Multicentric characterisation of lateral beam profiles generated by 6FFF beam of three 0.35 T MR-linac systems.

BACKGROUND: The physical characterisation of FFF-beam profiles in the presence of a magnetic field requires a new standardization procedure and formulation. PURPOSE: The aim of this multicentric experience is to propose new normalisation factors to allow for the calculation of standard parameters typical of flattened beams, such as dosimetric field size and penumbra, for a 6 MV FFF beam from an MR-linac. METHODS: The measurements were carried out on three ViewRay-MRIdiansystems. An equal set of measurements was acquired using the same equipment. Transverse beam profiles were acquired at seven different depthsand for six beam dimensions.The inflection point was estimated as the position of the maximum of a Gaussian fit obtained from the first derivative of the profiles. The position of the minimum and maximum points of the second derivative of the above Gaussian described the fall-off region, and the external peaks of the third derivative were considered as the in-field and out-field points. The profile normalisation was determined by imposing a 55% dose level at the inflection point and the renormalisation factors were calculated. RESULTS: The position of the inflection point, and the second and third derivatives peaks were analysed,and the renormalisation factors as a function of field size and depth were determined. The values of the unflatness and the slope have been calculated for different depths and field sizes. CONCLUSION: This study represents the first multi-centric evaluation of the profiles on different low-field MR-Linac systems and theset of renormalisation parameters to analyse the FFF-beam on that system was effectively proposed.

Efficacy of remdesivir-containing therapy in hospitalized COVID-19 patients: a prospective clinical experience

Objectivesremdesivir is currently approved for the treatment of COVID-19. The recommendation for using remdesivir in COVID-19 was based on the in vitro and in vivo activity of this drug against SARS-CoV-2. Methodsthis was a prospective, observational study conducted on a large population of patients hospitalized for COVID-19. The primary endpoint of the study was to evaluate the impact of remdesivir-containing therapy on 30-day mortality; secondary endpoint was the impact of remdesivir-containing therapy on the need of high flow oxygen therapy (HFNC) or non-invasive ventilation (NIV) or mechanical ventilation. Data were analyzed after propensity score matching. Results407 patients with SARS-CoV-2 pneumonia were consecutively enrolled. Out of these, 294 (72.2%) and 113 (27.8%) were respectively treated or not with remdesivir. Overall, 61 (14.9%) patients were treated during hospitalization with non-invasive or mechanical ventilation, while a 30-day mortality was observed in 21 (5.2%) patients with a global in-hospital mortality of 11%. Cox regression analysis, after propensity score matching, showed that therapies, including remdesivir-containing therapy, were not statistically associated with 30-day survival or mortality, while need of HFNC/NIV (HR 17.921, CI95% 0.954-336.73, p=0.044) and mechanical ventilation (HR 3.9, CI95% 5.36-16.2, p=0.003) resulted independently associated with 30-day mortality. Finally, therapies including or not remdesivir were not independently associated with a lower or higher risk of HFNC/NIV or mechanical ventilation. Conclusionsthis real-life experience about the remdesivir use in hospitalized patients with COVID-19 was not associated with significant increase in rates of survival or reduced use of HFNC/NIV or mechanical ventilation, compared to patients treated with other therapies not including remdesivir.