The Project is structured into four technical work packages (WP) and two WPs for project impact and administration:

  • WP1: SI-traceable primary standards for absorbed dose measurements – towards the development of primary standard
  • WP2: Secondary standards and reference methods for reference and relative dosimetry
  • WP3: Detector systems for measurements in the primary beam
  • WP4: Detector systems and methods for dosimetry outside primary beam – stray radiation
  • WP5: Creating impact
  • WP6: Management and coordination

WP1: SI-traceable primary standards for absorbed dose measurements – towards the development of primary standard

Lead partner: NPL

The aim of this work package is to provide the metrological input needed to support absolute dosimetry of particle beams with UHPDR, generated with conventional as well as novel laser-driven accelerators. The general acceptable levels of accuracy in radiation therapy, which in a simplified manner can be stated as ‘the dose delivered to the specification point”, may vary between 3.5 % and 5 % (k = 1) according to the IAEA Human Health Reports No 31. However, dosimetry at UHPDR beams is non-trivial as current radiotherapy dosimetry protocols are not designed for such conditions and because the detectors available for online measurements (such as ionisation chambers, diodes and diamond detectors) start to saturate when the dose rate/dose-per-pulse is increased beyond what is used in conventional radiotherapy (TRS 398 and AAPM TG-51). The UHPDR delivery regime creates new challenges for accurate dosimetry that need to be addressed, therefore the aim of this work package is to establish a primary standard for the absorbed dose measurements due to UHPDR electron and proton beams and commence developments of graphite calorimeters for absolute dosimetry for ultrashort, UHPDR charged particle beams generated with a laser-driven accelerators.

Task 1.1: to provide well characterised reference radiation fields for testing and traceable calibrations of dosimeters used FLASH radiotherapy. It comprises the modification and optimisation of accelerators available at primary standards dosimetry laboratories (PSDLs) in order to be able to generate reference electron beams with ultra-high dose per pulse. The available instruments and methods for the characterisation of beam properties will be verified, optimised if necessary and calibrated to operate in beams with UHPDR. The reference beams with UHPDR will be commissioned by determining the beam parameters which are relevant for the investigation and calibration of dosimeters in FLASH radiotherapy. The characteristics of the reference beams established at the PSDLs will be documented.

Task 1.2: to develop and test techniques as primary dosimetry standards in UHPDR electron and proton beams. Specifically, the Fricke dosimetry and the water calorimetry technique, which are two established primary dosimetry techniques in conventional radiotherapy, will be developed further for its applicability in electron beams with UHPDR. Additionally, graphite calorimetry will be employed for absorbed dose measurements of FLASH proton and VHEE electron beams. Corrections and conversions factors will be calculated and the uncertainty budget will be evaluated.

Task 1.3: to develop and evaluate absolute dosimetry methods via graphite calorimetry for ultrashort charged particle beams generated with laser-driven accelerators. A preliminary measurement will be carried out with FLASH proton beams at IC, where the response of a small portable graphite calorimeter will be compared with NPL proton primary standard graphite calorimeter. Appropriate correction factors will be calculated and uncertainties will be evaluated. Subsequently, measurements with a small portable graphite calorimeter will be performed with laser-driven electron and proton beams, supported by preliminary characterisation of the transported beams. Beam parameters for Monte Carlo simulations will be provided by the laser facility teams.

WP2: Secondary standards and reference methods for reference and relative dosimetry

Lead partner: METAS

The aim of this work package is to transfer traceable dosimetry into clinical and preclinical accelerators that deliver particle beams with UHPDR. Specifically, this work package concentrates, on the one hand, on the transfer from the primary standards developed in WP1 to their implementation in the reference dosimetry at (pre)clinical facilities. On the other hand, methods and methodologies will be developed that are needed to appropriately characterise and monitor these UHPDR particle beams.
In this work package, these steps towards traceable beams for these novel modalities are addressed individually, first for the case of the high dose-per-pulse electron accelerators (FLASH) and second for the laser driven accelerators as well as for short pulsed VHEE beams

Task 2.1: several detector types are investigated with regard to its suitability in the context of reference dosimetry. For the purpose of absolute reference dosimetry ionisation chambers, chemical detectors (Fricke and Methyl Viologen) as well as alanine detectors will be investigated, specifically for the dependence of the response on the dose rate. Further, film dosimetry as well as solid state detectors will be investigated and evaluated for its future use in relative dosimetry for the characterisation of the therapeutic fields.

Task 2.2: several types of detectors are investigated for its suitability in absolute dosimetry of laser-driven proton beams as well as in VHEE beams. Specifically, for different types of ionisation chambers the dependence of the ionisation current on the relevant beam parameters will be investigated and appropriate correction models will be proposed. Further, also alanine dosimetry will be evaluated with regard to its suitability as an absolute dosimetry detector.

Task 2.3: a formalism for reference dosimetry in FLASH beams will be derived, which forms the fundamentals for a future Code of Practice. For that, the reference conditions as well as a beam quality index will have to be established. Moreover, based on the outcome of the detector suitability study from Task 2.1, a procedure for a routine dose-rate assessment will be developed.

Task 2.4: film dosimetry as well as alanine dosimetry and ionisation chambers will be characterised for its use in relative dosimetry measurements for both, laser-driven protons as well as VHEE beams. The findings will be supported by means of Monte-Carlo simulations.

WP3: Detector systems for measurements in the primary beam

Lead partner: CHUV

The aim of this work package is to evaluate novel absolute and relative dosimetric systems, which are compatible with pre-clinical and clinical UHPDR FLASH and laser-driven accelerators. The project will explore other type of detectors, which are not necessarily used for primary measurement, but might be adequate in this case. The systems will be tailored to pre-clinical and clinical accelerators and will be evaluated for their use as secondary and working standards. In task 3.1, the monitoring of Flash electron beam will be improved to reach a dose delivery repeatability under 0.5 %, in order to have adequate dose delivery during the comparison of detectors. The various parameters of importance of the Flash-RT method will be reviewed and summarise to support the construction of a code of practice. In task 3.2, the identified beam parameters will be evaluated considering biology and medical physics practice. Detectors will be tested in clinical electron Flash beams in complement to the test at NMIs (WP2) in reference conditions and the improvement of the custom-built systems will be performed. In parallel, custom-built systems will be tested in clinical Flash proton beams. Finally, the selected detectors will be tested in real conditions in Flash electron beams. A contribution to the protocol will be drafted based on the report on the detector tests and the recommendations will be promoted, which will build the necessary framework for human application and guide manufacturers and users of future accelerators.

Task 3.1: to evaluate and validate electron FLASH beam monitoring systems, in order to ensure an adequate repeatability of the irradiation. The current systems are monitoring the beam intensity using existing components of the accelerators, such as Gun, HF, and collimator. This task will benefit those tasks using FLASH irradiation.

Task 3.2: to evaluate and validate novel traceable dosimetric systems under FLASH beam conditions. The current state-of-the-art method in FLASH beams relies on passive dosimetry, which is not sufficient for clinical use and demonstrate the strong need for the evaluation of active dosimeters.

Task 3.3: to evaluate and validate dosimetric systems for emerging pre-clinical facilities using laser-based plasma accelerators, which are considered as the next generation of radiotherapy accelerators.

WP4: Detector systems and methods for dosimetry outside primary beam – stray radiation

Lead partner: ADVACAM, Cristina Oancea

The aim of this work package is to develop traceable and validated methods for characterisation of stray radiation outside the UHPDR primary particle beam. Such mixed radiation fields are composed by radiation of different types and/or energy and cause parasitic doses to healthy tissue and critical organs outside the target volumes. This unwanted dose is crucial for the optimisation of the therapy in view of a personalised dose management. Three promising detection techniques are identified. They will be elaborated and further developed for purposes of measurement of stray radiation produced in UHPDR accelerators either conventional or laser-driven.

Task 4.1: to design an optimised Timepix3 (TPX3) based detector for measurements of stray radiation fields. Thanks to its high spatial, energy and time resolution, Timepix3 allows the visualisation of individual charged particle tracks and thus classification of different types of particles according to their track structure. Timepix3 based device measures the energy deposited in each pixel (direct LET measurement) as well as the time of arrival with precision 1.5 ns enabling time-of-flight spectrometry. Such TPX3 characteristics provide unique possibility to distinguish and characterise radiation components of mixed time-dependent stray radiation fields occurring close to UHPDR primary particle beam. Methods for characterisation of radiation components and for determination of the absorbed dose to water due to stray radiation will be developed.

Task 4.2: to test the response of thermoluminescent detectors (TLD) and optically stimulated luminescence (OSL) detectors in stray radiation fields outside the UHPDR primary particle beam. Both optically and thermally stimulated luminescence is used routinely in continuous fields worldwide. However, their suitability for detection in UHPDR particle fields needs to be investigated and verified. The results of this task will be beneficial for patients, because it would help to better understand and reduce the excessive exposure of healthy tissue by small dosimeters and using cheap methods. Further, this method will be beneficial for calibration of active dosimeters.

Task 4.3: to develop, optimise and characterise two Bonner Sphere Spectrometers based on gaseous proportional counters read out in current mode and fission chambers, respectively. These systems will allow to overcome the dead time issues associated with high intensity pulsed neutron fields, making possible to measure neutron energy spectra, which are essential for precise dose determination.

Task 4.4: to validate the methods for characterisation of stray radiation developed in T4.1-T4.3, provide traceability for absorbed dose to water from stray radiation due to FLASH electron beams, and compilation of the Best Practice Guide.

WP5: Creating impact

Lead partner: CMI, Jaroslav Šolc

The aim of this work package is to ensure that the work carried out in this project is correctly communicated to the relevant user communities and the knowledge gained during the project duration is available to interested parties. The WP consists of various activities related to the knowledge transfer, training, workshops, uptake and exploitation.

WP6: Management and coordination

Lead partner: PTB, Andreas Schüller

The aim of this work package is to coordinate the project, organize project meetings and provide project reporting.