Ronghu Mao1,#, Peng Chen1,#, Leijie Ma1, *, Hui Luo1,#, Bing Li1, Zhaoyang Lou1, Chengliang Yang1, Hongchang Lei1, Hong Ge1,*
1The Department of Radiation Oncology, The Affiliated Cancer Hospital of Zhengzhou University & Henan Cancer Hospital, Zhengzhou 450008, China
# All authors contributed equally to this work.
* Corresponding Authors: Hong Ge, gehong616@126.com
FLASH radiotherapy is a revolutionary novel technique defined by its core characteristic of ultra-high dose rate: the full therapeutic radiation dose is delivered in under one second. It can effectively suppress tumor proliferation while markedly mitigating radiation injury to adjacent healthy normal tissues and reducing adverse treatment effects.
The FLASH research team at the Affiliated Cancer Hospital of Zhengzhou University & Henan Cancer Hospital selected the Varian 23CX medical linear accelerator as the retrofitting platform. The scattering foil matched to the 9 MeV electron beam energy inside the accelerator was removed. By systematically optimizing and adjusting dose rate-related parameters including the filament current of the electron gun, electron gun high voltage settings, output power of the microwave power source, and charging frequency of the pulse modulator, we achieved a mean radiation dose rate of no less than 40 Gy/s at the accelerator isocenter, thus generating FLASH electron beams. We redesigned an external dose control system that precisely regulates the total dose of the FLASH electron beam by controlling the number of accelerator pulses, establishing a complete experimental platform for 9 MeV electron FLASH radiotherapy.
Dosimetric measurements were performed using HD-V2 radiochromic films, EBT3 films, and the PTW Advanced Markus plane-parallel ionization chamber. The measured beam parameters encompassed dose rate, ionization chamber collection efficiency, output stability, pulse linearity, field output factors, percentage depth dose (PDD) curves, and off-axis dose profiles. Key parameters of the retrofitted 9 MeV electron FLASH beam are listed as follows: repetition frequency: 360 Hz; pulse width: 4.5 μs; at a source-to-surface distance (SSD) of 100 cm, the mean dose rate was approximately 120 Gy/s, the per-pulse mean dose was roughly 0.333 Gy, and the instantaneous pulse dose rate reached ~7.4×10⁴ Gy/s. The FLASH system exhibited favorable output stability and excellent pulse linearity. PDD curves revealed slight shifts in characteristic depth parameters (R100, R90, R80, R50) toward greater depth for the FLASH beam compared with conventional 9 MeV electron beams. With the scattering foil removed, the off-axis dose distribution peaked along the central axis, presenting a sharp peaked profile. The acquired output factor data serve as fundamental parameters for dose calculation of centrally symmetric square fields.
The mean dose rate and instantaneous pulse dose rate of the retrofitted 9 MeV electron FLASH beam satisfy the dose rate threshold criteria for FLASH-RT; system output stability and dose linearity comply with clinically acceptable specifications. The PDD characteristics are largely consistent with those of conventional 9 MeV electron beams, alongside the sharp-peaked off-axis dose distribution. This study systematically constructed a dosimetric parameter database and stability control protocol for the platform, laying a solid foundation for subsequent investigations into the biological mechanisms of FLASH-RT and its clinical translation.
In December 2023, our hospital successfully administered FLASH radiotherapy to an elderly patient diagnosed with extramammary Paget’s disease of the scrotum. This milestone marked the official transition of our institution’s FLASH radiotherapy program from research and development to clinical translation. Relevant research outcomes have been published in authoritative domestic and international academic journals. At the National Symposium on FLASH Radiotherapy Technology held in 2025, our team presented China’s first human clinical trial employing FLASH radiotherapy. In 2026, our hospital was invited to deliver an oral presentation on real-world FLASH radiotherapy research at the Asia Session of FRPT (Flash Radiotherapy and Particle Therapy Conference), the premier annual global academic conference dedicated to FLASH radiotherapy and particle therapy, attracting extensive attention from international experts. In 2025, our FLASH research team participated in the formulation of China’s first expert consensus on electron FLASH radiotherapy, filling the domestic gap in this field. To date, dozens of patients have received FLASH radiotherapy at our hospital. Clinical data continue to be accumulated prospectively, and all enrolled patients have achieved anticipated therapeutic outcomes.
Prof. Hong Ge (MD & PhD) is currently the professor & doctoral supervisor of Zhengzhou University, China. She is also the Director of Department of Radiation Oncology, Henan Cancer Hospital. She has a series of academic appointments, selectively listed below:
- Central Plains Distinguished Physician, Henan Province, China
- Director, Henan Provincial Center for Radiation Therapy
- Young & Middle-Aged Expert with Outstanding Contributions, National Health Commission of the People’s Republic of China
- Recipient of Special Government Allowance from the State Council
- Chair, Radiation Oncology Branch, Henan Medical Association
- Vice President, Radiation Oncologist Branch, Chinese Medical Doctor Association
- Vice Chair, Radiation Therapy Quality Control Expert Committee, National Cancer Quality Control Center
- Member, Radiation Therapy Branch, Chinese Medical Association