Radiobiological effectiveness of iodouracil and the influence of atomic giant resonance

Abstract

Hadron therapy combined with nanotechnology has been proposed as an elegant alternative for cancer treatment. Internal amplification of electron emission causing radiobiological effectiveness in nanoinserted biomolecules is of prime importance and has been measured here for the iodouracil molecule. Our experiment involves the measurement of angle and energy resolved double differential cross section (DDCS) of electron emission from iodouraciil and uracil (and also water) in collisions with fast C 6+ ions. The electron emission from iodouracil is substantially enhanced over that from uracil or water. The enhancement is much larger than the state-of-the-art model for Coulomb ionization based on the continuum distorted wave-eikonal initial state (CDW-EIS) approximation. The electron sensitizing factor (≈ 2.4) is in excellent agreement with the strand-breaking sensitizing factor (≈ 2.0) for metal nanoparticle embedded in a DNA. The enhancement is explained in terms of collective excitation of strongly correlated 4d electrons, known as atomic giant dipole resonance (GDR) in I atoms. The GDR contribution to the enhancement is derived, which is in excellent agreement with recent theoretical prediction, thereby providing conclusive experimental evidence of the crucial role of collective excitation in radio sensitization.

Electron emission from bromouracil and uracil induced by protons and radiosensitization

“…The TCS for BrU is found to be 2500 Mb and that for uracil is 1600 Mb showing an enhancement of 1.6 times for bromouracil. A similar enhancement factor was also reported for the iodouracil molecule in collisions with higher energy ion beams [19], as well as for double strand breaking in case of the Pt nanoparticle embedded in plasmid DNA [5].…”

“…Theoretical calculations based on the CDW-EIS approximation has been discussed previously [19]. In brief, an independent particle approximation has been employed where the reaction is reduced to a one-active-electron process [39].…”

“…The studies on the dissociative electron attachment in case of few eV electrons impacting on 5-bromouracil (BrU) have also been reported [18]. The first study of the enhancement in electron emission from iodouracil and the influence of the atomic giant resonance has been reported recently [19] for higher energy [66 MeV C 6+ ions] collisions.…”

“…In case of simulating the proton trajectory [33] and for modelling its energy loss in biological medium, it is necessary to have an accurate estimation of the contributions from ionization, fragmentation and capture processes that occur during the collision. However, to the best of our knowledge no measurement exists on the DDCS of electron emission from BrU or other halouracils [except iodouracil [19]] when ionized by electrons or ions. In case of proton therapy, the incident beam energy vary around few hundreds of MeV.…”