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EXPANDING PROTON FLASH CAPABILITIES TO kGy /s WITHIN ms FOR CLINICAL APPLICATIONS AT HZB
Abstract
Background and aimsThe HZB Cyclotron facility is able to deliver proton FLASH irradiation, providing beamtime to Charité – Universitätsmedizin Berlin for in vivo and in vitro experiments. For these studies, a spread-out Bragg peak with a maximum dose rate of 100 Gy/s has been applied within 200 ms at a maximum energy of 68 MeV. Since then, various system upgrades have been implemented with the aim to increase the achieved dose rate and shorten the irradiation time. The involved components and their performance are presented below.
MethodsBetween the cyclotron and its injector, an electrostatic deflector has been installed, which is controlled by an FPGA board and acts as an adjustable beam shutter, providing irradiation times down to 1 ms. Within such short durations, the delivered beam intensity can be safely increased without damaging the vacuum window at the beam exit and without reaching the radiation safety limits. The increased dose rates from a mm-focused beam are then measured by an Advanced Markus Chamber (PTW-Freiburg, Germany) and monitored by an in-house developed transparent ionization chamber, connected to a UNIDOS webline electrometer (PTW-Freiburg, Germany).
ResultsBoth ionization chambers have shown a linear response with respect to the beam current for dose rates up to 4 kGy/s. An irradiation time of 1 ms has been achieved with a statistical fluctuation of 4%, while the clinical requirement of <2% dose uncertainty can be achieved with irradiation times longer than 2.5 ms.
ConclusionsThe updated FLASH capabilities of the HZB Cyclotron enable a reliable delivery, measurement and monitoring of proton dose rates in the order of several kGy/s within few ms. In combination with the available 3D range modulator, the parameter space for systematic clinical experiments is broadened remarkably.
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Kourkafas Georgios, Bundesmann Juergen, Fanselow Timo, Denker Andrea, Ehrhardt Vincent Henrique, Gollrad Johannes, Budach Volker, Weber Andreas, Kociok Norbert, Joussen Antonia M., Heufelder Jens. FLASH proton irradiation setup with a modulator wheel for a single mouse eye. Medical Physics. Vol. 48(4):1839–1845. 2021. Wiley. [Cross Ref]