Modifying a clinical linear accelerator for delivery of ultra-high dose rate irradiation

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title = "Modifying a clinical linear accelerator for delivery of ultra-high dose rate irradiation",
abstract = "Objectives: The purpose of this study was to modify a clinical linear accelerator, making it capable of electron beam ultra-high dose rate (FLASH) irradiation. Modifications had to be quick, reversible, and without interfering with clinical treatments. Methods: Performed modifications: (1) reduced distance with three setup positions, (2) adjusted/optimized gun current, modulator charge rate and beam steering values for a high dose rate, (3) delivery was controlled with a microcontroller on an electron pulse level, and (4) moving the primary and/or secondary scattering foils from the beam path. Results: The variation in dose for a five-pulse delivery was measured to be 1{\%} (using a diode, 4{\%} using film) during 10 minutes after a warm-up procedure, later increasing to 7{\%} (11{\%} using film). A FLASH irradiation dose rate was reached at the cross-hair foil, MLC, and wedge position, with ≥30, ≥80, and ≥300 Gy/s, respectively. Moving the scattering foils resulted in an increased output of ≥120, ≥250, and ≥1000 Gy/s, at the three positions. The beam flatness was 5{\%} at the cross-hair position for a 20 × 20 and a 10 × 10 cm2 area, with and without both scattering foils in the beam. The beam flatness was 10{\%} at the wedge position for a 6 and 2.5 cm diametric area, with and without the scattering foils in the beam path. Conclusions: A clinical accelerator was modified to produce ultra-high dose rates, high enough for FLASH irradiation. Future work aims to fine-tune the dose delivery, using the on-board transmission chamber signal and adjusting the dose-per-pulse.",
keywords = "FLASH, Irradiation, Linac, Ultra-high dose rate",
author = "Michael Lempart and B{\"o}rje Blad and Gabriel Adrian and Sven B{\"a}ck and Tommy Kn{\"o}{\"o}s and Crister Ceberg and Kristoffer Petersson",
year = "2019",
month = "2",
day = "10",
doi = "10.1016/j.radonc.2019.01.031",
language = "English",
journal = "Radiology and Oncology",
issn = "1879-0887",
publisher = "Elsevier",