Top Line: What does it take to move FLASH-RT from physics flex to clinic ready?
The Study: Flash-Skin I was a prospective phase 1 that investigated the feasibility of using standard, clinical, C-arm LINACs to deliver ultra high dose rate (UHDR) electron therapy. The trial included 7 patients with cutaneous melanoma metastases that were treated with 9 Gy x 3 fractions (2 fractions with UHDR, 1 fraction with conventional dose rate) using 9 MeV electrons from a modified Varian TrueBeam. What makes the trial worth your coffee isn’t the n=7 but the technical effort that went into delivering the treatment. The challenge with using conventional LINACs is that they measure dose internally and use feedback systems to adjust output in real time. With FLASH, dose is delivered so fast that these internal systems have to be disabled. This team did extensive clinical QA for over a year prior to going live using multiple redundant systems to detect machine output. They used optically stimulated luminescent dosimeters (OSLDs) mounted on the electron cone for dose reporting during live treatment, which had a precision of 3%. In addition, in vivo dosimetry at the skin surface had a gamma analysis (5%/3mm) pass rate >95% for all UHDR fractions, and skin dose was consistently within 5% of the planned dose. Finally, the number of delivered pulses using UHDR matched the planned number of pulses, which is a big deal when you consider that a UHDR fraction uses only a couple of pulses.
TBL: This trial showed that FLASH electron therapy can be delivered with a modified conventional LINAC with high reliability and accountability. | Dal Bello, Radiother Oncol 2025
The Study: Flash-Skin I was a prospective phase 1 that investigated the feasibility of using standard, clinical, C-arm LINACs to deliver ultra high dose rate (UHDR) electron therapy. The trial included 7 patients with cutaneous melanoma metastases that were treated with 9 Gy x 3 fractions (2 fractions with UHDR, 1 fraction with conventional dose rate) using 9 MeV electrons from a modified Varian TrueBeam. What makes the trial worth your coffee isn’t the n=7 but the technical effort that went into delivering the treatment. The challenge with using conventional LINACs is that they measure dose internally and use feedback systems to adjust output in real time. With FLASH, dose is delivered so fast that these internal systems have to be disabled. This team did extensive clinical QA for over a year prior to going live using multiple redundant systems to detect machine output. They used optically stimulated luminescent dosimeters (OSLDs) mounted on the electron cone for dose reporting during live treatment, which had a precision of 3%. In addition, in vivo dosimetry at the skin surface had a gamma analysis (5%/3mm) pass rate >95% for all UHDR fractions, and skin dose was consistently within 5% of the planned dose. Finally, the number of delivered pulses using UHDR matched the planned number of pulses, which is a big deal when you consider that a UHDR fraction uses only a couple of pulses.
TBL: This trial showed that FLASH electron therapy can be delivered with a modified conventional LINAC with high reliability and accountability. | Dal Bello, Radiother Oncol 2025