Background and Aims

During FLASH radiotherapy, secondary pulsed radiation fields are created outside of the primary beam. These fields, composed of radiation of different types and/or energy, can cause secondary doses to healthy tissue and critical organs outside of the target volumes. The main component is neutron radiation, contributing significantly to the secondary equivalent dose. For personalized dose management, especially for paediatric patients, the unwanted secondary dose must be reliably estimated and minimized. As a basis for reliable and traceable neutron dosimetry, neutron spectrometry for pulsed fields plays a key role in the proper characterization of the stray radiation fields.

Methods

In the framework of the project UHDpulse, two independent neutron spectrometric systems are being developed, based on Bonner sphere spectrometers (BSS). The first approach consists of adapting the front-end electronics of the LUPIN [M. Caresana et al., NIM A 712 (2013) 15], developed specifically for pulsed neutron fields, for use with a BSS. The second approach builds upon the BSS NEMUS [B. Wiegel and A.V. Alevra, NIM A 476 (2002) 36] with the standard ³He-filled proportional neutron counter replaced by a ²³⁵U-coated ionization chamber. Both approaches rely on active detection methods, being able to study in detail the time variation of the pulsed neutron fields.

Results

This contribution discusses both approaches and summarizes experimental tests.

Conclusions

An outline of future developments is presented.

This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

Background and Aims

Dosimetry for FLASH radiotherapy, VHEE radiotherapy as well as for laser-driven beams cause significant metrological challenges due to the ultra-high dose rates and pulsed structure of these beams, in particular for real time measurements with active dosimeters. It is not possible to simply apply existing Codes of Practice available for dosimetry in conventional external radiotherapy here. However, reliable standardized dosimetry is necessary for accurate comparisons in radiobiological experiments, to compare the efficacy of these new radiotherapy techniques and to enable safe clinical application. UHDpulse aims to develop the metrological tools needed for reliable real-time absorbed dose measurements of electron and proton beams with ultra-high dose rate, ultra-high dose per pulse or ultra-short pulse duration.

Methods

Within UHDpulse, primary and secondary absorbed dose standards and reference dosimetry methods are developed, the responses of available state-of-the-art detector systems are characterised, novel and custom-built active dosimetric systems and beam monitoring systems are designed, and methods for relative dosimetry and for the characterization of stray radiation are investigated.

Results

Prototypes of different active dosimetry systems show promising results for real-time dosimetry for particle beams with ultra-high pulse dose rates. The results of the UHDpulse project will be the input data for future Codes of Practice.

Conclusions

A brief overview of the progress in the UHDpulse project and the involved institutions will be given.

Acknowledgement: This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.

Background and Aims

During FLASH radiotherapy, secondary pulsed radiation fields are created outside of the primary beam. These fields, composed of radiation of different types and/or energy, can cause secondary doses to healthy tissue and critical organs outside of the target volumes. The main component is neutron radiation, contributing significantly to the secondary equivalent dose. For personalized dose management, especially for paediatric patients, the unwanted secondary dose must be reliably estimated and minimized. As a basis for reliable and traceable neutron dosimetry, neutron spectrometry for pulsed fields plays a key role in the proper characterization of the stray radiation fields.

Methods

In the framework of the project UHDpulse, two independent neutron spectrometric systems are being developed, based on Bonner sphere spectrometers (BSS). The first approach consists of adapting the front-end electronics of the LUPIN [M. Caresana et al., NIM A 712 (2013) 15], developed specifically for pulsed neutron fields, for use with a BSS. The second approach builds upon the BSS NEMUS [B. Wiegel and A.V. Alevra, NIM A 476 (2002) 36] with the standard ³He-filled proportional neutron counter replaced by a ²³⁵U-coated ionization chamber. Both approaches rely on active detection methods, being able to study in detail the time variation of the pulsed neutron fields.

Results

This contribution discusses both approaches and summarizes experimental tests.

Conclusions

An outline of future developments is presented.

This project 18HLT04 UHDpulse has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme.