Absolute cross section for DNA damage induced by low-energy (10 eV) electrons: Experimental refinements and sample characterization by AFM

Abstract

This work describes multiple experimental improvements for measuring absolute cross sections of DNA damage induced by low-energy electrons (LEE) in nanometer-thick films in vacuum. Measurements of such cross sections are particularly sensitive to film thickness and uniformity. Using atomic force microscopy (AFM) in 70% ethanol, we present a novel and effective method to determine plasmid DNA film thickness and uniformity that combines height histograms and force-distance curves. We also investigate film deposition with DNA intercalated with 1,3-diaminopropane (Dap) on tantalum-coated substrates as a convenient and cost-effective alternative to the previously-used graphite substrate. The tantalum substrate permits deposition of films very similar to those formed on graphite. Using these refinements and further optimizations of the experimental procedure, we measure an absolute cross section of (4.7 ± 1.5) x10-14 cm 2 for conformational damage to a 3197 base-pair plasmid induced by 10 eV electrons, which we believe should be considered as a reference value. I. INTRODUCTION: Ionizing radiation is widely employed in cancer therapy (e.g., in radiotherapy [1, 2], brachytherapy [3] and targeted radionuclide therapy (TRT) [4,5]), as well as in medical diagnostic imaging. In these applications, the radiation dose given to the patient should be known and controlled. In conventional cancer treatments, calculations of the absorbed dose rely on scattering cross sections (CSs) of the primary high-energy radiation. In more sophisticated treatments, such as therapies combining radiation

Clustered DNA Damages induced by 0.5 to 30 eV Electrons

“…Cross-sections (CSs) for LEE-induced clustered DNA damages are important input parameters in MC simulations to generate microscopic absorption doses and quantitate, down to the nanoscopic level, the biological effects of IR [101]. Recently, methods have been developed to obtain absolute CSs for LEE-induced DNA damages in thin-film experiments by applying mathematical survival models to the raw data [102,103,104]. Figure 2C shows the measured absolute CSs of DSB (open points) and the energy dependence (solid points) estimated from effective yields, assuming a constant electron penetration factor ( f ) of 0.29 ± 0.14 for all energies [103].…”

Contrast Enhancement for Portal Imaging in Nanoparticle-Enhanced Radiotherapy: A Monte Carlo Phantom Evaluation Using Flattening-Filter-Free Photon Beams

“…These liberated electrons cannot travel very far and deposit their energy quickly. The electrons either interact directly with the DNA of the surrounding cancer cells, or they ionize the surrounding water molecules to produce free radicals [14,15]. These ionized water molecules would further damage the DNA in the same way as the liberated electrons.…”

“…The amount of coherent scattering is insignificant and does not contribute significantly to the total photon interactions. Pair production is only dominant in an energy range higher than 25 MeV, which is generally out of the routine radiotherapy beam range (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). The probability of Compton scattering is largely independent of the atomic number of the material, but it is weakly dependent on photon energies.…”

Early Events in Radiobiology: Isolated and Cluster DNA Damage Induced by Initial Cations and Nonionizing Secondary Electrons

“…Figure shows the absolute value of the current passing through 5 ML films of plasmid DNA disorderly lyophilized on graphite and tantalum , or uniformly deposited parallel to a tantalum surface by intercalating diaminopropane (DAP) between the DNA molecules. , Details of the experiments are given in the Supporting Information. It is important to note that in transmission experiments the current is the same, whether charges are retained in the film or reach the substrate. , As seen from Figure , above 30 eV the current transmitted to the substrate changes sign; thus, ionization (i.e., positive hole formation) starts to dominate the total inelastic scattering cross section (CS).…”