  Background & Purpose: FLASH or ultra-high dose rate (UHDR) radiation therapy
(RT) has gained attention in recent years for its ability to spare normal
tissues relative to conventional dose rate (CDR) RT in various preclinical
trials. However, clinical implementation of this promising treatment option has
been limited because of the lack of availability of accelerators capable of
delivering UHDR RT. We established a framework for the acceptance,
commissioning, and periodic quality assurance (QA) of electron FLASH units and
present an example of commissioning.
  Methods: A protocol for acceptance, commissioning, and QA of UHDR linear
accelerators was established by combining and adapting standards and
professional recommendations for standard linear accelerators based on the
experience with UHDR at four clinical centers that use different UHDR devices.
Non-standard dosimetric beam parameters considered included pulse width, pulse
repetition frequency, dose per pulse, and instantaneous dose rate, together
with recommendations on how to acquire these measurements.
  Results: The 6 and 9 MeV beams of an UHDR electron device were commissioned
by using this developed protocol. Measurements were acquired with a combination
of ion chambers, beam current transformers (BCTs), and dose rate independent
passive dosimeters. The unit was calibrated according to the concept of
redundant dosimetry using a reference setup.
  Conclusions: This study provides detailed recommendations for the acceptance
testing, commissioning, and routine QA of low-energy electron UHDR linear
accelerators. The proposed framework is not limited to any specific unit,
making it applicable to all existing eFLASH units in the market. Through
practical insights and theoretical discourse, this document establishes a
benchmark for the commissioning of UHDR devices for clinical use.
