TWO-PARAMETRIC BEAM MODEL FOR DOSIMETRY OF THE PROCESS OF ELECTRON IRRADIATION OF MATERIALS WITH LOW DENSITY AND ATOMIC NUMBER

The work is devoted to studying the possibility of using a two-parametric model of an electron beam to describe the depth distributions of the electron dose in materials with a low density and an effective atomic number. In this model, the parameters are determined by fitting the semi-empirical model (PFSEM-method) to the results of meas-urements of the depth-dose distribution in a dosimetric wedge. The depth-dose distributions in a birchwood wedge were measured at the Institute of Nuclear Chemistry and Technology in Warsaw, Poland. The parameters of the electron beam incident on the wedge were determined by the PFSEM method. The Monte Carlo simulations of the depth-dose distribution in the wedge for the process of electron irradiation, the characteristics of which are deter-mined by the PFSEM method, have been carried out. It is shown that there is a satisfactory agreement between the measurement results and the Monte Carlo simulation of the depth-dose distribution. The advantages of describing depth-dose distributions in a wedge based on a two-parametric model of an electron beam in comparison with tradi-tional methods of polynomial approximation of measurement results are discussed.

An experimental study of focused very high energy electron beams for radiotherapy

Very high energy electron (VHEE) beams have been proposed as an alternative radiotherapy modality to megavoltage photons; they penetrate deeply without significant scattering in inhomogeneous tissue because of their high relativistic inertia. However, the depth dose distribution of a single, collimated VHEE beam is quasi-uniform, which can lead to healthy tissue being overexposed. This can be largely overcome by focusing the VHEE beam to a small spot. Here, we present experiments to demonstrate focusing as a means of concentrating dose into small volumetric elements inside a target. We find good agreement between measured dose distributions and Monte Carlo simulations. Focused radiation beams could be used to precisely target tumours or hypoxic regions of a tumour, which would enhance the efficacy of radiotherapy. The development of new accelerator technologies may provide future compact systems for delivering these focused beams to tumours, a concept that can also be extended to X-rays and hadrons.

Clinical Progress in Proton Radiotherapy: Biological Unknowns

Clinical use of proton radiation has massively increased over the past years. The main reason for this is the beneficial depth-dose distribution of protons that allows to reduce toxicity to normal tissues surrounding the tumor. Despite the experience in the clinical use of protons, the radiobiology after proton irradiation compared to photon irradiation remains to be completely elucidated. Proton radiation may lead to differential damages and activation of biological processes. Here, we will review the current knowledge of proton radiobiology in terms of induction of reactive oxygen species, hypoxia, DNA damage response, as well as cell death after proton irradiation and radioresistance.

Evaluation of low energy X-ray depth dose distribution by gafchromic film for dosimetry in food irradiation

Introduction: Dosimetry is of crucial importance in radiation processing of food. Among others, plastic film has been widely used for dosimetry in radiation therapy since its density is quite similar to the equivalent biological materials. In this study, the depth dose distribution was estimated by using gafchromic film for the purpose of dosimetry in food irradiation. Experimental: The HD-V2 gafchromic dosimetry film was employed to measure the interested dose instead of ion chamber. A stack of 19 PMMA (polymethyl methacrylate) sheets interleaved with 20 pieces of gafchromic film was made. The phantom was applied in the low energy X-ray beams (maximum 100 keV) to obtain the depth dose profile. Results: A significant correlation between absorbed doses (D) and color level or optical density (O.D.) of irradiated dosimetry films was observed. The fitting function has the form of , where a, b, c are the parameters to be fitted. The depth dose distribution in the 30 mm thickness phantom was inferred from the calibration. Conclusion: The present method and the depth dose profile to be obtained are very meaningful in the processing of foodstuffs by radiation.