Browsing by Author "Grosshans, David"

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    Brain Radiation Necrosis Outside the Target Volume After Proton Radiation Therapy: Analyses of Multiparametric Imaging and Proton Biologic Effectiveness
    (Elsevier, 2022) Bronk, Julianna K.; Amer, Ahmad; Khose, Swapnil; Flint, David; Adair, Antony; Yepes, Pablo; Grosshans, David; Johnson, Jason; Chung, Caroline
    Purpose We present the case of a 48-year-old patient with recurrent World Health Organization grade II meningioma in the left occipital region who underwent a subtotal resection, followed by postoperative proton therapy to residual disease and the resection cavity. Fourteen months after radiation treatment completion, surveillance imaging revealed numerous ring-enhancing infratentorial lesions, both within and outside of the high-dose field, of concern for viable tumor. We describe the use of advanced imaging and proton biologic effectiveness analyses to enable the diagnosis of radiation necrosis (RN) and ascertain intrinsic physical factors contributing to the development of RN in this patient. Methods and Materials Multiparametric magnetic resonance imaging (MRI) and Monte Carlo predictions of linear energy transfer (LET) and variable relative biologic effectiveness dose were performed. Results The dosimetric analysis revealed that of the 10 lesions, 9 were located outside of the clinical treatment volume and 6 received a dose of <60 Gy relative biologic effectiveness to 95% of the volume. However, increased proton LET values were found in lesions that received lower radiation doses. Dynamic susceptibility contrast and contrast-enhanced, as well as arterial spin labeling-perfusion MRI findings were consistent with RN. Subsequent follow-up imaging revealed no further progression, and the patient was disease-free at the time of this report. Conclusions We describe a case of brain RN after proton beam radiation outside of the high-dose radiation therapy volume. On initial radiographic detection of these lesions, the distant relationship between their anatomic location with respect to the patient's treatment history reduced the suspicion of RN. However, on closer examination of intrinsic physical variables, RN lesions were present in regions that received a lower dose but higher LETs. Although conventional multisequence MRI was inadequate to distinguish between RN and tumor progression, characterization of tissue physiology allowed for the correct diagnosis, highlighting the utility of advanced brain tumor imaging in the follow-up setting.
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    Intensity modulated proton arc therapy via geometry-based energy selection for ependymoma
    (Wiley, 2023) Cao, Wenhua; Li, Yupeng; Zhang, Xiaodong; Poenisch, Falk; Yepes, Pablo; Sahoo, Narayan; Grosshans, David; McGovern, Susan; Gunn, G. Brandon; Frank, Steven J.; Zhu, Xiaorong R.
    Purpose We developed and tested a novel method of creating intensity modulated proton arc therapy (IMPAT) plans that uses computing resources similar to those for regular intensity-modulated proton therapy (IMPT) plans and may offer a dosimetric benefit for patients with ependymoma or similar tumor geometries. Methods Our IMPAT planning method consists of a geometry-based energy selection step with major scanning spot contributions as inputs computed using ray-tracing and single-Gaussian approximation of lateral spot profiles. Based on the geometric relation of scanning spots and dose voxels, our energy selection module selects a minimum set of energy layers at each gantry angle such that each target voxel is covered by sufficient scanning spots as specified by the planner, with dose contributions above the specified threshold. Finally, IMPAT plans are generated by robustly optimizing scanning spots of the selected energy layers using a commercial proton treatment planning system (TPS). The IMPAT plan quality was assessed for four ependymoma patients. Reference three-field IMPT plans were created with similar planning objective functions and compared with the IMPAT plans. Results In all plans, the prescribed dose covered 95% of the clinical target volume (CTV) while maintaining similar maximum doses for the brainstem. While IMPAT and IMPT achieved comparable plan robustness, the IMPAT plans achieved better homogeneity and conformity than the IMPT plans. The IMPAT plans also exhibited higher relative biological effectiveness (RBE) enhancement than did the corresponding reference IMPT plans for the CTV in all four patients and brainstem in three of them. Conclusions The proposed method demonstrated potential as an efficient technique for IMPAT planning and may offer a dosimetric benefit for patients with ependymoma or tumors in close proximity to critical organs. IMPAT plans created using this method had elevated RBE enhancement associated with increased linear energy transfer (LET) in both targets and abutting critical organs.