Research Appraisals
Evidence-based critical appraisals of the latest medical research, systematically evaluated using Oxford CEBM methodology.
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Physics in medicine and biology
Lattice peak optimization: a mixed-integer framework for geometry-adaptive lattice radiotherapy
Objective.Lattice radiotherapy (LATTICE) delivers spatially distributed high-dose peaks within the tumor volume while maintaining lower doses in surrounding valley regions. Determining feasible peak locations is typically performed using heuristic or manual approaches, which may limit the number and spatial distribution of deliverable peaks. This work introduces a lattice peak optimization (LPO) framework that jointly optimizes peak placement and dose distribution to identify the maximum number of geometrically feasible peaks within the target.Approach.Proton LATTICE planning is formulated as a mixed-integer optimization problem that selects an optimal subset of peaks from a large set of candidate locations within the target. Binary variables represent peak selection and continuous variables model spot weights. The formulation enforces geometric feasibility between peaks while optimizing dosimetric objectives to improve peak-to-valley dose ratio (PVDR) and reduce organs-at-risk (OAR) dose. The resulting nonconvex problem is solved using iterative convex relaxation within an alternating direction method of multipliers framework.Main results.LPO was evaluated on three clinical cases with 150-400 candidate peak locations, from which 4-13 peaks were selected. Compared with 50-90 randomly generated LATTICE configurations per case, LPO consistently achieved higher PVDR and improved OAR sparing. In an abdominal case, the composite objective value was 2.93 (worst random), 2.40 (median random), 1.90 (best random), and 1.95 (LPO), with similar trends observed across all cases.Significance.A geometry-adaptive, mixed-integer optimization framework for lattice peak placement is presented, demonstrating improved PVDR and OAR sparing relative to manual and random LATTICE approaches. The present study evaluates performance of the proposed framework in the context of proton LATTICE planning; however, the framework is mathematically modality-agnostic and could in principle be applied to other radiation modalities.
27 May 2026
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Retrofitting a clinical pencil beam scanning proton therapy unit for 2D ultra-high dose rate scanning
Purpose.This work aimed to demonstrate how existing clinical infrastructure can be adapted to enable ultra-high dose rate (UHDR) pencil beam scanning (PBS) for FLASH research. Leveraging available hardware and minimizing modifications, we extended the capabilities of PSI Gantry 1, previously used as a flexible UHDR fixed-beam delivery platform, by enabling true 2D PBS for UHDR small-field irradiations through the addition of a second scanning direction and multiple gantry angles.Methods.A second (vertical) scanning direction was implemented by repurposing an existing steering magnet and integrating it into the control system. Inter-spot dead times were minimized through software optimizations that synchronized control processes and magnet settling times, optimizing the local average dose rate. A precise spot map acquisition process ensured accurate dose delivery across different gantry angles. Additionally, a1kHzlogging system was introduced, enabling the reconstruction of lateral dose and dose-rate distributions from recorded beam parameters.Results.Gantry 1 was successfully commissioned for 2D scanning of small fields (100×24mm2) at gantry angles from 0∘(beam towards floor) to-120∘. Dose-uniform field deliveries were achieved at local average dose rates up to75Gys-1. The reconstructed lateral dose distributions were in good agreement with CCD measurements regarding the90%iso-dose contour, while the dose-rate distributions were validated againstmicro-Diamonddetector measurements, confirming the precision of the recalculated dose rates.Conclusions.By repurposing existing hardware and optimizing beam delivery, Gantry 1 has been upgraded to a true 2D PBS UHDR scanning system, capable of delivering fields at local average dose rates exceeding70Gys-1. The high-frequency logging system enables future reanalysis of data as the mechanisms underlying the FLASH effect become clearer. This transformation makes Gantry 1 a versatile platform for preclinical research and small animal irradiation, advancing the investigation of the FLASH effect.
27 May 2026
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