimeter, the dose rate was varied between (0.3 - 900) mGy/pulse. The dose of the Fricke dosimeter was compared with measurements of two different ionization chamber types (Roos and Adv. Markus chamber) and additionally with alanine dosimeters of the PTB and EBT3 films. In addition, Fricke dosimeters with (0.1 - 10) Gy/pulse were irradiated at the CHUV with their UHD accelerator. The Fricke dose was compared with that of EBT3 film.
However, the measured values fit well into the series of measurements and indicate that the Fricke dosimeter is dose rate-dependent from >1 Gy/pulse. 

The information obtained from this was then used to establish the Fricke primary standard (total absorption). For this purpose, the current measurement was additionally calibrated traceable to a calibrated PTB current source in spring 2022. The primary realization of the absorbed dose to water for UHD electron radiation was compared with the calorimetric primary realization of PTB using alanine irradiations of the NRC (Canada) in summer 2022. The analysis of NRC shows that the two standards agree within the combined measurement uncertainty R METAS/PTB = 1.002 +/- 0.012 (k=1).

In addition, a specific Adv. Markus chamber was used by both METAS and PTB for comparison measurements. A close examination of these results has shown that for ionization chambers - used with FLASH-RT dose rates - not only an individual, serial number-specific determination of the saturation correction is essential, but also that the influence of the air pressure on the saturation correction must be taken into account to a higher degree than usual.

As WP2 leader, METAS was also involved in the project organization and project reporting. In this context, METAS co-authored interim reports, chaired the corresponding sessions at project meetings and monitored and presented the progress of the entire WP.

Umsetzung und Anwendungen
(Englisch)

The results obtained will be incorporated into publications. Based on the results, a draft code of practice for measurements in UHD electron radiation will be developed.
The further developments made in UHDpulse on the accelerator and on the reference dosimetry have allowed us to support the PSI project AALPINE. In this project, passive dosimeters (TLD and OSL) were irradiated with precisely defined doses at ultra-high dose rates.
Thanks to UHDpulse, METAS has a UHDPP (ultra-high dose per pulse) accelerator and is also known for this in the community. METAS is one of the few NMIs that has such an accelerator and can therefore perform reference dosimetry. Furthermore, the Fricke primary standard has been established at UHDPP.
METAS will endeavor to participate in further metrological projects in the field of dosimetry for FLASH radiotherapy. (EPM NRM call in 2023)

Publikationen / Ergebnisse
(Englisch)

METAS is directly involved in:

A. Schüller et al. The European Joint Research Project UHDpulse – Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates, Physica Medica, November 2020.

A review paper on the results of the entire project is in preparation. The paper will be published in Radiotherapy & Oncology.

At the newly created conference FRPT 2021 (FLASH Radiotherapy & Particle Therapy conference, ~700 participants) a presentation was given with the title: FRICKE DOSI-METRY AS A PRIMARY STANDARD AND REFERENCE FOR ABSORBED DOSE TO WATER IN ULTRA HIGH PULSE DOSE RATE ELECTRON BEAMS. The abstract was published in a special issue of Radiotherapy & Oncology.