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Title
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Biological image-guided radiotherapy in rectal cancer : challenges and pitfalls
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Author
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Abstract
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| Purpose To investigate the feasibility of integrating multiple imaging modalities for image-guided radiotherapy in rectal cancer. Patients and Methods Magnetic resonance imaging (MRI) and fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) were performed before, during, and after preoperative chemoradiotherapy (CRT) in patients with resectable rectal cancer. The FDG-PET signals were segmented with an adaptive threshold-based and a gradient-based method. Magnetic resonance tumor volumes (TVs) were manually delineated. A nonrigid registration algorithm was applied to register the images, and mismatch analyses were carried out between MR and FDG-PET TVs and between TVs over time. Tumor volumes delineated on the images after CRT were compared with the pathologic TV. Results Forty-five FDG-PET/CT and 45 MR images were analyzed from 15 patients. The mean MRI and FDG-PET TVs showed a tendency to shrink during and after CRT. In general, MRI showed larger TVs than FDG-PET. There was an approximately 50% mismatch between the FDG-PET TV and the MRI TV at baseline and during CRT. Sixty-one percent of the FDG-PET TV and 76% of the MRI TV obtained after 10 fractions of CRT remained inside the corresponding baseline TV. On MRI, residual tumor was still suspected in all 6 patients with a pathologic complete response, whereas FDG-PET showed a metabolic complete response in 3 of them. The FDG-PET TVs delineated with the gradient-based method matched closest with pathologic findings. Conclusions Integration of MRI and FDG-PET into radiotherapy seems feasible. Gradient-based segmentation is recommended for FDG-PET. Spatial variance between MRI and FDG-PET TVs should be taken into account for target definition. |
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Language
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English
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Source (journal)
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International journal of radiation oncology, biology, physics. - Bedford
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Publication
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Bedford
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2009
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ISSN
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0360-3016
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DOI
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10.1016/J.IJROBP.2008.11.031
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Volume/pages
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75
:3
(2009)
, p. 782-790
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ISI
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000270573100021
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Full text (Publisher's DOI)
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Full text (publisher's version - intranet only)
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