Michael Taylor (United Kingdom)
University of Manchester Precise GroupAuthor Of 1 Presentation
CAN PROTON FLASH BEAMS BE USED SAFELY WITH EXISTING SHIELDING?
Abstract
Background and Aims
The ultra-high dose rates thought to be required for the FLASH effect are two orders of magnitude higher than envisaged when current proton therapy shielding was designed. Existing proton therapy equipment offers the exciting prospect of such ultra-high dose rate beams, but consideration of personnel safety is essential. This work aims to assess the suitability of existing shielding for ultra-high dose rate proton beams in the Christie Proton Centre’s research facility.
Methods
A Monte-Carlo model of the shielding, beam delivery equipment and beam stop was created in MCNPX, and calculations carried out to determine neutron and photon flux in the surrounding areas. The model was used to identify areas that would require access restrictions to be in place for an ultra-high dose rate survey. Radiation surveys were carried out using a WENDI-2 detector and Thermo-Scientific FH-40-G Geiger counter to establish neutron and photon dose rates around the room, and to determine the extent of on-going access restriction requirements.
Results
An accelerator current of 800nA at 244MeV was achieved, providing an estimated in-room current of 79nA. Dose-rates at the maze entrance and a plant room above were found to be highest with dose rates exceeding 100µSv/h. The shielding was found to be suitable under these conditions, but only with a significant increase of restricted areas surrounding the research room.
Conclusions
The safe use of ultra-high dose rates for significant beam-on times in our research room using existing shielding is possible, but only by restricting access to some surrounding areas.