arXiv subjects

J. De Leon

Publications and source records attributed to J. De Leon.

3 recordsLinked to original sources

arXiv2026

MRI-guided cardiac radiotherapy using a 1.5 T MR-linac: surveying emerging patterns of care

Background: Cardiac tumours are rare and treated by surgical resections, which are complex, invasive and carry procedural risks. MRI-guided radiotherapy (MRgRT) noninvasively facilitates conformal dose deliveries using soft-tissue imaging and adaptive radiotherapy techniques. Aim: To assess the application of MRgRT for cardiac tumours, we conducted a patterns-of-care analysis with users of the 1.5T MR-linac. Materials & methods: A survey was distributed to users of the 1.5T MR-linac that treated patients with cardiac tumours. The survey included 30 questions concerning the patient cohort, imaging, treatment planning/simulation, radiotherapy treatment and treatment outcome. Results: Users from six international institutes completed the survey reporting twelve cardiac MRgRT treatments between 2021-2024. The median age[range] of the patients was 59[16-81] years with 50% of the cases concerning the treatment of primary tumours. The prescribed dose ranged between 30-60 Gy, with 30 Gy being prescribed the most (59%). In 75% of the cases, the treatment plans were delivered in five fractions with 6-8 Gy per fraction. Daily images were acquired with T1- and T2-weighted MRI and respiratory motion monitoring was performed in 92% of the cases using cine imaging. A single case was treated with intrafraction motion management using a novel vendor-provided gating solution on the MR-linac. Treatment outcomes were reported for 50% of the cases. All, but one case, attained local control using MRgRT without serious adverse events (grade$\geq$3). Conclusion: This study provides real-world insights into the feasibility and early outcomes to aid the development of cardiac MRgRT treatment recommendations and protocol harmonization.

physics.med-ph↗

arXiv2026

The GAPS programme at TNG: LXXVI. TOI-1533: a compact system hosting a super-Neptune-mass pair with disparate radii

The present-day architecture of planetary systems contains information about their formation and migration histories. The origin of hot Jupiters (HJs, P $\lesssim$ 10 d, $R_{\rm p} > 8 R_\oplus$) has long been a matter of debate. While most of them are found to be ``lonely'', there is a rare population of HJs hosting small companions on inner orbits (eight known as of May 2026). Their peculiar architecture suggests a gentle disc-migration mechanism. In this study, we present the discovery and characterisation of the multi-planet system TOI-1533, comprising an inner sub-Neptune (TOI-1533 b, $P_{\rm orb} = 3.63$ d, $R_{\rm p} = 3.15 R_\oplus$) and an outer hot giant planet (TOI-1533 c, $P_{\rm orb} = 8.06$ d, $R_{\rm p} > 7.5 R_\oplus$) with substantial H/He by mass ($ρ_{\rm p} < 0.48$ g cm$^{-3}$), both transiting an active K-dwarf star ($T_{\rm eff} \approx$ 5130 K; $V$ (mag) $\approx$ 11). Our joint modelling of stellar activity and planetary signals from radial velocities (HARPS-N) and transits (TESS) allows us to detect their Keplerian signals (approximately $10~σ$) and to isolate the stellar modulation. The inclusion of simultaneous photometry in the multi-dimensional Gaussian processes formalism was a fundamental addition to the spectroscopic activity indicators, enabling the disentanglement of stellar activity from planetary signals. The mass ratio of the two confirmed planets ($M_{\rm b} / M_{\rm c}$ about 0.8), together with the super-Neptune mass of the large outer companion ($M_{\rm c} \approx 40 M_\oplus$), makes this system unusual compared to the other few HJs with low-mass inner companions.

astro-ph.EP↗

arXiv2020

Three planets transiting the evolved star EPIC 249893012: a hot 8.8-M$_\oplus$ super-Earth and two warm 14.7 and 10.2-M$_\oplus$ sub-Neptunes

We report the discovery of a new planetary system with three transiting planets, one super-Earth and two sub-Neptunes, that orbit EPIC\,249893012, a G8\,IV-V evolved star ($M_\star$\,=\,1.05\,$\pm$\,0.05\,$M_\odot$, $R_\star$\,=\,1.71\,$\pm$\,0.04\,$R_\odot$, $T_\mathrm{eff}$\,=5430\,$\pm$\,85\,K). The star is just leaving the main sequence. We combined \ktwo \ photometry with IRCS adaptive-optics imaging and HARPS, HARPS-N, and CARMENES high-precision radial velocity measurements to confirm the planetary system, determine the stellar parameters, and measure radii, masses, and densities of the three planets. With an orbital period of $3.5949^{+0.0007}_{-0.0007}$ days, a mass of $8.75^{+1.09}_{-1.08}\ M_{\oplus}$ , and a radius of $1.95^{+0.09}_{-0.08}\ R_{\oplus}$, the inner planet b is compatible with nickel-iron core and a silicate mantle ($ρ_b= 6.39^{+1.19}_{-1.04}$ g cm$^{-3}$). Planets c and d with orbital periods of $15.624^{+0.001}_{-0.001}$ and $35.747^{+0.005}_{-0.005}$ days, respectively, have masses and radii of $14.67^{+1,84}_{-1.89}\ M_{\oplus}$ and $3.67^{+0.17}_{-0.14}\ R_{\oplus}$ and $10.18^{+2.46}_{-2.42}\ M_{\oplus}$ and $3.94^{+0.13}_{-0.12}\ R_{\oplus}$, respectively, yielding a mean density of $1.62^{+0.30}_{-0.29}$ and $0.91^{+0.25}_{-0.23}$ g cm$^{-3}$, respectively. The radius of planet b lies in the transition region between rocky and gaseous planets, but its density is consistent with a rocky composition. Its semimajor axis and the corresponding photoevaporation levels to which the planet has been exposed might explain its measured density today. In contrast, the densities and semimajor axes of planets c and d suggest a very thick atmosphere. The singularity of this system, which orbits a slightly evolved star that is just leaving the main sequence, makes it a good candidate for a deeper study from a dynamical point of view.

astro-ph.EP↗