Towards a high-dynamic dose-range irradiation setup for radiobioloy and radiophysiology

The number of cyclotrons capable of accelerating protons to about 20 MeV is increasing throughout the world. In Portugal, an IBA (Ion Beam Applications, Belgium) model Cyclone 18/9 cyclotron was installed at ICNAS (Instituto de Ciencias Nucleares Aplicadas a Saude) for positron emission tomography (PET) in 2010. Such facility is equipped with eight beam lines suitable for scientific research. Each beam line may deliver proton currents up to 150 μA (1×10
¹⁵
particles/s). Radiobiological and dosimetric studies, among others, can be performed using these beam lines. In this work, we report on experimental results and Geant4 and SRIM/TRIM simulations, which aim at investigating the possible use of the 18 -MeV proton beam from the PET cyclotron to irradiate a selected region of a target with 1mm diameter. We prove by simulation and experiment that we are indeed able to irradiate a selected region of a target with 1mm diameter (i.e., the beam spot is very sharp). In addition, simulations indicate that neutron and γ-ray dose on a realistic target is negligible down to at most the 1 % level when compared with the proton dose. Moreover, the experimental and simulation results show good beam uniformity in the target-selected region. In addition to the previously-mentioned results, we measured the Bragg peak of the protons from ICNAS cyclotron by using a stacked target consisting of aluminum foils interleaved with polyethylene sheets, readout by custom-made electronics. Finally, calculations show that the proposed irradiation setup may span 4 orders of magnitude, ranging from 1 cGy to 100 Gy. Such a setup could satisfy user requirements in several fields, including ion therapy radiobiological and animal studies and biological science.