Julian Marco Barbosa Shorto

This paper describes a methodology for the Three-Dimensional Calculation of Effective Dose Rates due to Radioactive Activation of Materials called Discretized Methodology and proves that this Methodology is more detailed and accurate than the Rapid Response Methodology. Furthermore, it tested in a hypothetical decommissioning problem. The methodology uses established and more easily accessible software, such as MAVRIC (Radiation Transport) and ORIGEN (Depletion and Transmutation), which makes it viable, instead of software that can carry it out in an integrated manner, and which are of prohibitive prices like ATTILA. Furthermore, the computational times used are recorded to serve as a standard for those who intend to carry out the methodology. A detailed and didactic description was chosen with the aim of making this work a guide for those who decide to continue it.

The accuracy required in small-field dosimetry for stereotactic radiosurgery imposes limitations on the conventional dosimetric calibration protocols used in radiotherapy. This study presents the development and validation of a computational model of the CyberKnife® system using the Monte Carlo method with the MCNP6 code. The main objective is to establish a validated computational model that enables future research and clinical applications in stereotactic radiosurgery. The model was developed to validate the 60 mm conical collimator, and the results were compared with experimental data from percentage depth dose (PDD) and lateral dose profile (LDP) curves at depths of 10 cm and 20 cm. The analyses revealed the influence of field size and photon source characteristics on the dose distribution, showing good agreement between the simulated and measured data within the established tolerance limits. These findings demonstrate that the proposed model accurately reproduces the CyberKnife® beam behavior and serves as a robust and promising tool for the investigation of treatment variables, support of therapeutic planning, and optimization of stereotactic radiosurgery protocols.

Accurately quantifying the energy loss rate of proton beams in liquid water is crucial for the precise application and improvement of proton therapy, whereas the slowing down of protons in water ices also plays an important role in astrophysics. However, precisely determining the electronic stopping power, particularly for the liquid phase, has been elusive so far. Experimental techniques are difficult to apply to volatile liquids, and the availability of sufficient reliable measurements has been limited to the solid and vapor phases. The accuracy of current models is typically limited to proton energies just above the energy loss maximum, making it difficult to predict radiation effects at an energy range of special relevance. We elucidate the phase differences in proton energy loss in water in a wide energy range ( 0.001 − 10 MeV ) by means of real-time time-dependent density functional theory combined with the Penn method. This nonperturbative model, more computationally efficient than current approaches, describes the phase effects in water in excellent agreement with available experimental data, revealing clear deviations around the maximum of the stopping power curve and below. As an important outcome, our calculations reveal that proton stopping quantities of liquid water and amorphous ice are identical, in agreement with recent similar observations for low-energy electrons, pointing out this equivalence for all charged particles. This could help to overcome the limitation in obtaining reliable experimental information for the biologically relevant liquid water target.

This study provides accurate results for the electronic stopping cross sections of H, He, N, and Ne in silicon in low to intermediate energy ranges using various non-perturbative theoretical methods, including real-time time-dependent density functional theory, transport cross section, and induced-density approach. Recent experimental findings [Ntemou et al., Phys. Rev. B 107, 155145 (2023)] revealed discrepancies between the estimates of density functional theory and the observed values. We show that these discrepancies vanish by considering the nonuniform electron density of the deeper silicon bands for ion velocities approaching zero (v → 0). This indicates that mechanisms such as “elevator” and “promotion,” which can dynamically excite deeper-band electrons, are active, enabling a localized free-electron gas to emulate ion energy loss, as pointed out by Lim et al. [Phys. Rev. Lett. 116, 043201 (2016)]. The observation and the description of a velocity-proportionality breakdown in electronic stopping cross sections at very low velocities are considered to be a signature of the contributions of deeper-band electrons.