Jianhan Sun, PhiRO Young Researcher Award

ESTRO 2026 Congress Report

 

 

Purpose/Objective

Research and clinical translation of FLASH radiotherapy (FLASH-RT) are currently constrained by the limited parameter flexibility of existing irradiation systems, making it impossible to systematically study the effects of energy, dose rate, and pulse structure on FLASH-RT within a single device. This study was designed to develop an accelerator-based irradiation system with widely adjustable energy and dose rate capability, enabling both clinical and preclinical FLASH research.

 

Material/Methods

An accelerator irradiation system was constructed, comprising a DC-SRF photocathode gun, a 2×9-cell superconducting linac, and integrated beam transport, control, and diagnostics. Electrons are generated via the photoelectric effect and accelerated using direct-current and radio-frequency (RF) fields, enabling precise and wide-range tuning of beam energy and charge through phase and amplitude control of the drive laser and RF. Dosimetry was performed with Faraday cups, scintillator screens, fast current transformers (FCT) and radiochromic films (RCF) across multiple beam modes. Dose and dose rate were modulated by varying pulse structure and bunch charge. Experimental terminals for cell and small-animal studies were also established.

Figure 1. (a) Schematic of the accelerator-based irradiation system. (b) Experimental station for cell and (c) mouse irradiation. (d) Three temporal structures of the electron beam.

 

Results

The system delivered stable electron energies from 1 to 30MeV, with the electron gun providing 1-3MeV beams and the 2×9-cell linac boosting energy up to 30MeV. Three time structures—single pulse, macro pulse, and continuous wave (CW)—were available, with freely adjustable duty cycle, pulse width, and bunch charge. As a result, dose rates were tunable from conventional (<0.1Gy/s) to ultra-high dose rate (>10,000Gy/s) levels with considerable stability and reproducibility. The electron gun achieved CW mode for over eight hours at a current of 0.1mA (≈7000Gy/s average dose rate). Accurate dose control was achieved across dose rate ranges, and RCF measurements showed reliable consistency.

Figure 2. Dosimetry and beam diagnostics results. (a) Three repeated measurements at 6MeV electron energy with average dose rates. (b) Five repeated measurements at 2MeV electron energy with average dose rates. (c) Stability test over eight hours at 0.1mA CW average current and the corresponding dose rate. (d) Micro pulse measured by FCT.

 

Conclusion

We developed a superconducting accelerator platform with broad energy and highly tunable dose rates, providing a stable, versatile tool for FLASH-RT mechanistic studies, protocol optimisation, and potential clinical translation.

 

Jianhan Sun

State Key Laboratory of Nuclear Physics and Technology and Institute of Heavy Ion Physics, School of Physics, Peking University, Beijing, China

E-mail: sunjianhan@stu.pku.edu.cn

 

References

[1] Huang S, Liu K, Zhao K, Chen J. DC-SRF photocathode gun. Chin Sci Bull 2022;68:1036–46.

[2] Sun J, Lv J, Tian S, Liu J, Zhang Z, Xu H, et al. Dosimetry study of high repetition rate 2 MeV electron beam from a continuous-wave photocathode gun. Phys Scr 2025;100:065010.

[3] Jia H, Li T, Wang T, Zhao Y, Zhang X, Xu H, et al. High-brightness megahertz-rate beam from a direct-current and superconducting radio-frequency combined photocathode gun. Phys Rev Res 2024;6:043165.

[4] Lv J, Sun J, Luo Y, Liu J, Wu D, Fang Y, et al. Ultra-high Dose Rate Irradiation Regulates Mitochondrial DNA-induced Interferon-β Secretion via Cytochrome c Leakage. MedComm 2025;6:e70457.