arXiv subjects

S. Gros

Publications and source records attributed to S. Gros.

5 recordsLinked to original sources

arXiv2025

Proposal and Evaluation of a Practical CBCT Dose Optimization Method

Objective: To propose a CBCT dose optimization method using readily available measurement equipment in radiation oncology departments. Approach: A 0.6cc air kerma (Kair) calibrated Farmer chamber measured Kair at isocenter for five default CBCT protocols (HEAD, PELVIS, LARGE PELVIS, THORAX, SPOTLIGHT) on a Varian TrueBeam linac. Imaging parameters were modified to reduce cumulative exposure by reducing projections (by 25%, 50%, 75%) in FDK reconstruction, or lowering single frame exposure by 25%, 50%, 70 to 75%. Cone Beam Dose Index (CBDI) and weighted CBDI (CBDI_w) were measured in CTDI phantoms to correlate with Kair. Image quality was assessed quantitatively (HU linearity, uniformity, low-contrast visibility, high-contrast resolution, spatial integrity) using Catphan604, and qualitatively via anthropomorphic phantoms. Results: A linear relationship between Kair, CTDI, and CBDI_w was established. High-contrast resolution and spatial integrity were unaffected by dose reduction (R < 0.5), while low-contrast visibility strongly correlated with exposure (R > 0.75). HU uniformity and linearity remained stable (<40 HU deviation), except for LARGE PELVIS at <50% single-frame exposure. 80 to 50% dose reduction retained clinically acceptable image quality with minimal artifacts or noise. Significance: CBCT protocols on TrueBeam linacs were optimized for dose reduction. The method enables easy implementation by radiotherapy physicists without diagnostic physics equipment or expertise.

physics.med-ph↗

arXiv2021

Multi-agent Battery Storage Management using MPC-based Reinforcement Learning

In this paper, we present the use of Model Predictive Control (MPC) based on Reinforcement Learning (RL) to find the optimal policy for a multi-agent battery storage system. A time-varying prediction of the power price and production-demand uncertainty are considered. We focus on optimizing an economic objective cost while avoiding very low or very high state of charge, which can damage the battery. We consider the bounded power provided by the main grid and the constraints on the power input and state of each agent. A parametrized MPC-scheme is used as a function approximator for the deterministic policy gradient method and RL optimizes the closed-loop performance by updating the parameters. Simulation results demonstrate that the proposed method is able to tackle the constraints and deliver the optimal policy.

eess.SY↗

arXiv2007

Nuclear Structure Relevant to Neutrinoless Double Beta Decay: 76Ge and 76Se

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the neutrino mass IF the nuclear matrix element were known. Theoretical calculations are uncertain and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of 76Ge and 76Se were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical (QRPA) calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations the changes are confined primarily to one orbit.

nucl-ex↗

arXiv2007

From chiral vibration to static chirality in ^{135}Nd

Electromagnetic transition probabilities have been measured for the intra- and inter-band transitions in the two sequences in the nucleus ^{135}Nd that were previously identified as a composite chiral pair of rotational bands. The measurements are in good agreement with results of a new combination of TAC and RPA calculations. The chiral character of the bands is affirmed and it is shown that their behavior is associated with a transition from a vibrational into a static chiral regime.

nucl-ex↗

arXiv2007

Pair correlations in nuclei involved in neutrinoless double beta decay: 76Ge and 76Se

Precision measurements were carried out to test the similarities between the ground states of 76Ge and 76Se. The extent to which these two nuclei can be characterized as consisting of correlated pairs of neutrons in a BCS-like ground state was studied. The pair removal (p,t) reaction was measured at the far forward angle of 3 degrees. The relative cross sections are consistent (at the 5% level) with the description of these nuclei in terms of a correlated pairing state outside the N=28 closed shells with no pairing vibrations. Data were also obtained for 74Ge and 78Se.

nucl-ex↗