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Purpose: High dose rate (HDR) brachytherapy rapidly delivers dose to targets with steep dose gradients. This treatment method must adhere to prescribed treatment plans with high spatiotemporal accuracy and precision, as failure to do so may degrade clinical outcomes. One approach to achieving this goal is to develop imaging techniques to track HDR sources in vivo in reference to surrounding anatomy. This work investigates the feasibility of using an isocentric C‐arm x‐ray imager and tomosynthesis methods to track Ir‐192 HDR brachytherapy sources in vivo over time (4D). Methods: A tomosynthesis imaging workflow was proposed and its achievable source detectability, localization accuracy, and spatiotemporal resolution were investigated in silico. An anthropomorphic female XCAT phantom was modified to include a vaginal cylinder applicator and Ir‐192 HDR source (0.5 × 0.5 × 5.0 mm3), and the workflow was carried out using the MC‐GPU Monte Carlo image simulation platform. Source detectability was characterized using the reconstructed source signal‐difference‐to‐noise‐ratio (SDNR), localization accuracy by the absolute 3D error in its measured centroid location, and spatiotemporal resolution by the full‐width‐at‐half‐maximum (FWHM) of line profiles through the source in each spatial dimension considering a maximum C‐arm angular velocity of 30° per second. The dependence of these parameters on acquisition angular range (θtot = 0°–90°), number of views, angular increment between views (Δθ = 0°–15°), and volumetric constraints imposed in reconstruction was evaluated. Organ voxel doses were tallied to derive the workflow's attributable effective dose. Results: The HDR source was readily detected and its centroid was accurately localized with the proposed workflow and method (SDNR: 10–40, 3D error: 0–0.144 mm). Tradeoffs were demonstrated for various combinations of image acquisition parameters; namely, increasing the tomosynthesis acquisition angular range improved resolution in the depth‐encoded direction, for example from 2.5 mm to 1.2 mm between θtot = 30o and θtot = 90o, at the cost of increasing acquisition time from 1 to 3 s. The best‐performing acquisition parameters (θtot = 90o, Δθ = 1°) yielded no centroid localization error, and achieved submillimeter source resolution (0.57 × 1.21 × 5.04 mm3 apparent source dimensions, FWHM). The total effective dose for the workflow was 263 µSv for its required pre‐treatment imaging component and 7.59 µSv per mid‐treatment acquisition thereafter, which is comparable to common diagnostic radiology exams. Conclusions: A system and method for tracking HDR brachytherapy sources in vivo using C‐arm tomosynthesis was proposed and its performance investigated in silico. Tradeoffs in source conspicuity, localization accuracy, spatiotemporal resolution, and dose were determined. The results suggest this approach is feasible for localizing an Ir‐192 HDR source in vivo with submillimeter spatial resolution, 1–3 second temporal resolution and minimal additional dose burden. [ABSTRACT FROM AUTHOR]

Purpose: To retrospectively validate the dose and dose rates delivered in XXX clinical trial fields via sub-millimeter spatial and <0.25 ms temporal resolution scintillation imaging., Methods: An ultra-fast intensified CMOS camera (4.5-12 kHz sampling rate) imaged the light response of a scintillator sheet at treatment isocenter and irradiated by pencil beam scanning proton fields, including XXX clinical fields. Dose and dose rate linearity studies were performed, followed by camera calibration, via EBT3 film. An EDGE diode detector was placed directly under the scintillator at the surface and at 5cm depth, for comparison with the imaging data and log files. Frame-by-frame analysis of image stacks yielded dose and dose-rate maps for each delivery at the surface. Using the percent depth dose curves and 3D spot profiles, the surface images were projected to 5 cm depth for comparison with a secondary diode and log file recordings., Results: Camera response was linear with dose (R 2 =0.9998) and beam current (R 2 =0.9883) from 2-12Gy and 20-210nA, respectively. Gamma analysis of the cumulative dose maps at 3%/2mm indicated a mean passing rate of 100% compared with film. Total irradiation time agreed with the log file recordings with an average deviation of 0.20±0.07ms. At the surface, the average imaged dose rate across the seven fields was 114±1Gy/s, agreeing with the diode within 1±1%. The dose at 5cm depth from the projected images (mean 8.4 Gy) agreed with the reported dose (log files) within 0.13±0.03 Gy (2±1%). The average dose rate from projected images at 5 cm depth was 62±1 Gy/s which agreed with the reported and diode values within 2±3%., Conclusion: This study provides the first independent validation of dose and dose rate for clinical proton XXX fields at unprecedented spatiotemporal resolution. Owing to the non-trivial dose rate distributions in PBS fields, such direct 2D dose rate mapping will be important in future pre-treatment plan quality assurance., (Copyright © 2024. Published by Elsevier Inc.)