Room: AAPM ePoster Library
Purpose: European Metrology Programme for Innovation and Research (EMPIR) UHDpulse project aims to develop the metrological tools needed to establish traceability in absorbed dose measurements of pulsed particle beams with ultra-high dose-rates. Delivery of doses at ultra-high dose-rate has been of particular interest due to remarkable reduction of normal tissue toxicity (known as the FLASH effect) with respect to conventional treatments. Pulses of particle beams with dose-rates orders of magnitude higher than in conventional radiotherapy present significant metrological challenges in dosimetry, which need to be addressed to enable the translation of these novel radiotherapy techniques to clinical practice.
Methods: the framework of this EMPIR project we investigated the relationship between the ion recombination effects of the PTW Roos chamber and a range of dose-per-pulse values from 0.03 to 5.26 Gy/pulse for 200 MeV very high energy electrons (VHEEs) and a 250 MeV FLASH proton beam with a dose-rate of 65 Gy/s. The chamber measurements were compared to NPL’s graphite calorimeters to determine ion recombination correction factors.
Results: collection efficiency of the Roos chamber, operated at 200 V, in a 5.26 Gy/pulse 200 MeV VHEE beam was found to be 10%. The ion recombination effect in 65 Gy/s FLASH proton beams is also substantial.
Conclusion: chambers, used routinely as secondary standard detectors in proton and electron radiotherapy, suffer from significant recombination effects with increased dose-rates when exposed to high dose-per-pulse VHEE and FLASH proton beams. Behaviour of ion chambers and other dosimeters needs to be well-understood before implementing them as secondary standard detectors in new radiotherapy applications such as FLASH and high dose-per-pulse VHEE RT. This work is a foundation towards development of metrology and tools traceable to national standards for these novel radiotherapy approaches. The framework and the main objectives of the EMPIR UHDpulse project will be discussed.
Funding Support, Disclosures, and Conflict of Interest: This project has received funding from the EMPIR programme co-financed by the Participating States and from the EU Horizon 2020 research and innovation programme.