Dosimetry modeling of focused kV x‐ray radiotherapy for wet age‐related macular degeneration

Purpose Wet (neovascular) age‐related macular degeneration (AMD) is the leading cause of blindness in the United States. The mainstay treatment requires monthly intravitreal injection of anti‐vascular endothelial growth factor (anti‐VEGF) drugs, associated with multiple visits, high cost, and the ri...

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Veröffentlicht in:Medical physics (Lancaster) 2020-10, Vol.47 (10), p.5123-5134
Hauptverfasser: Yan, Huagang, Sun, Weiyuan, Mruthyunjaya, Prithvi, Beadle, Beth, Yu, Weihong, Kanwal, Bushra, MacDonald, Carolyn A., Liu, Wu
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Sprache:eng
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Zusammenfassung:Purpose Wet (neovascular) age‐related macular degeneration (AMD) is the leading cause of blindness in the United States. The mainstay treatment requires monthly intravitreal injection of anti‐vascular endothelial growth factor (anti‐VEGF) drugs, associated with multiple visits, high cost, and the risk of procedural injury and infection. Anti‐VEGF drugs inhibit the formation of neovasculature but do not directly attack it. Radiotherapy can destroy neovasculature and potentially also inhibit wet‐AMD associated inflammation and fibrosis not addressed by VEGF inhibitors. However, the current collimation‐based radiotherapy device uses fixed 4 mm beams, which are prone to overtreat or undertreat the choroidal neovascularization (CNV) lesions because of their various sizes and shapes. This simulation study evaluates personalized conformal treatment with focused kV radiation using cutting‐edge polycapillary x‐ray optics. Methods Simulation of the polycapillary optics was achieved via Monte Carlo (MC)‐based three‐dimensional (3D) geometric ray tracing. Phase‐space files modeling the focused photons were generated. The method was previously verified by phantom measurements. The ultrasmall ~0.2 mm beam focal spot perpendicular to the beam direction enables spatially fractionated grid therapy, which has been shown to preferentially damage abnormal neovascular blood vessels vs normal ones. Geant4‐based MC simulations of scanning while rotating beam delivery were performed to conformally treat three clinical cases of large, medium, and small CNV lesions with regular and grid deliveries. Dose delivery uncertainties due to positioning errors were analyzed, including ±0.75 mm displacement in the three orthogonal directions and ±5° vertical/horizontal rotation of the eyeball. Results The simulated CNV treatments by 60‐kVp focused x‐ray beams show highly conformal delivery of dose to the lesion plus margin (0.75 mm) with sharp dose fall‐offs and controllable spatial modulation patterns. The 90%–10% isodose penumbra is
ISSN:0094-2405
2473-4209
DOI:10.1002/mp.14404