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Purpose: Our purpose was to develop a rodent model of brain radionecrosis using clinical linear accelerator based stereotactic radiosurgery. Methods and Materials: Single fraction maximum prescription points in the mouse's left hemisphere were irradiated using linear accelerator-based stereotactic radiosurgery with multiple arcs at 60 (n = 5), 100 (n = 5), and 140 (n = 5) Gy. Rats (n = 6) were similarly treated with 140 Gy. Gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) was used to track radiation injury in mice over weeks (100 and 140 Gy) or months (60 Gy). Target accuracy was measured by the distance from the prescription point to the center of the earliest Gd-MRI enhancement. Confirmation of necrosis via histology was performed at the subject endpoints. Results: Radiation injury as indicated by Gd-MRI was first identified at 2 weeks (140 Gy), 4 to 6 weeks (100 Gy), and 8 months (60 Gy). A volumetric time course showed rapid growth in the volume of Gd-MRI signal enhancement after the appearance of apparent necrosis. Histopathologic features were consistent with radionecrosis. Conclusions: The presented method uses a commonly available clinical linear accelerator to induce radiation necrosis in both mice and rats. The treatment is modeled after patient therapy for a more direct model of human tissue under a range of doses used in clinical neuro-ablation techniques. The short time to onset of apparent necrosis, accurate targeting of the prescription point, high incidence of necrosis, and similar pathologic features make this a suitable animal model for further research in radionecrosis.
RESUMO
BACKGROUND AND PURPOSE: Conical scintillation detectors are frequently used to measure geometric characteristics of radiotherapy modalities. However, their application to verify intensity-modulated radiotherapy plan delivery has not been investigated and requires a more detailed understanding of device response. This work evaluated the novel application of a conical scintillation detector to plan-specific quality assurance (QA) for intensity-modulated photon plans by evaluating device dependence on beam delivery and device acquisition parameters. MATERIALS AND METHODS: Measurements were made with a conical scintillation detector using beam delivery parameters of five photon beams (6-15 MV, including flattening filter free), three field sizes (1 × 1-5 × 5 cm2), and several dose rates (100-2000 MU/min) combined with device acquisition parameters of two frame rates (10 and 20 fps) and three gains (18-22 dB). A standardization equation to correct for gain and frame rate was investigated, and the remaining dose rate dependence was characterized. Device precision was evaluated using replicate measurements, and spatial uniformity was determined by irradiating different parts of the device. RESULTS: For each parameter combination, measurement reproducibility was 1.3%, and spatial uniformity was 1-2%. Scintillation intensity varied with gain, frame rate, and dose rate. Standardizing measurements for gain and frame rate was effective, but a dependence on dose rate caused errors at non-reference conditions (root mean squared error, RMSE: 0-152%). An additional dose rate correction specific to each combination of gain and frame rate improved accuracy (RMSE 0-17%). CONCLUSIONS: To consider the detector for plan-specific QA of intensity-modulated radiotherapy plans, correction factors are imperative to mitigate effects of delivery and acquisition parameters.
