Background and Aims

Advancement in accelerator technology has led to the development of systems capable of generating particle beams with ultra-high dose rates per pulse, facilitating investigations of radiation therapy modalities characterized by dose deliveries exceeding several hundred Gy/s. The FLASH effect is induced at rates greater than 40 Gy/s, subsequently reducing undesired healthy tissue damage, whilst maintaining comparable tumour control to conventional techniques. Further, laser-driven acceleration of charged particle beams produced with compact “plasma accelerators” are characterized by even higher dose rates per pulse (up to 10⁹ Gy/s) at quasi-instantaneous irradiations.

Methods

Despite this, dosimetry of these beams has proven to be technically challenging, requiring the development of novel strategies to replace already established methods for conventional radiotherapy. As such, a small portable graphite calorimeter has been developed and modified at National Physical Laboratory (NPL) to conduct absolute dose measurements of high dose rate per pulse proton beams.

Results

Proof of principle measurement of the absorbed dose of laser-driven proton beams have been carried out with this device, representing the first ever based on calorimetry techniques. Energetic proton beams of up to 40 MeV were produced using the VULCAN petawatt laser system of the Central Laser Facility of the Rutherford Appleton Laboratory. Doses per pulse of up to 3 Gy were measured, with negligible electromagnetic pulse (EMP) contribution to the signal.

Conclusions

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

Advancement in accelerator technology has led to the development of systems capable of generating particle beams with ultra-high dose rates per pulse, facilitating investigations of radiation therapy modalities characterized by dose deliveries exceeding several hundred Gy/s. The FLASH effect is induced at rates greater than 40 Gy/s, subsequently reducing undesired healthy tissue damage, whilst maintaining comparable tumour control to conventional techniques. Further, laser-driven acceleration of charged particle beams produced with compact “plasma accelerators” are characterized by even higher dose rates per pulse (up to 10⁹ Gy/s) at quasi-instantaneous irradiations.

Methods

Despite this, dosimetry of these beams has proven to be technically challenging, requiring the development of novel strategies to replace already established methods for conventional radiotherapy. As such, a small portable graphite calorimeter has been developed and modified at National Physical Laboratory (NPL) to conduct absolute dose measurements of high dose rate per pulse proton beams.

Results

Proof of principle measurement of the absorbed dose of laser-driven proton beams have been carried out with this device, representing the first ever based on calorimetry techniques. Energetic proton beams of up to 40 MeV were produced using the VULCAN petawatt laser system of the Central Laser Facility of the Rutherford Appleton Laboratory. Doses per pulse of up to 3 Gy were measured, with negligible electromagnetic pulse (EMP) contribution to the signal.

Conclusions

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

Laser-driven ion acceleration is attracting significant interest in the radiobiological community, as it allows to deliver dose in ultrashort bursts with high dose rates (10⁹-10¹⁰ Gy/s), opening up for investigation novel regimes of radiobiology. These studies require the implementation of bespoke and innovative arrangements for beam delivery and dosimetry.

Methods

The PW VULCAN and GEMINI laser systems at the Rutherford Appleton laboratory were used to generate, respectively, proton and carbon ion bunches. 35 MeV protons and 10 MeV/u carbon ions were magnetically selected and used to irradiate 2D and 3D biological samples, in single exposures. The 2D-samples were plated on a dish and placed inside a vertical holder while 3D models (Glioblastoma neurospheres) were immersed in cell culture medium and placed at the bottom of a thin-walled 3 mm diameter polypropylene tube. Dosimetry was performed on every shot by employing previously calibrated, unlaminated EBT3-Radio-Chromic Film (RCF) for carbon ion dosimetry, while standard EBT3-RCF was used for the proton measurements.

Results

Doses in the 1-5 Gy range with 10% dose variation over 3x3 mm² surface, were delivered to the cells and measured. The proton depth-dose profile along the 3 mm thick tube was evaluated with an EBT3-RCF stack phantom, showing a 5% dose uniformity along the whole tube thickness.

Conclusions

The irradiation and dosimetry approach enabled controlled irradiation of 2D and 3D samples, with a shot-to-shot precise dose determination.

Acknowledgements

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 programme.