arXiv subjects

David Meer

Publications and source records attributed to David Meer.

5 recordsLinked to original sources

arXiv2025

Quality assurance and reporting for FLASH clinical trials:the experience of the FEATHER trial

Research on ultra-high dose rate (UHDR) radiation therapy has indicated its potential to spare normal tissue while maintaining equivalent tumor control compared to conventional treatments. First clinical trials are underway. The randomized phase II/III FEATHER clinical trial at the Paul Scherrer Institute in collaboration with the University of Zurich Animal Hospital is one of the first curative domestic animal trials to be attempted, and it is designed to provide a good example for human trials. However, the lack of standardized quality assurance (QA) guidelines for FLASH clinical trials presents a significant challenge in trial design. This work aims to demonstrate the development and testing of QA and reporting procedures implemented in the FEATHER clinical trial. We have expanded the clinical QA program to include UHDR-specific QA and additional patient-specific QA. Furthermore, we have modified the monitor readout to enable time-resolved measurements, allowing delivery log files to be used for dose and dose rate recalculations. Finally, we developed a reporting strategy encompassing relevant parameters for retrospective studies. We evaluated our QA and reporting procedures with simulated treatments. This testing confirmed that our QA procedures effectively ensure the correct and safe delivery of the planned dose. Additionally, we demonstrated that we could reconstruct the delivered dose and dose rate using the delivery log files. We developed and used in practice a comprehensive QA and reporting protocol for a FLASH clinical trial at the Paul Scherrer Institute. This work aims to establish guidelines and standardize reporting practices for future advancements in the FLASH-RT field.

physics.med-ph↗

arXiv2022

Universal and dynamic ridge filter for pencil beam scanning particle therapy: novel concept for ultra-fast treatment delivery

Purpose In PBS particle therapy, short treatment delivery time is paramount for the efficient treatment of moving targets with motion mitigation techniques (such as breath-hold, rescanning, and gating). Energy and spot position change time are limiting factors in reducing treatment time. In this study, we designed a universal and dynamic energy modulator (ridge filter, RF) to broaden the Bragg peak, to reduce the number of energies and spots required to cover the target volume, thus lowering the treatment time. Methods Our RF unit comprises two identical RFs placed just before the isocenter. Both RFs move relative to each other, changing the Bragg peaks characteristics dynamically. We simulated different Bragg peak shapes with the RF in TOPAS and validated them experimentally. We then delivered single-field plans with 1Gy/fraction to different geometrical targets in water, to measure the dose delivery time using the RF and compare it with the clinical settings. Results Aligning the RFs in different positions produces different broadening in the Bragg peak; we achieved a maximum broadening of 2 cm. With RF we reduced the number of energies in a field by more than 60%, and the dose delivery time by 50%, for all geometrical targets investigated, without compromising the dose distribution transverse and distal fall-off. Conclusions Our novel universal and dynamic RF allows for the adaptation of the Bragg peak broadening for a spot and/or energy layer based on the requirement of dose shaping in the target volume. It significantly reduces the number of energy layers and spots to cover the target volume, and thus the treatment time. This RF design is ideal for ultra-fast treatment delivery within a single breath-hold (5-10 sec), efficient delivery of motion mitigation techniques, and small animal irradiation with ultra-high dose rates (FLASH).

physics.med-ph↗

arXiv2022

The lifetime of charged dust in the atmosphere

Windblown dust plays critical roles in numerous geophysical and biological systems, yet current models fail to explain the transport of coarse-mode particles (>5 $\mu$m) to great distances from their sources. For particles larger than a few microns, electrostatic effects have been invoked to account for longer-than-predicted atmospheric residence times. Although much effort has focused on elucidating the charging processes, comparatively little effort has been expended understanding the stability of charge on particles once electrified. Overall, electrostatic-driven transport requires that charge remain present on particles for days to weeks. Here, we present a set of experiments designed to explore the longevity of electrostatic charge on levitated airborne particles after a single charging event. Using an acoustic levitator, we measured the charge on particles of different material compositions suspended in atmospheric conditions for long periods of time. In dry environments, the total charge on particles decayed in over 1 week. The decay timescale decreased to days in humid environments. These results were independent of particle material and charge polarity. However, exposure to UV radiation could both increase or decrease the decay time depending on polarity. Our work suggests that the rate of charge decay on airborne particles is solely determined by ion capture from the air. Furthermore, using a one-dimensional sedimentation model, we predict that atmospheric dust of order 10 $\mu$m will experience the largest change in residence time due to electrostatic forces.

physics.geo-ph↗

arXiv2021

A Low Cost Duffing Oscillator

We describe an undergraduate project to build a Duffing oscillator. Although the ultimate goal was to demonstrate chaos, the overriding consideration was cost, as this was during COVID-19, and budgets were frozen. Previous designs used expensive parts that were out of the question in terms of cost. An inexpensive design whose centerpiece is a video tracking system is presented, along with some comments about aspects of the theory concerning the bi-stable case.

nlin.CD↗

arXiv2018

Medical Physics Commissioning

The medical commissioning is an important step to bring a particle gantry into clinical operation for tumour treatments. This involves the parametrization and characterization of all relevant systems including the beam delivery, the patient table, the imaging systems and the connection to all required software components. This article is limited to necessary tasks for the beam delivery system of a pencil beam scanning system. Usually the commissioning starts with the characterization of the unscanned beam and the calibration of the beam energy. The following steps are the parametrization of the scanning system, the commissioning of the beam position monitoring system and characterization of the spot size, all requiring precisions better than 1 mm. The commissioning effort for these tasks depends also on the gantry topology. Finally, the calibration of the dose measurement system ensures that any dose distribution can be delivered with an absolute precision better than 1%.

physics.med-ph↗