Vibrational Circular Dichroism study of chiral food additives: γ-valero- and γ-caprolactone.

γ-valerolactone and γ-caprolactone are commonly used as flavor additives in the food industry. In the present work we fully explore the molecular structure and conformational distribution of enantiopure γ-valerolactone and γ-caprolactone in solution state by using Vibrational Circular Dichroism (VCD) spectroscopy assisted by quantum chemical calculations. In order to establish the most accurate DFT method for this type of samples a set of methods and basis sets have been implemented and their performances have been compared. Subsequently, we have performed a complete vibrational assignment, which allowed to detect certain key vibrational features related to specific solution-state conformational speciation. In spite of the rigidity of the samples being studied, our results point to the incidence of conformational mixture in CCl4 solution in both samples.

An overview of recent developments in FLUKA PET tools.

The new developments of the FLUKA Positron-Emission-Tomography (PET) tools are detailed. FLUKA is a fully integrated Monte Carlo (MC) particle transport code, used for an extended range of applications, including Medical Physics. Recently, it provided the medical community with dedicated simulation tools for clinical applications, including the PET simulation package. PET is a well-established imaging technique in nuclear medicine, and a promising method for clinical in vivo treatment verification in hadrontherapy. The application of clinically established PET scanners to new irradiation environments such as hadrontherapy requires further experimental and theoretical research to which MC simulations could be applied. The FLUKA PET tools, besides featuring PET scanner models in its library, allow the configuration of new PET prototypes via the FLUKA Graphical User Interface (GUI) Flair. Both the beam time structure and scan time can be specified by the user, reproducing PET acquisitions in time, in a particle therapy scenario. Furthermore, different scoring routines allow the analysis of single and coincident events, and identification of parent isotopes generating annihilation events. Two reconstruction codes are currently supported: the Filtered Back-Projection (FBP) and Maximum-Likelihood Expectation Maximization (MLEM), the latter embedded in the tools. Compatibility with other reconstruction frameworks is also possible. The FLUKA PET tools package has been successfully tested for different detectors and scenarios, including conventional functional PET applications and in beam PET, either using radioactive sources, or simulating hadron beam irradiations. The results obtained so far confirm the FLUKA PET tools suitability to perform PET simulations in R&D environment.

Conformational properties of chiral tobacco alkaloids by DFT calculations and vibrational circular dichroism: (-)-S-anabasine.

A thorough DFT and MM study of the conformational landscape, molecular and electronic structures of (-)-S-anabasine is reported aimed to reveal the mechanism controlling its conformational preference. Although the conformational flexibility and diversity of this system is quite extensive, only two structures are populated both in gas-phase and solution (CCl4 and DMSO). NBO-aided electronic structure analyses performed for the eight conformers representing minima in the potential energy surface of (-)-S-anabasine indicate that both steric and electrostatic factors are determinant in the conformational distribution of the sample in gas phase. Nonetheless, hyperconjugative effects are the key force tipping the balance in the conformational equilibrium between the two main rotamers. Increasing the polarity of the medium (using the IEF-PCM formalism) barely affect the conformational energy profile, although a slight increase in the theoretical population of those structures more affected by electrostatic interactions is predicted. The validity of the theoretical models and calculated conformers populations are endorsed by the accurate reproduction of the IR and VCD spectra (recorded in pure liquid and in CCl4 solution) of the sample (that have been firstly recorded and assigned in the present work) which are consistent with the occurrence of a 2:1 conformational ratio.

Noise evaluation of Compton camera imaging for proton therapy.

Compton Cameras emerged as an alternative for real-time dose monitoring techniques for Particle Therapy (PT), based on the detection of prompt-gammas. As a consequence of the Compton scattering process, the gamma origin point can be restricted onto the surface of a cone (Compton cone). Through image reconstruction techniques, the distribution of the gamma emitters can be estimated, using cone-surfaces backprojections of the Compton cones through the image space, along with more sophisticated statistical methods to improve the image quality. To calculate the Compton cone required for image reconstruction, either two interactions, the last being photoelectric absorption, or three scatter interactions are needed. Because of the high energy of the photons in PT the first option might not be adequate, as the photon is not absorbed in general. However, the second option is less efficient. That is the reason to resort to spectral reconstructions, where the incoming γ energy is considered as a variable in the reconstruction inverse problem. Jointly with prompt gamma, secondary neutrons and scattered photons, not strongly correlated with the dose map, can also reach the imaging detector and produce false events. These events deteriorate the image quality. Also, high intensity beams can produce particle accumulation in the camera, which lead to an increase of random coincidences, meaning events which gather measurements from different incoming particles. The noise scenario is expected to be different if double or triple events are used, and consequently, the reconstructed images can be affected differently by spurious data. The aim of the present work is to study the effect of false events in the reconstructed image, evaluating their impact in the determination of the beam particle ranges. A simulation study that includes misidentified events (neutrons and random coincidences) in the final image of a Compton Telescope for PT monitoring is presented. The complete chain of detection, from the beam particle entering a phantom to the event classification, is simulated using FLUKA. The range determination is later estimated from the reconstructed image obtained from a two and three-event algorithm based on Maximum Likelihood Expectation Maximization. The neutron background and random coincidences due to a therapeutic-like time structure are analyzed for mono-energetic proton beams. The time structure of the beam is included in the simulations, which will affect the rate of particles entering the detector.

Measurement of charged particle yields from PMMA irradiated by a 220 MeV/u (12)C beam.

The radiation used in hadrontherapy treatments interacts with the patient body producing secondary particles, either neutral or charged, that can be used for dose and Bragg peak monitoring and to provide a fast feedback on the treatment plans. Recent results obtained from the authors on simplified setups (mono-energetic primary beams interacting with homogeneous tissue-like target) have already indicated the correlation that exists between the flux of these secondaries coming from the target (e.g. protons and photons) and the position of the primary beam Bragg peak. In this paper, the measurements of charged particle fluxes produced by the interaction of a 220 MeV/u carbon ion beam at GSI, Darmstadt, with a polymethyl methacrylate target are reported. The emission region of protons (p), deuterons (d) and tritons (t) has been characterized using a drift chamber while the particle time-of-flight, used to compute the kinetic energy spectra, was measured with a LYSO scintillator. The energy released in the LYSO crystal was used for particle identification purposes. The measurements were repeated with the setup at 60° and 90° with respect to the primary beam direction. The accuracy on the fragments emission profile reconstruction and its relationship with the Bragg peak position have been studied. Based on the acquired experimental evidence, a method to monitor the dose profile and the position of the Bragg peak inside the target is proposed.

Distributions of secondary particles in proton and carbon-ion therapy: a comparison between GATE/Geant4 and FLUKA Monte Carlo codes.

Monte Carlo simulations play a crucial role for in-vivo treatment monitoring based on PET and prompt gamma imaging in proton and carbon-ion therapies. The accuracy of the nuclear fragmentation models implemented in these codes might affect the quality of the treatment verification. In this paper, we investigate the nuclear models implemented in GATE/Geant4 and FLUKA by comparing the angular and energy distributions of secondary particles exiting a homogeneous target of PMMA. Comparison results were restricted to fragmentation of (16)O and (12)C. Despite the very simple target and set-up, substantial discrepancies were observed between the two codes. For instance, the number of high energy (>1 MeV) prompt gammas exiting the target was about twice as large with GATE/Geant4 than with FLUKA both for proton and carbon ion beams. Such differences were not observed for the predicted annihilation photon production yields, for which ratios of 1.09 and 1.20 were obtained between GATE and FLUKA for the proton beam and the carbon ion beam, respectively. For neutrons and protons, discrepancies from 14% (exiting protons-carbon ion beam) to 57% (exiting neutrons-proton beam) have been identified in production yields as well as in the energy spectra for neutrons.