arXiv subjects

Lawrie Skinner

Publications and source records attributed to Lawrie Skinner.

5 recordsLinked to original sources

arXiv2026

Addressing respiratory gating latency for accurate pulse delivery in preclinical electron FLASH irradiation on a clinical linear accelerator

Background: Clinical linear accelerators are an accessible platform for preclinical research on the biological effects of ultra rapid electron irradiation (FLASH). However, they are not inherently designed for the accurate pulse control required for experiments using a small number of relatively high-dose pulses, and available methods for beam control such as respiratory gating can be error prone owing to system latency. Here we experimentally characterize the temporal latency of the respiratory gating system for controlling beam-on and beam-off at the individual linac pulse level. Methods and Materials: We used programmable controller boards and a relay circuit to monitor and control delivery of specific numbers of pulses through the built-in monitor chamber and respiratory gating system of a Varian Trilogy linac. We implemented two methods an adaptive method using only the delivered pulse signal, and a synchronization method additionally using the linac internal pulse-timing signal and characterized their performance for standard and customized pulse sequences. Results: Characterizing the latency parameters permitted choosing optimal timing parameters that maximized the rate of successfully delivering the desired number of pulses using both adaptive and synchronization methods. Conclusions: We demonstrated that accounting for latency and/or using the ability to read the prior information on expected pulse timing can provide high accuracy in delivering specified numbers of pulses. This reliability is critical for accurate dose delivery in preclinical FLASH research of single fraction and especially fractionated dosing regimens. The ability to generate custom pulse sequences enables more detailed exploration of the temporal dependence of biological FLASH effects.

physics.med-ph↗

arXiv2026

Non-invasive Reversible Software-based Electron FLASH Irradiation Configuration of a Linear Accelerator in Clinical Use

Configuring clinical linear accelerators (linacs) for ultra-high dose rate (UHDR) electron experiments typically requires invasive hardware manipulation and/or irreversible manufacturer modifications, limiting broader implementation. We present an independently developed UHDR electron configuration of a clinical TrueBeam linac that allows reversible switching between preclinical UHDR and conventional (CONV) modes using only non-invasive software settings. UHDR mode was achieved via service mode software with RF and beam current settings typical of a photon beam, the photon target and monitor chamber retracted, and a clinically unused low-energy scattering foil inserted. An external AC current transformer (ACCT) for beam monitoring, anatomy-specific collimator, and sample holder were mounted on the accessory tray, with external ion chamber in solid water for exit dose monitoring. Percent depth dose (PDD) was measured for UHDR and CONV beams. Dose-per-pulse (DPP) was varied by adjusting gun voltage and quantified with radiochromic film at different source-to-surface distances (SSD). Beam profiles assessed dose uniformity and usable field size. Dose calibration was established between film, ACCT, and ion chamber, and day-to-day reproducibility was tested. PDD confirmed similar energies for UHDR (12.8MeV) and CONV (11.9MeV) beams with matching profiles through mouse thickness. Maximum DPP exceeded 0.5Gy, reaching ~1.5Gy for collimated in vivo setups and ~0.7Gy at extended SSD for tissue culture. Field flatness and symmetry were maintained, supporting organ-specific irradiations and up to 5cm fields for culture. Calibration showed strong linearity across detectors, and output variation was <4%. We demonstrated accurate, reproducible UHDR delivery on a widely available clinical linac with no invasive hardware manipulation, enabling preclinical FLASH research on a clinical treatment machine.

physics.med-ph↗

arXiv2026

Ultra-Sharp Upright Photon Radiotherapy via Low Energy Extended Distance: An Alternative to FLASH for high flux Sources

Standard 6 megavolt (MV) radiotherapy is limited by source size and secondary electron range to minimum radiological penumbra widths of ~2-3 mm. This study investigates sharper beams via upright radiotherapy with lower energies and extended source-to-patient distances. A 2.5 MV beam from a clinical linac was delivered at a 4 m source-to-phantom distance (2.5 MV-ED). Lateral profiles and percent depth doses were measured in a solid water phantom with radiochromic film and an ion chamber. These single beam measurements were used to benchmark TOPAS Monte Carlo simulations. The validated 2.5 MV-ED model was then used to simulate upright deliveries with a conical beam geometry. These simulations were compared against equivalent plans generated for standard 6 MV-FFF coplanar deliveries at 1 m from the source. The 2.5 MV-ED single 28x28 mm^2 beam produced a measured 80%-20% penumbra of 1.0 +-0.1 mm, compared to 2.4 mm Jaw-defined penumbra for a standard 6MV-FFF beam. The doses at 10 cm depth were 52% vs. 56%, and the surface doses were 22% vs. 38% for the 2.5MV-ED and standard 6 MV-FFF respectively. Conical geometry Monte-Carlo simulations using the 2.5 MV-ED beams demonstrated significantly sharper composite dose fall-off in all cardinal directions compared to coplanar 6MV-FFF plans. For a spatially fractionated lattice example plan with 5 mm diameter high dose spheres, the 2.5 MV-ED conical approach achieved a peak-to-valley dose ratio of 4.5-5.2, compared to the 2.6-2.9 achievable with a standard 6 MV-FFF clinical system. Low-energy, extended-distance photon beams can provide sharper penumbra and lower surface dose, while maintaining comparable depth-dose penetration as standard 6 MV setups. Combined with upright patient setups, ultra-sharp dose distributions with enhanced treatment conformity, reduced toxicity, and higher-fidelity dose modulation are possible.

physics.med-ph↗

arXiv2023

Dosimetric calibration of an anatomically specific ultra-high dose rate electron irradiation platform for preclinical FLASH radiobiology experiments

We characterized the dosimetric properties of a clinical linear accelerator configured to deliver ultra-high dose rate (UHDR) irradiation to mice and cell-culture FLASH radiobiology experiments. UHDR electron beams were controlled by a microcontroller and relay interfaced with the respiratory gating system. We produced beam collimators with indexed stereotactic mouse positioning devices to provide anatomically specific preclinical treatments. Treatment delivery was monitored directly with an ionization chamber, and charge measurements were correlated with radiochromic film at the entry surface of the mice. The setup for conventional (CONV) dose rate irradiation was similar but the source-to-surface distance was longer. Monte Carlo simulations and film dosimetry were used to characterize beam properties and dose distributions. The mean electron beam energies before the flattening filter were 18.8 MeV (UHDR) and 17.7 MeV (CONV), with corresponding values at the mouse surface of 17.2 MeV and 16.2 MeV. The charges measured with an external ion chamber were linearly correlated with the mouse entrance dose. Use of relay gating for pulse control initially led to a delivery failure rate of 20% ($+/-$ 1 pulse); adjustments to account for the linac latency improved this rate to <1/20. Beam field sizes for two anatomically specific mouse collimators (4x4 $cm^2$ for whole-abdomen and 1.5x1.5 $cm^2$ for unilateral lung irradiation) were accurate within <5% and had low radiation leakage (<4%). Normalizing the dose at the center of the mouse (~0.75 cm depth) produced UHDR and CONV doses to the irradiated volumes with >95% agreement. We successfully configured a clinical linear accelerator for increased output and developed a robust preclinical platform for anatomically specific irradiation, with highly accurate and precise temporal and spatial dose delivery, for both CONV and UHDR applications.

physics.med-ph↗

arXiv2023

Multi-Institutional Audit of FLASH and Conventional Dosimetry with a 3D-Printed Anatomically Realistic Mouse Phantom

We conducted a multi-institutional audit of dosimetric variability between FLASH and conventional dose rate (CONV) electron irradiations by using an anatomically realistic 3D-printed mouse phantom. A CT scan of a live mouse was used to create a 3D model of bony anatomy, lungs, and soft tissue. A dual-nozzle 3D printer was used to print the mouse phantom using acrylonitrile butadiene styrene ($~1.02 g/cm^3$) and polylactic acid ($~1.24 g/cm^3$) simultaneously to simulate soft tissue and bone densities, respectively. The lungs were printed separately using lightweight polylactic acid ($~0.64 g/cm^3$). Hounsfield units (HU) and densities were compared with the reference CT scan of the live mouse. Print-to-print reproducibility of the phantom was assessed. Three institutions were each provided a phantom, and each institution performed two replicates of irradiations at selected mouse anatomic regions. The average dose difference between FLASH and CONV dose distributions and deviation from the prescribed dose were measured with radiochromic film. Compared to the reference CT scan, CT scans of the phantom demonstrated mass density differences of $0.10 g/cm^3$ for bone, $0.12 g/cm^3$ for lung, and $0.03 g/cm^3$ for soft tissue regions. Between phantoms, the difference in HU for soft tissue and bone was <10 HU from print to print. Lung exhibited the most variation (54 HU) but minimally affected dose distribution (<0.5% dose differences between phantoms). The mean difference between FLASH and CONV from the first replicate to the second decreased from 4.3% to 1.2%, and the mean difference from the prescribed dose decreased from 3.6% to 2.5% for CONV and 6.4% to 2.7% for FLASH. The framework presented here is promising for credentialing of multi-institutional studies of FLASH preclinical research to maximize the reproducibility of biological findings.

physics.med-ph↗