Rapid and reversible adaptation of a clinical linear accelerator for electron FLASH radiotherapy

Purpose: The aim of this work was to establish a procedure that allows the conversion of a standard clinical LINAC
into a “FLASH” LINAC capable of delivering ultra-high dose rates above 40 Gy/s, with minimal, fully reversible
modifications to the device. A dosimetric characterization of the resulting treatment beam is presented.
Methods: A LINAC was modified to emit a 10 MeV electron FLASH beam. Modifications included the integration
of a pulse control unit which consisted out of a scintillation detector and a transistor circuit. Beam parameters
were optimized to maximize dose output. Beam characterization measurements were performed with different
detectors in water: ionization chamber, diamond detector, radiographic films and scintillation detector. The
resulting doses per pulse (DPP) and dose rates at different source-surface-distances (SSD) as well as the output
reproducibility were determined. The beam was characterized with depth dose curves and lateral profiles.
Results: Conversion of a LINAC to FLASH mode was feasible in less than 30 min. Output was between
DPP$_{SSD-56cm}$ = 1.69 ± 0.02 Gy and DPP$_{SSD-100cm}$ = 0.53 ± 0.01 Gy or dose rates between 676 ± 8 Gy/s and 213 ± 4 Gy/s. ... mehrReproducibility of DPP was better than 0.8 %. FLASH depth dose curves showed a higher range (R80 = 39.8 mm vs. 34.6 mm) and lateral beam profiles had a reduced flatness (from 5.5 % to 12.7 %) at SSD = 56 cm.
Conclusion: We present a fully reversible conversion method requiring minimal modifications to a LINAC to
produce electron FLASH beams. The achieved DPP and mean dose rates demonstrated high reproducibility,
meeting criteria for FLASH applications, and markedly simplifying access to this technology for broader
implementation.