Search

• A linear accelerator within a clinical context was converted to deliver ultra-high dose rate with 16 MeV electron beams. • The converted linear accelerator can deliver up to 256 Gy/s average dose rate at the isocenter with conventional setups commonly used for clinical treatments. • The characteristics of field sizes up to 10x10 cm2 were equivalent between conventional and ultra-high dose rate deliveries. • The stability of the deliveries was within ± 2.5% under several different conditions. • The image guidance capabilities of the linear accelerator were retained and the use of CBCT was demonstrated for isocentric setup of phantoms for ultra-high dose rate irradiations. Radiotherapy delivery with ultra-high dose rates (UHDR) has consistently produced normal tissue sparing while maintaining efficacy for tumour control in preclinical studies, known as the FLASH effect. Modified clinical electron linacs have been used for pre-clinical studies at reduced source-surface distance (SSD) and novel intra-operative devices are becoming available. In this context, we modified a clinical linac to deliver 16 MeV UHDR electron beams with an isocentric setup. The first Varian TrueBeam (SN 1001) was clinically operative between 2009–2022, it was then decommissioned and converted into a research platform. The 18 MeV electron beam was converted into the experimental 16 MeV UHDR. Modifications were performed by Varian and included a software patch, thinner scattering foil and beam tuning. The dose rate, beam characteristics and reproducibility were measured with electron applicators at SSD = 100 cm. The dose per pulse at isocenter was up to 1.28 Gy/pulse, corresponding to average and instantaneous dose rates up to 256 Gy/s and 3⋅105 Gy/s, respectively. Beam characteristics were equivalent between 16 MeV UHDR and conventional for field sizes up to 10x10cm2 and an overall beam reproducibility within ± 2.5% was measured. We report on the first technical conversion of a Varian TrueBeam to produce 16 MeV UHDR electron beams. This research platform will allow isocenter experiments and deliveries with conventional setups up to field sizes of 10x10 cm2 within a hospital environment, reducing the gap between preclinical and clinical electron FLASH investigations. [ABSTRACT FROM AUTHOR]