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Chen, George

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Chen

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Chen, George

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Author's Publications: search.filters.isAuthorOfPublication.3425a56a-0850-487c-a873-e33e67e132b7

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    Effects of Interfractional Anatomical Changes on Water-Equivalent Pathlength in Charged-Particle Radiotherapy of Lung Cancer
    (Oxford University Press (OUP), 2009) Mori, Shinichiro; Lu, Hsiao-Ming; Wolfgang, John; Choi, Noah; Chen, George
    Intrafractional motion and interfractional changes affect the accuracy of the delivered dose in radiotherapy, particularly in charged-particle radiotherapy. Most recent studies are focused on intrafractional motion (respiratory motion). Here, we report a quantitative simulation analysis of the effects of interfractional changes on water-equivalent pathlength (WEL) in charged-particle lung therapy. Serial four-dimensional (4D) CT scans were performed under free breathing conditions; the time span between the first and second 4DCT scans was five weeks. We quantified WEL changes between the first and second CT scans due to interfractional changes (tumor shrinkage and tissue density changes) and compared the particle-beam-stopping point between the serial 4DCT scans with use of the same initial bolus. Both tumor-shrinkage and lung-density changes were observed in a single patient over the course of therapy. The lung density decreased by approximately 0.1 g/cm3 between the first and second-CT scans, resulting in a 1.5 cm WEL changes. Tumor shrinkage resulted in approximately 3 cm WEL changes. If the same initial bolus and plan were used through the treatment course, an unexpected significant beam overshoot would occur by interfractional changes due to tumor shrinkage and lung density variation.
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    Assessing Residual Motion for Gated Proton-Beam Radiotherapy
    (Oxford University Press (OUP), 2007) Sharp, Gregory; Lu, Hsiao-Ming; Trofimov, Alexei; Tang, Xiaoli; Jiang, Steve B.; Turcotte, Julie; Gierga, David; Chen, George; Hong, Theodore
    Gated radiation therapy is a promising method for improving the dose conformality of treatments to moving targets and reducing the total volume of irradiated tissue. Target motion is of particular concern in proton beam radiotherapy, due to the finite range of proton dose deposition in tissue. Gating allows one to reduce the extent of variation, due to respiration, of the radiological depth to target during treatment delivery. However, respiratory surrogates typically used for gating do not always accurately reflect the position of the internal target. For instance, a phase delay often exists between the internal motion and the motion of the surrogate. Another phenomenon, baseline drifting refers to a gradual change in the exhale position over time, which generally affects the external and internal markers differently. This study examines the influence of these two physiological phenomena on gated radiotherapy using an external surrogate.