AB005. Radioprotection assessment of an accelerator-based boron neutron capture therapy lab

Background: An Accelerator Development Lab (LDA) is under advanced construction at the National Atomic Energy Commission (CNEA), Argentina. At its core, the LDA holds a high-current/low-energy deuteron accelerator and the future patient irradiation room. Surrounding them are the control room, workshops, and other public areas. A 1.45-MV electro-static-quadrupole accelerator placed in the accelerator room will generate a 30-mA deuteron beam to be transported to a ¹³C or ⁹Be target, physically placed at the irradiation room inside of a beam shaping assembly (BSA). On the target, 5–5.7×10¹² neutrons/s with energies up to ~6 MeV are produced by a (d,n) reaction (~70% of the intensity is <1 MeV). The BSA is made up of Al, Teflon^®, Pb, and boronated paraffin. The radiation sources at the LDA are (I) neutrons, (II) prompt gamma-rays from neutron-induced reactions, (III) X-rays produced in the accelerator column, and (IV) delayed gamma-rays from the decay of activated materials. The objective of this work is to estimate occupational and public doses both during and after accelerator operation and, based on these results, to establish a preliminary radiological zoning of the facility. Effective doses during routine operation were calculated throughout the LDA to support this assessment.

Methods: Neutron and photon fluxes were simulated with the MCNP6 code. Flux-to-effective dose factors were taken from the Publication 116 of the International Commission on Radiological Protection (ICRP-116). Reaction cross-sections from evaluated databases were used to calculate induced radioactivity. Routinary operation is planned as 8 hours of irradiation followed by 16 hours of downtime, totalizing 2,000 hours of irradiation per year. The adopted dose restrictions (ARs) are 0.1 and 6 mSv/y for the public and workers, respectively. Total doses are the sum of the contributions of sources 1–4.

Results: Doses during irradiation are 1 and 42 mSv/h in the accelerator and the irradiation rooms, respectively. In the peripheral rooms, doses are <0.050 mSv/y, well below the public’s AR. Right after shutting down the accelerator and next to the BSA (i.e., the most activated element), the dose is 2 mSv/h, and decays below the worker’s AR 7 hours after.

Conclusions: Effective doses on routinary operation were calculated along the LDA. In the peripheral rooms (where the public or workers will stay during irradiation), the doses fit the public’s AR, hence, can be classified as public access areas. The irradiation and the accelerator room must be classified as controlled areas, with access forbidden during irradiation and time-limited during the first hours of downtime.

Keywords: Accelerator based-boron neutron capture therapy; electrostatic-quadrupole-accelerator; induced radioactivity; radiation protection