ESTRO 2024 - Abstract Book

S3228

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Keywords: Proton therapy, Neutron dose, staff and public

1004

Mini-Oral

Radiation Shielding Assessment for FLASH Proton Beams

Mark J Hardy 1,2 , Michael J Taylor 3 , Michael Merchant 3 , Karen Kirkby 3 , Ranald I MacKay 2

1 Clatterbridge Cancer Centre NHS Foundation Trust, Medical Physics, Liverpool, United Kingdom. 2 The Christie NHS Foundation Trust, Christie Medical Physics and Engineering, Manchester, United Kingdom. 3 University of Manchester, Precise Group, Manchester, United Kingdom

Purpose/Objective:

The FLASH effect has been shown in pre-clinical studies to reduce toxicity for ultra-high dose rate radiotherapy beams. They can be delivered by some existing clinical proton systems, making protons an attractive modality for research and clinical implementation of FLASH. The proton beam current required to achieve the FLASH effect is ~170 times higher than used conventionally, a magnitude of current for which radiation shielding was not designed. This work aims to establish if the radiation shielding for an existing UK scanning beam proton facility is adequate for the delivery of FLASH dose rate beams, using this as a pilot study to determine the ideal combination of radiation surveys and Monte-Carlo simulations to assess shielding suitability for FLASH proton beam use in other centres.

Material/Methods:

Dose rate assessments were made using a fixed research beam line, fed by a Varian ProBeam cyclotron at the Christie Proton Centre, Manchester, UK. The room was designed to house a standard rotating gantry for potential future clinical use, and the beam terminated in a water tank. Following a safety assessment using scaled-up measurements from a standard radiation survey, a comprehensive FLASH radiation survey was carried out at key locations around the facility using a proton beam with the maximum nozzle current of 76.4nA at 244MeV. All surveys used a WENDI-2 detector for neutron measurements and a FH-40-G wide range multi-purpose scintillation counter for photon measurements. Monte-Carlo simulations using MCNPX v2.5.0 were used to predict the effective dose rates surrounding the vault for FLASH proton beam use, and validated using survey measurements. Runs with 10 7 histories were used, with statistics based on the standard deviation of multiple runs. Fluence to effective dose conversion factors from ICRP 74 [1] ware used to aid validation, and from ICRP 116 [2] to determine the effective dose using the most recent neutron radiation weighting factors.