LAUSR

PURPOSE While FLASH-RT is a promising novel technique which has the potential to achieve a better therapeutic ratio between tumor control and normal tissue complications, the ultra high pulsed dose rates (UHPDR) mean that experimental dosimetry is very challenging. There is a need for real-time dosimeters in the development and implementation of FLASH-RT. In this work, we characterize a novel plastic scintillator capable of temporal resolution short enough (2.5 ms) to resolve individual pulses. METHODS We characterized a novel plastic dosimeter for use in a linac converted to deliver 16 MeV electrons at 100 Gy/s UHPDR average dose rates. The linearity and reproducibility was established by comparing relative measurements with a pinpoint ionization chamber placed at 10 cm water-equivalent depth where the electrometer is not saturated by the high dose per pulse. The accuracy was established by comparing the plastic scintillator dose measurements with EBT-XD Gafchromic radiochromic films, the current reference dosimeter for UHPDR. Finally, the plastic scintillator was compared against EBT-XD films for on-line dosimetry of two in-vitro experiments performed at UHPDR. RESULTS Relative ion chamber measurements were linear with plastic scintillator response within ≤1% over 4-20 Gy and pulse frequencies (18-180 Hz). When characterized under reference conditions with NIST-traceability, the plastic scintillator maintained its dose response under UHPDR conditions and agreed with EBT-XD film dose measurements within 4% under reference conditions and 6% for experimental on-line dosimetry. CONCLUSION The plastic scintillator shows a linear and reproducible response, and is able to accurately measure the radiation absorbed dose delivered by 16 MeV electrons at UHPDR. The dose is measured accurately in real-time with a greater level of precision than that achieved with radiochromic film. This article is protected by copyright. All rights reserved.