Analysis on radiation protection of FLASH treatment in conventional proton therapy facilities
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Updated: Oct 31, 2026
Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies
Published on: February 6, 2019
Yuanyuan Wang1,2, Chan Deng3, Nan Gao1
1Hefei Ion Medical Center, the First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, China.
Background:
FLASH radiotherapy is an advanced radiotherapy technique featuring ultra-high dose-rate irradiation. Previous preclinical studies have shown that it can significantly reduce damage to normal tissues while preserving the ability to kill tumor cells. Due to the very high current intensity of FLASH radiotherapy, the effectiveness of radiation shielding in current proton therapy facilities needs to be evaluated prior to clinical studies.
Purpose:
Based on the existing shielding conditions of a ProBeam proton therapy system for conventional proton therapy treatment, we studied the shielding effectiveness of FLASH treatment in both the transmission and Bragg-peak modes.
Methods:
Under the conditions of single-point irradiation using a proton beam with the highest clinical energy of 244MeV, and the beam intensity of 5nA, 10nA, and 20nA at the nozzle, the ambient equivalent dose rate outside the shielding door was measured with neutron and γ detector, in order to determine the linear relationship between the current intensity and the ambient dose rate. In addition, a gantry room was used as the study object, and the layout design of the points of interest was carried out according to the layout of the proton treatment facility and the transport path and direction of the proton beam, and the most unfavorable working conditions were set for each point of interest. The beam energy was set to 244 MeV, with a cylindrical water phantom (20 cm in diameter) and a solid water block (40 × 40 × 40 cm3) placed at the isocenter. The current at the nozzle was set to 20 nA, and comprehensive environmental dose rate measurements were carried out for the proton radiation workplace.
Results:
A linear relationship was observed between nozzle current and ambient dose equivalent rate. Based on the linear relationship, when the current was extrapolated to a FLASH current of 170 nA, the measured instantaneous dose rates at some locations were relatively high, with the maximum value of 74.04 µSv/h recorded outside the shielding door. Under the conservative assumption that the total annual beam delivery time is 5 h (treating 6 patients per hour), the maximum annual occupational exposure doses for radiation workers under the transmission and Bragg Peak modes are 0.370 mSv and 0.236 mSv, respectively, which are well below the annual occupational dose limit.
Conclusions:
The results indicate that, under existing conventional shielding conditions, the radiation risk posed to the environment outside the treatment room by FLASH irradiation using the Varian ProBeam proton therapy system is safe and controllable, and the annual occupational radiation dose for radiation workers is well below the annual dose equivalent limit. This provides important radiation safety justification for the clinical implementation of FLASH technology in existing proton therapy facilities.
