Fremont, CA – 03/26/2026 – IntraOp Medical Corporation today announced the successful completion of the IMPulse Trial, the world’s first human dose escalation study of single fraction FLASH radiotherapy (FLASH RT) for cutaneous melanoma metastases. The findings, together with a companion physics and dosimetry study, were conducted in collaboration with Lausanne University Hospital (CHUV) using the IntraOp® Mobetron® UHDR, the first and only mobile linear accelerator capable of delivering both conventional dose rate and ultra high dose rate (UHDR) FLASH electron therapy.
Two landmark peer reviewed papers have now been published:
1. Clinical Trial Results
A phase I dose escalation of FLASH radiotherapy in patients with cutaneous metastases from melanoma: The IMPulse trial (Radiotherapy & Oncology).
This study reports the first-in-human dose escalation of FLASH RT up to 28 Gy delivered in ~90 ms, without observing dose limiting toxicities (DLTs) at any dose level. (https://doi.org/10.1016/j.radonc.2026.111414)
2. Machine Performance & Dosimetry
Machine stability and dosimetry for ultra high dose rate FLASH radiotherapy human clinical protocol (JACMP).
This investigation demonstrates the Mobetron’s exceptional output and energy stability over a 26 month period, validating its robustness for clinical FLASH applications even without real time beam monitoring. https://doi.org/10.1002/acm2.70102
Breakthrough Clinical Findings: FLASH RT up to 28 Gy Delivered Safely in Humans
Between June 2021 and September 2024, CHUV treated 15 lesions in 11 patients, using single fraction FLASH RT at 22, 24, 26, and 28 Gy. No DLTs were observed across any dose level, and the maximum tolerated dose (MTD) was not reached. The trial demonstrated:
• Favorable acute tolerance even at historically skin intolerable single fraction doses (>24 Gy).
• No increase in adverse event severity with dose escalation up to 28 Gy.
• 100% in field tumor response (partial or complete) at most dose levels.
• A delayed Grade 3 epithelitis observed at 28 Gy (investigator rated) was still within manageable limits and scored lower by blinded central review.
These findings mark the highest FLASH doses ever delivered safely in human patients and provide strong evidence supporting a potential FLASH sparing effect at high single fraction doses. (https://doi.org/10.1016/j.radonc.2026.111414)
Exceptional Mobetron Performance Ensures Reliability for FLASH Clinical Workflows
The companion physics paper reports an extensive 26 month evaluation of the upgraded Mobetron, confirming:
• Short term output stability ≤1% for UHDR and ≤0.6% for CDR.
• Long term output constancy within 2% for both modes.
• Energy stability (R50) consistently within clinically accepted tolerances (<2 mm).
• Delivered clinical doses remained within 4% of prescription for all IMPulse patients.
• Mobetron maintained stability even after downtime, without requiring special recalibration.
These results validate the Mobetron as a highly stable, clinically reliable UHDR platform, uniquely suited for FLASH RT research and human treatment. (https://doi.org/10.1002/acm2.70102)
Implications for the Future of FLASH Radiotherapy
The Mobetron’s performance in IMPulse demonstrates that:
• FLASH RT at clinically meaningful doses is feasible, stable, and safe.
• UHDR delivery can be achieved without complex facility upgrades, thanks to Mobetron’s unique mobile architecture.
• The technology is now ready to support larger scale clinical trials, including future Phase II and Phase III studies.
IntraOp continues to work with clinical partners globally to expand the evidence base for FLASH radiotherapy in melanoma, skin cancers, and additional anatomical sites.
About IntraOp Medical Corporation
IntraOp Medical is a global leader in radiation oncology innovation and the manufacturer of the Mobetron®, the world’s first mobile linear accelerator designed for intraoperative radiotherapy (IORT) and advanced FLASH radiotherapy research. With installations around the world, the Mobetron provides clinicians unprecedented flexibility to deliver precision electron therapy directly in the operating suite or for dedicated FLASH research applications.