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Updated: Jul 1, 2026

Sample Preparation and Experimental Design for In Situ Multi-Beam Transmission Electron Microscopy Irradiation Experiments
Published on: June 27, 2022
Using hydrated electron temporal measurement as dosimetry of individual electron FLASH beam pulses
Xu Cao1, Aubrey Parks2, William Thomas2
1Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, USA; School of Life Science and Technology, Xidian University, Xi'an, Shaanxi, China; Thayer school of Engineering, Dartmouth College, Hanover, NH 03755, USA.
Purpose:
This study explores the use of hydrated electron absorbance from water radiolysis as a real-time, tissue-equivalent dosimetry method for radiotherapy. While promising, its behavior under ultrahigh dose rates typical of FLASH radiotherapy remains unclear. We investigated the relationship between radiation dose and hydrated electron optical absorption under FLASH conditions.
Methods:
Pure water in a quartz cuvette was irradiated with 9 MeV ultra-high dose rate (UHDR) electron beams, and transient absorbance profiles of hydrated electrons were measured using a multi-pass optical technique. The absorbance per unit radiation dose was quantified for each individual pulse and validated by radiochromic EBT-XD film.
Results:
The cumulative absorbance of hydrated electrons showed an inconsistent linear relationship with dose per pulse, but normalization by pulse width revealed a strong linear correlation with instantaneous dose rate. This enabled accurate pulse dose determination by multiplying the instantaneous dose rate by the known pulse width. Dose measurements obtained through hydrated electron detection showed strong agreement with film dosimetry within a 10 % margin across a wide range of average dose rates, from 32.7 Gy/s to 392.4 Gy/s.
Conclusion:
We present a hydrated electron-based method for indirect, pulse-resolved dose quantification in FLASH radiotherapy. The agreement between the calculated dose and radiochromic EBT-XD film measurements suggests that this approach holds promise for developing tissue-equivalent dosimeters for FLASH radiotherapy applications.
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