University of Seville / Centro Nacional de Aceleradores

Radiobiological effectiveness of protons 

Trainee: Anna Baratto Roldán
Supervisor: Joaquín Gómez Camacho 

Cancer is one of the leading causes of mortality worldwide, killing more than one million people per year just in Europe. Accelerator based hadron therapy is nowadays one of the most promising techniques in the fight against cancer, and many dedicated accelerators are being installed in hospital-based clinical centres around the world. However, more research is required in order to understand deeply the interaction mechanisms and the biological effectiveness of hadrons (protons and heavy nuclei) on both cancerous and healthy cells.

The aim of the project is to study the behaviour of the Relative Biological Effectiveness – RBE of protons along the depth-dose profile of the proton beam as it is absorbed in tissues. To this end, the already existing 18 MeV external beam-line at the National Centre of Accelerators – CNA, will be adapted to perform irradiations of biological samples and study the response of radiochromic films.

Firstly, the Fellow will work at the 18 MeV proton cyclotron facility at the CNA to ensure an overall optimization of the beam diagnostics for the determination of all the essential beam parameters. This includes the measurement of energy, intensity profiles, fluences and homogeneities of the proton beam in correspondence to the target position, in order to define the best beamline set up suitable for the irradiation of biological samples. Therefore, a framework for cells studies will be provided, as well as important information for a critical performance assessment of all diagnostics R&D in this WP.

Once the mentioned framework is ready, dedicated setups, allowing for the irradiation of cell cultures in controlled environment, will be mounted on the external 18 MeV proton beam-line. This part of the work will be carried out in collaboration with groups of biologists, which will lately analyze the cultures. At this stage, for example, it could be interesting to study the “low-dose hyperradiosensitivity (LDHRS)” phenomenon with protons, to understand the dependence of LDHRS on the type of radiation and linear energy transfer (LET).

Finally, each step of the Fellow’s work will involve Monte Carlo simulations, which will be performed to compare experimental measurements with simulated data. These calculations, mostly carried out with the Geant4 toolkit, will involve both macroscopic quantities (dose, fluence, LET etc.) and the characterization of the radiation quality through microdosimetry quantities (distributions of lineal energy, energy imparted etc) in order to obtain the magnitudes needed to apply theoretical RBE models.