Monte Carlo dosimetry modeling of focused <scp>kV</scp> x‐ray radiotherapy of eye diseases with potential nanoparticle dose enhancement

H, Yan; Ma, Xiangyu; Sun, Weiyuan; Mendez, Stacy; Stryker, Stefan; Starr-Baier, Sean; Delliturri, Gianpiero; Zhu, Dengsong; Nath, Ravinder; Chen, Zhe; Roberts, Kenneth B.; MacDonald, Carolyn A.; Liu, Wu

doi:10.1002/mp.13144

Cited by 9 publications

(18 citation statements)

References 59 publications

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“…The output focus perpendicular to the beam direction can be <0.2 mm for a modern polycapillary lens and the small focus is maintained over~5 mm in the depth direction. 35,38 The divergence of the output beam after the focal zone may be roughly estimated based on the output radius of the x-ray lens and the output focal length, which is only about 1-2°. Using an older multifiber technique, 39 the output focus can be as small as 0.5 mm.…”

Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

“…We recently investigated the feasibility of using focused xray beams to treat ocular melanoma by phantom experiments and MC simulations. 38 In brief, the proof-of-concept experiments were conducted by placing a 24-Watt low power 45 kVp test x-ray source at the input focus of an XOS model 3204 polycapillary x-ray lens. PMMA slabs sandwiched with EBT3 Gafchromic films perpendicular to the x-ray beam around the output focus of the lens were irradiated by a single focused x-ray beam.…”

Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

“…The MC simulations agree with the measurements within 10% for the beam FWHM and depth dose. 38 Because the MC modeling of the focused beam was verified by phantom measurements, 38 in this work, we will use the same validated MC simulation model (based on in-house lens simulation and Geant4 v.10.04.p02 dose calculation) to study the feasibility of focused kV x-ray treatment of wet-AMD in patient geometry and demonstrate significant dosimetric advantages compared to the current state-of-the-art RT treatment. More specific goals include to improve plan quality for treatment cases of various size, to evaluate treatment delivery robustness, and to demonstrate the potential for grid therapy.…”

Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

“…50 The simulated x-ray delivery system is illustrated in Fig 2. Considering the photon energy, x-ray source focal spot size, and the desired~0.2 mm lens output focus size, a new lens was designed with the key parameters listed in Table I. The lens consists of a collimating and a focusing half with the same channel size and lens diameters as the physical lens used in our previous phantom study, 38 but has longer physical length and focal lengths to allow slower bending of the channels for higher transmission of the higher energy photons and the desired output focus size. A phase-space file of photons at the output end of the lens was generated using the source energy spectrum via MC-based 3D geometric ray tracing of the lens by our in-house software.…”

Section: A Treatment System Designmentioning

confidence: 99%

“…Each beamlet exiting the capillary is divergent; however, the divergence is limited by the critical angle, unlike a fully divergent x‐ray source. The output focus perpendicular to the beam direction can be <0.2 mm for a modern polycapillary lens and the small focus is maintained over ~5 mm in the depth direction 35,38 . The divergence of the output beam after the focal zone may be roughly estimated based on the output radius of the x‐ray lens and the output focal length, which is only about 1–2°.…”

Section: Introductionmentioning

confidence: 99%

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

Sun

Mruthyunjaya

et al. 2020

Medical Physics

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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. Geant4based 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 AE0.75 mm displacement in the three orthogonal directions and AE5°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 <0.5 mm. With a prescription dose of 16 Gy to the lesions, the critical structure doses are well below the tolerance. The average CNV dose varies within 10% (mostly within 4%) due to 0.75-mm linear displacements and 5-degree gaze angle rotation of the eyeball. Conclusion: Focused kV technique allows personalized treatment of CNV lesions and reduces unwanted radiation to adjacent healthy tissue. The simulated dose distribution is superior to currently available techniques.

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Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

Section: B Focused Kv X-ray Treatmentmentioning

confidence: 99%

Section: A Treatment System Designmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Sun

Mruthyunjaya

et al. 2020

Medical Physics

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Radio‐luminescent imaging for rapid, high‐resolution eye plaque loading verification

Jean²,

Grafil³

et al. 2022

Medical Physics

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Background: Eye plaque brachytherapy is currently an optimal therapy for intraocular cancers. Due to the lack of an effective and practical technique to measure the seed radioactivity distribution, current quality assurance (QA) practice according to the American Association of Physicists in Medicine TG129 only stipulates that the plaque assembly be visually inspected. Consequently, uniform seed activity is routinely adopted to avoid possible loading mistakes of differential seed loading. However, modulated dose delivery, which represents a general trend in radiotherapy to provide more personalized treatment for a given tumor and patient, requires differential activities in the loaded seeds. Purpose: In this study, a fast and low-cost radio-luminescent imaging and dose calculating system to verify the seed activity distribution for differential loading was developed. Methods: A proof -of -concept system consisting of a thin scintillator sheet coupled to a camera/lens system was constructed. A seed-loaded plaque can be placed directly on the scintillator surface with the radioactive seeds facing the scintillator. The camera system collects the radioluminescent signal generated by the scintillator on its opposite side. The predicted dose distribution in the scintillator's sensitive layer was calculated using a Monte Carlo simulation with the planned plaque loading pattern of I-125 seeds. Quantitative comparisons of the distribution of relative measured signal intensity and that of the relative predicted dose in the sensitive layer were performed by gamma analysis, similar to intensity-modulated radiation therapy QA. Results: Data analyses showed high gamma (3%/0.3 mm, global, 20% threshold) passing rates for correct seed loadings and low passing rates with distinguished high gamma value area for incorrect loadings, indicating that possible errors may be detected. The measurement and analysis only required a few extra minutes, significantly shorter than the time to assay the extra verification seeds the physicist already must perform as recommended by TG129. Conclusions: Radio-luminescent QA can be used to facilitate and assure the implementation of intensity-modulated, customized plaque loading.

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High resolution imaging with focused kV x‐rays for small animal radio‐neuromodulation

et al. 2023

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Background: High precision radiotherapy with small irradiator size has potential in many treatment applications involving small shallow targets, with small animal radio-neuromodulation as an intriguing example. A focused kV technique based on novel usage of polycapillary x-ray lenses can focus x-ray beams to <0.2 mm in diameter, which is ideal for such uses. Purpose: Such an application also requires high resolution CT images for treatment planning and setup. In this work, we demonstrate the feasibility of using a virtual focal spot generated with an x-ray lens to perform high-resolution CBCT acquisition. Method: The experiment with x-ray lens was set up on an x-ray tabletop system to generate a virtual focal spot. The flood field images with and without the x-ray lens were first compared. A pinhole image was acquired for the virtual focal spot and compared with the one acquired with the conventional focal spot without the lens. The planar imaging resolution with and without the lens were evaluated using a line pair resolution phantom. The spatial resolution of the two settings were estimated by reconstructing a 0.15-mm wire phantom and comparing its full width half maximum (FWHM). A CBCT scan of a rodent head was also acquired to further demonstrate the improved resolution using the x-ray lens. Result: The proposed imaging setup with x-ray lens had a limited exposure area of 5 cm by 5 cm on the detector, which was suitable for guiding radioneuromodulation to a small target in rodent brain. Compared to conventional imaging acquisition with a measured x-ray focal spot of 0.395 mm FWHM, the virtual focal spot size was measured at 0.175 mm. The reduction in focal spot size with lens leads to an almost doubled planar imaging resolution and a 26% enhancement in 3D spatial resolution. A realistic CBCT acquisition of a rodent head mimicked the imaging acquisition step for radio-neuromodulation and further showed the improved visualization for fine structures. Conclusion: This work demonstrated that the focused kV x-ray technique was capable of generating small focal spot size of <0.2 mm, which substantially improved x-ray imaging resolution for small animal imaging.

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Monte Carlo dosimetry modeling of focused kV x‐ray radiotherapy of eye diseases with potential nanoparticle dose enhancement

Cited by 9 publications

References 59 publications

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

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

Radio‐luminescent imaging for rapid, high‐resolution eye plaque loading verification

High resolution imaging with focused kV x‐rays for small animal radio‐neuromodulation

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