Search

Traditionally, the verification of complex photonradiotherapy treatments, like Intensity Modulated Radiation Therapy (IMRT), has been carried out by means of radiographic films, which are inserted in a water-equivalent phantom and irradiated by an accelerator. The radiographic films have to be developed and read with a scanner. The dose map is then obtained as a function of the optic density. The use of these films has some disadvantages such as the manipulation sensitivity and the time-consuming film development process. In addition, the increased use of digital radiometers is leading to the disappearance of films and development devices. Despite these inconveniences, films have some advantages which until today could not have been achieved by any other method: first they provide excellent spatial resolution (<, This work is supported by Spanish Research Project Nos. FPA2013-47327-C2-1-R and FPA2014-53290-C2-2-P; by Andalusian Research Project No. P12-FQM-1605; by Radia 2 Contract No. 68/83-Ref. 0214/0129; and by Consolider-Ingenio 2010 Project No. CSD2007-004.

A feasibility study of an experimental setup for the irradiation of biological samples at the cyclotron facility installed at the National Centre of Accelerators (Seville, Spain) is presented. This cyclotron, which counts on an external beam line for interdisciplinary research purposes, produces an 18 MeV proton beam, which is suitable for the irradiation of mono-layer cultures for the measurement of proton cell damages and Relative Biological Effectiveness (RBE) at energies below the beam nominal value. Measurements of this kind are of interest for proton therapy, since the variation of proton RBE at the distal edge of the Bragg curve may have implications in clinical proton therapy treatments. In the following, the characteristics of the beam line and the solutions implemented for the irradiation of biological samples are described. When dealing with the irradiation of cell cultures, low beam intensities and broad homogeneous irradiation fields are required, in order to assure that all the cells receive the same dose with a suitable dose rate. At the cyclotron, these constraints have been achieved by completely defocusing the beam, intercepting the beam path with tungsten scattering foils and varying the exit-window-to-sample distance. The properties of the proton beam thus obtained have been analysed and compared with Monte Carlo simulations. The results of this comparison, as well as the experimental measurement of the lateral dose profiles expected at the position of samples are presented. Meaningful dose rates of about 2–3 Gy/min have been obtained. Homogeneous lateral dose profiles, with maximum deviations of 5%, have been measured at a distance of approximately 50 cm in air from the exit window, placing a tungsten scattering foil of 200 µm in the beam path., This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant No. 675265, OMA—Optimization of Medical Accelerators, from the Spanish Ministry of Economy and Competitiveness under Grant No. FPA2016-77689-C2-1-R, and from the Council for Innovation, Science and Commerce of the Andalusian Government under Grant No. P12-FQM-1605.