Validation of an ultrahigh dose rate pulsed electron beam monitoring system using a current transformer for FLASH preclinical studies

Abstract
Purpose: The Oriatron eRT6 is a linear accelerator (linac) used in FLASH preclinical
studies able to reach dose rates ranging from conventional (CONV) up
to ultrahigh (UHDR). This work describes the implementation of commercially
available beam current transformers (BCTs) as online monitoring tools compatible
with CONV and UHDR irradiations for preclinical FLASH studies.
Methods: Two BCTs were used to measure the output of the Oriatron eRT6
linac. First, the correspondence between the set nominal beam parameters and
those measured by the BCTs was checked. Then, we established the relationship
between the total exit charge (measured by BCTs) and the absorbed dose
to water. The influence of the pulse width (PW) and the pulse repetition frequency
(PRF) at UHDR was characterized, as well as the short- and long-term
stabilities of the relationship between the exit charge and the dose at CONV
and UHDR.
Results: The BCTs were able to determine consistently the number of pulses,
PW, and PRF. For fixed PW and pulse height, the exit charge measured from
BCTs was correlated with the dose, and linear relationships were found with
uncertainties of 0.5 % and 3 % in CONV and UHDR mode, respectively. Shortand
long-term stabilities of the dose-to-charge ratio were below 1.6 %.
Conclusions: We implemented commercially available BCTs and demonstrated
their ability to act as online beam monitoring systems to support FLASH
preclinical studies with CONV and UHDR irradiations. The implemented BCTs
support dosimetric measurements, highlight variations among multiple measurements
in a row, enable monitoring of the physics parameters used for irradiation,
and are an important step for the safety of the clinical translation of
FLASH radiation therapy