Dose-response dependencies of OSL dosimeters in conventional linacs and 1.5T MR-linacs: an experimental and Monte Carlo study

Objective. This work focuses on the optically stimulated luminescence dosimetry (OSLD) dose-response characterization, with emphasis on 1.5T MR-Linacs.Approach. Throughout this study, the nanoDots OSLDs (Landauer, USA) were considered. In groups of three, the mean OSLD response was measured in a conventional linac and an MR-Linac under various irradiation conditions to investigate (i) dose-response linearity with and without the 1.5T magnetic field, (ii) signal fading rate and its dependencies, (iii) beam quality, detector orientation and dose rate dependencies in a conventional linac, (iii) potential MR imaging related effects on OSLD response and (iv) detector orientation dependence in an MR-Linac. Monte Carlo calculations were performed to further quantify angular dependence after rotating the detector around its central axis parallel to the magnetic field, and determine the magnetic field correction factors,kB,Q,for all cardinal detector orientations.Main results. OSLD dose-response supralinearity in an MR-Linac setting was found to agree within uncertainties with the corresponding one in a conventional linac, for the axial detector orientation investigated. Signal fading rate does not depend on irradiation conditions for the range of 3-30 d considered. OSLD angular (orientation) dependence is more pronounced under the presence of a magnetic field. OSLDs irradiated with and without real-time T2w MR imaging enabled during irradiation yielded the same response within uncertainties.kB,Qvalues were determined for all three cardinal orientations. Corrections needed reached up to 6.4%. However, if OSLDs are calibrated in the axial orientation and then irradiated in an MR-Linac placed again in the axial orientation (perpendicular to the magnetic field), then simulations suggest thatkB,Qcan be considered unity within uncertainties, irrespective of the incident beam angle.Significance. This work contributes towards OSLD dose-response characterization and relevant correction factors availability. OSLDs are suitable for QA checks in MR-based beam gating applications andin vivodosimetry in MR-Linacs.

Remote neuropsychological evaluation of older adults

The use of technological means in the process of neuropsychological assessment has been proposed as a technique with promising results in the field of detection of neurocognitive disorders for community-dwelling older adults. Especially during the pandemic period due to COVID-19, telemedicine assumed to be vital in the field of early diagnosis of cognitive disorders and highlighted the clinical utility of remote methods of neuropsychological assessmentby video-conference. This descriptive study presents the development of a remote neuropsychological assessment protocol by selecting appropriate validated tests as part of a more comprehensive evaluation for older adults dwelling in the community. We recruited participants from the Athens Alzheimer's Association center in collaboration with the Hellenic Neuropsychological Society, in Athens, Greece, regarding the period between April 2020 and October 2021. 90 individuals, tested for the first time, were categorized into three groups according to their diagnosis which included: (a) Mild Cognitive Impairment (MCI), (b) Alzheimer's disease, (c) cognitively healthy older adults. The presented protocol outlines the main considerations of a framework about remote neuropsychological assessment, which can maximize the effectiveness of interventions and continuity regarding the care of older adults. The recommendations outlined in the presented protocol highlight strengths and limitations that should be taken into account in remote control procedures. Although the protocol was created in response to pandemic restrictions, tele-neuropsychology shows promise as a way to improve access opportunity to neurodiagnostic services for rural aging and underserved populations, which lack specialized healthcare services. Further application to different populations will add validity to the presented descriptive protocol.